rename for consistency - merchant - Merchant backend to process payments, run by merchants

commit 1680844affef7b5ce63effb5f6cbf274c835dfae
parent 9f6610110475dfc0e6ef9bf35d0f3ca71b7f4dbf
Author: Christian Grothoff <grothoff@gnunet.org>
Date:   Thu, 29 Jan 2026 18:05:24 +0900

rename for consistency

Diffstat:
M src/backend/Makefile.am  | 4 ++--
M src/backend/taler-merchant-httpd_dispatcher.c  | 2 +-
A src/backend/taler-merchant-httpd_post-templates-ID.c  | 1782 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
A src/backend/taler-merchant-httpd_post-templates-ID.h  | 40 ++++++++++++++++++++++++++++++++++++++++
D src/backend/taler-merchant-httpd_post-using-templates.c  | 1782 -------------------------------------------------------------------------------
D src/backend/taler-merchant-httpd_post-using-templates.h  | 40 ----------------------------------------

6 files changed, 1825 insertions(+), 1825 deletions(-)
diff --git a/src/backend/Makefile.am b/src/backend/Makefile.am
@@ -237,8 +237,8 @@ taler_merchant_httpd_SOURCES = \
     taler-merchant-httpd_post-orders-ID-paid.h \
   taler-merchant-httpd_post-orders-ID-refund.c \
     taler-merchant-httpd_post-orders-ID-refund.h \
-  taler-merchant-httpd_post-using-templates.c \
-    taler-merchant-httpd_post-using-templates.h \
+  taler-merchant-httpd_post-templates-ID.c \
+    taler-merchant-httpd_post-templates-ID.h \
   taler-merchant-httpd_post-reports-ID.c \
     taler-merchant-httpd_post-reports-ID.h \
   taler-merchant-httpd_private-get-statistics-amount-SLUG.c \
diff --git a/src/backend/taler-merchant-httpd_dispatcher.c b/src/backend/taler-merchant-httpd_dispatcher.c
@@ -98,7 +98,7 @@
 #include "taler-merchant-httpd_post-orders-ID-claim.h"
 #include "taler-merchant-httpd_post-orders-ID-paid.h"
 #include "taler-merchant-httpd_post-orders-ID-pay.h"
-#include "taler-merchant-httpd_post-using-templates.h"
+#include "taler-merchant-httpd_post-templates-ID.h"
 #include "taler-merchant-httpd_post-orders-ID-refund.h"
 #include "taler-merchant-httpd_spa.h"
 #include "taler-merchant-httpd_statics.h"
diff --git a/src/backend/taler-merchant-httpd_post-templates-ID.c b/src/backend/taler-merchant-httpd_post-templates-ID.c
@@ -0,0 +1,1782 @@
+/*
+  This file is part of TALER
+  (C) 2022-2026 Taler Systems SA
+
+  TALER is free software; you can redistribute it and/or modify
+  it under the terms of the GNU Affero General Public License as
+  published by the Free Software Foundation; either version 3,
+  or (at your option) any later version.
+
+  TALER is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public
+  License along with TALER; see the file COPYING.  If not,
+  see <http://www.gnu.org/licenses/>
+*/
+
+/**
+ * @file taler-merchant-httpd_post-using-templates.c
+ * @brief implementing POST /using-templates request handling
+ * @author Priscilla HUANG
+ * @author Christian Grothoff
+ */
+#include "platform.h"
+#include "taler-merchant-httpd_post-templates-ID.h"
+#include "taler-merchant-httpd_private-post-orders.h"
+#include "taler-merchant-httpd_helper.h"
+#include "taler-merchant-httpd_exchanges.h"
+#include "taler_merchant_util.h"
+#include <taler/taler_json_lib.h>
+#include <regex.h>
+
+
+/**
+ * Item selected from inventory_selection.
+ */
+struct InventoryTemplateItemContext
+{
+  /**
+   * Product ID as referenced in inventory.
+   */
+  const char *product_id;
+
+  /**
+   * Unit quantity string as provided by the client.
+   */
+  const char *unit_quantity;
+
+  /**
+   * Parsed integer quantity.
+   */
+  uint64_t quantity_value;
+
+  /**
+   * Parsed fractional quantity.
+   */
+  uint32_t quantity_frac;
+
+  /**
+   * Product details from the DB (includes price array).
+   */
+  struct TALER_MERCHANTDB_ProductDetails pd;
+
+  /**
+   * Categories referenced by the product.
+   */
+  uint64_t *categories;
+
+  /**
+   * Length of @e categories.
+   */
+  size_t num_categories;
+};
+
+
+/**
+ * Our context.
+ */
+enum UsePhase
+{
+  /**
+   * Parse request payload into context fields.
+   */
+  USE_PHASE_PARSE_REQUEST,
+
+  /**
+   * Fetch template details from the database.
+   */
+  USE_PHASE_LOOKUP_TEMPLATE,
+
+  /**
+   * Parse template.
+   */
+  USE_PHASE_PARSE_TEMPLATE,
+
+  /**
+   * Load additional details (like products and
+   * categories) needed for verification and
+   * price computation.
+   */
+  USE_PHASE_DB_FETCH,
+
+  /**
+   * Validate request and template compatibility.
+   */
+  USE_PHASE_VERIFY,
+
+  /**
+   * Compute price of the order.
+   */
+  USE_PHASE_COMPUTE_PRICE,
+
+  /**
+   * Handle tip.
+   */
+  USE_PHASE_CHECK_TIP,
+
+  /**
+   * Check if client-supplied total amount matches
+   * our calculation (if we did any).
+   */
+  USE_PHASE_CHECK_TOTAL,
+
+  /**
+   * Construct the internal order request body.
+   */
+  USE_PHASE_CREATE_ORDER,
+
+  /**
+   * Submit the order to the shared order handler.
+   */
+  USE_PHASE_SUBMIT_ORDER,
+
+  /**
+   * Finished successfully with MHD_YES.
+   */
+  USE_PHASE_FINISHED_MHD_YES,
+
+  /**
+   * Finished with MHD_NO.
+   */
+  USE_PHASE_FINISHED_MHD_NO
+};
+
+struct UseContext
+{
+  /**
+   * Context for our handler.
+   */
+  struct TMH_HandlerContext *hc;
+
+  /**
+   * Internal handler context we are passing into the
+   * POST /private/orders handler.
+   */
+  struct TMH_HandlerContext ihc;
+
+  /**
+   * Phase we are currently in.
+   */
+  enum UsePhase phase;
+
+  /**
+   * Template type from the contract.
+   */
+  enum TALER_MERCHANT_TemplateType template_type;
+
+  /**
+   * Information set in the #USE_PHASE_PARSE_REQUEST phase.
+   */
+  struct
+  {
+    /**
+     * Summary override from request, if any.
+     */
+    const char *summary;
+
+    /**
+     * Amount provided by the client.
+     */
+    struct TALER_Amount amount;
+
+    /**
+     * Tip provided by the client.
+     */
+    struct TALER_Amount tip;
+
+    /**
+     * True if @e amount was not provided.
+     */
+    bool no_amount;
+
+    /**
+     * True if @e tip was not provided.
+     */
+    bool no_tip;
+
+    /**
+     * Parsed fields for inventory templates.
+     */
+    struct
+    {
+      /**
+       * Selected products from inventory_selection.
+       */
+      struct InventoryTemplateItemContext *items;
+
+      /**
+       * Length of @e items.
+       */
+      unsigned int items_len;
+
+    } inventory;
+
+    /**
+     * Request details if this is a paivana instantiation.
+     */
+    struct
+    {
+
+      /**
+       * Target website for the request.
+       */
+      const char *website;
+
+      /**
+       * Unique client identifier, consisting of
+       * current time, "-", and the hash of a nonce,
+       * the website and the current time.
+       */
+      const char *paivana_id;
+
+    } paivana;
+
+  } parse_request;
+
+  /**
+   * Information set in the #USE_PHASE_LOOKUP_TEMPLATE phase.
+   */
+  struct
+  {
+
+    /**
+     * Our template details from the DB.
+     */
+    struct TALER_MERCHANTDB_TemplateDetails etp;
+
+  } lookup_template;
+
+  /**
+   * Information set in the #USE_PHASE_PARSE_TEMPLATE phase.
+   */
+  struct TALER_MERCHANT_TemplateContract template_contract;
+
+  /**
+   * Information set in the #USE_PHASE_COMPUTE_PRICE phase.
+   */
+  struct
+  {
+
+    /**
+     * Per-currency totals across selected products (without tips).
+     */
+    struct TALER_Amount *totals;
+
+    /**
+     * Length of @e totals.
+     */
+    unsigned int totals_len;
+
+    /**
+     * Array of payment choices, used with Paviana.
+     */
+    json_t *choices;
+
+  } compute_price;
+
+};
+
+
+/**
+ * Clean up inventory items.
+ *
+ * @param items_len length of @a items
+ * @param[in] items item array to free
+ */
+static void
+cleanup_inventory_items (unsigned int items_len,
+                         struct InventoryTemplateItemContext items[static
+                                                                   items_len])
+{
+  for (unsigned int i = 0; i < items_len; i++)
+  {
+    struct InventoryTemplateItemContext *item = &items[i];
+
+    TALER_MERCHANTDB_product_details_free (&item->pd);
+    GNUNET_free (item->categories);
+  }
+  GNUNET_free (items);
+}
+
+
+/**
+ * Clean up a `struct UseContext *`
+ *
+ * @param[in] cls a `struct UseContext *`
+ */
+static void
+cleanup_use_context (void *cls)
+{
+  struct UseContext *uc = cls;
+
+  TALER_MERCHANTDB_template_details_free (&uc->lookup_template.etp);
+  if (NULL !=
+      uc->parse_request.inventory.items)
+    cleanup_inventory_items (uc->parse_request.inventory.items_len,
+                             uc->parse_request.inventory.items);
+  GNUNET_free (uc->compute_price.totals);
+  uc->compute_price.totals_len = 0;
+  json_decref (uc->compute_price.choices);
+  if (NULL != uc->ihc.cc)
+    uc->ihc.cc (uc->ihc.ctx);
+  GNUNET_free (uc->ihc.infix);
+  json_decref (uc->ihc.request_body);
+  GNUNET_free (uc);
+}
+
+
+/**
+ * Finalize a template use request.
+ *
+ * @param[in,out] uc use context
+ * @param ret handler return value
+ */
+static void
+use_finalize (struct UseContext *uc,
+              MHD_RESULT ret)
+{
+  uc->phase = (MHD_YES == ret)
+    ? USE_PHASE_FINISHED_MHD_YES
+    : USE_PHASE_FINISHED_MHD_NO;
+}
+
+
+/**
+ * Finalize after JSON parsing result.
+ *
+ * @param[in,out] uc use context
+ * @param res parse result
+ */
+static void
+use_finalize_parse (struct UseContext *uc,
+                    enum GNUNET_GenericReturnValue res)
+{
+  GNUNET_assert (GNUNET_OK != res);
+  use_finalize (uc,
+                (GNUNET_NO == res)
+                ? MHD_YES
+                : MHD_NO);
+}
+
+
+/**
+ * Reply with error and finalize the request.
+ *
+ * @param[in,out] uc use context
+ * @param http_status HTTP status code
+ * @param ec error code
+ * @param detail error detail
+ */
+static void
+use_reply_with_error (struct UseContext *uc,
+                      unsigned int http_status,
+                      enum TALER_ErrorCode ec,
+                      const char *detail)
+{
+  MHD_RESULT mret;
+
+  mret = TALER_MHD_reply_with_error (uc->hc->connection,
+                                     http_status,
+                                     ec,
+                                     detail);
+  use_finalize (uc,
+                mret);
+}
+
+
+/* ***************** USE_PHASE_PARSE_REQUEST **************** */
+
+/**
+ * Parse request data for inventory templates.
+ *
+ * @param[in,out] uc use context
+ * @return #GNUNET_OK on success
+ */
+static enum GNUNET_GenericReturnValue
+parse_using_templates_inventory_request (
+  struct UseContext *uc)
+{
+  const json_t *inventory_selection;
+  struct GNUNET_JSON_Specification spec[] = {
+    GNUNET_JSON_spec_array_const ("inventory_selection",
+                                  &inventory_selection),
+    GNUNET_JSON_spec_end ()
+  };
+  enum GNUNET_GenericReturnValue res;
+
+  GNUNET_assert (NULL == uc->ihc.request_body);
+  res = TALER_MHD_parse_json_data (uc->hc->connection,
+                                   uc->hc->request_body,
+                                   spec);
+  if (GNUNET_OK != res)
+  {
+    GNUNET_break_op (0);
+    use_finalize_parse (uc,
+                        res);
+    return GNUNET_SYSERR;
+  }
+
+  if ( (! uc->parse_request.no_amount) &&
+       (! TMH_test_exchange_configured_for_currency (
+          uc->parse_request.amount.currency)) )
+  {
+    GNUNET_break_op (0);
+    use_reply_with_error (uc,
+                          MHD_HTTP_CONFLICT,
+                          TALER_EC_MERCHANT_GENERIC_CURRENCY_MISMATCH,
+                          "Currency is not supported by backend");
+    return GNUNET_SYSERR;
+  }
+
+  for (size_t i = 0; i < json_array_size (inventory_selection); i++)
+  {
+    struct InventoryTemplateItemContext item = { 0 };
+    struct GNUNET_JSON_Specification ispec[] = {
+      GNUNET_JSON_spec_string ("product_id",
+                               &item.product_id),
+      GNUNET_JSON_spec_string ("quantity",
+                               &item.unit_quantity),
+      GNUNET_JSON_spec_end ()
+    };
+    const char *err_name;
+    unsigned int err_line;
+
+    res = GNUNET_JSON_parse (json_array_get (inventory_selection,
+                                             i),
+                             ispec,
+                             &err_name,
+                             &err_line);
+    if (GNUNET_OK != res)
+    {
+      GNUNET_break_op (0);
+      use_reply_with_error (uc,
+                            MHD_HTTP_BAD_REQUEST,
+                            TALER_EC_GENERIC_PARAMETER_MALFORMED,
+                            "inventory_selection");
+      return GNUNET_SYSERR;
+    }
+
+    GNUNET_array_append (uc->parse_request.inventory.items,
+                         uc->parse_request.inventory.items_len,
+                         item);
+  }
+  return GNUNET_OK;
+}
+
+
+/**
+ * Parse request data for paivana templates.
+ *
+ * @param[in,out] uc use context
+ * @return #GNUNET_OK on success
+ */
+static enum GNUNET_GenericReturnValue
+parse_using_templates_paivana_request (
+  struct UseContext *uc)
+{
+  struct GNUNET_JSON_Specification spec[] = {
+    GNUNET_JSON_spec_string ("website",
+                             &uc->parse_request.paivana.website),
+    GNUNET_JSON_spec_string ("paivana_id",
+                             &uc->parse_request.paivana.paivana_id),
+    GNUNET_JSON_spec_end ()
+  };
+  enum GNUNET_GenericReturnValue res;
+  struct GNUNET_HashCode sh;
+  unsigned long long tv;
+  const char *dash;
+
+  GNUNET_assert (NULL == uc->ihc.request_body);
+  res = TALER_MHD_parse_json_data (uc->hc->connection,
+                                   uc->hc->request_body,
+                                   spec);
+  if (GNUNET_OK != res)
+  {
+    GNUNET_break_op (0);
+    use_finalize_parse (uc,
+                        res);
+    return GNUNET_SYSERR;
+  }
+  if (1 !=
+      sscanf (uc->parse_request.paivana.paivana_id,
+              "%llu-",
+              &tv))
+  {
+    GNUNET_break_op (0);
+    use_reply_with_error (uc,
+                          MHD_HTTP_BAD_REQUEST,
+                          TALER_EC_GENERIC_PARAMETER_MALFORMED,
+                          "paivana_id");
+    return GNUNET_SYSERR;
+  }
+  dash = strchr (uc->parse_request.paivana.paivana_id,
+                 '-');
+  GNUNET_assert (NULL != dash);
+  if (GNUNET_OK !=
+      GNUNET_STRINGS_string_to_data (dash + 1,
+                                     strlen (dash + 1),
+                                     &sh,
+                                     sizeof (sh)))
+  {
+    GNUNET_break_op (0);
+    use_reply_with_error (uc,
+                          MHD_HTTP_BAD_REQUEST,
+                          TALER_EC_GENERIC_PARAMETER_MALFORMED,
+                          "paivana_id");
+    return GNUNET_SYSERR;
+  }
+  return GNUNET_OK;
+}
+
+
+/**
+ * Main function for the #USE_PHASE_PARSE_REQUEST.
+ *
+ * @param[in,out] uc context to update
+ */
+static void
+handle_phase_parse_request (
+  struct UseContext *uc)
+{
+  const char *template_type = NULL;
+  struct GNUNET_JSON_Specification spec[] = {
+    GNUNET_JSON_spec_mark_optional (
+      GNUNET_JSON_spec_string ("template_type",
+                               &template_type),
+      NULL),
+    GNUNET_JSON_spec_mark_optional (
+      TALER_JSON_spec_amount_any ("tip",
+                                  &uc->parse_request.tip),
+      &uc->parse_request.no_tip),
+    GNUNET_JSON_spec_mark_optional (
+      GNUNET_JSON_spec_string ("summary",
+                               &uc->parse_request.summary),
+      NULL),
+    GNUNET_JSON_spec_mark_optional (
+      TALER_JSON_spec_amount_any ("amount",
+                                  &uc->parse_request.amount),
+      &uc->parse_request.no_amount),
+    GNUNET_JSON_spec_end ()
+  };
+  enum GNUNET_GenericReturnValue res;
+
+  res = TALER_MHD_parse_json_data (uc->hc->connection,
+                                   uc->hc->request_body,
+                                   spec);
+  if (GNUNET_OK != res)
+  {
+    GNUNET_break_op (0);
+    use_finalize_parse (uc,
+                        res);
+    return;
+  }
+  if (NULL == template_type)
+    template_type = "fixed-order";
+  uc->template_type
+    = TALER_MERCHANT_template_type_from_string (
+        template_type);
+  switch (uc->template_type)
+  {
+  case TALER_MERCHANT_TEMPLATE_TYPE_FIXED_ORDER:
+    /* nothig left to do */
+    uc->phase++;
+    return;
+  case TALER_MERCHANT_TEMPLATE_TYPE_PAIVANA:
+    res = parse_using_templates_paivana_request (uc);
+    if (GNUNET_OK == res)
+      uc->phase++;
+    return;
+  case TALER_MERCHANT_TEMPLATE_TYPE_INVENTORY_CART:
+    res = parse_using_templates_inventory_request (uc);
+    if (GNUNET_OK == res)
+      uc->phase++;
+    return;
+  case TALER_MERCHANT_TEMPLATE_TYPE_INVALID:
+    break;
+  }
+  GNUNET_break (0);
+  use_reply_with_error (
+    uc,
+    MHD_HTTP_BAD_REQUEST,
+    TALER_EC_GENERIC_PARAMETER_MALFORMED,
+    "template_type");
+}
+
+
+/* ***************** USE_PHASE_LOOKUP_TEMPLATE **************** */
+
+/**
+ * Main function for the #USE_PHASE_LOOKUP_TEMPLATE.
+ *
+ * @param[in,out] uc context to update
+ */
+static void
+handle_phase_lookup_template (
+  struct UseContext *uc)
+{
+  struct TMH_MerchantInstance *mi = uc->hc->instance;
+  const char *template_id = uc->hc->infix;
+  enum GNUNET_DB_QueryStatus qs;
+
+  qs = TMH_db->lookup_template (TMH_db->cls,
+                                mi->settings.id,
+                                template_id,
+                                &uc->lookup_template.etp);
+  switch (qs)
+  {
+  case GNUNET_DB_STATUS_HARD_ERROR:
+    /* Clean up and fail hard */
+    GNUNET_break (0);
+    use_reply_with_error (uc,
+                          MHD_HTTP_INTERNAL_SERVER_ERROR,
+                          TALER_EC_GENERIC_DB_FETCH_FAILED,
+                          "lookup_template");
+    return;
+  case GNUNET_DB_STATUS_SOFT_ERROR:
+    /* this should be impossible (single select) */
+    GNUNET_break (0);
+    use_reply_with_error (uc,
+                          MHD_HTTP_INTERNAL_SERVER_ERROR,
+                          TALER_EC_GENERIC_DB_FETCH_FAILED,
+                          "lookup_template");
+    return;
+  case GNUNET_DB_STATUS_SUCCESS_NO_RESULTS:
+    /* template not found! */
+    use_reply_with_error (uc,
+                          MHD_HTTP_NOT_FOUND,
+                          TALER_EC_MERCHANT_GENERIC_TEMPLATE_UNKNOWN,
+                          template_id);
+    return;
+  case GNUNET_DB_STATUS_SUCCESS_ONE_RESULT:
+    /* all good */
+    break;
+  }
+  if (uc->template_type !=
+      TALER_MERCHANT_template_type_from_contract (
+        uc->lookup_template.etp.template_contract))
+  {
+    GNUNET_break_op (0);
+    use_reply_with_error (
+      uc,
+      MHD_HTTP_CONFLICT,
+      TALER_EC_MERCHANT_POST_USING_TEMPLATES_WRONG_TYPE,
+      "template_contract has different type");
+    return;
+  }
+  uc->phase++;
+}
+
+
+/* ***************** USE_PHASE_PARSE_TEMPLATE **************** */
+
+
+/**
+ * Parse template.
+ *
+ * @param[in,out] uc use context
+ */
+static void
+handle_phase_template_contract (struct UseContext *uc)
+{
+  const char *err_name;
+  enum GNUNET_GenericReturnValue res;
+
+  res = TALER_MERCHANT_template_contract_parse (
+    uc->lookup_template.etp.template_contract,
+    &uc->template_contract,
+    &err_name);
+  if (GNUNET_OK != res)
+  {
+    GNUNET_break (0);
+    use_reply_with_error (uc,
+                          MHD_HTTP_INTERNAL_SERVER_ERROR,
+                          TALER_EC_GENERIC_DB_FETCH_FAILED,
+                          err_name);
+    return;
+  }
+  uc->phase++;
+}
+
+
+/* ***************** USE_PHASE_DB_FETCH **************** */
+
+/**
+ * Fetch DB data for inventory templates.
+ *
+ * @param[in,out] uc use context
+ */
+static void
+handle_phase_db_fetch (struct UseContext *uc)
+{
+  struct TMH_MerchantInstance *mi = uc->hc->instance;
+
+  switch (uc->template_type)
+  {
+  case TALER_MERCHANT_TEMPLATE_TYPE_FIXED_ORDER:
+    uc->phase++;
+    return;
+  case TALER_MERCHANT_TEMPLATE_TYPE_PAIVANA:
+    uc->phase++;
+    return;
+  case TALER_MERCHANT_TEMPLATE_TYPE_INVENTORY_CART:
+    break;
+  case TALER_MERCHANT_TEMPLATE_TYPE_INVALID:
+    GNUNET_assert (0);
+  }
+
+  for (unsigned int i = 0;
+       i < uc->parse_request.inventory.items_len;
+       i++)
+  {
+    struct InventoryTemplateItemContext *item =
+      &uc->parse_request.inventory.items[i];
+    enum GNUNET_DB_QueryStatus qs;
+
+    qs = TMH_db->lookup_product (TMH_db->cls,
+                                 mi->settings.id,
+                                 item->product_id,
+                                 &item->pd,
+                                 &item->num_categories,
+                                 &item->categories);
+    switch (qs)
+    {
+    case GNUNET_DB_STATUS_HARD_ERROR:
+      GNUNET_break (0);
+      use_reply_with_error (uc,
+                            MHD_HTTP_INTERNAL_SERVER_ERROR,
+                            TALER_EC_GENERIC_DB_FETCH_FAILED,
+                            "lookup_product");
+      return;
+    case GNUNET_DB_STATUS_SOFT_ERROR:
+      GNUNET_break (0);
+      use_reply_with_error (uc,
+                            MHD_HTTP_INTERNAL_SERVER_ERROR,
+                            TALER_EC_GENERIC_DB_FETCH_FAILED,
+                            "lookup_product");
+      return;
+    case GNUNET_DB_STATUS_SUCCESS_NO_RESULTS:
+      use_reply_with_error (uc,
+                            MHD_HTTP_NOT_FOUND,
+                            TALER_EC_MERCHANT_GENERIC_PRODUCT_UNKNOWN,
+                            item->product_id);
+      return;
+    case GNUNET_DB_STATUS_SUCCESS_ONE_RESULT:
+      break;
+    }
+  }
+  uc->phase++;
+}
+
+
+/* *************** Helpers for USE_PHASE_VERIFY ***************** */
+
+/**
+ * Check if the given product ID appears in the array of allowed_products.
+ *
+ * @param allowed_products JSON array of product IDs allowed by the template, may be NULL
+ * @param product_id product ID to check
+ * @return true if the product ID is in the list
+ */
+static bool
+product_id_allowed (const json_t *allowed_products,
+                    const char *product_id)
+{
+  const json_t *entry;
+  size_t idx;
+
+  if (NULL == allowed_products)
+    return false;
+  json_array_foreach ((json_t *) allowed_products, idx, entry)
+  {
+    if (! json_is_string (entry))
+    {
+      GNUNET_break (0);
+      continue;
+    }
+    if (0 == strcmp (json_string_value (entry),
+                     product_id))
+      return true;
+  }
+  return false;
+}
+
+
+/**
+ * Check if any product category is in the selected_categories list.
+ *
+ * @param allowed_categories JSON array of categories allowed by the template, may be NULL
+ * @param num_categories length of @a categories
+ * @param categories list of categories of the selected product
+ * @return true if any category of the product is in the list of allowed categories matches
+ */
+static bool
+category_allowed (const json_t *allowed_categories,
+                  size_t num_categories,
+                  const uint64_t categories[num_categories])
+{
+  const json_t *entry;
+  size_t idx;
+
+  if (NULL == allowed_categories)
+    return false;
+  json_array_foreach ((json_t *) allowed_categories,
+                      idx,
+                      entry)
+  {
+    uint64_t selected_id;
+
+    if (! json_is_integer (entry))
+    {
+      GNUNET_break (0);
+      continue;
+    }
+    if (0 > json_integer_value (entry))
+    {
+      GNUNET_break (0);
+      continue;
+    }
+    selected_id = (uint64_t) json_integer_value (entry);
+    for (size_t i = 0; i < num_categories; i++)
+    {
+      if (categories[i] == selected_id)
+        return true;
+    }
+  }
+  return false;
+}
+
+
+/**
+ * Verify request data for inventory templates.
+ * Checks that the selected products are allowed
+ * for this template.
+ *
+ * @param[in,out] uc use context
+ * @return #GNUNET_OK on success
+ */
+static enum GNUNET_GenericReturnValue
+verify_using_templates_inventory (struct UseContext *uc)
+{
+  if (uc->template_contract.details.inventory.choose_one &&
+      (1 != uc->parse_request.inventory.items_len))
+  {
+    GNUNET_break_op (0);
+    use_reply_with_error (uc,
+                          MHD_HTTP_CONFLICT,
+                          TALER_EC_GENERIC_PARAMETER_MALFORMED,
+                          "inventory_selection");
+    return GNUNET_SYSERR;
+  }
+  if (uc->template_contract.details.inventory.selected_all)
+    return GNUNET_OK;
+  for (unsigned int i = 0;
+       i < uc->parse_request.inventory.items_len;
+       i++)
+  {
+    struct InventoryTemplateItemContext *item =
+      &uc->parse_request.inventory.items[i];
+    const char *eparam = NULL;
+
+    if (GNUNET_OK !=
+        TALER_MERCHANT_vk_process_quantity_inputs (
+          TALER_MERCHANT_VK_QUANTITY,
+          item->pd.allow_fractional_quantity,
+          true,
+          0,
+          false,
+          item->unit_quantity,
+          &item->quantity_value,
+          &item->quantity_frac,
+          &eparam))
+    {
+      GNUNET_break_op (0);
+      use_reply_with_error (uc,
+                            MHD_HTTP_BAD_REQUEST,
+                            TALER_EC_GENERIC_PARAMETER_MALFORMED,
+                            eparam);
+      return GNUNET_SYSERR;
+    }
+
+    if (0 == item->pd.price_array_length)
+    {
+      GNUNET_break (0);
+      use_reply_with_error (uc,
+                            MHD_HTTP_INTERNAL_SERVER_ERROR,
+                            TALER_EC_GENERIC_INTERNAL_INVARIANT_FAILURE,
+                            "price_array");
+      return GNUNET_SYSERR;
+    }
+  }
+
+  for (unsigned int i = 0;
+       i < uc->parse_request.inventory.items_len;
+       i++)
+  {
+    struct InventoryTemplateItemContext *item =
+      &uc->parse_request.inventory.items[i];
+
+    if (product_id_allowed (uc->template_contract.details.inventory.
+                            selected_products,
+                            item->product_id))
+      continue;
+    if (category_allowed (
+          uc->template_contract.details.inventory.selected_categories,
+          item->num_categories,
+          item->categories))
+      continue;
+    GNUNET_break_op (0);
+    use_reply_with_error (
+      uc,
+      MHD_HTTP_CONFLICT,
+      TALER_EC_MERCHANT_POST_USING_TEMPLATES_WRONG_PRODUCT,
+      item->product_id);
+    return GNUNET_SYSERR;
+  }
+  return GNUNET_OK;
+}
+
+
+/**
+ * Verify request data for fixed-order templates.
+ * As here we cannot compute the total amount, either
+ * the template or the client request must provide it.
+ *
+ * @param[in,out] uc use context
+ * @return #GNUNET_OK on success
+ */
+static enum GNUNET_GenericReturnValue
+verify_using_templates_fixed (
+  struct UseContext *uc)
+{
+  if ( (! uc->parse_request.no_amount) &&
+       (! uc->template_contract.no_amount) )
+  {
+    GNUNET_break_op (0);
+    use_reply_with_error (uc,
+                          MHD_HTTP_CONFLICT,
+                          TALER_EC_MERCHANT_POST_USING_TEMPLATES_AMOUNT_CONFLICT_TEMPLATES_CONTRACT_AMOUNT,
+                          NULL);
+    return GNUNET_SYSERR;
+  }
+  if (uc->parse_request.no_amount &&
+      uc->template_contract.no_amount)
+  {
+    GNUNET_break_op (0);
+    use_reply_with_error (uc,
+                          MHD_HTTP_CONFLICT,
+                          TALER_EC_MERCHANT_POST_USING_TEMPLATES_NO_AMOUNT,
+                          NULL);
+    return GNUNET_SYSERR;
+  }
+  return GNUNET_OK;
+}
+
+
+/**
+ * Verify request data for paivana templates.
+ *
+ * @param[in,out] uc use context
+ * @return #GNUNET_OK on success
+ */
+static enum GNUNET_GenericReturnValue
+verify_using_templates_paivana (
+  struct UseContext *uc)
+{
+  if (NULL != uc->template_contract.details.paivana.website_regex)
+  {
+    regex_t ex;
+    bool allowed = false;
+
+    if (0 != regcomp (&ex,
+                      uc->template_contract.details.paivana.website_regex,
+                      REG_NOSUB | REG_EXTENDED))
+    {
+      GNUNET_break_op (0);
+      return GNUNET_SYSERR;
+    }
+    if (0 ==
+        regexec (&ex,
+                 uc->parse_request.paivana.website,
+                 0, NULL,
+                 0))
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                  "Website `%s' allowed by template\n",
+                  uc->parse_request.paivana.website);
+      allowed = true;
+    }
+    regfree (&ex);
+    if (! allowed)
+      return GNUNET_SYSERR;
+  }
+  return GNUNET_OK;
+}
+
+
+/**
+ * Verify that the client request is structurally acceptable for the specified
+ * template.  Does NOT check the total amount being reasonable.
+ *
+ * @param[in,out] uc use context
+ */
+static void
+handle_phase_verify (
+  struct UseContext *uc)
+{
+  enum GNUNET_GenericReturnValue res = GNUNET_SYSERR;
+
+  if ( (NULL != uc->parse_request.summary) &&
+       (NULL != uc->template_contract.summary) )
+  {
+    GNUNET_break_op (0);
+    use_reply_with_error (uc,
+                          MHD_HTTP_CONFLICT,
+                          TALER_EC_MERCHANT_POST_USING_TEMPLATES_SUMMARY_CONFLICT_TEMPLATES_CONTRACT_SUBJECT,
+                          NULL);
+    return;
+  }
+  if ( (NULL == uc->parse_request.summary) &&
+       (NULL == uc->template_contract.summary) )
+  {
+    GNUNET_break_op (0);
+    use_reply_with_error (uc,
+                          MHD_HTTP_CONFLICT,
+                          TALER_EC_MERCHANT_POST_USING_TEMPLATES_NO_SUMMARY,
+                          NULL);
+    return;
+  }
+  if ( (! uc->parse_request.no_amount) &&
+       (NULL != uc->template_contract.currency) &&
+       (0 != strcasecmp (uc->template_contract.currency,
+                         uc->parse_request.amount.currency)) )
+  {
+    GNUNET_break_op (0);
+    use_reply_with_error (uc,
+                          MHD_HTTP_CONFLICT,
+                          TALER_EC_MERCHANT_GENERIC_CURRENCY_MISMATCH,
+                          uc->template_contract.currency);
+    return;
+  }
+  switch (uc->template_type)
+  {
+  case TALER_MERCHANT_TEMPLATE_TYPE_FIXED_ORDER:
+    res = verify_using_templates_fixed (uc);
+    break;
+  case TALER_MERCHANT_TEMPLATE_TYPE_PAIVANA:
+    res = verify_using_templates_paivana (uc);
+    break;
+  case TALER_MERCHANT_TEMPLATE_TYPE_INVENTORY_CART:
+    res = verify_using_templates_inventory (uc);
+    break;
+  case TALER_MERCHANT_TEMPLATE_TYPE_INVALID:
+    GNUNET_assert (0);
+  }
+  if (GNUNET_OK == res)
+    uc->phase++;
+}
+
+
+/* ***************** USE_PHASE_COMPUTE_PRICE **************** */
+
+
+/**
+ * Compute the line total for a product based on quantity.
+ *
+ * @param unit_price price per unit
+ * @param quantity integer quantity
+ * @param quantity_frac fractional quantity (0..TALER_MERCHANT_UNIT_FRAC_BASE-1)
+ * @param[out] line_total resulting line total
+ * @return #GNUNET_OK on success
+ */
+static enum GNUNET_GenericReturnValue
+compute_line_total (const struct TALER_Amount *unit_price,
+                    uint64_t quantity,
+                    uint32_t quantity_frac,
+                    struct TALER_Amount *line_total)
+{
+  struct TALER_Amount tmp;
+
+  GNUNET_assert (GNUNET_OK ==
+                 TALER_amount_set_zero (unit_price->currency,
+                                        line_total));
+  if ( (0 != quantity) &&
+       (0 >
+        TALER_amount_multiply (line_total,
+                               unit_price,
+                               (uint32_t) quantity)) )
+  {
+    GNUNET_break (0);
+    return GNUNET_SYSERR;
+  }
+  if (0 == quantity_frac)
+    return GNUNET_OK;
+  if (0 >
+      TALER_amount_multiply (&tmp,
+                             unit_price,
+                             quantity_frac))
+  {
+    GNUNET_break (0);
+    return GNUNET_SYSERR;
+  }
+  TALER_amount_divide (&tmp,
+                       &tmp,
+                       TALER_MERCHANT_UNIT_FRAC_BASE);
+  if (0 >
+      TALER_amount_add (line_total,
+                        line_total,
+                        &tmp))
+  {
+    GNUNET_break (0);
+    return GNUNET_SYSERR;
+  }
+  return GNUNET_OK;
+}
+
+
+/**
+ * Find the price of the given @a item in the specified
+ * @a currency.
+ *
+ * @param currency currency to search price in
+ * @param item item to check prices of
+ * @return NULL if a suitable price was not found
+ */
+static const struct TALER_Amount *
+find_item_price_in_currency (
+  const char *currency,
+  const struct InventoryTemplateItemContext *item)
+{
+  for (size_t j = 0; j < item->pd.price_array_length; j++)
+  {
+    if (0 == strcasecmp (item->pd.price_array[j].currency,
+                         currency))
+      return &item->pd.price_array[j];
+  }
+  return NULL;
+}
+
+
+/**
+ * Compute totals for all currencies shared across selected products.
+ *
+ * @param[in,out] uc use context
+ * @return #GNUNET_OK on success (including no price due to no items)
+ *         #GNUNET_NO if we could not find a price in any accepted currency
+ *                    for all selected products
+ *         #GNUNET_SYSERR on arithmetic issues (internal error)
+ */
+static enum GNUNET_GenericReturnValue
+compute_totals_per_currency (struct UseContext *uc)
+{
+  const struct InventoryTemplateItemContext *items
+    = uc->parse_request.inventory.items;
+  unsigned int items_len = uc->parse_request.inventory.items_len;
+
+  if (0 == items_len)
+    return GNUNET_OK;
+  for (size_t i = 0; i < items[0].pd.price_array_length; i++)
+  {
+    const struct TALER_Amount *price
+      = &items[0].pd.price_array[i];
+    struct TALER_Amount zero;
+
+    if (! TMH_test_exchange_configured_for_currency (price->currency))
+      continue;
+    GNUNET_assert (GNUNET_OK ==
+                   TALER_amount_set_zero (price->currency,
+                                          &zero));
+    GNUNET_array_append (uc->compute_price.totals,
+                         uc->compute_price.totals_len,
+                         zero);
+  }
+  if (0 == uc->compute_price.totals_len)
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                "No currency supported by our configuration in which we have prices for first selected product!\n");
+    return GNUNET_NO;
+  }
+  /* Loop through items, ensure each currency exists and sum totals. */
+  for (unsigned int i = 0; i < items_len; i++)
+  {
+    const struct InventoryTemplateItemContext *item = &items[i];
+    unsigned int c = 0;
+
+    while (c < uc->compute_price.totals_len)
+    {
+      struct TALER_Amount *total = &uc->compute_price.totals[c];
+      const struct TALER_Amount *unit_price;
+      struct TALER_Amount line_total;
+
+      unit_price = find_item_price_in_currency (total->currency,
+                                                item);
+      if (NULL == unit_price)
+      {
+        /* Drop the currency: we have no price in one of
+           the selected products */
+        GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                    "Product `%s' has no price in %s: dropping currency\n",
+                    item->product_id,
+                    total->currency);
+        *total = uc->compute_price.totals[--uc->compute_price.totals_len];
+        continue;
+      }
+      if (GNUNET_OK !=
+          compute_line_total (unit_price,
+                              item->quantity_value,
+                              item->quantity_frac,
+                              &line_total))
+      {
+        GNUNET_break (0);
+        return GNUNET_SYSERR;
+      }
+      if (0 >
+          TALER_amount_add (total,
+                            total,
+                            &line_total))
+      {
+        GNUNET_break (0);
+        return GNUNET_SYSERR;
+      }
+      c++;
+    }
+  }
+  if (0 == uc->compute_price.totals_len)
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                "No currency available in which we have prices for all selected products!\n");
+    GNUNET_free (uc->compute_price.totals);
+  }
+  return (0 == uc->compute_price.totals_len)
+    ? GNUNET_NO
+    : GNUNET_OK;
+}
+
+
+/**
+ * Compute total for only the given @a currency.
+ *
+ * @param items_len length of @a items
+ * @param items inventory items
+ * @param currency currency to total
+ * @param[out] total computed total
+ * @return #GNUNET_OK on success
+ *         #GNUNET_NO if we could not find a price in any accepted currency
+ *                    for all selected products
+ *         #GNUNET_SYSERR on arithmetic issues (internal error)
+ */
+static enum GNUNET_GenericReturnValue
+compute_inventory_total (unsigned int items_len,
+                         const struct InventoryTemplateItemContext *items,
+                         const char *currency,
+                         struct TALER_Amount *total)
+{
+  GNUNET_assert (NULL != currency);
+  GNUNET_assert (GNUNET_OK ==
+                 TALER_amount_set_zero (currency,
+                                        total));
+  for (unsigned int i = 0; i < items_len; i++)
+  {
+    const struct InventoryTemplateItemContext *item = &items[i];
+    const struct TALER_Amount *unit_price;
+    struct TALER_Amount line_total;
+
+    unit_price = find_item_price_in_currency (currency,
+                                              item);
+    if (NULL == unit_price)
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                  "compute_inventory_total: no price in %s for product `%s'\n",
+                  currency,
+                  item->product_id);
+      return GNUNET_NO;
+    }
+    if (GNUNET_OK !=
+        compute_line_total (unit_price,
+                            item->quantity_value,
+                            item->quantity_frac,
+                            &line_total))
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                  "compute_inventory_total: line total failed for %s in %s\n",
+                  item->product_id,
+                  currency);
+      return GNUNET_SYSERR;
+    }
+    if (0 >
+        TALER_amount_add (total,
+                          total,
+                          &line_total))
+    {
+      GNUNET_break (0);
+      return GNUNET_SYSERR;
+    }
+  }
+  return GNUNET_OK;
+}
+
+
+/**
+ * Compute total price.
+ *
+ * @param[in,out] uc use context
+ */
+static void
+handle_phase_compute_price (struct UseContext *uc)
+{
+  const char *primary_currency;
+  enum GNUNET_GenericReturnValue ret;
+
+  switch (uc->template_type)
+  {
+  case TALER_MERCHANT_TEMPLATE_TYPE_FIXED_ORDER:
+    uc->compute_price.totals
+      = GNUNET_new (struct TALER_Amount);
+    uc->compute_price.totals_len
+      = 1;
+    if (uc->parse_request.no_amount)
+    {
+      GNUNET_assert (! uc->template_contract.no_amount);
+      *uc->compute_price.totals
+        = uc->template_contract.amount;
+    }
+    else
+    {
+      GNUNET_assert (uc->template_contract.no_amount);
+      *uc->compute_price.totals
+        = uc->parse_request.amount;
+    }
+    uc->phase++;
+    return;
+  case TALER_MERCHANT_TEMPLATE_TYPE_INVENTORY_CART:
+    /* handled below */
+    break;
+  case TALER_MERCHANT_TEMPLATE_TYPE_PAIVANA:
+    {
+      const struct TALER_MERCHANT_TemplateContractPaivana *tcp
+        = &uc->template_contract.details.paivana;
+      json_t *choices;
+
+      choices = json_array ();
+      GNUNET_assert (NULL != choices);
+      for (size_t i = 0; i < tcp->choices_len; i++)
+      {
+        /* Make deep copy, we're going to MODIFY it! */
+        struct TALER_MERCHANT_ContractChoice choice
+          = tcp->choices[i];
+
+        choice.no_tip = uc->parse_request.no_tip;
+        if (! uc->parse_request.no_tip)
+        {
+          if (GNUNET_YES !=
+              TALER_amount_cmp_currency (&choice.amount,
+                                         &uc->parse_request.tip))
+            continue; /* tip does not match choice currency */
+          choice.tip = uc->parse_request.tip;
+          if (0 >
+              TALER_amount_add (&choice.amount,
+                                &choice.amount,
+                                &uc->parse_request.tip))
+          {
+            GNUNET_break (0);
+            use_reply_with_error (uc,
+                                  MHD_HTTP_INTERNAL_SERVER_ERROR,
+                                  TALER_EC_GENERIC_FAILED_COMPUTE_AMOUNT,
+                                  "tip");
+            return;
+          }
+        }
+        GNUNET_assert (0 ==
+                       json_array_append_new (
+                         choices,
+                         TALER_MERCHANT_json_from_contract_choice (&choice,
+                                                                   true)));
+      }
+      if (0 == json_array_size (choices))
+      {
+        GNUNET_break_op (0);
+        json_decref (choices);
+        use_reply_with_error (uc,
+                              MHD_HTTP_CONFLICT,
+                              TALER_EC_MERCHANT_POST_USING_TEMPLATES_NO_CURRENCY,
+                              "tip");
+        return;
+      }
+      uc->compute_price.choices = choices;
+    }
+    /* Note: we already did the tip and pricing
+       fully here, so we skip these phases. */
+    uc->phase = USE_PHASE_CREATE_ORDER;
+    return;
+  case TALER_MERCHANT_TEMPLATE_TYPE_INVALID:
+    GNUNET_assert (0);
+  }
+  primary_currency = uc->template_contract.currency;
+  if (! uc->parse_request.no_amount)
+    primary_currency = uc->parse_request.amount.currency;
+  if (! uc->parse_request.no_tip)
+    primary_currency = uc->parse_request.tip.currency;
+  if (NULL == primary_currency)
+  {
+    ret = compute_totals_per_currency (uc);
+  }
+  else
+  {
+    uc->compute_price.totals
+      = GNUNET_new (struct TALER_Amount);
+    uc->compute_price.totals_len
+      = 1;
+    ret = compute_inventory_total (
+      uc->parse_request.inventory.items_len,
+      uc->parse_request.inventory.items,
+      primary_currency,
+      uc->compute_price.totals);
+  }
+  if (GNUNET_SYSERR == ret)
+  {
+    use_reply_with_error (
+      uc,
+      MHD_HTTP_INTERNAL_SERVER_ERROR,
+      TALER_EC_GENERIC_FAILED_COMPUTE_AMOUNT,
+      "calculation of currency totals failed");
+    return;
+  }
+  if (GNUNET_NO == ret)
+  {
+    use_reply_with_error (uc,
+                          MHD_HTTP_CONFLICT,
+                          TALER_EC_MERCHANT_POST_USING_TEMPLATES_NO_CURRENCY,
+                          NULL);
+    return;
+  }
+
+  uc->phase++;
+}
+
+
+/* ***************** USE_PHASE_CHECK_TIP **************** */
+
+
+/**
+ * Check that tip specified is reasonable and add to total.
+ *
+ * @param[in,out] uc use context
+ */
+static void
+handle_phase_check_tip (struct UseContext *uc)
+{
+  struct TALER_Amount *total_amount;
+
+  if (uc->parse_request.no_tip)
+  {
+    uc->phase++;
+    return;
+  }
+  if (0 == uc->compute_price.totals_len)
+  {
+    if (! TMH_test_exchange_configured_for_currency (
+          uc->parse_request.tip.currency))
+    {
+      GNUNET_break_op (0);
+      use_reply_with_error (uc,
+                            MHD_HTTP_CONFLICT,
+                            TALER_EC_MERCHANT_GENERIC_CURRENCY_MISMATCH,
+                            "Tip currency is not supported by backend");
+      return;
+    }
+    uc->compute_price.totals
+      = GNUNET_new (struct TALER_Amount);
+    uc->compute_price.totals_len
+      = 1;
+    *uc->compute_price.totals
+      = uc->parse_request.tip;
+    uc->phase++;
+    return;
+  }
+  GNUNET_assert (1 == uc->compute_price.totals_len);
+  total_amount = &uc->compute_price.totals[0];
+  if (GNUNET_YES !=
+      TALER_amount_cmp_currency (&uc->parse_request.tip,
+                                 total_amount))
+  {
+    GNUNET_break_op (0);
+    use_reply_with_error (uc,
+                          MHD_HTTP_CONFLICT,
+                          TALER_EC_MERCHANT_GENERIC_CURRENCY_MISMATCH,
+                          uc->parse_request.tip.currency);
+    return;
+  }
+  if (0 >
+      TALER_amount_add (total_amount,
+                        total_amount,
+                        &uc->parse_request.tip))
+  {
+    GNUNET_break (0);
+    use_reply_with_error (uc,
+                          MHD_HTTP_INTERNAL_SERVER_ERROR,
+                          TALER_EC_GENERIC_FAILED_COMPUTE_AMOUNT,
+                          "tip");
+    return;
+  }
+  uc->phase++;
+}
+
+
+/* ***************** USE_PHASE_CHECK_TOTAL **************** */
+
+/**
+ * Check that if the client specified a total,
+ * it matches our own calculation.
+ *
+ * @param[in,out] uc use context
+ */
+static void
+handle_phase_check_total (struct UseContext *uc)
+{
+  GNUNET_assert (1 <= uc->compute_price.totals_len);
+  if (! uc->parse_request.no_amount)
+  {
+    GNUNET_assert (1 == uc->compute_price.totals_len);
+    GNUNET_assert (GNUNET_YES ==
+                   TALER_amount_cmp_currency (&uc->parse_request.amount,
+                                              &uc->compute_price.totals[0]));
+    if (0 !=
+        TALER_amount_cmp (&uc->parse_request.amount,
+                          &uc->compute_price.totals[0]))
+    {
+      GNUNET_break_op (0);
+      use_reply_with_error (uc,
+                            MHD_HTTP_CONFLICT,
+                            TALER_EC_MERCHANT_POST_USING_TEMPLATES_AMOUNT_CONFLICT_TEMPLATES_CONTRACT_AMOUNT,
+                            TALER_amount2s (&uc->compute_price.totals[0]));
+      return;
+    }
+  }
+  uc->phase++;
+}
+
+
+/* ***************** USE_PHASE_CREATE_ORDER **************** */
+
+
+/**
+ * Create order request for inventory templates.
+ *
+ * @param[in,out] uc use context
+ */
+static void
+create_using_templates_inventory (struct UseContext *uc)
+{
+  json_t *inventory_products;
+  json_t *choices;
+
+  inventory_products = json_array ();
+  GNUNET_assert (NULL != inventory_products);
+  for (unsigned int i = 0;
+       i < uc->parse_request.inventory.items_len;
+       i++)
+  {
+    const struct InventoryTemplateItemContext *item =
+      &uc->parse_request.inventory.items[i];
+
+    GNUNET_assert (0 ==
+                   json_array_append_new (
+                     inventory_products,
+                     GNUNET_JSON_PACK (
+                       GNUNET_JSON_pack_string ("product_id",
+                                                item->product_id),
+                       GNUNET_JSON_pack_string ("unit_quantity",
+                                                item->unit_quantity))));
+  }
+  choices = json_array ();
+  GNUNET_assert (NULL != choices);
+  for (unsigned int i = 0;
+       i < uc->compute_price.totals_len;
+       i++)
+  {
+    GNUNET_assert (0 ==
+                   json_array_append_new (
+                     choices,
+                     GNUNET_JSON_PACK (
+                       TALER_JSON_pack_amount ("amount",
+                                               &uc->compute_price.totals[i]),
+                       GNUNET_JSON_pack_allow_null (
+                         TALER_JSON_pack_amount ("tip",
+                                                 uc->parse_request.no_tip
+                                                ? NULL
+                                                : &uc->parse_request.tip))
+                       )));
+  }
+
+  uc->ihc.request_body
+    = GNUNET_JSON_PACK (
+        GNUNET_JSON_pack_allow_null (
+          GNUNET_JSON_pack_string ("otp_id",
+                                   uc->lookup_template.etp.otp_id)),
+        GNUNET_JSON_pack_array_steal ("inventory_products",
+                                      inventory_products),
+        GNUNET_JSON_pack_object_steal (
+          "order",
+          GNUNET_JSON_PACK (
+            GNUNET_JSON_pack_uint64 ("version",
+                                     1),
+            GNUNET_JSON_pack_array_steal ("choices",
+                                          choices),
+            GNUNET_JSON_pack_string ("summary",
+                                     NULL == uc->parse_request.summary
+                                   ? uc->template_contract.summary
+                                   : uc->parse_request.summary))));
+}
+
+
+/**
+ * Create order request for fixed-order templates.
+ *
+ * @param[in,out] uc use context
+ */
+static void
+create_using_templates_fixed (struct UseContext *uc)
+{
+  uc->ihc.request_body
+    = GNUNET_JSON_PACK (
+        GNUNET_JSON_pack_allow_null (
+          GNUNET_JSON_pack_string ("otp_id",
+                                   uc->lookup_template.etp.otp_id)),
+        GNUNET_JSON_pack_object_steal (
+          "order",
+          GNUNET_JSON_PACK (
+            TALER_JSON_pack_amount (
+              "amount",
+              &uc->compute_price.totals[0]),
+            GNUNET_JSON_pack_allow_null (
+              TALER_JSON_pack_amount ("tip",
+                                      uc->parse_request.no_tip
+                                      ? NULL
+                                      : &uc->parse_request.tip)),
+            GNUNET_JSON_pack_string (
+              "summary",
+              NULL == uc->parse_request.summary
+            ? uc->template_contract.summary
+            : uc->parse_request.summary))));
+}
+
+
+/**
+ * Create order request for paivana templates.
+ *
+ * @param[in,out] uc use context
+ */
+static void
+create_using_templates_paivana (struct UseContext *uc)
+{
+  uc->ihc.request_body
+    = GNUNET_JSON_PACK (
+        GNUNET_JSON_pack_string (
+          "session_id",
+          uc->parse_request.paivana.paivana_id),
+        GNUNET_JSON_pack_object_steal (
+          "order",
+          GNUNET_JSON_PACK (
+            GNUNET_JSON_pack_uint64 ("version",
+                                     1),
+            GNUNET_JSON_pack_array_incref ("choices",
+                                           uc->compute_price.choices),
+            GNUNET_JSON_pack_string (
+              "summary",
+              NULL == uc->parse_request.summary
+              ? uc->template_contract.summary
+              : uc->parse_request.summary),
+            GNUNET_JSON_pack_string ("fulfillment_url",
+                                     uc->parse_request.paivana.website))));
+}
+
+
+static void
+handle_phase_create_order (struct UseContext *uc)
+{
+  GNUNET_assert (NULL == uc->ihc.request_body);
+  switch (uc->template_type)
+  {
+  case TALER_MERCHANT_TEMPLATE_TYPE_FIXED_ORDER:
+    create_using_templates_fixed (uc);
+    break;
+  case TALER_MERCHANT_TEMPLATE_TYPE_PAIVANA:
+    create_using_templates_paivana (uc);
+    break;
+  case TALER_MERCHANT_TEMPLATE_TYPE_INVENTORY_CART:
+    create_using_templates_inventory (uc);
+    break;
+  case TALER_MERCHANT_TEMPLATE_TYPE_INVALID:
+    GNUNET_assert (0);
+  }
+  uc->phase++;
+}
+
+
+/* ***************** Main handler **************** */
+
+MHD_RESULT
+TMH_post_using_templates_ID (
+  const struct TMH_RequestHandler *rh,
+  struct MHD_Connection *connection,
+  struct TMH_HandlerContext *hc)
+{
+  struct UseContext *uc = hc->ctx;
+
+  (void) rh;
+  if (NULL == uc)
+  {
+    uc = GNUNET_new (struct UseContext);
+    uc->hc = hc;
+    hc->ctx = uc;
+    hc->cc = &cleanup_use_context;
+    uc->ihc.instance = hc->instance;
+    uc->phase = USE_PHASE_PARSE_REQUEST;
+    uc->template_type = TALER_MERCHANT_TEMPLATE_TYPE_INVALID;
+  }
+
+  while (1)
+  {
+    switch (uc->phase)
+    {
+    case USE_PHASE_PARSE_REQUEST:
+      handle_phase_parse_request (uc);
+      break;
+    case USE_PHASE_LOOKUP_TEMPLATE:
+      handle_phase_lookup_template (uc);
+      break;
+    case USE_PHASE_PARSE_TEMPLATE:
+      handle_phase_template_contract (uc);
+      break;
+    case USE_PHASE_DB_FETCH:
+      handle_phase_db_fetch (uc);
+      break;
+    case USE_PHASE_VERIFY:
+      handle_phase_verify (uc);
+      break;
+    case USE_PHASE_COMPUTE_PRICE:
+      handle_phase_compute_price (uc);
+      break;
+    case USE_PHASE_CHECK_TIP:
+      handle_phase_check_tip (uc);
+      break;
+    case USE_PHASE_CHECK_TOTAL:
+      handle_phase_check_total (uc);
+      break;
+    case USE_PHASE_CREATE_ORDER:
+      handle_phase_create_order (uc);
+      break;
+    case USE_PHASE_SUBMIT_ORDER:
+      return TMH_private_post_orders (
+        NULL,    /* not even used */
+        connection,
+        &uc->ihc);
+    case USE_PHASE_FINISHED_MHD_YES:
+      return MHD_YES;
+    case USE_PHASE_FINISHED_MHD_NO:
+      return MHD_NO;
+    }
+  }
+}
diff --git a/src/backend/taler-merchant-httpd_post-templates-ID.h b/src/backend/taler-merchant-httpd_post-templates-ID.h
@@ -0,0 +1,40 @@
+/*
+  This file is part of TALER
+  (C) 2022 Taler Systems SA
+
+  TALER is free software; you can redistribute it and/or modify it under the
+  terms of the GNU General Public License as published by the Free Software
+  Foundation; either version 3, or (at your option) any later version.
+
+  TALER is distributed in the hope that it will be useful, but WITHOUT ANY
+  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+  A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License along with
+  TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+*/
+/**
+ * @file taler-merchant-httpd_post-using-templates.h
+ * @brief headers for POST /using-templates handler
+ * @author Priscilla Huang
+ */
+#ifndef TALER_MERCHANT_HTTPD_POST_TEMPLATES_ID_H
+#define TALER_MERCHANT_HTTPD_POST_TEMPLATES_ID_H
+
+#include "taler-merchant-httpd.h"
+
+/**
+ * Generate a template that customer can use it. Returns an MHD_RESULT.
+ *
+ * @param rh details about this request handler
+ * @param connection the MHD connection to handle
+ * @param[in,out] hc context with further information about the request
+ * @return MHD result code
+ */
+MHD_RESULT
+TMH_post_using_templates_ID (const struct TMH_RequestHandler *rh,
+                             struct MHD_Connection *connection,
+                             struct TMH_HandlerContext *hc);
+
+
+#endif
diff --git a/src/backend/taler-merchant-httpd_post-using-templates.c b/src/backend/taler-merchant-httpd_post-using-templates.c
@@ -1,1782 +0,0 @@
-/*
-  This file is part of TALER
-  (C) 2022-2026 Taler Systems SA
-
-  TALER is free software; you can redistribute it and/or modify
-  it under the terms of the GNU Affero General Public License as
-  published by the Free Software Foundation; either version 3,
-  or (at your option) any later version.
-
-  TALER is distributed in the hope that it will be useful, but
-  WITHOUT ANY WARRANTY; without even the implied warranty of
-  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-  GNU General Public License for more details.
-
-  You should have received a copy of the GNU General Public
-  License along with TALER; see the file COPYING.  If not,
-  see <http://www.gnu.org/licenses/>
-*/
-
-/**
- * @file taler-merchant-httpd_post-using-templates.c
- * @brief implementing POST /using-templates request handling
- * @author Priscilla HUANG
- * @author Christian Grothoff
- */
-#include "platform.h"
-#include "taler-merchant-httpd_post-using-templates.h"
-#include "taler-merchant-httpd_private-post-orders.h"
-#include "taler-merchant-httpd_helper.h"
-#include "taler-merchant-httpd_exchanges.h"
-#include "taler_merchant_util.h"
-#include <taler/taler_json_lib.h>
-#include <regex.h>
-
-
-/**
- * Item selected from inventory_selection.
- */
-struct InventoryTemplateItemContext
-{
-  /**
-   * Product ID as referenced in inventory.
-   */
-  const char *product_id;
-
-  /**
-   * Unit quantity string as provided by the client.
-   */
-  const char *unit_quantity;
-
-  /**
-   * Parsed integer quantity.
-   */
-  uint64_t quantity_value;
-
-  /**
-   * Parsed fractional quantity.
-   */
-  uint32_t quantity_frac;
-
-  /**
-   * Product details from the DB (includes price array).
-   */
-  struct TALER_MERCHANTDB_ProductDetails pd;
-
-  /**
-   * Categories referenced by the product.
-   */
-  uint64_t *categories;
-
-  /**
-   * Length of @e categories.
-   */
-  size_t num_categories;
-};
-
-
-/**
- * Our context.
- */
-enum UsePhase
-{
-  /**
-   * Parse request payload into context fields.
-   */
-  USE_PHASE_PARSE_REQUEST,
-
-  /**
-   * Fetch template details from the database.
-   */
-  USE_PHASE_LOOKUP_TEMPLATE,
-
-  /**
-   * Parse template.
-   */
-  USE_PHASE_PARSE_TEMPLATE,
-
-  /**
-   * Load additional details (like products and
-   * categories) needed for verification and
-   * price computation.
-   */
-  USE_PHASE_DB_FETCH,
-
-  /**
-   * Validate request and template compatibility.
-   */
-  USE_PHASE_VERIFY,
-
-  /**
-   * Compute price of the order.
-   */
-  USE_PHASE_COMPUTE_PRICE,
-
-  /**
-   * Handle tip.
-   */
-  USE_PHASE_CHECK_TIP,
-
-  /**
-   * Check if client-supplied total amount matches
-   * our calculation (if we did any).
-   */
-  USE_PHASE_CHECK_TOTAL,
-
-  /**
-   * Construct the internal order request body.
-   */
-  USE_PHASE_CREATE_ORDER,
-
-  /**
-   * Submit the order to the shared order handler.
-   */
-  USE_PHASE_SUBMIT_ORDER,
-
-  /**
-   * Finished successfully with MHD_YES.
-   */
-  USE_PHASE_FINISHED_MHD_YES,
-
-  /**
-   * Finished with MHD_NO.
-   */
-  USE_PHASE_FINISHED_MHD_NO
-};
-
-struct UseContext
-{
-  /**
-   * Context for our handler.
-   */
-  struct TMH_HandlerContext *hc;
-
-  /**
-   * Internal handler context we are passing into the
-   * POST /private/orders handler.
-   */
-  struct TMH_HandlerContext ihc;
-
-  /**
-   * Phase we are currently in.
-   */
-  enum UsePhase phase;
-
-  /**
-   * Template type from the contract.
-   */
-  enum TALER_MERCHANT_TemplateType template_type;
-
-  /**
-   * Information set in the #USE_PHASE_PARSE_REQUEST phase.
-   */
-  struct
-  {
-    /**
-     * Summary override from request, if any.
-     */
-    const char *summary;
-
-    /**
-     * Amount provided by the client.
-     */
-    struct TALER_Amount amount;
-
-    /**
-     * Tip provided by the client.
-     */
-    struct TALER_Amount tip;
-
-    /**
-     * True if @e amount was not provided.
-     */
-    bool no_amount;
-
-    /**
-     * True if @e tip was not provided.
-     */
-    bool no_tip;
-
-    /**
-     * Parsed fields for inventory templates.
-     */
-    struct
-    {
-      /**
-       * Selected products from inventory_selection.
-       */
-      struct InventoryTemplateItemContext *items;
-
-      /**
-       * Length of @e items.
-       */
-      unsigned int items_len;
-
-    } inventory;
-
-    /**
-     * Request details if this is a paivana instantiation.
-     */
-    struct
-    {
-
-      /**
-       * Target website for the request.
-       */
-      const char *website;
-
-      /**
-       * Unique client identifier, consisting of
-       * current time, "-", and the hash of a nonce,
-       * the website and the current time.
-       */
-      const char *paivana_id;
-
-    } paivana;
-
-  } parse_request;
-
-  /**
-   * Information set in the #USE_PHASE_LOOKUP_TEMPLATE phase.
-   */
-  struct
-  {
-
-    /**
-     * Our template details from the DB.
-     */
-    struct TALER_MERCHANTDB_TemplateDetails etp;
-
-  } lookup_template;
-
-  /**
-   * Information set in the #USE_PHASE_PARSE_TEMPLATE phase.
-   */
-  struct TALER_MERCHANT_TemplateContract template_contract;
-
-  /**
-   * Information set in the #USE_PHASE_COMPUTE_PRICE phase.
-   */
-  struct
-  {
-
-    /**
-     * Per-currency totals across selected products (without tips).
-     */
-    struct TALER_Amount *totals;
-
-    /**
-     * Length of @e totals.
-     */
-    unsigned int totals_len;
-
-    /**
-     * Array of payment choices, used with Paviana.
-     */
-    json_t *choices;
-
-  } compute_price;
-
-};
-
-
-/**
- * Clean up inventory items.
- *
- * @param items_len length of @a items
- * @param[in] items item array to free
- */
-static void
-cleanup_inventory_items (unsigned int items_len,
-                         struct InventoryTemplateItemContext items[static
-                                                                   items_len])
-{
-  for (unsigned int i = 0; i < items_len; i++)
-  {
-    struct InventoryTemplateItemContext *item = &items[i];
-
-    TALER_MERCHANTDB_product_details_free (&item->pd);
-    GNUNET_free (item->categories);
-  }
-  GNUNET_free (items);
-}
-
-
-/**
- * Clean up a `struct UseContext *`
- *
- * @param[in] cls a `struct UseContext *`
- */
-static void
-cleanup_use_context (void *cls)
-{
-  struct UseContext *uc = cls;
-
-  TALER_MERCHANTDB_template_details_free (&uc->lookup_template.etp);
-  if (NULL !=
-      uc->parse_request.inventory.items)
-    cleanup_inventory_items (uc->parse_request.inventory.items_len,
-                             uc->parse_request.inventory.items);
-  GNUNET_free (uc->compute_price.totals);
-  uc->compute_price.totals_len = 0;
-  json_decref (uc->compute_price.choices);
-  if (NULL != uc->ihc.cc)
-    uc->ihc.cc (uc->ihc.ctx);
-  GNUNET_free (uc->ihc.infix);
-  json_decref (uc->ihc.request_body);
-  GNUNET_free (uc);
-}
-
-
-/**
- * Finalize a template use request.
- *
- * @param[in,out] uc use context
- * @param ret handler return value
- */
-static void
-use_finalize (struct UseContext *uc,
-              MHD_RESULT ret)
-{
-  uc->phase = (MHD_YES == ret)
-    ? USE_PHASE_FINISHED_MHD_YES
-    : USE_PHASE_FINISHED_MHD_NO;
-}
-
-
-/**
- * Finalize after JSON parsing result.
- *
- * @param[in,out] uc use context
- * @param res parse result
- */
-static void
-use_finalize_parse (struct UseContext *uc,
-                    enum GNUNET_GenericReturnValue res)
-{
-  GNUNET_assert (GNUNET_OK != res);
-  use_finalize (uc,
-                (GNUNET_NO == res)
-                ? MHD_YES
-                : MHD_NO);
-}
-
-
-/**
- * Reply with error and finalize the request.
- *
- * @param[in,out] uc use context
- * @param http_status HTTP status code
- * @param ec error code
- * @param detail error detail
- */
-static void
-use_reply_with_error (struct UseContext *uc,
-                      unsigned int http_status,
-                      enum TALER_ErrorCode ec,
-                      const char *detail)
-{
-  MHD_RESULT mret;
-
-  mret = TALER_MHD_reply_with_error (uc->hc->connection,
-                                     http_status,
-                                     ec,
-                                     detail);
-  use_finalize (uc,
-                mret);
-}
-
-
-/* ***************** USE_PHASE_PARSE_REQUEST **************** */
-
-/**
- * Parse request data for inventory templates.
- *
- * @param[in,out] uc use context
- * @return #GNUNET_OK on success
- */
-static enum GNUNET_GenericReturnValue
-parse_using_templates_inventory_request (
-  struct UseContext *uc)
-{
-  const json_t *inventory_selection;
-  struct GNUNET_JSON_Specification spec[] = {
-    GNUNET_JSON_spec_array_const ("inventory_selection",
-                                  &inventory_selection),
-    GNUNET_JSON_spec_end ()
-  };
-  enum GNUNET_GenericReturnValue res;
-
-  GNUNET_assert (NULL == uc->ihc.request_body);
-  res = TALER_MHD_parse_json_data (uc->hc->connection,
-                                   uc->hc->request_body,
-                                   spec);
-  if (GNUNET_OK != res)
-  {
-    GNUNET_break_op (0);
-    use_finalize_parse (uc,
-                        res);
-    return GNUNET_SYSERR;
-  }
-
-  if ( (! uc->parse_request.no_amount) &&
-       (! TMH_test_exchange_configured_for_currency (
-          uc->parse_request.amount.currency)) )
-  {
-    GNUNET_break_op (0);
-    use_reply_with_error (uc,
-                          MHD_HTTP_CONFLICT,
-                          TALER_EC_MERCHANT_GENERIC_CURRENCY_MISMATCH,
-                          "Currency is not supported by backend");
-    return GNUNET_SYSERR;
-  }
-
-  for (size_t i = 0; i < json_array_size (inventory_selection); i++)
-  {
-    struct InventoryTemplateItemContext item = { 0 };
-    struct GNUNET_JSON_Specification ispec[] = {
-      GNUNET_JSON_spec_string ("product_id",
-                               &item.product_id),
-      GNUNET_JSON_spec_string ("quantity",
-                               &item.unit_quantity),
-      GNUNET_JSON_spec_end ()
-    };
-    const char *err_name;
-    unsigned int err_line;
-
-    res = GNUNET_JSON_parse (json_array_get (inventory_selection,
-                                             i),
-                             ispec,
-                             &err_name,
-                             &err_line);
-    if (GNUNET_OK != res)
-    {
-      GNUNET_break_op (0);
-      use_reply_with_error (uc,
-                            MHD_HTTP_BAD_REQUEST,
-                            TALER_EC_GENERIC_PARAMETER_MALFORMED,
-                            "inventory_selection");
-      return GNUNET_SYSERR;
-    }
-
-    GNUNET_array_append (uc->parse_request.inventory.items,
-                         uc->parse_request.inventory.items_len,
-                         item);
-  }
-  return GNUNET_OK;
-}
-
-
-/**
- * Parse request data for paivana templates.
- *
- * @param[in,out] uc use context
- * @return #GNUNET_OK on success
- */
-static enum GNUNET_GenericReturnValue
-parse_using_templates_paivana_request (
-  struct UseContext *uc)
-{
-  struct GNUNET_JSON_Specification spec[] = {
-    GNUNET_JSON_spec_string ("website",
-                             &uc->parse_request.paivana.website),
-    GNUNET_JSON_spec_string ("paivana_id",
-                             &uc->parse_request.paivana.paivana_id),
-    GNUNET_JSON_spec_end ()
-  };
-  enum GNUNET_GenericReturnValue res;
-  struct GNUNET_HashCode sh;
-  unsigned long long tv;
-  const char *dash;
-
-  GNUNET_assert (NULL == uc->ihc.request_body);
-  res = TALER_MHD_parse_json_data (uc->hc->connection,
-                                   uc->hc->request_body,
-                                   spec);
-  if (GNUNET_OK != res)
-  {
-    GNUNET_break_op (0);
-    use_finalize_parse (uc,
-                        res);
-    return GNUNET_SYSERR;
-  }
-  if (1 !=
-      sscanf (uc->parse_request.paivana.paivana_id,
-              "%llu-",
-              &tv))
-  {
-    GNUNET_break_op (0);
-    use_reply_with_error (uc,
-                          MHD_HTTP_BAD_REQUEST,
-                          TALER_EC_GENERIC_PARAMETER_MALFORMED,
-                          "paivana_id");
-    return GNUNET_SYSERR;
-  }
-  dash = strchr (uc->parse_request.paivana.paivana_id,
-                 '-');
-  GNUNET_assert (NULL != dash);
-  if (GNUNET_OK !=
-      GNUNET_STRINGS_string_to_data (dash + 1,
-                                     strlen (dash + 1),
-                                     &sh,
-                                     sizeof (sh)))
-  {
-    GNUNET_break_op (0);
-    use_reply_with_error (uc,
-                          MHD_HTTP_BAD_REQUEST,
-                          TALER_EC_GENERIC_PARAMETER_MALFORMED,
-                          "paivana_id");
-    return GNUNET_SYSERR;
-  }
-  return GNUNET_OK;
-}
-
-
-/**
- * Main function for the #USE_PHASE_PARSE_REQUEST.
- *
- * @param[in,out] uc context to update
- */
-static void
-handle_phase_parse_request (
-  struct UseContext *uc)
-{
-  const char *template_type = NULL;
-  struct GNUNET_JSON_Specification spec[] = {
-    GNUNET_JSON_spec_mark_optional (
-      GNUNET_JSON_spec_string ("template_type",
-                               &template_type),
-      NULL),
-    GNUNET_JSON_spec_mark_optional (
-      TALER_JSON_spec_amount_any ("tip",
-                                  &uc->parse_request.tip),
-      &uc->parse_request.no_tip),
-    GNUNET_JSON_spec_mark_optional (
-      GNUNET_JSON_spec_string ("summary",
-                               &uc->parse_request.summary),
-      NULL),
-    GNUNET_JSON_spec_mark_optional (
-      TALER_JSON_spec_amount_any ("amount",
-                                  &uc->parse_request.amount),
-      &uc->parse_request.no_amount),
-    GNUNET_JSON_spec_end ()
-  };
-  enum GNUNET_GenericReturnValue res;
-
-  res = TALER_MHD_parse_json_data (uc->hc->connection,
-                                   uc->hc->request_body,
-                                   spec);
-  if (GNUNET_OK != res)
-  {
-    GNUNET_break_op (0);
-    use_finalize_parse (uc,
-                        res);
-    return;
-  }
-  if (NULL == template_type)
-    template_type = "fixed-order";
-  uc->template_type
-    = TALER_MERCHANT_template_type_from_string (
-        template_type);
-  switch (uc->template_type)
-  {
-  case TALER_MERCHANT_TEMPLATE_TYPE_FIXED_ORDER:
-    /* nothig left to do */
-    uc->phase++;
-    return;
-  case TALER_MERCHANT_TEMPLATE_TYPE_PAIVANA:
-    res = parse_using_templates_paivana_request (uc);
-    if (GNUNET_OK == res)
-      uc->phase++;
-    return;
-  case TALER_MERCHANT_TEMPLATE_TYPE_INVENTORY_CART:
-    res = parse_using_templates_inventory_request (uc);
-    if (GNUNET_OK == res)
-      uc->phase++;
-    return;
-  case TALER_MERCHANT_TEMPLATE_TYPE_INVALID:
-    break;
-  }
-  GNUNET_break (0);
-  use_reply_with_error (
-    uc,
-    MHD_HTTP_BAD_REQUEST,
-    TALER_EC_GENERIC_PARAMETER_MALFORMED,
-    "template_type");
-}
-
-
-/* ***************** USE_PHASE_LOOKUP_TEMPLATE **************** */
-
-/**
- * Main function for the #USE_PHASE_LOOKUP_TEMPLATE.
- *
- * @param[in,out] uc context to update
- */
-static void
-handle_phase_lookup_template (
-  struct UseContext *uc)
-{
-  struct TMH_MerchantInstance *mi = uc->hc->instance;
-  const char *template_id = uc->hc->infix;
-  enum GNUNET_DB_QueryStatus qs;
-
-  qs = TMH_db->lookup_template (TMH_db->cls,
-                                mi->settings.id,
-                                template_id,
-                                &uc->lookup_template.etp);
-  switch (qs)
-  {
-  case GNUNET_DB_STATUS_HARD_ERROR:
-    /* Clean up and fail hard */
-    GNUNET_break (0);
-    use_reply_with_error (uc,
-                          MHD_HTTP_INTERNAL_SERVER_ERROR,
-                          TALER_EC_GENERIC_DB_FETCH_FAILED,
-                          "lookup_template");
-    return;
-  case GNUNET_DB_STATUS_SOFT_ERROR:
-    /* this should be impossible (single select) */
-    GNUNET_break (0);
-    use_reply_with_error (uc,
-                          MHD_HTTP_INTERNAL_SERVER_ERROR,
-                          TALER_EC_GENERIC_DB_FETCH_FAILED,
-                          "lookup_template");
-    return;
-  case GNUNET_DB_STATUS_SUCCESS_NO_RESULTS:
-    /* template not found! */
-    use_reply_with_error (uc,
-                          MHD_HTTP_NOT_FOUND,
-                          TALER_EC_MERCHANT_GENERIC_TEMPLATE_UNKNOWN,
-                          template_id);
-    return;
-  case GNUNET_DB_STATUS_SUCCESS_ONE_RESULT:
-    /* all good */
-    break;
-  }
-  if (uc->template_type !=
-      TALER_MERCHANT_template_type_from_contract (
-        uc->lookup_template.etp.template_contract))
-  {
-    GNUNET_break_op (0);
-    use_reply_with_error (
-      uc,
-      MHD_HTTP_CONFLICT,
-      TALER_EC_MERCHANT_POST_USING_TEMPLATES_WRONG_TYPE,
-      "template_contract has different type");
-    return;
-  }
-  uc->phase++;
-}
-
-
-/* ***************** USE_PHASE_PARSE_TEMPLATE **************** */
-
-
-/**
- * Parse template.
- *
- * @param[in,out] uc use context
- */
-static void
-handle_phase_template_contract (struct UseContext *uc)
-{
-  const char *err_name;
-  enum GNUNET_GenericReturnValue res;
-
-  res = TALER_MERCHANT_template_contract_parse (
-    uc->lookup_template.etp.template_contract,
-    &uc->template_contract,
-    &err_name);
-  if (GNUNET_OK != res)
-  {
-    GNUNET_break (0);
-    use_reply_with_error (uc,
-                          MHD_HTTP_INTERNAL_SERVER_ERROR,
-                          TALER_EC_GENERIC_DB_FETCH_FAILED,
-                          err_name);
-    return;
-  }
-  uc->phase++;
-}
-
-
-/* ***************** USE_PHASE_DB_FETCH **************** */
-
-/**
- * Fetch DB data for inventory templates.
- *
- * @param[in,out] uc use context
- */
-static void
-handle_phase_db_fetch (struct UseContext *uc)
-{
-  struct TMH_MerchantInstance *mi = uc->hc->instance;
-
-  switch (uc->template_type)
-  {
-  case TALER_MERCHANT_TEMPLATE_TYPE_FIXED_ORDER:
-    uc->phase++;
-    return;
-  case TALER_MERCHANT_TEMPLATE_TYPE_PAIVANA:
-    uc->phase++;
-    return;
-  case TALER_MERCHANT_TEMPLATE_TYPE_INVENTORY_CART:
-    break;
-  case TALER_MERCHANT_TEMPLATE_TYPE_INVALID:
-    GNUNET_assert (0);
-  }
-
-  for (unsigned int i = 0;
-       i < uc->parse_request.inventory.items_len;
-       i++)
-  {
-    struct InventoryTemplateItemContext *item =
-      &uc->parse_request.inventory.items[i];
-    enum GNUNET_DB_QueryStatus qs;
-
-    qs = TMH_db->lookup_product (TMH_db->cls,
-                                 mi->settings.id,
-                                 item->product_id,
-                                 &item->pd,
-                                 &item->num_categories,
-                                 &item->categories);
-    switch (qs)
-    {
-    case GNUNET_DB_STATUS_HARD_ERROR:
-      GNUNET_break (0);
-      use_reply_with_error (uc,
-                            MHD_HTTP_INTERNAL_SERVER_ERROR,
-                            TALER_EC_GENERIC_DB_FETCH_FAILED,
-                            "lookup_product");
-      return;
-    case GNUNET_DB_STATUS_SOFT_ERROR:
-      GNUNET_break (0);
-      use_reply_with_error (uc,
-                            MHD_HTTP_INTERNAL_SERVER_ERROR,
-                            TALER_EC_GENERIC_DB_FETCH_FAILED,
-                            "lookup_product");
-      return;
-    case GNUNET_DB_STATUS_SUCCESS_NO_RESULTS:
-      use_reply_with_error (uc,
-                            MHD_HTTP_NOT_FOUND,
-                            TALER_EC_MERCHANT_GENERIC_PRODUCT_UNKNOWN,
-                            item->product_id);
-      return;
-    case GNUNET_DB_STATUS_SUCCESS_ONE_RESULT:
-      break;
-    }
-  }
-  uc->phase++;
-}
-
-
-/* *************** Helpers for USE_PHASE_VERIFY ***************** */
-
-/**
- * Check if the given product ID appears in the array of allowed_products.
- *
- * @param allowed_products JSON array of product IDs allowed by the template, may be NULL
- * @param product_id product ID to check
- * @return true if the product ID is in the list
- */
-static bool
-product_id_allowed (const json_t *allowed_products,
-                    const char *product_id)
-{
-  const json_t *entry;
-  size_t idx;
-
-  if (NULL == allowed_products)
-    return false;
-  json_array_foreach ((json_t *) allowed_products, idx, entry)
-  {
-    if (! json_is_string (entry))
-    {
-      GNUNET_break (0);
-      continue;
-    }
-    if (0 == strcmp (json_string_value (entry),
-                     product_id))
-      return true;
-  }
-  return false;
-}
-
-
-/**
- * Check if any product category is in the selected_categories list.
- *
- * @param allowed_categories JSON array of categories allowed by the template, may be NULL
- * @param num_categories length of @a categories
- * @param categories list of categories of the selected product
- * @return true if any category of the product is in the list of allowed categories matches
- */
-static bool
-category_allowed (const json_t *allowed_categories,
-                  size_t num_categories,
-                  const uint64_t categories[num_categories])
-{
-  const json_t *entry;
-  size_t idx;
-
-  if (NULL == allowed_categories)
-    return false;
-  json_array_foreach ((json_t *) allowed_categories,
-                      idx,
-                      entry)
-  {
-    uint64_t selected_id;
-
-    if (! json_is_integer (entry))
-    {
-      GNUNET_break (0);
-      continue;
-    }
-    if (0 > json_integer_value (entry))
-    {
-      GNUNET_break (0);
-      continue;
-    }
-    selected_id = (uint64_t) json_integer_value (entry);
-    for (size_t i = 0; i < num_categories; i++)
-    {
-      if (categories[i] == selected_id)
-        return true;
-    }
-  }
-  return false;
-}
-
-
-/**
- * Verify request data for inventory templates.
- * Checks that the selected products are allowed
- * for this template.
- *
- * @param[in,out] uc use context
- * @return #GNUNET_OK on success
- */
-static enum GNUNET_GenericReturnValue
-verify_using_templates_inventory (struct UseContext *uc)
-{
-  if (uc->template_contract.details.inventory.choose_one &&
-      (1 != uc->parse_request.inventory.items_len))
-  {
-    GNUNET_break_op (0);
-    use_reply_with_error (uc,
-                          MHD_HTTP_CONFLICT,
-                          TALER_EC_GENERIC_PARAMETER_MALFORMED,
-                          "inventory_selection");
-    return GNUNET_SYSERR;
-  }
-  if (uc->template_contract.details.inventory.selected_all)
-    return GNUNET_OK;
-  for (unsigned int i = 0;
-       i < uc->parse_request.inventory.items_len;
-       i++)
-  {
-    struct InventoryTemplateItemContext *item =
-      &uc->parse_request.inventory.items[i];
-    const char *eparam = NULL;
-
-    if (GNUNET_OK !=
-        TALER_MERCHANT_vk_process_quantity_inputs (
-          TALER_MERCHANT_VK_QUANTITY,
-          item->pd.allow_fractional_quantity,
-          true,
-          0,
-          false,
-          item->unit_quantity,
-          &item->quantity_value,
-          &item->quantity_frac,
-          &eparam))
-    {
-      GNUNET_break_op (0);
-      use_reply_with_error (uc,
-                            MHD_HTTP_BAD_REQUEST,
-                            TALER_EC_GENERIC_PARAMETER_MALFORMED,
-                            eparam);
-      return GNUNET_SYSERR;
-    }
-
-    if (0 == item->pd.price_array_length)
-    {
-      GNUNET_break (0);
-      use_reply_with_error (uc,
-                            MHD_HTTP_INTERNAL_SERVER_ERROR,
-                            TALER_EC_GENERIC_INTERNAL_INVARIANT_FAILURE,
-                            "price_array");
-      return GNUNET_SYSERR;
-    }
-  }
-
-  for (unsigned int i = 0;
-       i < uc->parse_request.inventory.items_len;
-       i++)
-  {
-    struct InventoryTemplateItemContext *item =
-      &uc->parse_request.inventory.items[i];
-
-    if (product_id_allowed (uc->template_contract.details.inventory.
-                            selected_products,
-                            item->product_id))
-      continue;
-    if (category_allowed (
-          uc->template_contract.details.inventory.selected_categories,
-          item->num_categories,
-          item->categories))
-      continue;
-    GNUNET_break_op (0);
-    use_reply_with_error (
-      uc,
-      MHD_HTTP_CONFLICT,
-      TALER_EC_MERCHANT_POST_USING_TEMPLATES_WRONG_PRODUCT,
-      item->product_id);
-    return GNUNET_SYSERR;
-  }
-  return GNUNET_OK;
-}
-
-
-/**
- * Verify request data for fixed-order templates.
- * As here we cannot compute the total amount, either
- * the template or the client request must provide it.
- *
- * @param[in,out] uc use context
- * @return #GNUNET_OK on success
- */
-static enum GNUNET_GenericReturnValue
-verify_using_templates_fixed (
-  struct UseContext *uc)
-{
-  if ( (! uc->parse_request.no_amount) &&
-       (! uc->template_contract.no_amount) )
-  {
-    GNUNET_break_op (0);
-    use_reply_with_error (uc,
-                          MHD_HTTP_CONFLICT,
-                          TALER_EC_MERCHANT_POST_USING_TEMPLATES_AMOUNT_CONFLICT_TEMPLATES_CONTRACT_AMOUNT,
-                          NULL);
-    return GNUNET_SYSERR;
-  }
-  if (uc->parse_request.no_amount &&
-      uc->template_contract.no_amount)
-  {
-    GNUNET_break_op (0);
-    use_reply_with_error (uc,
-                          MHD_HTTP_CONFLICT,
-                          TALER_EC_MERCHANT_POST_USING_TEMPLATES_NO_AMOUNT,
-                          NULL);
-    return GNUNET_SYSERR;
-  }
-  return GNUNET_OK;
-}
-
-
-/**
- * Verify request data for paivana templates.
- *
- * @param[in,out] uc use context
- * @return #GNUNET_OK on success
- */
-static enum GNUNET_GenericReturnValue
-verify_using_templates_paivana (
-  struct UseContext *uc)
-{
-  if (NULL != uc->template_contract.details.paivana.website_regex)
-  {
-    regex_t ex;
-    bool allowed = false;
-
-    if (0 != regcomp (&ex,
-                      uc->template_contract.details.paivana.website_regex,
-                      REG_NOSUB | REG_EXTENDED))
-    {
-      GNUNET_break_op (0);
-      return GNUNET_SYSERR;
-    }
-    if (0 ==
-        regexec (&ex,
-                 uc->parse_request.paivana.website,
-                 0, NULL,
-                 0))
-    {
-      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
-                  "Website `%s' allowed by template\n",
-                  uc->parse_request.paivana.website);
-      allowed = true;
-    }
-    regfree (&ex);
-    if (! allowed)
-      return GNUNET_SYSERR;
-  }
-  return GNUNET_OK;
-}
-
-
-/**
- * Verify that the client request is structurally acceptable for the specified
- * template.  Does NOT check the total amount being reasonable.
- *
- * @param[in,out] uc use context
- */
-static void
-handle_phase_verify (
-  struct UseContext *uc)
-{
-  enum GNUNET_GenericReturnValue res = GNUNET_SYSERR;
-
-  if ( (NULL != uc->parse_request.summary) &&
-       (NULL != uc->template_contract.summary) )
-  {
-    GNUNET_break_op (0);
-    use_reply_with_error (uc,
-                          MHD_HTTP_CONFLICT,
-                          TALER_EC_MERCHANT_POST_USING_TEMPLATES_SUMMARY_CONFLICT_TEMPLATES_CONTRACT_SUBJECT,
-                          NULL);
-    return;
-  }
-  if ( (NULL == uc->parse_request.summary) &&
-       (NULL == uc->template_contract.summary) )
-  {
-    GNUNET_break_op (0);
-    use_reply_with_error (uc,
-                          MHD_HTTP_CONFLICT,
-                          TALER_EC_MERCHANT_POST_USING_TEMPLATES_NO_SUMMARY,
-                          NULL);
-    return;
-  }
-  if ( (! uc->parse_request.no_amount) &&
-       (NULL != uc->template_contract.currency) &&
-       (0 != strcasecmp (uc->template_contract.currency,
-                         uc->parse_request.amount.currency)) )
-  {
-    GNUNET_break_op (0);
-    use_reply_with_error (uc,
-                          MHD_HTTP_CONFLICT,
-                          TALER_EC_MERCHANT_GENERIC_CURRENCY_MISMATCH,
-                          uc->template_contract.currency);
-    return;
-  }
-  switch (uc->template_type)
-  {
-  case TALER_MERCHANT_TEMPLATE_TYPE_FIXED_ORDER:
-    res = verify_using_templates_fixed (uc);
-    break;
-  case TALER_MERCHANT_TEMPLATE_TYPE_PAIVANA:
-    res = verify_using_templates_paivana (uc);
-    break;
-  case TALER_MERCHANT_TEMPLATE_TYPE_INVENTORY_CART:
-    res = verify_using_templates_inventory (uc);
-    break;
-  case TALER_MERCHANT_TEMPLATE_TYPE_INVALID:
-    GNUNET_assert (0);
-  }
-  if (GNUNET_OK == res)
-    uc->phase++;
-}
-
-
-/* ***************** USE_PHASE_COMPUTE_PRICE **************** */
-
-
-/**
- * Compute the line total for a product based on quantity.
- *
- * @param unit_price price per unit
- * @param quantity integer quantity
- * @param quantity_frac fractional quantity (0..TALER_MERCHANT_UNIT_FRAC_BASE-1)
- * @param[out] line_total resulting line total
- * @return #GNUNET_OK on success
- */
-static enum GNUNET_GenericReturnValue
-compute_line_total (const struct TALER_Amount *unit_price,
-                    uint64_t quantity,
-                    uint32_t quantity_frac,
-                    struct TALER_Amount *line_total)
-{
-  struct TALER_Amount tmp;
-
-  GNUNET_assert (GNUNET_OK ==
-                 TALER_amount_set_zero (unit_price->currency,
-                                        line_total));
-  if ( (0 != quantity) &&
-       (0 >
-        TALER_amount_multiply (line_total,
-                               unit_price,
-                               (uint32_t) quantity)) )
-  {
-    GNUNET_break (0);
-    return GNUNET_SYSERR;
-  }
-  if (0 == quantity_frac)
-    return GNUNET_OK;
-  if (0 >
-      TALER_amount_multiply (&tmp,
-                             unit_price,
-                             quantity_frac))
-  {
-    GNUNET_break (0);
-    return GNUNET_SYSERR;
-  }
-  TALER_amount_divide (&tmp,
-                       &tmp,
-                       TALER_MERCHANT_UNIT_FRAC_BASE);
-  if (0 >
-      TALER_amount_add (line_total,
-                        line_total,
-                        &tmp))
-  {
-    GNUNET_break (0);
-    return GNUNET_SYSERR;
-  }
-  return GNUNET_OK;
-}
-
-
-/**
- * Find the price of the given @a item in the specified
- * @a currency.
- *
- * @param currency currency to search price in
- * @param item item to check prices of
- * @return NULL if a suitable price was not found
- */
-static const struct TALER_Amount *
-find_item_price_in_currency (
-  const char *currency,
-  const struct InventoryTemplateItemContext *item)
-{
-  for (size_t j = 0; j < item->pd.price_array_length; j++)
-  {
-    if (0 == strcasecmp (item->pd.price_array[j].currency,
-                         currency))
-      return &item->pd.price_array[j];
-  }
-  return NULL;
-}
-
-
-/**
- * Compute totals for all currencies shared across selected products.
- *
- * @param[in,out] uc use context
- * @return #GNUNET_OK on success (including no price due to no items)
- *         #GNUNET_NO if we could not find a price in any accepted currency
- *                    for all selected products
- *         #GNUNET_SYSERR on arithmetic issues (internal error)
- */
-static enum GNUNET_GenericReturnValue
-compute_totals_per_currency (struct UseContext *uc)
-{
-  const struct InventoryTemplateItemContext *items
-    = uc->parse_request.inventory.items;
-  unsigned int items_len = uc->parse_request.inventory.items_len;
-
-  if (0 == items_len)
-    return GNUNET_OK;
-  for (size_t i = 0; i < items[0].pd.price_array_length; i++)
-  {
-    const struct TALER_Amount *price
-      = &items[0].pd.price_array[i];
-    struct TALER_Amount zero;
-
-    if (! TMH_test_exchange_configured_for_currency (price->currency))
-      continue;
-    GNUNET_assert (GNUNET_OK ==
-                   TALER_amount_set_zero (price->currency,
-                                          &zero));
-    GNUNET_array_append (uc->compute_price.totals,
-                         uc->compute_price.totals_len,
-                         zero);
-  }
-  if (0 == uc->compute_price.totals_len)
-  {
-    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
-                "No currency supported by our configuration in which we have prices for first selected product!\n");
-    return GNUNET_NO;
-  }
-  /* Loop through items, ensure each currency exists and sum totals. */
-  for (unsigned int i = 0; i < items_len; i++)
-  {
-    const struct InventoryTemplateItemContext *item = &items[i];
-    unsigned int c = 0;
-
-    while (c < uc->compute_price.totals_len)
-    {
-      struct TALER_Amount *total = &uc->compute_price.totals[c];
-      const struct TALER_Amount *unit_price;
-      struct TALER_Amount line_total;
-
-      unit_price = find_item_price_in_currency (total->currency,
-                                                item);
-      if (NULL == unit_price)
-      {
-        /* Drop the currency: we have no price in one of
-           the selected products */
-        GNUNET_log (GNUNET_ERROR_TYPE_INFO,
-                    "Product `%s' has no price in %s: dropping currency\n",
-                    item->product_id,
-                    total->currency);
-        *total = uc->compute_price.totals[--uc->compute_price.totals_len];
-        continue;
-      }
-      if (GNUNET_OK !=
-          compute_line_total (unit_price,
-                              item->quantity_value,
-                              item->quantity_frac,
-                              &line_total))
-      {
-        GNUNET_break (0);
-        return GNUNET_SYSERR;
-      }
-      if (0 >
-          TALER_amount_add (total,
-                            total,
-                            &line_total))
-      {
-        GNUNET_break (0);
-        return GNUNET_SYSERR;
-      }
-      c++;
-    }
-  }
-  if (0 == uc->compute_price.totals_len)
-  {
-    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
-                "No currency available in which we have prices for all selected products!\n");
-    GNUNET_free (uc->compute_price.totals);
-  }
-  return (0 == uc->compute_price.totals_len)
-    ? GNUNET_NO
-    : GNUNET_OK;
-}
-
-
-/**
- * Compute total for only the given @a currency.
- *
- * @param items_len length of @a items
- * @param items inventory items
- * @param currency currency to total
- * @param[out] total computed total
- * @return #GNUNET_OK on success
- *         #GNUNET_NO if we could not find a price in any accepted currency
- *                    for all selected products
- *         #GNUNET_SYSERR on arithmetic issues (internal error)
- */
-static enum GNUNET_GenericReturnValue
-compute_inventory_total (unsigned int items_len,
-                         const struct InventoryTemplateItemContext *items,
-                         const char *currency,
-                         struct TALER_Amount *total)
-{
-  GNUNET_assert (NULL != currency);
-  GNUNET_assert (GNUNET_OK ==
-                 TALER_amount_set_zero (currency,
-                                        total));
-  for (unsigned int i = 0; i < items_len; i++)
-  {
-    const struct InventoryTemplateItemContext *item = &items[i];
-    const struct TALER_Amount *unit_price;
-    struct TALER_Amount line_total;
-
-    unit_price = find_item_price_in_currency (currency,
-                                              item);
-    if (NULL == unit_price)
-    {
-      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
-                  "compute_inventory_total: no price in %s for product `%s'\n",
-                  currency,
-                  item->product_id);
-      return GNUNET_NO;
-    }
-    if (GNUNET_OK !=
-        compute_line_total (unit_price,
-                            item->quantity_value,
-                            item->quantity_frac,
-                            &line_total))
-    {
-      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
-                  "compute_inventory_total: line total failed for %s in %s\n",
-                  item->product_id,
-                  currency);
-      return GNUNET_SYSERR;
-    }
-    if (0 >
-        TALER_amount_add (total,
-                          total,
-                          &line_total))
-    {
-      GNUNET_break (0);
-      return GNUNET_SYSERR;
-    }
-  }
-  return GNUNET_OK;
-}
-
-
-/**
- * Compute total price.
- *
- * @param[in,out] uc use context
- */
-static void
-handle_phase_compute_price (struct UseContext *uc)
-{
-  const char *primary_currency;
-  enum GNUNET_GenericReturnValue ret;
-
-  switch (uc->template_type)
-  {
-  case TALER_MERCHANT_TEMPLATE_TYPE_FIXED_ORDER:
-    uc->compute_price.totals
-      = GNUNET_new (struct TALER_Amount);
-    uc->compute_price.totals_len
-      = 1;
-    if (uc->parse_request.no_amount)
-    {
-      GNUNET_assert (! uc->template_contract.no_amount);
-      *uc->compute_price.totals
-        = uc->template_contract.amount;
-    }
-    else
-    {
-      GNUNET_assert (uc->template_contract.no_amount);
-      *uc->compute_price.totals
-        = uc->parse_request.amount;
-    }
-    uc->phase++;
-    return;
-  case TALER_MERCHANT_TEMPLATE_TYPE_INVENTORY_CART:
-    /* handled below */
-    break;
-  case TALER_MERCHANT_TEMPLATE_TYPE_PAIVANA:
-    {
-      const struct TALER_MERCHANT_TemplateContractPaivana *tcp
-        = &uc->template_contract.details.paivana;
-      json_t *choices;
-
-      choices = json_array ();
-      GNUNET_assert (NULL != choices);
-      for (size_t i = 0; i < tcp->choices_len; i++)
-      {
-        /* Make deep copy, we're going to MODIFY it! */
-        struct TALER_MERCHANT_ContractChoice choice
-          = tcp->choices[i];
-
-        choice.no_tip = uc->parse_request.no_tip;
-        if (! uc->parse_request.no_tip)
-        {
-          if (GNUNET_YES !=
-              TALER_amount_cmp_currency (&choice.amount,
-                                         &uc->parse_request.tip))
-            continue; /* tip does not match choice currency */
-          choice.tip = uc->parse_request.tip;
-          if (0 >
-              TALER_amount_add (&choice.amount,
-                                &choice.amount,
-                                &uc->parse_request.tip))
-          {
-            GNUNET_break (0);
-            use_reply_with_error (uc,
-                                  MHD_HTTP_INTERNAL_SERVER_ERROR,
-                                  TALER_EC_GENERIC_FAILED_COMPUTE_AMOUNT,
-                                  "tip");
-            return;
-          }
-        }
-        GNUNET_assert (0 ==
-                       json_array_append_new (
-                         choices,
-                         TALER_MERCHANT_json_from_contract_choice (&choice,
-                                                                   true)));
-      }
-      if (0 == json_array_size (choices))
-      {
-        GNUNET_break_op (0);
-        json_decref (choices);
-        use_reply_with_error (uc,
-                              MHD_HTTP_CONFLICT,
-                              TALER_EC_MERCHANT_POST_USING_TEMPLATES_NO_CURRENCY,
-                              "tip");
-        return;
-      }
-      uc->compute_price.choices = choices;
-    }
-    /* Note: we already did the tip and pricing
-       fully here, so we skip these phases. */
-    uc->phase = USE_PHASE_CREATE_ORDER;
-    return;
-  case TALER_MERCHANT_TEMPLATE_TYPE_INVALID:
-    GNUNET_assert (0);
-  }
-  primary_currency = uc->template_contract.currency;
-  if (! uc->parse_request.no_amount)
-    primary_currency = uc->parse_request.amount.currency;
-  if (! uc->parse_request.no_tip)
-    primary_currency = uc->parse_request.tip.currency;
-  if (NULL == primary_currency)
-  {
-    ret = compute_totals_per_currency (uc);
-  }
-  else
-  {
-    uc->compute_price.totals
-      = GNUNET_new (struct TALER_Amount);
-    uc->compute_price.totals_len
-      = 1;
-    ret = compute_inventory_total (
-      uc->parse_request.inventory.items_len,
-      uc->parse_request.inventory.items,
-      primary_currency,
-      uc->compute_price.totals);
-  }
-  if (GNUNET_SYSERR == ret)
-  {
-    use_reply_with_error (
-      uc,
-      MHD_HTTP_INTERNAL_SERVER_ERROR,
-      TALER_EC_GENERIC_FAILED_COMPUTE_AMOUNT,
-      "calculation of currency totals failed");
-    return;
-  }
-  if (GNUNET_NO == ret)
-  {
-    use_reply_with_error (uc,
-                          MHD_HTTP_CONFLICT,
-                          TALER_EC_MERCHANT_POST_USING_TEMPLATES_NO_CURRENCY,
-                          NULL);
-    return;
-  }
-
-  uc->phase++;
-}
-
-
-/* ***************** USE_PHASE_CHECK_TIP **************** */
-
-
-/**
- * Check that tip specified is reasonable and add to total.
- *
- * @param[in,out] uc use context
- */
-static void
-handle_phase_check_tip (struct UseContext *uc)
-{
-  struct TALER_Amount *total_amount;
-
-  if (uc->parse_request.no_tip)
-  {
-    uc->phase++;
-    return;
-  }
-  if (0 == uc->compute_price.totals_len)
-  {
-    if (! TMH_test_exchange_configured_for_currency (
-          uc->parse_request.tip.currency))
-    {
-      GNUNET_break_op (0);
-      use_reply_with_error (uc,
-                            MHD_HTTP_CONFLICT,
-                            TALER_EC_MERCHANT_GENERIC_CURRENCY_MISMATCH,
-                            "Tip currency is not supported by backend");
-      return;
-    }
-    uc->compute_price.totals
-      = GNUNET_new (struct TALER_Amount);
-    uc->compute_price.totals_len
-      = 1;
-    *uc->compute_price.totals
-      = uc->parse_request.tip;
-    uc->phase++;
-    return;
-  }
-  GNUNET_assert (1 == uc->compute_price.totals_len);
-  total_amount = &uc->compute_price.totals[0];
-  if (GNUNET_YES !=
-      TALER_amount_cmp_currency (&uc->parse_request.tip,
-                                 total_amount))
-  {
-    GNUNET_break_op (0);
-    use_reply_with_error (uc,
-                          MHD_HTTP_CONFLICT,
-                          TALER_EC_MERCHANT_GENERIC_CURRENCY_MISMATCH,
-                          uc->parse_request.tip.currency);
-    return;
-  }
-  if (0 >
-      TALER_amount_add (total_amount,
-                        total_amount,
-                        &uc->parse_request.tip))
-  {
-    GNUNET_break (0);
-    use_reply_with_error (uc,
-                          MHD_HTTP_INTERNAL_SERVER_ERROR,
-                          TALER_EC_GENERIC_FAILED_COMPUTE_AMOUNT,
-                          "tip");
-    return;
-  }
-  uc->phase++;
-}
-
-
-/* ***************** USE_PHASE_CHECK_TOTAL **************** */
-
-/**
- * Check that if the client specified a total,
- * it matches our own calculation.
- *
- * @param[in,out] uc use context
- */
-static void
-handle_phase_check_total (struct UseContext *uc)
-{
-  GNUNET_assert (1 <= uc->compute_price.totals_len);
-  if (! uc->parse_request.no_amount)
-  {
-    GNUNET_assert (1 == uc->compute_price.totals_len);
-    GNUNET_assert (GNUNET_YES ==
-                   TALER_amount_cmp_currency (&uc->parse_request.amount,
-                                              &uc->compute_price.totals[0]));
-    if (0 !=
-        TALER_amount_cmp (&uc->parse_request.amount,
-                          &uc->compute_price.totals[0]))
-    {
-      GNUNET_break_op (0);
-      use_reply_with_error (uc,
-                            MHD_HTTP_CONFLICT,
-                            TALER_EC_MERCHANT_POST_USING_TEMPLATES_AMOUNT_CONFLICT_TEMPLATES_CONTRACT_AMOUNT,
-                            TALER_amount2s (&uc->compute_price.totals[0]));
-      return;
-    }
-  }
-  uc->phase++;
-}
-
-
-/* ***************** USE_PHASE_CREATE_ORDER **************** */
-
-
-/**
- * Create order request for inventory templates.
- *
- * @param[in,out] uc use context
- */
-static void
-create_using_templates_inventory (struct UseContext *uc)
-{
-  json_t *inventory_products;
-  json_t *choices;
-
-  inventory_products = json_array ();
-  GNUNET_assert (NULL != inventory_products);
-  for (unsigned int i = 0;
-       i < uc->parse_request.inventory.items_len;
-       i++)
-  {
-    const struct InventoryTemplateItemContext *item =
-      &uc->parse_request.inventory.items[i];
-
-    GNUNET_assert (0 ==
-                   json_array_append_new (
-                     inventory_products,
-                     GNUNET_JSON_PACK (
-                       GNUNET_JSON_pack_string ("product_id",
-                                                item->product_id),
-                       GNUNET_JSON_pack_string ("unit_quantity",
-                                                item->unit_quantity))));
-  }
-  choices = json_array ();
-  GNUNET_assert (NULL != choices);
-  for (unsigned int i = 0;
-       i < uc->compute_price.totals_len;
-       i++)
-  {
-    GNUNET_assert (0 ==
-                   json_array_append_new (
-                     choices,
-                     GNUNET_JSON_PACK (
-                       TALER_JSON_pack_amount ("amount",
-                                               &uc->compute_price.totals[i]),
-                       GNUNET_JSON_pack_allow_null (
-                         TALER_JSON_pack_amount ("tip",
-                                                 uc->parse_request.no_tip
-                                                ? NULL
-                                                : &uc->parse_request.tip))
-                       )));
-  }
-
-  uc->ihc.request_body
-    = GNUNET_JSON_PACK (
-        GNUNET_JSON_pack_allow_null (
-          GNUNET_JSON_pack_string ("otp_id",
-                                   uc->lookup_template.etp.otp_id)),
-        GNUNET_JSON_pack_array_steal ("inventory_products",
-                                      inventory_products),
-        GNUNET_JSON_pack_object_steal (
-          "order",
-          GNUNET_JSON_PACK (
-            GNUNET_JSON_pack_uint64 ("version",
-                                     1),
-            GNUNET_JSON_pack_array_steal ("choices",
-                                          choices),
-            GNUNET_JSON_pack_string ("summary",
-                                     NULL == uc->parse_request.summary
-                                   ? uc->template_contract.summary
-                                   : uc->parse_request.summary))));
-}
-
-
-/**
- * Create order request for fixed-order templates.
- *
- * @param[in,out] uc use context
- */
-static void
-create_using_templates_fixed (struct UseContext *uc)
-{
-  uc->ihc.request_body
-    = GNUNET_JSON_PACK (
-        GNUNET_JSON_pack_allow_null (
-          GNUNET_JSON_pack_string ("otp_id",
-                                   uc->lookup_template.etp.otp_id)),
-        GNUNET_JSON_pack_object_steal (
-          "order",
-          GNUNET_JSON_PACK (
-            TALER_JSON_pack_amount (
-              "amount",
-              &uc->compute_price.totals[0]),
-            GNUNET_JSON_pack_allow_null (
-              TALER_JSON_pack_amount ("tip",
-                                      uc->parse_request.no_tip
-                                      ? NULL
-                                      : &uc->parse_request.tip)),
-            GNUNET_JSON_pack_string (
-              "summary",
-              NULL == uc->parse_request.summary
-            ? uc->template_contract.summary
-            : uc->parse_request.summary))));
-}
-
-
-/**
- * Create order request for paivana templates.
- *
- * @param[in,out] uc use context
- */
-static void
-create_using_templates_paivana (struct UseContext *uc)
-{
-  uc->ihc.request_body
-    = GNUNET_JSON_PACK (
-        GNUNET_JSON_pack_string (
-          "session_id",
-          uc->parse_request.paivana.paivana_id),
-        GNUNET_JSON_pack_object_steal (
-          "order",
-          GNUNET_JSON_PACK (
-            GNUNET_JSON_pack_uint64 ("version",
-                                     1),
-            GNUNET_JSON_pack_array_incref ("choices",
-                                           uc->compute_price.choices),
-            GNUNET_JSON_pack_string (
-              "summary",
-              NULL == uc->parse_request.summary
-              ? uc->template_contract.summary
-              : uc->parse_request.summary),
-            GNUNET_JSON_pack_string ("fulfillment_url",
-                                     uc->parse_request.paivana.website))));
-}
-
-
-static void
-handle_phase_create_order (struct UseContext *uc)
-{
-  GNUNET_assert (NULL == uc->ihc.request_body);
-  switch (uc->template_type)
-  {
-  case TALER_MERCHANT_TEMPLATE_TYPE_FIXED_ORDER:
-    create_using_templates_fixed (uc);
-    break;
-  case TALER_MERCHANT_TEMPLATE_TYPE_PAIVANA:
-    create_using_templates_paivana (uc);
-    break;
-  case TALER_MERCHANT_TEMPLATE_TYPE_INVENTORY_CART:
-    create_using_templates_inventory (uc);
-    break;
-  case TALER_MERCHANT_TEMPLATE_TYPE_INVALID:
-    GNUNET_assert (0);
-  }
-  uc->phase++;
-}
-
-
-/* ***************** Main handler **************** */
-
-MHD_RESULT
-TMH_post_using_templates_ID (
-  const struct TMH_RequestHandler *rh,
-  struct MHD_Connection *connection,
-  struct TMH_HandlerContext *hc)
-{
-  struct UseContext *uc = hc->ctx;
-
-  (void) rh;
-  if (NULL == uc)
-  {
-    uc = GNUNET_new (struct UseContext);
-    uc->hc = hc;
-    hc->ctx = uc;
-    hc->cc = &cleanup_use_context;
-    uc->ihc.instance = hc->instance;
-    uc->phase = USE_PHASE_PARSE_REQUEST;
-    uc->template_type = TALER_MERCHANT_TEMPLATE_TYPE_INVALID;
-  }
-
-  while (1)
-  {
-    switch (uc->phase)
-    {
-    case USE_PHASE_PARSE_REQUEST:
-      handle_phase_parse_request (uc);
-      break;
-    case USE_PHASE_LOOKUP_TEMPLATE:
-      handle_phase_lookup_template (uc);
-      break;
-    case USE_PHASE_PARSE_TEMPLATE:
-      handle_phase_template_contract (uc);
-      break;
-    case USE_PHASE_DB_FETCH:
-      handle_phase_db_fetch (uc);
-      break;
-    case USE_PHASE_VERIFY:
-      handle_phase_verify (uc);
-      break;
-    case USE_PHASE_COMPUTE_PRICE:
-      handle_phase_compute_price (uc);
-      break;
-    case USE_PHASE_CHECK_TIP:
-      handle_phase_check_tip (uc);
-      break;
-    case USE_PHASE_CHECK_TOTAL:
-      handle_phase_check_total (uc);
-      break;
-    case USE_PHASE_CREATE_ORDER:
-      handle_phase_create_order (uc);
-      break;
-    case USE_PHASE_SUBMIT_ORDER:
-      return TMH_private_post_orders (
-        NULL,    /* not even used */
-        connection,
-        &uc->ihc);
-    case USE_PHASE_FINISHED_MHD_YES:
-      return MHD_YES;
-    case USE_PHASE_FINISHED_MHD_NO:
-      return MHD_NO;
-    }
-  }
-}
diff --git a/src/backend/taler-merchant-httpd_post-using-templates.h b/src/backend/taler-merchant-httpd_post-using-templates.h
@@ -1,40 +0,0 @@
-/*
-  This file is part of TALER
-  (C) 2022 Taler Systems SA
-
-  TALER is free software; you can redistribute it and/or modify it under the
-  terms of the GNU General Public License as published by the Free Software
-  Foundation; either version 3, or (at your option) any later version.
-
-  TALER is distributed in the hope that it will be useful, but WITHOUT ANY
-  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
-  A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
-
-  You should have received a copy of the GNU General Public License along with
-  TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
-*/
-/**
- * @file taler-merchant-httpd_post-using-templates.h
- * @brief headers for POST /using-templates handler
- * @author Priscilla Huang
- */
-#ifndef TALER_MERCHANT_HTTPD_POST_USING_TEMPLATES_H
-#define TALER_MERCHANT_HTTPD_POST_USING_TEMPLATES_H
-
-#include "taler-merchant-httpd.h"
-
-/**
- * Generate a template that customer can use it. Returns an MHD_RESULT.
- *
- * @param rh details about this request handler
- * @param connection the MHD connection to handle
- * @param[in,out] hc context with further information about the request
- * @return MHD result code
- */
-MHD_RESULT
-TMH_post_using_templates_ID (const struct TMH_RequestHandler *rh,
-                             struct MHD_Connection *connection,
-                             struct TMH_HandlerContext *hc);
-
-
-#endif

	merchant Merchant backend to process payments, run by merchants
	Log \| Files \| Refs \| Submodules \| README \| LICENSE

M	src/backend/Makefile.am	\|	4	++--
M	src/backend/taler-merchant-httpd_dispatcher.c	\|	2	+-
A	src/backend/taler-merchant-httpd_post-templates-ID.c	\|	1782	+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
A	src/backend/taler-merchant-httpd_post-templates-ID.h	\|	40	++++++++++++++++++++++++++++++++++++++++
D	src/backend/taler-merchant-httpd_post-using-templates.c	\|	1782	-------------------------------------------------------------------------------
D	src/backend/taler-merchant-httpd_post-using-templates.h	\|	40	----------------------------------------