#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdbool.h>
#include <string.h>

#include "libsprite.h"

#define LOGDBG(...) printf(__VA_ARGS__);

/* reads four bytes, 00, 11, 22 and 33, of a byte array b to give 0x33221100 */
#define BTUINT(b) (b[0] | (b[1] << 8) | (b[2] << 16) | (b[3] << 24))

/* reverse the byte order of a word such that 0xAABBCCDD becomes 0xDDCCBBAA */
#define BSWAP(word) (((word & (0x000000ff)) << 24) | ((word & 0x0000ff00) << 8) | ((word & 0x00ff0000) >> 8) | ((word & 0xff000000) >> 24))

struct rosprite_header {
	uint32_t width_words; /* width in words */
	/* height defined in sprite struct */
	uint32_t first_used_bit; /* old format only (spriteType = 0) */
	uint32_t last_used_bit;
	uint32_t image_size; /* bytes */
	uint32_t mask_size; /* bytes */
};

struct rosprite_mask_state {
	uint32_t x;
	uint32_t y;
	uint32_t first_used_bit;
	uint32_t row_max_bit;
	uint32_t height;
	uint32_t current_byte_index;
	uint32_t current_word;
	uint32_t bpp;
};

static struct rosprite_mode oldmodes[] = {
/*0*/{ .colorbpp = 1, .maskbpp = 1, .mask_width = 1, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*1*/{ .colorbpp = 2, .maskbpp = 1, .mask_width = 2, .xdpi = 45, .ydpi = 45, .color_model = rosprite_rgb },
/*2*/{ .colorbpp = 4, .maskbpp = 1, .mask_width = 4, .xdpi = 22, .ydpi = 45, .color_model = rosprite_rgb },

/*3*/{ .colorbpp = 0, .maskbpp = 0, .mask_width = 0, .xdpi = 0,  .ydpi = 0,  .color_model = rosprite_rgb },

/*4*/{ .colorbpp = 1, .maskbpp = 1, .mask_width = 1, .xdpi = 45, .ydpi = 45, .color_model = rosprite_rgb },
/*5*/{ .colorbpp = 2, .maskbpp = 1, .mask_width = 2, .xdpi = 22, .ydpi = 45, .color_model = rosprite_rgb },

/*6*/{ .colorbpp = 0, .maskbpp = 0, .mask_width = 0, .xdpi = 0,  .ydpi = 0,  .color_model = rosprite_rgb },
/*7*/{ .colorbpp = 0, .maskbpp = 0, .mask_width = 0, .xdpi = 0,  .ydpi = 0,  .color_model = rosprite_rgb },

/*8*/{ .colorbpp = 2, .maskbpp = 1, .mask_width = 2, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*9*/{ .colorbpp = 4, .maskbpp = 1, .mask_width = 4, .xdpi = 45, .ydpi = 45, .color_model = rosprite_rgb },
/*10*/{.colorbpp = 8, .maskbpp = 1, .mask_width = 8, .xdpi = 22, .ydpi = 45, .color_model = rosprite_rgb },
/*11*/{.colorbpp = 2, .maskbpp = 1, .mask_width = 2, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*12*/{.colorbpp = 4, .maskbpp = 1, .mask_width = 4, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*13*/{.colorbpp = 8, .maskbpp = 1, .mask_width = 8, .xdpi = 45, .ydpi = 45, .color_model = rosprite_rgb },
/*14*/{.colorbpp = 4, .maskbpp = 1, .mask_width = 4, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*15*/{.colorbpp = 8, .maskbpp = 1, .mask_width = 8, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*16*/{.colorbpp = 4, .maskbpp = 1, .mask_width = 4, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*17*/{.colorbpp = 4, .maskbpp = 1, .mask_width = 4, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*18*/{.colorbpp = 1, .maskbpp = 1, .mask_width = 1, .xdpi = 90, .ydpi = 90, .color_model = rosprite_rgb },
/*19*/{.colorbpp = 2, .maskbpp = 1, .mask_width = 2, .xdpi = 90, .ydpi = 90, .color_model = rosprite_rgb },
/*20*/{.colorbpp = 4, .maskbpp = 1, .mask_width = 4, .xdpi = 90, .ydpi = 90, .color_model = rosprite_rgb },
/*21*/{.colorbpp = 8, .maskbpp = 1, .mask_width = 8, .xdpi = 90, .ydpi = 90, .color_model = rosprite_rgb },
/*22*/{.colorbpp = 4, .maskbpp = 1, .mask_width = 4, .xdpi =180, .ydpi = 90, .color_model = rosprite_rgb },
/*23*/{.colorbpp = 1, .maskbpp = 1, .mask_width = 1, .xdpi = 90, .ydpi = 90, .color_model = rosprite_rgb },
/*24*/{.colorbpp = 8, .maskbpp = 1, .mask_width = 8, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*25*/{.colorbpp = 1, .maskbpp = 1, .mask_width = 1, .xdpi = 90, .ydpi = 90, .color_model = rosprite_rgb },
/*26*/{.colorbpp = 2, .maskbpp = 1, .mask_width = 2, .xdpi = 90, .ydpi = 90, .color_model = rosprite_rgb },
/*27*/{.colorbpp = 4, .maskbpp = 1, .mask_width = 4, .xdpi = 90, .ydpi = 90, .color_model = rosprite_rgb },
/*28*/{.colorbpp = 8, .maskbpp = 1, .mask_width = 8, .xdpi = 90, .ydpi = 90, .color_model = rosprite_rgb },
/*29*/{.colorbpp = 1, .maskbpp = 1, .mask_width = 1, .xdpi = 90, .ydpi = 90, .color_model = rosprite_rgb },
/*30*/{.colorbpp = 2, .maskbpp = 1, .mask_width = 2, .xdpi = 90, .ydpi = 90, .color_model = rosprite_rgb },
/*31*/{.colorbpp = 4, .maskbpp = 1, .mask_width = 4, .xdpi = 90, .ydpi = 90, .color_model = rosprite_rgb },
/*32*/{.colorbpp = 8, .maskbpp = 1, .mask_width = 8, .xdpi = 90, .ydpi = 90, .color_model = rosprite_rgb },
/*33*/{.colorbpp = 1, .maskbpp = 1, .mask_width = 1, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*34*/{.colorbpp = 2, .maskbpp = 1, .mask_width = 2, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*35*/{.colorbpp = 4, .maskbpp = 1, .mask_width = 4, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*36*/{.colorbpp = 8, .maskbpp = 1, .mask_width = 8, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*37*/{.colorbpp = 1, .maskbpp = 1, .mask_width = 1, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*38*/{.colorbpp = 2, .maskbpp = 1, .mask_width = 2, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*39*/{.colorbpp = 4, .maskbpp = 1, .mask_width = 4, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*40*/{.colorbpp = 8, .maskbpp = 1, .mask_width = 8, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*41*/{.colorbpp = 1, .maskbpp = 1, .mask_width = 1, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*42*/{.colorbpp = 2, .maskbpp = 1, .mask_width = 2, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*43*/{.colorbpp = 4, .maskbpp = 1, .mask_width = 4, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*44*/{.colorbpp = 1, .maskbpp = 1, .mask_width = 1, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*45*/{.colorbpp = 2, .maskbpp = 1, .mask_width = 2, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*46*/{.colorbpp = 4, .maskbpp = 1, .mask_width = 4, .xdpi = 90, .ydpi = 45, .color_model = rosprite_rgb },
/*47*/{.colorbpp = 8, .maskbpp = 1, .mask_width = 8, .xdpi = 45, .ydpi = 45, .color_model = rosprite_rgb },
/*48*/{.colorbpp = 4, .maskbpp = 1, .mask_width = 4, .xdpi = 45, .ydpi = 90, .color_model = rosprite_rgb },
/*49*/{.colorbpp = 8, .maskbpp = 1, .mask_width = 8, .xdpi = 45, .ydpi = 90, .color_model = rosprite_rgb }
};

/* table for converting a 5bit channel into an 8bit channel (used for 16bpp to 32bpp conversion) */
static const uint8_t sprite_16bpp_translate[] = {
	0x00, 0x08, 0x10, 0x18, 0x20, 0x29, 0x31, 0x39,
	0x41, 0x4a, 0x52, 0x5a, 0x62, 0x6a, 0x73, 0x7b,
	0x83, 0x8b, 0x94, 0x9c, 0xa4, 0xac, 0xb4, 0xbd,
	0xc5, 0xcd, 0xd5, 0xde, 0xe6, 0xee, 0xf6, 0xff
};

/* palettes generated with palette2c.c
 * which in turn requires sprite_load_palette(FILE* f)
 * defined in this file
 */
static const uint32_t sprite_1bpp_palette[] = { 0xffffffff, 0xff };

static const uint32_t sprite_2bpp_palette[] = { 0xffffffff, 0xbbbbbbff, 0x777777ff, 0xff };

static const uint32_t sprite_4bpp_palette[] = {
0xffffffff, 0xddddddff, 0xbbbbbbff, 0x999999ff,
0x777777ff, 0x555555ff, 0x333333ff, 0xff,
0x4499ff, 0xeeee00ff, 0xcc00ff, 0xdd0000ff,
0xeeeebbff, 0x558800ff, 0xffbb00ff, 0xbbffff
};

static const uint32_t sprite_8bpp_palette[] = {
0xff, 0x111111ff, 0x222222ff, 0x333333ff,
0x440000ff, 0x551111ff, 0x662222ff, 0x773333ff,
0x44ff, 0x111155ff, 0x222266ff, 0x333377ff,
0x440044ff, 0x551155ff, 0x662266ff, 0x773377ff,
0x880000ff, 0x991111ff, 0xaa2222ff, 0xbb3333ff,
0xcc0000ff, 0xdd1111ff, 0xee2222ff, 0xff3333ff,
0x880044ff, 0x991155ff, 0xaa2266ff, 0xbb3377ff,
0xcc0044ff, 0xdd1155ff, 0xee2266ff, 0xff3377ff,
0x4400ff, 0x115511ff, 0x226622ff, 0x337733ff,
0x444400ff, 0x555511ff, 0x666622ff, 0x777733ff,
0x4444ff, 0x115555ff, 0x226666ff, 0x337777ff,
0x444444ff, 0x555555ff, 0x666666ff, 0x777777ff,
0x884400ff, 0x995511ff, 0xaa6622ff, 0xbb7733ff,
0xcc4400ff, 0xdd5511ff, 0xee6622ff, 0xff7733ff,
0x884444ff, 0x995555ff, 0xaa6666ff, 0xbb7777ff,
0xcc4444ff, 0xdd5555ff, 0xee6666ff, 0xff7777ff,
0x8800ff, 0x119911ff, 0x22aa22ff, 0x33bb33ff,
0x448800ff, 0x559911ff, 0x66aa22ff, 0x77bb33ff,
0x8844ff, 0x119955ff, 0x22aa66ff, 0x33bb77ff,
0x448844ff, 0x559955ff, 0x66aa66ff, 0x77bb77ff,
0x888800ff, 0x999911ff, 0xaaaa22ff, 0xbbbb33ff,
0xcc8800ff, 0xdd9911ff, 0xeeaa22ff, 0xffbb33ff,
0x888844ff, 0x999955ff, 0xaaaa66ff, 0xbbbb77ff,
0xcc8844ff, 0xdd9955ff, 0xeeaa66ff, 0xffbb77ff,
0xcc00ff, 0x11dd11ff, 0x22ee22ff, 0x33ff33ff,
0x44cc00ff, 0x55dd11ff, 0x66ee22ff, 0x77ff33ff,
0xcc44ff, 0x11dd55ff, 0x22ee66ff, 0x33ff77ff,
0x44cc44ff, 0x55dd55ff, 0x66ee66ff, 0x77ff77ff,
0x88cc00ff, 0x99dd11ff, 0xaaee22ff, 0xbbff33ff,
0xcccc00ff, 0xdddd11ff, 0xeeee22ff, 0xffff33ff,
0x88cc44ff, 0x99dd55ff, 0xaaee66ff, 0xbbff77ff,
0xcccc44ff, 0xdddd55ff, 0xeeee66ff, 0xffff77ff,
0x88ff, 0x111199ff, 0x2222aaff, 0x3333bbff,
0x440088ff, 0x551199ff, 0x6622aaff, 0x7733bbff,
0xccff, 0x1111ddff, 0x2222eeff, 0x3333ffff,
0x4400ccff, 0x5511ddff, 0x6622eeff, 0x7733ffff,
0x880088ff, 0x991199ff, 0xaa22aaff, 0xbb33bbff,
0xcc0088ff, 0xdd1199ff, 0xee22aaff, 0xff33bbff,
0x8800ccff, 0x9911ddff, 0xaa22eeff, 0xbb33ffff,
0xcc00ccff, 0xdd11ddff, 0xee22eeff, 0xff33ffff,
0x4488ff, 0x115599ff, 0x2266aaff, 0x3377bbff,
0x444488ff, 0x555599ff, 0x6666aaff, 0x7777bbff,
0x44ccff, 0x1155ddff, 0x2266eeff, 0x3377ffff,
0x4444ccff, 0x5555ddff, 0x6666eeff, 0x7777ffff,
0x884488ff, 0x995599ff, 0xaa66aaff, 0xbb77bbff,
0xcc4488ff, 0xdd5599ff, 0xee66aaff, 0xff77bbff,
0x8844ccff, 0x9955ddff, 0xaa66eeff, 0xbb77ffff,
0xcc44ccff, 0xdd55ddff, 0xee66eeff, 0xff77ffff,
0x8888ff, 0x119999ff, 0x22aaaaff, 0x33bbbbff,
0x448888ff, 0x559999ff, 0x66aaaaff, 0x77bbbbff,
0x88ccff, 0x1199ddff, 0x22aaeeff, 0x33bbffff,
0x4488ccff, 0x5599ddff, 0x66aaeeff, 0x77bbffff,
0x888888ff, 0x999999ff, 0xaaaaaaff, 0xbbbbbbff,
0xcc8888ff, 0xdd9999ff, 0xeeaaaaff, 0xffbbbbff,
0x8888ccff, 0x9999ddff, 0xaaaaeeff, 0xbbbbffff,
0xcc88ccff, 0xdd99ddff, 0xeeaaeeff, 0xffbbffff,
0xcc88ff, 0x11dd99ff, 0x22eeaaff, 0x33ffbbff,
0x44cc88ff, 0x55dd99ff, 0x66eeaaff, 0x77ffbbff,
0xccccff, 0x11ddddff, 0x22eeeeff, 0x33ffffff,
0x44ccccff, 0x55ddddff, 0x66eeeeff, 0x77ffffff,
0x88cc88ff, 0x99dd99ff, 0xaaeeaaff, 0xbbffbbff,
0xcccc88ff, 0xdddd99ff, 0xeeeeaaff, 0xffffbbff,
0x88ccccff, 0x99ddddff, 0xaaeeeeff, 0xbbffffff,
0xccccccff, 0xddddddff, 0xeeeeeeff, 0xffffffff
};

uint32_t sprite_read_word(FILE* stream)
{
	unsigned char b[4];
	size_t bytesRead = fread(b, 1, 4, stream);
	
	if (bytesRead != 4) {
		printf("Unexpected EOF\n"); /* TODO, have better error handling, don't exit here */
		exit(EXIT_FAILURE);
	}

	return BTUINT(b);
}

void sprite_read_bytes(FILE* stream, uint8_t* buf, size_t count)
{
	size_t bytesRead = fread(buf, 1, count, stream);
	
	if (bytesRead != count) {
		printf("Unexpected EOF\n");
		exit(EXIT_FAILURE);
	}
}

static struct rosprite_mode sprite_get_mode(uint32_t spriteMode)
{
	struct rosprite_mode mode;

	uint32_t spriteType = (spriteMode & 0x78000000) >> 27; /* preserve bits 27-30 only */

	if (spriteType != 0) {
		bool hasEightBitAlpha = (spriteMode & 0x80000000) >> 31; /* bit 31 */
		/* new modes have 1bpp masks (PRM5a-111)
		 * unless bit 31 is set (http://select.riscos.com/prm/graphics/sprites/alphachannel.html)
		 */
		mode.maskbpp = (hasEightBitAlpha ? 8 : 1);
		mode.mask_width = mode.maskbpp;
		mode.xdpi = (spriteMode & 0x07ffc000) >> 14; /* preserve bits 14-26 only */
		mode.ydpi = (spriteMode & 0x00003ffe) >> 1; /* preserve bits 1-13 only */

		mode.color_model = rosprite_rgb;
		switch (spriteType) {
		case 1:
			mode.colorbpp = 1; break;
		case 2:
			mode.colorbpp = 2; break;
		case 3:
			mode.colorbpp = 4; break;
		case 4:
			mode.colorbpp = 8; break;
		case 5:
			mode.colorbpp = 16; break;
		case 6:
			mode.colorbpp = 32; break;
		case 7:
			mode.colorbpp = 32;
			mode.color_model = rosprite_cmyk;
			break;
		case 8:
			mode.colorbpp = 24; break;
		default:
			assert(false);
		}
	} else {
		/* clone station mode and return */
		assert(spriteMode < 256); /* don't think you can have modes over 255? */
		assert(oldmodes[spriteMode].colorbpp > 0); 

		mode = oldmodes[spriteMode];
	}

	/* illegal mode check */
	assert(mode.colorbpp > 0);
	assert(mode.xdpi > 0);
	assert(mode.ydpi > 0);

	return mode;
}

static uint32_t sprite_palette_lookup(struct rosprite* sprite, uint32_t pixel)
{
	uint32_t translated_pixel;
	 /* because we're dealing with 8bpp or less */
	if (sprite->has_palette) {
		assert(pixel <= sprite->palettesize); /* TODO: what to do if your color depth is bigger than palette? */
		translated_pixel = sprite->palette[pixel];
	} else {
		switch (sprite->mode.colorbpp) {
		case 8:
			assert(pixel < 256);
			translated_pixel = sprite_8bpp_palette[pixel];
			break;
		case 4:
			assert(pixel < 16);
			translated_pixel = sprite_4bpp_palette[pixel];
			break;
		case 2:
			assert(pixel < 4);
			translated_pixel = sprite_2bpp_palette[pixel];
			break;
		case 1:
			assert(pixel < 2);
			translated_pixel = sprite_1bpp_palette[pixel];
			break;
		default:
			assert(false);
		}
	}
	return translated_pixel;
}

static inline uint32_t sprite_cmyk_to_rgb(uint32_t cmyk)
{
        uint8_t c = cmyk & 0xff;
        uint8_t m = (cmyk & 0xff00) >> 8;
        uint8_t y = (cmyk & 0xff0000) >> 16;
        uint8_t k = cmyk >> 24;
 
        /* Convert to CMY colourspace */
        uint8_t C = c + k;
        uint8_t M = m + k;
        uint8_t Y = y + k;
 
        /* And to RGB */
        uint8_t r = 255 - C;
        uint8_t g = 255 - M;
        uint8_t b = 255 - Y;
 
        return r << 24 | g << 16 | b << 8;
}

static uint32_t sprite_upscale_color(uint32_t pixel, struct rosprite_mode* mode, bool* has_alpha_pixel_data)
{
	switch (mode->colorbpp) {
	case 32:
		if (mode->color_model == rosprite_rgb) {
			/* swap from 0xAABBGGRR to 0xRRGGBBAA */
			pixel = BSWAP(pixel);

			uint8_t alpha = pixel & 0xff;
			if (alpha == 0x00) {
				if (!(*has_alpha_pixel_data)) {
					pixel = pixel | 0xff;
				}
			} else {
				*has_alpha_pixel_data = true;
			}
			return pixel;
		} else {
			return sprite_cmyk_to_rgb(pixel);
		}
	case 24:
		/* reverse byte order */
		return BSWAP(pixel);
	case 16:
		/* incoming format is b_00000000000000000bbbbbgggggrrrrr */
		{
			uint8_t red   = pixel & 31;
			uint8_t green = (pixel & (31 << 5)) >> 5;
			uint8_t blue  = (pixel & (31 << 10)) >> 10;

			/* sanity check */
			assert(red < 32);
			assert(green < 32);
			assert(blue < 32);

			pixel =   (sprite_16bpp_translate[red] << 24)
					| (sprite_16bpp_translate[green] << 16)
					| (sprite_16bpp_translate[blue] << 8);
		return pixel;
		}
	case 8:
	case 4:
	case 2:
	case 1:
		assert(false); /* shouldn't need to call for <= 8bpp, since a palette lookup will return 32bpp */
	default:
		assert(false); /* unknown bpp */
	}
}

static inline void sprite_fix_alpha(uint32_t* image, uint32_t pixels)
{
	for (uint32_t i = 0; i <= pixels; i++) {
		image[i] = image[i] & 0xffffff00;
	}
}

static struct rosprite_mask_state* sprite_init_mask_state(struct rosprite* sprite, struct rosprite_header* header, uint8_t* mask)
{
	struct rosprite_mask_state* mask_state = malloc(sizeof(struct rosprite_mask_state));

	mask_state->x = header->first_used_bit;
	mask_state->y = 0;
	mask_state->first_used_bit = header->first_used_bit;
	mask_state->row_max_bit = sprite->width * sprite->mode.mask_width;
	mask_state->height = sprite->height;
	mask_state->bpp = sprite->mode.mask_width;
	mask_state->current_word = BTUINT(mask);
	mask_state->current_byte_index = 4;

	return mask_state;
}

/* Get the next mask byte.
 * Mask of 0xff denotes 100% opaque, 0x00 denotes 100% transparent
 */
static uint32_t sprite_next_mask_pixel(uint8_t* mask, struct rosprite_mask_state* mask_state)
{
	/* a 1bpp mask (for new mode sprites), each row is word aligned (therefore potential righthand wastage */	
	const uint32_t bitmask = (1 << mask_state->bpp) - 1;
	const uint32_t offset_into_word = mask_state->x % 32;
	uint32_t pixel = (mask_state->current_word & (bitmask << offset_into_word)) >> offset_into_word;

	if (mask_state->x + mask_state->bpp < mask_state->row_max_bit && offset_into_word + mask_state->bpp == 32) {
		mask_state->current_word = BTUINT((mask + mask_state->current_byte_index));
		mask_state->current_byte_index += 4;
	}

	mask_state->x += mask_state->bpp;
	if (mask_state->x >= mask_state->row_max_bit) {
		mask_state->x = mask_state->first_used_bit;

		if (mask_state->y + 1 < mask_state->height) {
			mask_state->current_word = BTUINT((mask + mask_state->current_byte_index));
			mask_state->current_byte_index += 4;
		}

		mask_state->y++;
	}

	/*
	 * if the mask is 1bpp, make sure the whole byte is 0x00 or 0xff
	 */
	if (mask_state->bpp < 8) {
		pixel = (pixel & 1) ? 0xff : 0x00;
	}

	return pixel;
}

static void sprite_load_high_color(uint8_t* image_in, uint8_t* mask, struct rosprite* sprite, struct rosprite_header* header)
{
	struct rosprite_mask_state* mask_state = NULL;
	if (sprite->has_mask) mask_state = sprite_init_mask_state(sprite, header, mask);

	sprite->image = malloc(sprite->width * sprite->height * 4); /* all image data is 32bpp going out */

	uint32_t currentByteIndex = 0;
	const uint32_t bpp = sprite->mode.colorbpp;
	const uint32_t bytesPerPixel = bpp / 8;
	const uint32_t row_max_bit = header->width_words * 32 - (31 - header->last_used_bit); /* Last used bit in row */

	bool has_alpha_pixel_data = false;

	/* Spec says that there must be no left-hand wastage */
	assert(header->first_used_bit == 0);
	
	for (uint32_t y = 0; y < sprite->height; y++) {
		uint32_t x_pixels = 0;
		for (uint32_t x = 0; x < row_max_bit; x += bpp) {
			uint32_t pixel = 0;
			for (uint32_t j = 0; j < bytesPerPixel; j++) {
				uint8_t b = image_in[currentByteIndex++];
				pixel = pixel | (b << (j * 8));
			}
			
			bool old_has_alpha = has_alpha_pixel_data;
			pixel = sprite_upscale_color(pixel, &(sprite->mode), &has_alpha_pixel_data);
			if (old_has_alpha != has_alpha_pixel_data) {
				sprite_fix_alpha(sprite->image, (y * sprite->width) + x_pixels - 1);
			}
			if (sprite->has_mask) {
				uint8_t mask_pixel = sprite_next_mask_pixel(mask, mask_state);
				pixel = (pixel & 0xffffff00) | mask_pixel;
			}
			sprite->image[y*sprite->width + x_pixels] = pixel;
			x_pixels++;
		}

		/* Ensure byte index is pointing at start of next row */
		if (y + 1 < sprite->height) {
			currentByteIndex = (currentByteIndex + 3) & ~3; /* Round up to next multiple of 4 */
		}
	}

	if (sprite->has_mask) free(mask_state);
}

static void sprite_load_low_color(uint8_t* image_in, uint8_t* mask, struct rosprite* sprite, struct rosprite_header* header)
{
	struct rosprite_mask_state* mask_state = NULL;
	if (sprite->has_mask) mask_state = sprite_init_mask_state(sprite, header, mask);

	sprite->image = malloc(sprite->width * sprite->height * 4); /* all image data is 32bpp going out */

	const uint32_t bpp = sprite->mode.colorbpp;
	const uint32_t row_max_bit = header->width_words * 32 - (31 - header->last_used_bit); /* Last used bit in row */
	const uint32_t bitmask = (1 << bpp) - 1; /* creates a mask of 1s that is bpp bits wide */

	uint32_t current_byte_index = 0;
	uint32_t currentword = BTUINT((image_in + current_byte_index));
	current_byte_index += 4;
	
	for (uint32_t y = 0; y < sprite->height; y++) {
		uint32_t x_pixels = 0;
		for (uint32_t x = header->first_used_bit; x < row_max_bit ; x += bpp) {
			const uint32_t offset_into_word = x % 32;

			uint32_t pixel = (currentword & (bitmask << offset_into_word)) >> offset_into_word;
			pixel = sprite_palette_lookup(sprite, pixel); /* lookup returns 32bpp */
			if (sprite->has_mask) {
				uint8_t mask_pixel = sprite_next_mask_pixel(mask, mask_state);
				pixel = (pixel & 0xffffff00) | mask_pixel;
			}
			sprite->image[y*sprite->width + x_pixels] = pixel;
			x_pixels++;

			/* If we're not at the end of the row and we've processed all of this word, fetch the next one */
			if (x + bpp < row_max_bit && offset_into_word + bpp == 32) {
				currentword = BTUINT((image_in + current_byte_index));
				current_byte_index += 4;
			}
		}

		/* Advance to first word of next row */
		if (y + 1 < sprite->height) {
			currentword = BTUINT((image_in + current_byte_index));
			current_byte_index += 4;
		}
	}

	if (sprite->has_mask) free(mask_state);
}

struct rosprite* sprite_load_sprite(FILE* spritefile)
{
	uint32_t nextSpriteOffset = sprite_read_word(spritefile);

	struct rosprite* sprite = malloc(sizeof(struct rosprite));
	struct rosprite_header* header = malloc(sizeof(struct rosprite_header));

	sprite_read_bytes(spritefile, sprite->name, 12);
	sprite->name[12] = '\0';

	header->width_words     = sprite_read_word(spritefile) + 1; /* file has width - 1 and height - 1 */
	sprite->height          = sprite_read_word(spritefile) + 1;
	header->first_used_bit  = sprite_read_word(spritefile); /* old format only (spriteType = 0) */
	header->last_used_bit   = sprite_read_word(spritefile);

	uint32_t imageOffset    = sprite_read_word(spritefile);
	assert(imageOffset >= 44); /* should never be smaller than the size of the header) */

	uint32_t maskOffset     = sprite_read_word(spritefile);
	uint32_t spriteModeWord = sprite_read_word(spritefile);

	sprite->mode = sprite_get_mode(spriteModeWord);

	/* TODO left-hand wastage */
	
	assert((header->last_used_bit + 1) % sprite->mode.colorbpp == 0);
	/*assert(header->width_words % sprite->mode->colorbpp == 0);*/
	sprite->width = (header->width_words * 32 - header->first_used_bit - (31 - header->last_used_bit)) / sprite->mode.colorbpp;

	sprite->palettesize     = imageOffset - 44;
	sprite->has_palette     = (sprite->palettesize > 0);


	/* sprite has no mask if imageOffset == maskOffset */
	if (imageOffset == maskOffset) {
		sprite->has_mask   = false;
		header->image_size = nextSpriteOffset - 44 - sprite->palettesize;
		header->mask_size  = 0;
	} else {
		sprite->has_mask   = true;
		header->image_size = maskOffset - imageOffset;
		header->mask_size  = nextSpriteOffset - 44 - sprite->palettesize - header->image_size;
	}
	
	if (sprite->has_palette) {
		assert(sprite->palettesize % 8 == 0);
		sprite->palette = malloc(sizeof(uint32_t) * sprite->palettesize);
		uint32_t paletteEntries = sprite->palettesize / 8;

		/* Each palette entry is two words big
		 * The second word is a duplicate of the first
		 * I think this is in case you ever wanted flashing colours
		 * PRM1-730
		 */
		for (uint32_t j = 0; j < paletteEntries; j++) {
			uint32_t word1 = sprite_read_word(spritefile);
			uint32_t word2 = sprite_read_word(spritefile);
			assert(word1 == word2); /* TODO: if they aren't, START FLASHING */
			
			/* swap rr and bb parts (seems to give the right result, but where is it documented? PRM1-731 */
			uint32_t entry = ((word1 & 0xff000000) >> 16) | (word1 & 0x00ff0000) | ((word1 & 0x0000ff00) << 16) | 0xff;
			sprite->palette[j] = entry;
		}
	}

	uint8_t* image = malloc(header->image_size);
	sprite_read_bytes(spritefile, image, header->image_size);

	uint8_t* mask = NULL;
	if (sprite->has_mask) {
		mask = malloc(header->mask_size);
		sprite_read_bytes(spritefile, mask, header->mask_size);
	}

	/* sanity check image_size */
	assert((header->width_words) * 4 * (sprite->height) == header->image_size);
	/* TODO: sanity check mask_size */
	if (sprite->mode.colorbpp > 8) {
		sprite_load_high_color(image, mask, sprite, header);
	} else {
		sprite_load_low_color(image, mask, sprite, header);
	}

	free(image);
	free(mask);
	free(header);

	return sprite;
}

struct rosprite_area* rosprite_load_file(FILE* f)
{
	struct rosprite_area* sprite_area = malloc(sizeof(struct rosprite_area));

	sprite_area->sprite_count = sprite_read_word(f);

	uint32_t firstSpriteOffset = sprite_read_word(f);
	/*uint32_t firstFreeWordOffset = */sprite_read_word(f); /* TODO: use this for some sanity checking? */
	sprite_area->extension_size = 16 - firstSpriteOffset;

	sprite_area->extension_words = NULL;
	if (sprite_area->extension_size > 0) {
		sprite_area->extension_words = malloc(sprite_area->extension_size); /* where to free() this? */
		sprite_read_bytes(f, sprite_area->extension_words, (size_t) (sprite_area->extension_size));
	}

	sprite_area->sprites = malloc(sizeof(struct rosprite*) * sprite_area->sprite_count); /* allocate array of pointers */
	for (uint32_t i = 0; i < sprite_area->sprite_count; i++) {
		struct rosprite* sprite = sprite_load_sprite(f);
		sprite_area->sprites[i] = sprite;
	}

	return sprite_area;
}

void rosprite_destroy_sprite_area(struct rosprite_area* sprite_area)
{
	for (uint32_t i = 0; i < sprite_area->sprite_count; i++) {
		struct rosprite* sprite = sprite_area->sprites[i];
		if (sprite->has_palette) free(sprite->palette);
		free(sprite->image);
		free(sprite);
	}

	free(sprite_area->sprites);
	if (sprite_area->extension_size > 0) free(sprite_area->extension_words);
	free(sprite_area);
}

struct rosprite_palette* rosprite_load_palette(FILE* f)
{
	/* Palette file is in groups of 6 bytes, each is a VDU 19 (set palette)
	 * http://www.drobe.co.uk/show_manual.php?manual=/sh-cgi?manual=Vdu%26page=19 */

	/* TODO: currently assume palette has linear entries (2nd byte in is 00, 01, 02 etc) */
	struct rosprite_palette* palette = malloc(sizeof(struct rosprite_palette));

	palette->palette = malloc(sizeof(uint32_t) * 256); /* allocate 256 whether we need them all or not */

	uint32_t c = 0;
	uint8_t b[6];

	size_t bytesRead = fread(&b, 1, 6, f); /* TODO: make this use a pluggable read function */
	assert(bytesRead % 6 == 0);
	while (bytesRead == 6) {
		assert(b[0] == 19); /* VDU 19 */

		/* only process logical colours */
		if (b[2] == 16) {
			/*assert(c == b[1]);*/
	
			uint32_t entry = (b[3] << 24) | (b[4] << 16) | (b[5] << 8) | 0xff; /* last byte is alpha */
			palette->palette[c] = entry;
	
			c++;
			assert(c <= 256);
		}

		bytesRead = fread(&b, 1, 6, f);
		assert(bytesRead % 6 == 0);
	}

	palette->size = c;

	return palette;
}

void rosprite_destroy_palette(struct rosprite_palette* palette)
{
	free(palette->palette);
	free(palette);
}