#include "image.h"
#include <bio.h>

/* write to b the result of decompressing c with the algorithm
described in image(6), using w as scratch space with sliding window
size NMEM */
int
decompress(Biobuf *b, uchar *c, int clen)
{
	uchar w[2*NMEM];
	uchar *u, *we, *ce, *p, *pe;
	int n, o;

	u = w;
	we = w + 2*NMEM;
	ce = c + clen;
	while(c < ce) {
		if(*c & 0x80) {
			n = (*c & 0x7F) + 1;
			if(c + n > ce) {
				werrstr("truncated cdata");
				return -1;
			}

			/* flush and slide the window if necessary */
			if(u + n > we) {
				if(Bwrite(b, w, NMEM) < NMEM)
					sysfatal("write: %r");
				memmove(w, w+NMEM, u - (w+NMEM));
				u -= NMEM;
			}

			memmove(u, c+1, n);
			u += n;
			c += 1 + n;
		} else {
			if(c + 1 > ce) {
				werrstr("truncated code word");
				return -1;
			}
			n = ((*c & 0x7C) >> 2) + 3;
			o = ((*c & 0x3) << 8 | *(c+1)) + 1;
			if(u - o < w) {
				werrstr("invalid offset");
				return -1;
			}

			/* flush and slide the window if necessary */
			if(u + n > we) {
				if(Bwrite(b, w, NMEM) < NMEM)
					sysfatal("write: %r");
				memmove(w, w+NMEM, u - (w+NMEM));
				u -= NMEM;
			}

			p = u-o;
			pe = p + n;
			while(p < pe)
				*u++ = *p++;
			c += 2;
		}
	}

	if(Bwrite(b, w, u-w) != u-w)
		sysfatal("write: %r");
	return 0;
}

void
usage(void)
{
	fprint(2, "usage: %s <img.bit\n", argv0);
	exits("usage");
}

void
main(int argc, char **argv)
{
	ImgHdr hdr;
	Biobuf bin, bout;
	int ncblock;
	uchar *cbuf;
	int y, n, nexty, csz;

	ARGBEGIN {
	default:
		usage();
	} ARGEND

	if(argc != 0)
		usage();

	if(fmtinstall('R', Rfmt) < 0 || fmtinstall('P', Pfmt) < 0 || fmtinstall('H', Hfmt) < 0)
		sysfatal("fmtinstall: %r");

	if(readimghdr(0, &hdr) < 0)
		sysfatal("read header: %r");

	if(!hdr.compressed) {
		fprint(1, "%H", hdr);
		execl("/bin/cat", "cat", nil);
		sysfatal("exec cat: %r");
	}
	hdr.compressed = 0;
	fprint(1, "%H", hdr);

	if(Binit(&bin, 0, OREAD) < 0 || Binit(&bout, 1, OWRITE) < 0)
		sysfatal("Binit: %r");
	ncblock = _compblocksize(hdr.r, chantodepth(hdr.chan));
	if((cbuf = malloc(ncblock)) == nil)
		sysfatal("alloc buf: %r");

	for(y = hdr.r.min.y; y < hdr.r.max.y; y = nexty) {
		if((n = Bread(&bin, cbuf, 24)) != 24) {
			if(n < 0)
				sysfatal("line %d: cblock header: %r", y);
			sysfatal("line %d: cblock header: short read: %d/24", y, n);
		}

		nexty = atoi((char *)cbuf);
		if(nexty < y || nexty > hdr.r.max.y)
			sysfatal("line %d: out of sequence next y: %d", y, nexty);

		csz = atoi((char *)cbuf + 12);
		if(csz > ncblock || csz < 0)
			sysfatal("line %d: unusual cblock size: %d/%d", y, csz, ncblock);

		if((n = Bread(&bin, cbuf, csz)) != csz) {
			if(n < 0)
				sysfatal("line %d: cblock: %r", y);
			sysfatal("line %d: cblock: short read: %d/%d", y, n, csz);
		}

		if(decompress(&bout, cbuf, csz) < 0)
			sysfatal("line %d: %r", y);
	}

	exits(nil);
}

/*
image(6)
/sys/src/libmemdraw/cread.c
/sys/src/libdraw/computil.c
/sys/src/libmemdraw/cload.c
*/