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

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

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

#define FLAG_OVERWRITE 0x0400 /* Draw each frame on a clean slate (unsure). */
#define FLAG_PALETTE   0x1000 /* Image contains embedded palette. */
#define FLAG_LOOPING   0x2000 /* Loop over all frames in the image (unsure). */

struct lbx_image {
	uint16_t width, height;
	uint16_t wtf1;
	uint16_t frames, leadin;
	uint16_t flags;

	FILE *f;
	long foff;

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

	uint32_t offsets[];
};

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

	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.frames, sizeof tmp.frames,  1, f) != 1) goto readerr;
	if (fread(&tmp.leadin, sizeof tmp.leadin,  1, f) != 1) goto readerr;
	if (fread(&tmp.flags,  sizeof tmp.flags,   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.frames = letohs(tmp.frames); tmp.foff += sizeof tmp.frames;
	tmp.leadin = letohs(tmp.leadin); tmp.foff += sizeof tmp.leadin;
	tmp.flags  = letohs(tmp.flags);  tmp.foff += sizeof tmp.flags;

	/* Format constraints. */
	if (tmp.frames <= tmp.leadin) {
		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.flags & ~(FLAG_PALETTE|FLAG_OVERWRITE|FLAG_LOOPING)));

	new = malloc(sizeof *new + (tmp.frames+1) * sizeof *new->offsets);
	if (!new) {
		lbx_errno = -errno;
		return NULL;
	}

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

	rc = fread(new->offsets, sizeof *new->offsets, new->frames+1, f);
	if (rc < new->frames+1)
		goto readerr;
	new->foff += sizeof *new->offsets * (new->frames+1);

	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);
	assert(img->mask);

	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;
	}

	memset(&img->mask[img->currenty][img->currentx], 1, count);

	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;
}

static unsigned char **allocframebuffer(size_t width, size_t height)
{
	unsigned char **new, *tmp;
	size_t i;

	tmp = calloc(height, width);
	if (!tmp) {
		lbx_errno = -errno;
		return NULL;
	}

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

	for (i = 0; i < height; i++) {
		new[i] = tmp + i * width;
	}

	return new;
}

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) {
		img->framedata = allocframebuffer(img->width, img->height);
		if (!img->framedata)
			return NULL;
	}

	if (!img->mask) {
		img->mask = allocframebuffer(img->width, img->height);
		if (!img->mask)
			return NULL;
	}

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

	if (img->flags & FLAG_OVERWRITE) {
		/* Clear the slate. */
		memset(img->framedata[0], 0, img->width * img->height);
		memset(img->mask[0],      0, img->width * img->height);
	} else {
		/* 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->wtf1)+(img->frames+1)*(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->flags & FLAG_PALETTE))
		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,
		.haspalette = (_Bool)(img->flags & FLAG_PALETTE),
	};

	/* There seems to be two ways of specifying that an image loops. */
	if (img->flags & FLAG_LOOPING) {
		info->loopstart = 0;
		info->looping   = 1;
	} else if (img->leadin != img->frames - 1) {
		info->loopstart = img->leadin;
		info->looping   = 1;
	}
}

unsigned char **lbximg_getmask(struct lbx_image *img)
{
	return img->mask;
}

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

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

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

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

	free(img);
}