#include <stddef.h>
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include "wav.h"

void dtmf_freqs(char c, int *a, int *b) {
  switch (c) {
  case '1':
  case '2':
  case '3':
  case 'A':
    *a = 697;
    break;
  case '4':
  case '5':
  case '6':
  case 'B':
    *a = 770;
    break;
  case '7':
  case '8':
  case '9':
  case 'C':
    *a = 852;
    break;
  case '*':
  case '0':
  case '#':
  case 'D':
    *a = 941;
    break;
  default:
    *a = 0;
  }

  switch (c) {
  case '1':
  case '4':
  case '7':
  case '*':
    *b = 1209;
    break;
  case '2':
  case '5':
  case '8':
  case '0':
    *b = 1336;
    break;
  case '3':
  case '6':
  case '9':
  case '#':
    *b = 1477;
    break;
  case 'A':
  case 'B':
  case 'C':
  case 'D':
    *b = 1633;
    break;
  default:
    *b = 0;
  }
}

int16_t dtmf_gen(char c, int t, int rate) {
  int a, b;
  dtmf_freqs(c, &a, &b);
  double v = 0.5 * sin(2.0 * M_PI * (double)a * ((double)t / (double)rate));
  v += 0.5 * sin(2.0 * M_PI * (double)b * ((double)t / (double)rate));
  return v * 32767.0;
}

int main(int argc, char *argv[]) {
  /* usage */
  if (argc != 5) {
    fprintf(stderr, "usage: %s <wave file> <dtmf> <width> <spacing>\n", argv[0]);
    return 2;
  }

  /* read arguments */
  char *outfilename = argv[1];
  char *dtmf = argv[2];
  int width, spacing;
  sscanf(argv[3], "%d", &width);
  sscanf(argv[4], "%d", &spacing);

  /* open output file */
  FILE *fout = fopen(outfilename, "w");
  if (fout == NULL) {
    fprintf(stderr, "could not open '%s' for writing.\n", outfilename);
    return 1;
  }
  
  /* create header */
  struct wav_header wav_header;
  memcpy(wav_header.riff_magic, "RIFF", 4);
  memcpy(wav_header.wave_magic, "WAVE", 4);
  memcpy(wav_header.format_magic, "fmt ", 4);
  memcpy(wav_header.data_magic, "data", 4);
  wav_header.format_size = 16;
  wav_header.format_type = 1;
  wav_header.channels = 1;
  wav_header.sample_rate = 44100;
  wav_header.bits_per_sample = 16;
  wav_header.rate1 = (wav_header.sample_rate * wav_header.bits_per_sample * wav_header.channels) / 8;
  wav_header.rate2 = (wav_header.bits_per_sample * wav_header.channels) / 8;

  /* go past header */ 
  fseek(fout, sizeof(wav_header), SEEK_SET);

  /* generate sound */
  int num_digits = strlen(dtmf);
  uint32_t sample_count = wav_header.sample_rate * num_digits * (width + spacing);

  for (int digit_index = 0; digit_index < num_digits; digit_index++) {
    char digit = dtmf[digit_index];

    /* emit dtmf tone */
    for (int t = 0; t < (float)wav_header.sample_rate * (float)(width) / 1000.0f; t++) {
      int16_t sample = dtmf_gen(digit, t, wav_header.sample_rate);
      fwrite(&sample, sizeof(int16_t), 1, fout);
    }

    /* emit spacing */
    fseek(fout, (float)wav_header.sample_rate * (float)(spacing) / 1000.0f, SEEK_CUR);
  }

  /* update header */
  wav_header.size = ftell(fout) - 8;
  wav_header.data_size = ftell(fout) - sizeof(wav_header);
  
  /* write header */
  fseek(fout, 0, SEEK_SET);
  fwrite(&wav_header, sizeof(wav_header), 1, fout);

  /* close file */
  fclose(fout);
  
  return 0;
}