/*
  This file is part of TALER
  (C) 2014 Christian Grothoff (and other contributing authors)

  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, If not, see <http://www.gnu.org/licenses/>
*/

/**
 * @file util.c
 * @brief Common utility functions
 * @author Sree Harsha Totakura <sreeharsha@totakura.in> 
 * @author Florian Dold
 * @author Benedikt Mueller
 */

#include "platform.h"
#include "taler_util.h"
#include <gnunet/gnunet_common.h>
#include <gnunet/gnunet_util_lib.h>
#include <gcrypt.h>

#define CURVE "Ed25519"

#define AMOUNT_FRAC_BASE 1000000
#define AMOUNT_FRAC_LEN 6



static void
fatal_error_handler (void *cls, int wtf, const char *msg)
{
  LOG_ERROR("Fatal error in Gcrypt: %s\n", msg);
  abort();
}


/**
 * Initialize Gcrypt library.
 */
void
TALER_gcrypt_init()
{
  gcry_set_fatalerror_handler (&fatal_error_handler, NULL);
  TALER_assert_as(gcry_check_version(NEED_LIBGCRYPT_VERSION),
                  "libgcrypt version mismatch");
  /* Disable secure memory.  */
  gcry_control (GCRYCTL_DISABLE_SECMEM, 0);
  gcry_control (GCRYCTL_INITIALIZATION_FINISHED, 0);
}


/**
 * Generate a ECC private key.
 *
 * @return the s-expression representing the generated ECC private key; NULL
 *           upon error
 */
gcry_sexp_t
TALER_genkey ()
{
  gcry_sexp_t priv_sexp;
  gcry_sexp_t s_keyparam;
  int rc;
  
  if (0 != (rc = gcry_sexp_build (&s_keyparam, NULL,
                                  "(genkey(ecc(curve \"" CURVE "\")"
                                  "(flags eddsa)))")))
  {
    LOG_GCRY_ERROR ("gcry_sexp_build", rc);
    return NULL;
  }
  if (0 != (rc = gcry_pk_genkey (&priv_sexp, s_keyparam)))
  {
    LOG_GCRY_ERROR ("gcry_pk_genkey", rc);
    gcry_sexp_release (s_keyparam);
    return NULL;
  }
  gcry_sexp_release (s_keyparam);
  if (0 != (rc = gcry_pk_testkey (priv_sexp)))
  {
    LOG_GCRY_ERROR("gcry_pk_testkey", rc);
    gcry_sexp_release (priv_sexp);
    return NULL;
  }
  return priv_sexp;
}


/**
 * Parse money amount description, in the format "A:B.C".
 *
 * @param str amount description
 * @param denom amount to write the result to
 * @return GNUNET_OK if the string is a valid amount specification,
 *         GNUNET_SYSERR if it is invalid.
 */
int
TALER_string_to_amount (const char *str, struct TALER_Amount *denom)
{
  unsigned int i; // pos in str
  int n; // number tmp
  unsigned int c; // currency pos
  uint32_t b; // base for suffix

  memset (denom, 0, sizeof (struct TALER_Amount));

  i = n = c = 0;

  while (isspace(str[i]))
    i++;

  if (0 == str[i])
  {
    printf("null before currency\n");
    return GNUNET_SYSERR;
  }
  
  while (str[i] != ':')
  {
    if (0 == str[i])
    {
      printf("null before colon");
      return GNUNET_SYSERR;
    }
    if (c > 3)
    {
      printf("currency too long\n");
      return GNUNET_SYSERR;
    }
    denom->currency[c] = str[i];
    c++;
    i++;
  }

  // skip colon
  i++;

  if (0 == str[i])
  {
    printf("null before value\n");
    return GNUNET_SYSERR;
  }

  while (str[i] != '.')
  {
    if (0 == str[i])
    {
      return GNUNET_OK;
    }
    n = str[i] - '0';
    if (n < 0 || n > 9)
    {
      printf("invalid character '%c' before comma at %u\n", (char) n, i);
      return GNUNET_SYSERR;
    }
    denom->value = (denom->value * 10) + n;
    i++;
  }

  // skip the dot
  i++;

  if (0 == str[i])
  {
    printf("null after dot");
    return GNUNET_SYSERR;
  }

  b = 100000;

  while (0 != str[i])
  {
    n = str[i] - '0';
    if (b == 0 || n < 0 || n > 9)
    {
      printf("error after comma");
      return GNUNET_SYSERR;
    }
    denom->fraction += n * b;
    b /= 10;
    i++;
  }

  return GNUNET_OK;
}


/**
 * FIXME
 */
struct TALER_AmountNBO 
TALER_amount_hton (struct TALER_Amount d)
{
  struct TALER_AmountNBO dn;
  dn.value = htonl (d.value);
  dn.fraction = htonl (d.fraction);
  memcpy (dn.currency, d.currency, TALER_CURRENCY_LEN);

  return dn;
}


/**
 * FIXME
 */
struct TALER_Amount
TALER_amount_ntoh (struct TALER_AmountNBO dn)
{
  struct TALER_Amount d;
  d.value = ntohl (dn.value);
  d.fraction = ntohl (dn.fraction);
  memcpy (d.currency, dn.currency, sizeof(dn.currency));

  return d;
}


/**
 * Compare the value/fraction of two amounts.  Does not compare the currency,
 * i.e. comparing amounts with the same value and fraction but different
 * currency would return 0.
 *
 * @param a1 first amount
 * @param a2 second amount
 * @return result of the comparison
 */
int
TALER_amount_cmp (struct TALER_Amount a1, struct TALER_Amount a2)
{
  a1 = TALER_amount_normalize (a1);
  a2 = TALER_amount_normalize (a2);
  if (a1.value == a2.value)
  {
    if (a1.fraction < a2.fraction)
      return -1;
    if (a1.fraction > a2.fraction)
      return 1;
    return 0;
  }
  if (a1.value < a2.value)
    return -1;
  return 1;
}


/**
 * Perform saturating subtraction of amounts.
 *
 * @param a1 amount to subtract from
 * @param a2 amount to subtract
 * @return (a1-a2) or 0 if a2>=a1
 */
struct TALER_Amount
TALER_amount_subtract (struct TALER_Amount a1, struct TALER_Amount a2)
{
  a1 = TALER_amount_normalize (a1);
  a2 = TALER_amount_normalize (a2);

  if (a1.value < a2.value)
  {
    a1.value = 0;
    a1.fraction = 0;
    return a1;
  }

  if (a1.fraction < a2.fraction)
  {
    if (0 == a1.value)
    {
      a1.fraction = 0;
      return a1;
    }
    a1.fraction += AMOUNT_FRAC_BASE;
    a1.value -= 1;
  }

  a1.fraction -= a2.fraction;
  a1.value -= a2.value;

  return a1;
}


/**
 * Perform saturating addition of amounts.
 *
 * @param a1 first amount to add
 * @param a2 second amount to add
 * @return sum of a1 and a2
 */
struct TALER_Amount
TALER_amount_add (struct TALER_Amount a1, struct TALER_Amount a2)
{
  a1 = TALER_amount_normalize (a1);
  a2 = TALER_amount_normalize (a2);

  a1.value += a2.value;
  a1.fraction += a2.fraction;

  if (0 == a1.currency[0])
  {
    memcpy (a2.currency, a1.currency, TALER_CURRENCY_LEN);
  }

  if (0 == a2.currency[0])
  {
    memcpy (a1.currency, a2.currency, TALER_CURRENCY_LEN);
  }

  if (0 != a1.currency[0] && 0 != memcmp (a1.currency, a2.currency, TALER_CURRENCY_LEN))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_WARNING, "adding mismatching currencies\n");
  }

  if (a1.value < a2.value)
  {
    a1.value = UINT32_MAX;
    a2.value = UINT32_MAX;
    return a1;
  }

  return TALER_amount_normalize (a1);
}


/**
 * Normalize the given amount.
 *
 * @param amout amount to normalize
 * @return normalized amount
 */
struct TALER_Amount
TALER_amount_normalize (struct TALER_Amount amount)
{
  while (amount.value != UINT32_MAX && amount.fraction >= AMOUNT_FRAC_BASE)
  {
    amount.fraction -= AMOUNT_FRAC_BASE;
    amount.value += 1;
  }
  return amount;
}


/**
 * Convert amount to string.
 *
 * @param amount amount to convert to string
 * @return freshly allocated string representation
 */
char *
TALER_amount_to_string (struct TALER_Amount amount)
{
  char tail[AMOUNT_FRAC_LEN + 1] = { 0 };
  char curr[TALER_CURRENCY_LEN + 1] = { 0 };
  char *result = NULL;
  int len;

  memcpy (curr, amount.currency, TALER_CURRENCY_LEN);

  amount = TALER_amount_normalize (amount);
  if (0 != amount.fraction)
  {
    unsigned int i;
    uint32_t n = amount.fraction;
    for (i = 0; (i < AMOUNT_FRAC_LEN) && (n != 0); i++)
    {
      tail[i] = '0' + (n / (AMOUNT_FRAC_BASE / 10));
      n = (n * 10) % (AMOUNT_FRAC_BASE);
    }
    tail[i] = 0;
    len = GNUNET_asprintf (&result, "%s:%lu.%s", curr, (unsigned long) amount.value, tail);
  }
  else
  {
    len = GNUNET_asprintf (&result, "%s:%lu", curr, (unsigned long) amount.value);
  }
  GNUNET_assert (len > 0);
  return result;
}



/**
 * Return the base32crockford encoding of the given buffer.
 *
 * The returned string will be freshly allocated, and must be free'd
 * with GNUNET_free.
 *
 * @param buffer with data
 * @param size size of the buffer
 * @return freshly allocated, null-terminated string
 */
char *
TALER_data_to_string_alloc (const void *buf, size_t size)
{
  char *str_buf;
  size_t len = size * 8;
  char *end;

  if (len % 5 > 0)
    len += 5 - len % 5;
  len /= 5;
  str_buf = GNUNET_malloc (len + 1);
  end = GNUNET_STRINGS_data_to_string (buf, size, str_buf, len);
  if (NULL == end)
  {
    GNUNET_free (str_buf);
    return NULL;
  }
  *end = '\0';
  return str_buf;
}


/**
 * Get encoded binary data from a configuration.
 *
 * @return GNUNET_OK on success
 *         GNUNET_NO is the value does not exist
 *         GNUNET_SYSERR on encoding error
 */
int
TALER_configuration_get_data (const struct GNUNET_CONFIGURATION_Handle *cfg,
                              const char *section, const char *option,
                              void *buf, size_t buf_size)
{
  char *enc;
  int res;
  size_t data_size;
  if (GNUNET_OK != (res = GNUNET_CONFIGURATION_get_value_string (cfg, section, option, &enc)))
    return res;
  data_size = (strlen (enc) * 5) / 8;
  if (data_size != buf_size)
  {
    GNUNET_free (enc);
    return GNUNET_SYSERR;
  }
  if (GNUNET_OK != GNUNET_STRINGS_string_to_data (enc, strlen (enc),
                                                  buf, buf_size))
  {
    GNUNET_free (enc);
    return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}


static void
derive_refresh_key (const struct GNUNET_HashCode *secret,
                    struct GNUNET_CRYPTO_SymmetricInitializationVector *iv,
                    struct GNUNET_CRYPTO_SymmetricSessionKey *skey)
{
  static const char ctx_key[] = "taler-key-skey";
  static const char ctx_iv[] = "taler-key-iv";

  GNUNET_assert (GNUNET_YES == 
                 GNUNET_CRYPTO_kdf (skey, sizeof (struct GNUNET_CRYPTO_SymmetricSessionKey),
                                    ctx_key, strlen (ctx_key),
                                    secret, sizeof (struct GNUNET_HashCode),
                                    NULL, 0));
  GNUNET_assert (GNUNET_YES ==
                 GNUNET_CRYPTO_kdf (iv, sizeof (struct GNUNET_CRYPTO_SymmetricInitializationVector),
                                    ctx_iv, strlen (ctx_iv),
                                    secret, sizeof (struct GNUNET_HashCode),
                                    NULL, 0));
}


int
TALER_refresh_decrypt (const void *input, size_t input_size, const struct GNUNET_HashCode *secret, void *result)
{
  struct GNUNET_CRYPTO_SymmetricInitializationVector iv;
  struct GNUNET_CRYPTO_SymmetricSessionKey skey;

  derive_refresh_key (secret, &iv, &skey);

  return GNUNET_CRYPTO_symmetric_decrypt (input, input_size, &skey, &iv, result);
}


int
TALER_refresh_encrypt (const void *input, size_t input_size, const struct GNUNET_HashCode *secret, void *result)
{
  struct GNUNET_CRYPTO_SymmetricInitializationVector iv;
  struct GNUNET_CRYPTO_SymmetricSessionKey skey;

  derive_refresh_key (secret, &iv, &skey);

  return GNUNET_CRYPTO_symmetric_encrypt (input, input_size, &skey, &iv, result);
}


void
TALER_hash_context_start (struct TALER_HashContext *hc)
{
  GNUNET_assert (0 == gcry_md_open (&hc->hd, GCRY_MD_SHA512, 0));
}


void
TALER_hash_context_read (struct TALER_HashContext *hc, void *buf, size_t size)
{
  gcry_md_write (hc->hd, buf, size);
}


void
TALER_hash_context_finish (struct TALER_HashContext *hc,
                           struct GNUNET_HashCode *r_hash)
{
  void *res = gcry_md_read (hc->hd, 0);
  GNUNET_assert (NULL != res);
  if (NULL != r_hash)
    memcpy (r_hash, res, sizeof (struct GNUNET_HashCode));
  gcry_md_close (hc->hd);
}


/* end of util.c */