#ifdef HAVE_CONFIG_H
#	include "config.h"
#endif

#include <stdlib.h>
#include <stdint.h>
#include <assert.h>
#include <errno.h>

#include "byteorder.h"
#include "misc.h"
#include "lbx.h"
#include "image.h"

struct lbx_image {
	uint16_t width, height;
	uint16_t wtf1;
	uint16_t offs, frames;
	uint16_t pal;

	FILE *f;
	long foff;

	int currentframe;
	int currentx, currenty;
	unsigned char **framedata;

	uint32_t offsets[];
};

struct lbx_image *lbximg_fopen(FILE *f)
{
	struct lbx_image tmp = {.f = f}, *new = NULL;

	if (fread(&tmp.width,  sizeof tmp.width,   1, f) != 1) goto readerr;
	if (fread(&tmp.height, sizeof tmp.height,  1, f) != 1) goto readerr;
	if (fread(&tmp.wtf1,   sizeof tmp.wtf1,    1, f) != 1) goto readerr;
	if (fread(&tmp.offs,   sizeof tmp.offs,    1, f) != 1) goto readerr;
	if (fread(&tmp.frames, sizeof tmp.frames,  1, f) != 1) goto readerr;
	if (fread(&tmp.pal,    sizeof tmp.pal,     1, f) != 1) goto readerr;

	tmp.width  = letohs(tmp.width);  tmp.foff += sizeof tmp.width;
	tmp.height = letohs(tmp.height); tmp.foff += sizeof tmp.height;
	tmp.wtf1   = letohs(tmp.wtf1);   tmp.foff += sizeof tmp.wtf1;
	tmp.offs   = letohs(tmp.offs);   tmp.foff += sizeof tmp.offs;
	tmp.frames = letohs(tmp.frames); tmp.foff += sizeof tmp.frames;
	tmp.pal    = letohs(tmp.pal);    tmp.foff += sizeof tmp.pal;

	/* For some reason, the format seems to need this. */
	tmp.offs++;
	tmp.frames++;

	/* Format constraints. */
	if (tmp.offs <= tmp.frames) {
		lbx_errno = LBX_EFORMAT;
		return NULL;
	}

	/*
	 * DEBUG ONLY.  These assertions exist to catch otherwise valid image
	 * files which differ from what I believe to be true of all LBX images.
	 * If we never find any exceptions, we can replace the assertions with
	 * assumptions.
	 */
	_lbx_assert(tmp.wtf1 == 0);
	_lbx_assert(tmp.offs == tmp.frames + 1);
	_lbx_assert(tmp.pal  == 0 || tmp.pal == 0x1000);

	new = malloc(sizeof *new + tmp.offs * sizeof *new->offsets);
	if (!new) {
		lbx_errno = -errno;
		return NULL;
	}

	*new = tmp;
	new->currentframe = -1;

	if (fread(new->offsets, sizeof *new->offsets, new->offs, f)!= new->offs)
		goto readerr;
	new->foff += sizeof *new->offsets * new->offs;

	return new;
readerr:
	if (feof(f)) {
		lbx_errno = LBX_EEOF;
	} else {
		lbx_errno = -errno;
	}

	free(new);
	return NULL;
}

static int _lbx_drawrow(int first, struct lbx_image *img)
{
	uint16_t type, yval, count, xval;
	unsigned char *pos;
	unsigned char abyss;
	size_t rc;

	assert(img->framedata);

	if (fread(&type, sizeof type, 1, img->f) != 1) goto readerr;
	type = letohs(type); img->foff += sizeof type;

	if (first) {
		img->currentx = 0;
		img->currenty = 0;
		type = 0;
	}

	if (type == 0) {
		if (fread(&yval,  sizeof yval,  1, img->f) != 1) goto readerr;
		yval = letohs(yval); img->foff += sizeof yval;
		if (yval == 1000)
			return 1;
		if (fread(&count, sizeof count, 1, img->f) != 1) goto readerr;
		count = letohs(count); img->foff += sizeof count;
		if (fread(&xval,  sizeof xval,  1, img->f) != 1) goto readerr;
		xval = letohs(xval); img->foff += sizeof xval;
		if (xval == 1000)
			return 1;

		/* Ensure that the row fits in the image. */
		if (img->height - img->currenty <= yval || xval >= img->width) {
			lbx_errno = LBX_EFORMAT;
			return -1;
		}

		img->currenty += yval;
		img->currentx  = xval;
	} else {
		if (fread(&xval,  sizeof xval,  1, img->f) != 1) goto readerr;
		xval = letohs(xval); img->foff += sizeof xval;

		if (img->width - img->currentx <= xval) {
			lbx_errno = LBX_EFORMAT;
			return -1;
		}
		img->currentx += xval;

		count = type;

	}

	if (count > img->width - img->currentx) {
		lbx_errno = LBX_EFORMAT;
		return -1;
	}

	pos = &img->framedata[img->currenty][img->currentx];
	rc  = fread(pos, 1, count, img->f);
	img->currentx += rc;
	img->foff     += rc;

	if (rc < count)
		goto readerr;

	if (count % 2) {
		if (fread(&abyss, 1, 1, img->f) != 1)
			goto readerr;
		img->foff += 1;
	}

	return 0;
readerr:
	if (feof(img->f)) {
		lbx_errno = LBX_EEOF;
	} else {
		lbx_errno = -errno;
	}
	return -1;
}

unsigned char **lbximg_getframe(struct lbx_image *img, int frame)
{
	if (frame >= img->frames || frame < 0) {
		lbx_errno = LBX_ERANGE;
		return NULL;
	}

	if (!img->framedata) {
		unsigned char *tmp;
		int i;

		tmp = malloc(img->width * img->height);
		if (!tmp) {
			lbx_errno = -errno;
			return NULL;
		}

		img->framedata = malloc(img->height * sizeof *img->framedata);
		if (!img->framedata) {
			lbx_errno = -errno;
			free(tmp);
			return NULL;
		}

		for (i = 0; i < img->height; i++) {
			img->framedata[i] = tmp + i * img->width;
		}
	}

	/* Start over if we are backtracking. */
	if (img->currentframe > frame)
		img->currentframe == -1;

	/* We must have previous frame decoded to continue. */
	if (frame > img->currentframe + 1) {
		if (!lbximg_getframe(img, frame-1))
			return NULL;
	}

	if (img->currentframe != frame) {
		int rc, first = 1;

		if (_lbx_fseek(img->f, &img->foff, img->offsets[frame]) == -1)
			return NULL;

		do {
			rc = _lbx_drawrow(first, img);
			if (rc == -1)
				return NULL;
			first = 0;

			if (!rc && img->foff > img->offsets[frame+1]) {
				lbx_errno = LBX_EFORMAT;
				return NULL;
			}
		} while (!rc);
	}

	img->currentframe = frame;
	return img->framedata;
}

int lbximg_loadpalette(FILE *f, struct lbx_colour palette[static 256])
{
	uint8_t entry[4];
	int i;

	for (i = 0; i < 256; i++) {
		if (fread(entry, sizeof entry, 1, f) != 1) {
			lbx_errno = (feof(f)) ? LBX_EEOF : -errno;
			return -1;
		}

		if (entry[0] != 1) {
			lbx_errno = LBX_EFORMAT;
			return -1;
		}

		palette[i] = (struct lbx_colour){
			.red   = entry[1] << 2,
			.green = entry[2] << 2,
			.blue  = entry[3] << 2,
		};
	}

	return 0;
}

int
lbximg_getpalette(struct lbx_image *img, struct lbx_colour palette[static 256])
{
	size_t hdrlen = 6*(sizeof img->pal)+(img->offs)*(sizeof *img->offsets);
	unsigned int i;
	size_t rc;

	uint16_t start, count;
	uint8_t  entry[4];

	/* Do nothing if the image doesn't have embedded palette data. */
	if (img->pal == 0)
		return 0;

	/* Palette data is located right after the header. */
	if (_lbx_fseek(img->f, &img->foff, hdrlen) == -1)
		return -1;
	
	/* Palette header */
	if (fread(&start, sizeof start, 1, img->f) != 1) goto readerr;
	if (fread(&count, sizeof count, 1, img->f) != 1) goto readerr;
	start = letohs(start); img->foff += sizeof start;
	count = letohs(count); img->foff += sizeof count;

	if (start + count > 256) {
		lbx_errno = LBX_EFORMAT;
		return -1;
	}

	if (hdrlen + 2*sizeof start + count*sizeof entry > img->offsets[0]) {
		lbx_errno = LBX_EFORMAT;
		return -1;
	}

	for (i = 0; i < count; i++) {
		rc = fread(entry, 1, sizeof entry, img->f);
		img->foff += rc;

		if (rc < sizeof entry) {
			goto readerr;
		}

		if (entry[0] != 0) {
			lbx_errno = LBX_EFORMAT;
			return -1;
		}

		palette[start + i] = (struct lbx_colour){
			.red   = entry[1] << 2,
			.green = entry[2] << 2,
			.blue  = entry[3] << 2,
		};
	}

	return 0;
readerr:
	lbx_errno = feof(img->f) ? LBX_EEOF : -errno;
	return -1;
}

void lbximg_getinfo(struct lbx_image *img, struct lbx_imginfo *info)
{
	*info = (struct lbx_imginfo) {
		.width   = img->width,
		.height  = img->height,
		.nframes = img->frames,
	};
}

void lbximg_close(struct lbx_image *img)
{
	if (!img) return;

	if (img->framedata) {
		free(img->framedata[0]);
		free(img->framedata);
	}

	if (img->f) {
		fclose(img->f);
	}

	free(img);
}