#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;
}
.