/*
 * Copyright (c) 2021 Clementine Computing LLC.
 *
 * This file is part of PopuFare.
 *
 * PopuFare 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 of the License, or
 * (at your option) any later version.
 *
 * PopuFare 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 Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with PopuFare.  If not, see <https://www.gnu.org/licenses/>.
 *
 */

#include "fareqr.h"

int fareqr_encode(char *tok_public, char *tok_secret, char *tok_cred, char *fareqr_str) {
  int i, r;
  uint8_t x,y,z;
  uint8_t *src_data = NULL, *dst_data = NULL;
  int src_data_n = 0, dst_data_n = 0;

  src_data = (uint8_t *)malloc(sizeof(uint8_t)*LINE_BUFFER_SIZE);
  dst_data = (uint8_t *)malloc(sizeof(uint8_t)*LINE_BUFFER_SIZE);

  for (i=0; tok_cred[i]; i++) {
    x = (uint8_t)tok_secret[i];
    y = (uint8_t)tok_cred[i];
    z = x^y;
    src_data[i] = z;
    src_data_n++;
  }

  for (i=0; i<src_data_n; i++) {
    x = (uint8_t)tok_secret[i];
  }

  dst_data_n = Base64encode_len(src_data_n);

  r = Base64encode((char *)dst_data, (const char *)src_data, src_data_n);

  if (fareqr_str) {
    snprintf(fareqr_str, LINE_BUFFER_SIZE-1, "@%s%%%s$\n", tok_public, dst_data);
  }

  free(src_data);
  free(dst_data);

  return 0;
}


int fareqr_decode(char *fareqr_s, char *check_pub, char *tok_secret, char *dst_cred) {
  int i, n;
  char *p, *stop_tok;
  int pub_tok_read_len = 0, check_pub_len = 0;

  char *enc_str = NULL, *dec_str = NULL, *plain_str=NULL;
  uint8_t x,y,z;

  if (fareqr_s[0] != '@') { return -1; }
  stop_tok = strchr(fareqr_s, '%');
  if (!stop_tok) { return -2; }
  if (!tok_secret) { return -3; }

  if (check_pub) {
    check_pub_len = strlen(check_pub);
    for ( p = (fareqr_s+1); p < stop_tok; p++) {
      if (pub_tok_read_len >= check_pub_len) { return -3; }
      if ( (*p) != check_pub[pub_tok_read_len] ) { return -4; }
      pub_tok_read_len++;
    }
  }

  enc_str = (char *)malloc(sizeof(char)*LINE_BUFFER_SIZE);
  dec_str = (char *)malloc(sizeof(char)*LINE_BUFFER_SIZE);
  plain_str = (char *)malloc(sizeof(char)*LINE_BUFFER_SIZE);
  for (n=0, p = (stop_tok+1); (*p) && ((*p) != '$'); p++, n++) {
    enc_str[n] = *p;
  }
  enc_str[n] = '\0';
  Base64decode(dec_str, enc_str);

  for (i=0; dec_str[i]; i++) {
    if (tok_secret[i]==0) { return -5; }
    x = (uint8_t)dec_str[i];
    y = (uint8_t)tok_secret[i];
    z = (x^y);
    plain_str[i] = (char)z;
  }
  plain_str[i]='\0';



  printf("%s\n", plain_str);

  if (dst_cred) {
    for (i=0; dec_str[i]; i++) {
      dst_cred[i] = dec_str[i];
    }
    dst_cred[i] = '\0';
  }

  free(enc_str);
  free(dec_str);
  free(plain_str);

  return 0;
}

// return negative on error or not found
// 0 on success (found)
//
int fareqr_lookup_seed_secret(char *seedfn, char *pub, char *priv) {
  int i;
  FILE *fp;
  char buf[LINE_BUFFER_SIZE] = {0};
  int pos = 0, ch=0, line_no=0, src_n;
  char *p = NULL;
  char *tok0_ptr=NULL,
       *tok1_ptr=NULL;

  uint8_t z;

  fp = fopen(seedfn, "r");
  if (!fp) { perror(seedfn); return -2;}
  while (!feof(fp)) {
    ch = fgetc(fp);

    // process line if we reach a newline or eof
    //
    if (feof(fp) || (ch == '\n')) {

      // if the line is empty or a comment, skip
      //
      if ((pos==0) || (buf[0] == '#')) {

      }

      // get tokens out of line, using ' ' as the
      // delimeter
      //
      else {
        tok0_ptr = buf;
        tok1_ptr = strchr(buf, ' ');
        if (tok1_ptr) {
          *tok1_ptr = '\0';
          tok1_ptr++;


          // Cechk it against our supplied 'pulbic' key
          //
          if (strcmp(pub, tok0_ptr)==0) {

            // If we've found it, copy it over to the `priv`
            // above and return
            //
            for (i=0; tok1_ptr[i]; i++) {
              priv[i] = tok1_ptr[i];
            }
            priv[i]='\0';
            return 0;

          }
        }

        line_no++;
      }

      pos=0;
      buf[0]='\0';
      continue;
    }

    buf[pos] = ch;
    pos++;
    buf[pos] = '\0';
  }
  fclose(fp);

  return -1;
}

// to compile:
// gcc -D__FAREQR_MAIN__ fareqr.c b64.c -o fareqr
//

#ifdef __FAREQR_MAIN__

void show_help(FILE *ofp) {
  fprintf(ofp, "\nusage:\n\n");
  fprintf(ofp, "  fareqr encode <pubkey> <privatekey> <str>\n");
  fprintf(ofp, "  fareqr decode <privatekey> <encstr>\n");
  fprintf(ofp, "  fareqr dbdecode <qrseedfile> <pubkey> <encstr>\n");
  fprintf(ofp, "  fareqr help\n");
  fprintf(ofp, "\n");
  fprintf(ofp, "fareqr is a program to help with encoding and decoding 'fareqr' strings.\n");
  fprintf(ofp, "\n");
  fprintf(ofp, "A fareqr string is of the form:\n");
  fprintf(ofp, "\n");
  fprintf(ofp, "  @<pubkey>%%<b64(xor(privkey,credential))>$\n");
  fprintf(ofp, "\n");
  fprintf(ofp, "Where `<b64(xor(privkey,credential))>` is the base64 encoded XOR of the private key\n");
  fprintf(ofp, "and the credential to be presented. The reasoning behind the XOR is to not allow a\n");
  fprintf(ofp, "snooper to get credential information if exposed to the string and the base64\n");
  fprintf(ofp, "encoding is to make it easily transportable.\n");
  fprintf(ofp, "\n");
  fprintf(ofp, "The <qrseedfile> is a text file of <pubkey> <privkey> pairs.\n");
  fprintf(ofp, "\n");
  fprintf(ofp, "Here is some example usage:\n");
  fprintf(ofp, "\n");
  fprintf(ofp, "  $ fareqr encode 'wu9XouSh' 'ohNgizahkephain3aosoh2AeH1aethoo4cie6oiSaezimaighai2eiVaefahfien' ';123456789060535?'\n");
  fprintf(ofp, "  @wu9XouSh%VFl8VF1PV19TXEBeUVxdBl4=\n");
  fprintf(ofp, "  $ fareqr decode 'ohNgizahkephain3aosoh2AeH1aethoo4cie6oiSaezimaighai2eiVaefahfien' '@wu9XouSh%VFl8VF1PV19TXEBeUVxdBl4=$'\n");
  fprintf(ofp, "  ;123456789060535?\n");
  fprintf(ofp, "  $ echo 'wu9XouSh ohNgizahkephain3aosoh2AeH1aethoo4cie6oiSaezimaighai2eiVaefahfien' > ./qr.seed\n");
  fprintf(ofp, "  $ fareqr dbdecode ./qr.seed 'wu9XouSh' '@wu9XouSh%VFl8VF1PV19TXEBeUVxdBl4=$'\n");
  fprintf(ofp, "  ;123456789060535?\n");
  fprintf(ofp, "\n");
  fprintf(ofp, "Where 'wu9XouSh' is the public key, 'ohNgizahkephain3aosoh2AeH1aethoo4cie6oiSaezimaighai2eiVaefahfien' is the private key and\n");
  fprintf(ofp, "';123456789060535?' is the credential information to be encoded.\n");
  fprintf(ofp, "\n");
  fprintf(ofp, "\n");
  fflush(ofp);
}

/* 
 *
 * quick test/start:
 *
 * $ fareqr encode 'wu9XouSh' 'ohNgizahkephain3aosoh2AeH1aethoo4cie6oiSaezimaighai2eiVaefahfien' ';123456789060535?'
 * @wu9XouSh%VFl8VF1PV19TXEBeUVxdBl4=
 *
 * $ fareqr decode 'ohNgizahkephain3aosoh2AeH1aethoo4cie6oiSaezimaighai2eiVaefahfien' '@wu9XouSh%VFl8VF1PV19TXEBeUVxdBl4=$' 
 * ;123456789060535?
 *
 * $ fareqr dbdecode 'wu9XouSh' '@wu9XouSh%VFl8VF1PV19TXEBeUVxdBl4=$'
 * ;123456789060535?
 *
 */

int main(int argc, char **argv) {
  int i, r;
  char *tok_public = NULL,
       *tok_secret = NULL,
       *tok_cred = NULL,
       *fareqr_str = NULL;

  uint8_t x,y,z;

  uint8_t *src_data = NULL, *dst_data = NULL;
  int src_data_n = 0, dst_data_n = 0;

  char *fn = NULL;

  if (argc <= 1) {
    show_help(stderr);
    exit(1);
  }

  if (strcmp(argv[1], "encode")==0) {
    if (argc>2) {
      tok_public = strdup(argv[2]);
      if (argc>3) {
        tok_secret = strdup(argv[3]);
        if (argc>4) {
          tok_cred = strdup(argv[4]);
        }
      }
    }

    if ((!tok_public) || (!tok_secret) || (!tok_cred)) {
      show_help(stderr);
      if (tok_public) { free(tok_public); }
      if (tok_secret) { free(tok_secret); }
      if (tok_cred) { free(tok_cred); }
      exit(2);
    }

    fareqr_str = (char *)malloc(sizeof(char)*LINE_BUFFER_SIZE);
    r = fareqr_encode(tok_public, tok_secret, tok_cred, fareqr_str);
    if (r==0) {
      printf("%s\n", fareqr_str);
    }
  }

  else if (strcmp(argv[1], "decode")==0) {
    if (argc>2) {
      tok_secret = strdup(argv[2]);
      if (argc>3) {
        fareqr_str = strdup(argv[3]);
      }
    }
    r = fareqr_decode(fareqr_str, tok_public, tok_secret, NULL);
    if (r<0) {
      fprintf(stderr, "error, failed to decode qr fare string (%i)\n", r);
    }
  }

  else if (strcmp(argv[1], "dbdecode")==0) {
    if (argc>2) {
      fn = strdup(argv[2]);
      if (argc>3) {
        tok_public = strdup(argv[3]);
        if (argc>4) {
          fareqr_str = strdup(argv[4]);
        }
      }
    }
    tok_secret = (char *)malloc(sizeof(char)*LINE_BUFFER_SIZE);
    tok_secret[0] = '\0';
    r = fareqr_lookup_seed_secret(fn, tok_public, tok_secret);
    if (r<0) {
      fprintf(stderr, "could not find '%s' in db '%s', exiting (got %i)\n",
          tok_public, fn, r);
    }
    else {
      r = fareqr_decode(fareqr_str, tok_public, tok_secret, NULL);
      if (r<0) {
        fprintf(stderr, "error, failed to decode qr fare string (%i)\n", r);
      }
    }
  }

  else if (strcmp(argv[1], "help")==0) {
    show_help(stdout);
    exit(0);
  }
  else {
    fprintf(stderr, "unknown operation '%s'\n", argv[1]);
    show_help(stderr);
    exit(3);
  }

  if (tok_public) { free(tok_public); }
  if (tok_secret) { free(tok_secret); }
  if (tok_cred) { free(tok_cred); }
  if (fareqr_str) { free(fareqr_str); }

  if (src_data) { free(src_data); }
  if (dst_data) { free(dst_data); }
  if (fn) { free(fn); }
}

#endif