#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <unistd.h>
#include <byteswap.h>
#include <string.h>
#include <math.h>


#define MAX_CH 4
#define MAX_TICK 100000
#define SAMPLE_RATE   44100
#define SAMPLES_PER_TICK   50

#define MAX_SAMPLE (SAMPLES_PER_TICK*MAX_TICK)

uint8_t active_note[MAX_CH][MAX_TICK];

double periods[128];


double
freq (int n)
{
  return 440. * pow (2., ((double) (n - 69)) / 12.);
}


void
calc_freqs (void)
{
  unsigned i;

  for (i = 0; i < 128; ++i)
    periods[i] = ((double) SAMPLE_RATE) / freq (i);
}




void
on (unsigned t, unsigned ch, unsigned n)
{
  memset (&active_note[ch][t], n, MAX_TICK - t);
}

void
off (unsigned t, unsigned ch, unsigned n)
{
  memset (&active_note[ch][t], 0, MAX_TICK - t);
}


void
mtrk (FILE *f, long pos, long end)
{

  uint32_t t = 0, v, m, dt;
  uint8_t k;

  end += pos;


  while (pos < end) {

    fseek (f, pos, SEEK_SET);

    dt = 0;

    do {
      fread (&v, 1, 1, f);
      pos++;
      dt <<= 7;
      dt |= v & 0x7f;
    } while (v & 0x80);


    t += dt;

    fread (&v, 1, 1, f);

    if (v & 0x80) {
      m = v;
      pos++;
    } else
      fseek (f, pos, SEEK_SET);


    switch (m & 0xf0) {
    case 0x80:
      fread (&k, 1, 1, f);
      fread (&v, 1, 1, f);
      pos += 2;
      off (t, m & 0xf, k);
      //printf ("%d: OFF %d %d %d\n", t,m &0xf, k, v);
      break;

    case 0x90:
      fread (&k, 1, 1, f);
      fread (&v, 1, 1, f);
      pos += 2;
      //printf ("%d: ON %d %d %d\n", t, m&0xf,k, v);
      on (t, m & 0xf, k);
      break;

    case 0xf0:
      switch (m) {
      case 0xff:
        fread (&v, 1, 1, f);
        pos++;

        switch (v) {
        case 0x3:
          fread (&k, 1, 1, f);
          pos++;
          pos += k;
          break;

        case 0x54:
          pos += 6;
          break;

        case 0x51:
          pos += 4;
          break;

        case 0x58:
          pos += 5;
          break;

        case 0x2f:
          pos++;
          break;

        default:
          printf ("?2 FF %x\n", v);
          exit (0);
          break;
        }

        break;

      default:
        printf ("?1 %x\n", m);
        exit (0);
      }

      break;

    default:
      printf ("?0 %x\n", m);
      exit (0);


    }
  }
}





int
parse_chunk (FILE *f)
{
  char fcc[5] = { 0 };
  uint32_t len;
  long o;

  if (fread (fcc, 4, 1, f) != 1)
    return -1;

  if (fread (&len, 4, 1, f) != 1)
    return -1;

  len = bswap_32 (len);

  o = ftell (f);

  printf ("%s for %d bytes at %d\n", fcc, (int) len, (int) o);

  if (!strcmp (fcc, "MTrk"))
    mtrk (f, o, len);

  fseek (f, o + len, SEEK_SET);

  return 0;
}


void
play (FILE *f)
{
  unsigned s, c, t;
  int8_t v;
  double d;


  calc_freqs();


  for (s = 0; s < MAX_SAMPLE; ++s) {
    t = s / SAMPLES_PER_TICK;
    v = 0;

    for (c = 0; c < MAX_CH; ++c) {
      if (active_note[c][t]) {
        d = ((double) s) / periods[active_note[c][t]];
        d = fmod (d, 1.0);

        if (d < 0.5)
          v--;
        else
          v++;
      }
    }


    v += (s % 3) * 2;
    v -= 2;

    if (v < 0) v = -120;
    else v = 120;

    fwrite (&v, 1, 1, f);
  }
}

int
main (int argc, char *argv[])
{
  FILE *f;

  f = fopen ("fugue21.mid", "rb");

  while (!parse_chunk (f));

  fclose (f);

  f = fopen ("fugue21.raw", "wb");
  play (f);
  fclose (f);



  return 0;
}