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

Point
fmulpt(Point p, double f)
{
	return Pt(p.x*f, p.y*f);
}

int
linesz(ImgHdr h)
{
	return Dx(h.r) * chantodepth(h.chan)/8;
}

void
scaleline(uchar *dst, uchar *src, int dstlen, int nc, double s)
{
	int x, c;

	for(x = 0; x < dstlen; x++) {
		for(c = 0; c < nc; c++)
			dst[x*nc + c] = src[(int)(x/s)*nc + c];
	}
}

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

void
main(int argc, char **argv)
{
	Biobuf bdst, bsrc;
	double scale;
	ImgHdr hdst, hsrc;
	uchar *buf, *src, *dst;
	int nc, n, dstline, srcline;

	ARGBEGIN {
	default:
		usage();
	} ARGEND
	if(argc != 1)
		usage();

	scale = atof(argv[0]);

	if(fmtinstall('H', Hfmt) < 0)
		sysfatal("fmtinstall");
	if(Binit(&bsrc, 0, OREAD) < 0 || Binit(&bdst, 1, OWRITE) < 0)
		sysfatal("Binit");

	if(readimghdr(0, &hsrc) < 0)
		sysfatal("header: %r");
	hdst = (ImgHdr){0, hsrc.chan, Rpt(fmulpt(hsrc.r.min, scale), fmulpt(hsrc.r.max, scale))};
	if(!eqrect(hdst.r, canonrect(hdst.r)))
		sysfatal("bad scale");

	Bprint(&bdst, "%H", hdst);

	nc = chantodepth(hsrc.chan)/8;
	if((buf = malloc(linesz(hdst) + linesz(hsrc))) == nil)
		sysfatal("alloc: %r");
	dst = buf;
	src = buf + linesz(hdst);

	srcline = -1;
	for(dstline = 0; dstline < Dy(hdst.r); dstline++) {
		if(srcline < (int)(dstline/scale)) {
			for(; srcline < (int)(dstline/scale); srcline++) {
				if((n = Bread(&bsrc, src, linesz(hsrc))) < 0)
					sysfatal("read src: %r");
				else if(n == 0)
					sysfatal("unexpected eof: %d/%d", srcline, Dy(hsrc.r));
			}

			scaleline(dst, src, Dx(hdst.r), nc, scale);
		}

		if(Bwrite(&bdst, dst, linesz(hdst)) != linesz(hdst))
			sysfatal("write dst: %r");
	}

	exits(nil);
}