#include <u.h>
#include <libc.h>
#include <bio.h>

typedef struct Tag {
	u8int	quality;
	char	encvers[9+1];
	u8int	rev;
	u8int	vbr;
	int	lowpass;
	u32int	peak;
	u16int	trackgain;
	u16int	albumgain;
	u8int	encflags;
	u8int	ath;
	u8int	bitrate;

	u16int	delay;
	u16int	padding;
	u8int	shape;
	u8int	stereo;
	u8int	unwise;
	u8int	srcfreq;
	u8int	gain;
	u8int	surround;
	u16int	preset;
	u32int	length;
	u16int	crc;
	u16int	tagcrc;
} Tag;

void
gtag(Tag *t, uchar *p)
{
	t->quality = *p++;

	memcpy(t->encvers, p, 9);
	t->encvers[9] = '\0';
	p += 9;

	t->rev = *p >> 4;
	t->vbr = *p++ & 0x0F;

	t->lowpass = *p++ * 100;

	// FIXME -- endianness and float
	t->peak  = *p++ << 24;
	t->peak |= *p++ << 16;
	t->peak |= *p++ << 8;
	t->peak |= *p++;

	t->trackgain  = *p++ << 8;
	t->trackgain |= *p++;

	t->albumgain  = *p++ << 8;
	t->albumgain |= *p++;

	t->encflags = *p >> 4;
	t->ath = *p++ & 0x0F;

	t->bitrate = *p++;

	t->delay  = *p++ << 4;
	t->delay |= *p >> 4;
	t->padding  = (*p++ & 0x0F) << 8;
	t->padding |= *p++;

	t->shape = *p >> 6;
	t->stereo = (*p >> 3) & 0x07;
	t->unwise = (*p >> 2) & 0x01;
	t->srcfreq = *p++ & 0x3;

	t->gain = *p++;

	t->surround = (*p >> 3) & 0x07;
	t->preset  = (*p++ & 0x07) << 8;
	t->preset |= *p++;

	t->length  = *p++ << 24;
	t->length |= *p++ << 16;
	t->length |= *p++ << 8;
	t->length |= *p++;

	t->crc  = *p++ << 8;
	t->crc |= *p++;

	t->tagcrc  = *p++ << 8;
	t->tagcrc |= *p;
}

u32int
gss32(uchar *p)
{
	u32int x;
	x  = *p++ << 21;
	x |= *p++ << 14;
	x |= *p++ << 7;
	x |= *p;
	return x;
}

int
quality2V(int quality)
{
	return (100 - quality) / 10;
}

int
quality2q(int quality)
{
	return (100 - quality) % 10;
}

void
usage(void)
{
	fprint(2, "usage: %s [file]\n", argv0);
	exits("usage");
}

void
main(int argc, char **argv)
{
	int fd;
	Biobuf bin;
	uchar buf[36];
	int id3len;
	Tag tag;

	ARGBEGIN {
	default:
		usage();
	} ARGEND

	switch(argc) {
	case 0:
		fd = 0;
		break;
	case 1:
		if((fd = open(argv[0], OREAD)) < 0)
			sysfatal("open %s: %r", argv[0]);
		break;
	default:
		usage();
		SET(fd);
	}

	Binit(&bin, fd, OREAD);

	if(Bread(&bin, buf, 10) < 10)
		sysfatal("read header: %r");
	if(strncmp((char *)buf, "ID3", 3) == 0) {
//		fprint(2, "saw id3 tag\n");
		id3len = 10 + gss32(buf+6);
		if(Bseek(&bin, id3len, 0) < 0)
			sysfatal("seek frame: %r");
		if(Bread(&bin, buf, 2) < 2)
			sysfatal("read frame: %r");
	} else {
		id3len = 0;
	}
	if(buf[0] != 0xFF || (buf[1] & 0xE0) != 0xE0)
		sysfatal("no sync word");
	// FIXME -- check for a xing tag
	if(Bseek(&bin, id3len + 0x9B, 0) < 0)
		sysfatal("seek tag: %r");
	if(Bread(&bin, buf, sizeof buf) < 0)
		sysfatal("read tag: %r");

	gtag(&tag, buf);
	print("encoder	%s\n", tag.encvers);
	print("revision	%d\n", tag.rev);
	print("quality	%d\n", tag.quality);
	print("V	%d\n", quality2V(tag.quality));
	print("q	%d\n", quality2q(tag.quality));
	print("vbr	%d\n", tag.vbr);
	print("lowpass	%d Hz\n", tag.lowpass);
	print("peak	%#.8x\n", tag.peak);
	print("trackgain	%#.4x\n", tag.trackgain);
	print("albumgain	%#.4x\n", tag.albumgain);
	print("flags	%#x\n", tag.encflags);
	print("ath	%d\n", tag.ath);
	print("bitrate	%d kb/s\n", tag.bitrate);
	print("delay	%d\n", tag.delay);
	print("padding	%d\n", tag.padding);
	print("shape	%d\n", tag.shape);
	print("stereo	%d\n", tag.stereo);
	print("unwise	%d\n", tag.unwise);
	print("srcfreq	%d\n", tag.srcfreq);
	print("gain	%d\n", tag.gain);
	print("surround	%d\n", tag.surround);
	print("preset	%d\n", tag.preset);
	print("length	%d\n", tag.length);
	print("cec	%#.4x\n", tag.crc);
	print("tagcrc	%#.4x\n", tag.tagcrc);

	exits(nil);
}

/* http://gabriel.mp3-tech.org/mp3infotag.html */