1 files changed, 199 insertions, 0 deletions
diff --git a/packages/taler-wallet-core/src/denomSelection.ts b/packages/taler-wallet-core/src/denomSelection.ts
new file mode 100644
index 000000000..ecc1fa881
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+++ b/packages/taler-wallet-core/src/denomSelection.ts
@@ -0,0 +1,199 @@
+/*
+ This file is part of GNU Taler
+ (C) 2021-2024 Taler Systems S.A.
+
+ GNU 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.
+
+ GNU 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
+ GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+/**
+ * Selection of denominations for withdrawals.
+ *
+ * @author Florian Dold
+ */
+
+/**
+ * Imports.
+ */
+import {
+  AbsoluteTime,
+  AmountJson,
+  Amounts,
+  DenomSelectionState,
+  ForcedDenomSel,
+  Logger,
+} from "@gnu-taler/taler-util";
+import { DenominationRecord, timestampAbsoluteFromDb } from "./db.js";
+import { isWithdrawableDenom } from "./denominations.js";
+
+const logger = new Logger("denomSelection.ts");
+
+/**
+ * Get a list of denominations (with repetitions possible)
+ * whose total value is as close as possible to the available
+ * amount, but never larger.
+ */
+export function selectWithdrawalDenominations(
+  amountAvailable: AmountJson,
+  denoms: DenominationRecord[],
+  denomselAllowLate: boolean = false,
+): DenomSelectionState {
+  let remaining = Amounts.copy(amountAvailable);
+
+  const selectedDenoms: {
+    count: number;
+    denomPubHash: string;
+  }[] = [];
+
+  let totalCoinValue = Amounts.zeroOfCurrency(amountAvailable.currency);
+  let totalWithdrawCost = Amounts.zeroOfCurrency(amountAvailable.currency);
+  let earliestDepositExpiration: AbsoluteTime | undefined;
+  let hasDenomWithAgeRestriction = false;
+
+  denoms = denoms.filter((d) => isWithdrawableDenom(d, denomselAllowLate));
+  denoms.sort((d1, d2) => Amounts.cmp(d2.value, d1.value));
+
+  if (logger.shouldLogTrace()) {
+    logger.trace(
+      `selecting withdrawal denoms for ${Amounts.stringify(amountAvailable)}`,
+    );
+  }
+
+  for (const d of denoms) {
+    const cost = Amounts.add(d.value, d.fees.feeWithdraw).amount;
+    const res = Amounts.divmod(remaining, cost);
+    const count = res.quotient;
+    remaining = Amounts.sub(remaining, Amounts.mult(cost, count).amount).amount;
+    if (count > 0) {
+      totalCoinValue = Amounts.add(
+        totalCoinValue,
+        Amounts.mult(d.value, count).amount,
+      ).amount;
+      totalWithdrawCost = Amounts.add(
+        totalWithdrawCost,
+        Amounts.mult(cost, count).amount,
+      ).amount;
+      selectedDenoms.push({
+        count,
+        denomPubHash: d.denomPubHash,
+      });
+      hasDenomWithAgeRestriction =
+        hasDenomWithAgeRestriction || d.denomPub.age_mask > 0;
+      const expireDeposit = timestampAbsoluteFromDb(d.stampExpireDeposit);
+      if (!earliestDepositExpiration) {
+        earliestDepositExpiration = expireDeposit;
+      } else {
+        earliestDepositExpiration = AbsoluteTime.min(
+          expireDeposit,
+          earliestDepositExpiration,
+        );
+      }
+    }
+
+    if (logger.shouldLogTrace()) {
+      logger.trace(
+        `denom_pub_hash=${
+          d.denomPubHash
+        }, count=${count}, val=${Amounts.stringify(
+          d.value,
+        )}, wdfee=${Amounts.stringify(d.fees.feeWithdraw)}`,
+      );
+    }
+
+    if (Amounts.isZero(remaining)) {
+      break;
+    }
+  }
+
+  if (logger.shouldLogTrace()) {
+    logger.trace("(end of denom selection)");
+  }
+
+  earliestDepositExpiration ??= AbsoluteTime.never();
+
+  return {
+    selectedDenoms,
+    totalCoinValue: Amounts.stringify(totalCoinValue),
+    totalWithdrawCost: Amounts.stringify(totalWithdrawCost),
+    earliestDepositExpiration: AbsoluteTime.toProtocolTimestamp(
+      earliestDepositExpiration,
+    ),
+    hasDenomWithAgeRestriction,
+  };
+}
+
+export function selectForcedWithdrawalDenominations(
+  amountAvailable: AmountJson,
+  denoms: DenominationRecord[],
+  forcedDenomSel: ForcedDenomSel,
+  denomselAllowLate: boolean,
+): DenomSelectionState {
+  const selectedDenoms: {
+    count: number;
+    denomPubHash: string;
+  }[] = [];
+
+  let totalCoinValue = Amounts.zeroOfCurrency(amountAvailable.currency);
+  let totalWithdrawCost = Amounts.zeroOfCurrency(amountAvailable.currency);
+  let earliestDepositExpiration: AbsoluteTime | undefined;
+  let hasDenomWithAgeRestriction = false;
+
+  denoms = denoms.filter((d) => isWithdrawableDenom(d, denomselAllowLate));
+  denoms.sort((d1, d2) => Amounts.cmp(d2.value, d1.value));
+
+  for (const fds of forcedDenomSel.denoms) {
+    const count = fds.count;
+    const denom = denoms.find((x) => {
+      return Amounts.cmp(x.value, fds.value) == 0;
+    });
+    if (!denom) {
+      throw Error(
+        `unable to find denom for forced selection (value ${fds.value})`,
+      );
+    }
+    const cost = Amounts.add(denom.value, denom.fees.feeWithdraw).amount;
+    totalCoinValue = Amounts.add(
+      totalCoinValue,
+      Amounts.mult(denom.value, count).amount,
+    ).amount;
+    totalWithdrawCost = Amounts.add(
+      totalWithdrawCost,
+      Amounts.mult(cost, count).amount,
+    ).amount;
+    selectedDenoms.push({
+      count,
+      denomPubHash: denom.denomPubHash,
+    });
+    hasDenomWithAgeRestriction =
+      hasDenomWithAgeRestriction || denom.denomPub.age_mask > 0;
+    const expireDeposit = timestampAbsoluteFromDb(denom.stampExpireDeposit);
+    if (!earliestDepositExpiration) {
+      earliestDepositExpiration = expireDeposit;
+    } else {
+      earliestDepositExpiration = AbsoluteTime.min(
+        expireDeposit,
+        earliestDepositExpiration,
+      );
+    }
+  }
+
+  earliestDepositExpiration ??= AbsoluteTime.never();
+
+  return {
+    selectedDenoms,
+    totalCoinValue: Amounts.stringify(totalCoinValue),
+    totalWithdrawCost: Amounts.stringify(totalWithdrawCost),
+    earliestDepositExpiration: AbsoluteTime.toProtocolTimestamp(
+      earliestDepositExpiration,
+    ),
+    hasDenomWithAgeRestriction,
+  };
+}