#include <stdio.h>

#include <stdio.h>
#include <string.h>
#include <errno.h>

#include "io.h"
#include "mp3info.h"
#include "util.h"

static int bitrate_tbl[2][3][16] = {
{
/* MPEG 2 & 2.5 */
{0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96,112,128,144,160,0}, /* Layer III */
{0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96,112,128,144,160,0}, /* Layer II */
{0, 32, 48, 56, 64, 80, 96,112,128,144,160,176,192,224,256,0} /* Layer I */
},
{
/* MPEG 1 */
{0, 32, 40, 48, 56, 64, 80, 96,112,128,160,192,224,256,320,0}, /* Layer III */
{0, 32, 48, 56, 64, 80, 96,112,128,160,192,224,256,320,384,0}, /* Layer II */
{0, 32, 64, 96,128,160,192,224,256,288,320,352,384,416,448,0} /* Layer I */
}
};

static int freq_tbl[4][3] = {
{32000, 16000, 8000}, /* MPEG 2.5 */
{ 0, 0, 0}, /* reserved */
{22050, 24000, 16000}, /* MPEG 2 */
{44100, 48000, 32000} /* MPEG 1 */
};

MP3INFO* mp3_info(char *filename)
{
static MP3INFO *info = NULL;
FILE *fd;
char tmp[128], hdrSize[4];
unsigned long bitHeader;
int try_count = 0, skip, file_size, hdr_skip;
float frameSize;

if (! (fd = fopen(filename, "r"))) {
err_msg(strerror(errno));
return NULL;
}

if (info)
free((char*)info);
info = (MP3INFO*)malloc(sizeof(MP3INFO));

fseek(fd, 0, SEEK_END);
file_size = ftell(fd);
fseek(fd, 0, SEEK_SET);

fread(&tmp[1], 1, 3, fd);

do {
tmp[0]=tmp[1];
tmp[1]=tmp[2];
tmp[2]=tmp[3];

fread(&tmp[3], 1, 1, fd);

/* check for ID3v2 tag */
if ((try_count == 0) && (! strncmp(tmp, "ID3", 3))) {
/* skip id3v2 version and flags */
fread(tmp, 1, 2, fd);

/* read id3v2 header size */
fread(hdr_size, 1, 4, fd);

/* compute bytes to skip */

hdr_skip = ((int)hdr_size[3] |
((int)hdr_size[2] << (8 - 1)) |
((int)hdr_size[1] << (16 - 2)) |
((int)hdr_size[0] << (24 - 3))) + 10;

/* skip */
fseek(fd, hdr_skip, SEEK_SET);

/* and get (hopefully) the first frame header */
fread(tmp, 1, 4, fd);
}

bit_header = (unsigned long)(
( (tmp[0] & 255) << 24) | ( (tmp[1] & 255) << 16) |
( (tmp[2] & 255) << 8) | ( (tmp[3] & 255) )
);

info->sync = (bit_header >> 21)&0x7ff;
info->version = ((bit_header >> 19)&0x3);
info->layer = ((bit_header >> 17)&0x3);
info->bitrate = ((bit_header >> 12)&0xf);
info->freq = ((bit_header >> 10)&0x3);

try_count++;
if (try_count >= 500)
return NULL;
} while (info->sync!=0x7ff || info->version==1 ||
info->layer==0 || info->bitrate==0xf ||
info->freq==3);

info->protect = ((bit_header >> 16)&0x1);

/* get index & calc brate from it */
info->bitrate =
bitrate_tbl[info->version & 1][info->layer - 1][info->bitrate];

info->freq = freq_tbl[info->version][info->freq];

info->padding = ((bit_header >> 9)&0x1);
info->channels = ((bit_header >> 6)&0x3);
info->ext = ((bit_header >> 4)&0x3);
info->copyright = ((bit_header >> 3)&0x1);
info->original = ((bit_header >> 2)&0x1);
info->emphasis = (bit_header & 0x3);

skip=0;

/* is there a variable bit rate bit */
if (info->version == 3 ) { /* mpeg version 1 */
if (info->channels == 3)
skip = 17; /* Single Channel */
else
skip = 32;
} else { /* mpeg version 2 or 2.5 */
if (info->channels==3 )
skip = 9; /* Single Channel */
else
skip = 17;
}

/* read next twelve bits in */
fread(tmp, 1, skip, fd);
fread(tmp, 1, 12, fd);

if (! strncmp("Xing", tmp, 4)) {
/* Got a varible bitrate */
bit_header = (unsigned long) (
(tmp[4] << 24) |
(tmp[5] << 16) |
(tmp[6] << 8) |
(tmp[7])
);
if (bit_header & 1) { /* there is frame data */
/* get the num of frames */
bit_header = (unsigned long)(
(tmp[8] << 24) |
(tmp[9] << 16) |
(tmp[10] << 8) |
(tmp[11])
);

frame_size = (float)file_size / (float)bit_header;
info->bitrate =
(int)(( frame_size * (float)info->freq) /
( 1000.0 * ( (info->layer==3) ? 12.0 : 144.0)) );
}
}

info->seconds = (8 * file_size) / 1000;
if (info->bitrate)
info->seconds = info->seconds/info->bitrate;
else
info->seconds=0;

fclose(fd);
return info;
}