.{Color, Surface, new_surface} := @use("./lib.hb");
.{log, memory} := @use("../../stn/src/lib.hb")

BitmapFileHeader := packed struct {
	img_type: u16,
	size: u32,
	reserved_1: u16,
	reserved_2: u16,
	offset: u32,
}

BitmapInfoHeader := packed struct {
	size: u32,
	width: i32,
	height: i32,
	planes: u16,
	bits: u16,
	compression: u32,
	image_size: u32,
	x_resolution: i32,
	y_resolution: i32,
	n_colours: u32,
	important_colours: u32,
}

BitmapColorHeader := packed struct {
	red_mask: u32,
	green_mask: u32,
	blue_mask: u32,
	alpha_mask: u32,
	color_space_type: u32,
	unused: u32,
}

surface_from_bmp := fn(bmp: ^u8): Surface {
	file_header := @as(^BitmapFileHeader, @bitcast(bmp))
	if file_header.img_type != 0x4D42 {
		log.error("failed to load bmp image: not a bmp image, idiot\0")
		return idk
	}
	info_header := @as(^BitmapInfoHeader, @bitcast(bmp + @sizeof(BitmapFileHeader)))
	bmp += file_header.offset

	px := info_header.width * info_header.height
	ptr := @as(^Color, @bitcast(bmp))
	tmp := @as(Color, idk)
	row := @as(i32, 0)

	loop if row == info_header.height / 2 break else {
		col := @as(i32, 0)
		loop if col == info_header.width break else {
			top_index := row * info_header.width + col
			bottom_index := (info_header.height - 1 - row) * info_header.width + col

			tmp = *(ptr + top_index);
			*(ptr + top_index) = *(ptr + bottom_index);
			*(ptr + bottom_index) = tmp

			col += 1
		}
		row += 1
	}

	return .(@bitcast(bmp), info_header.width, info_header.height)
}

new_surface_from_bmp := fn(bmp: ^u8): Surface {
	file_header := @as(^BitmapFileHeader, @bitcast(bmp))
	if file_header.img_type != 0x4D42 {
		log.error("failed to load bmp image: not a bmp image, idiot\0")
		return idk
	}
	info_header := @as(^BitmapInfoHeader, @bitcast(bmp + @sizeof(BitmapFileHeader)))
	bmp += file_header.offset

	width := @as(uint, @intcast(info_header.width))
	height := @as(uint, @intcast(info_header.height))

	surface := new_surface(width, height)
	top_start_idx := surface.buf
	bottom_start_idx := surface.buf + width * (height - 1)
	rows_to_copy := height
	top_cursor := @as(^Color, @bitcast(bmp))
	bottom_cursor := top_cursor + width * (height - 1)

	loop if rows_to_copy <= 1 break else {
		@inline(memory.copy, Color, top_cursor, bottom_start_idx, @bitcast(width))
		@inline(memory.copy, Color, bottom_cursor, top_start_idx, @bitcast(width))

		top_start_idx += surface.width
		bottom_start_idx -= surface.width
		top_cursor += width
		bottom_cursor -= width
		rows_to_copy -= 2
	}

	if rows_to_copy == 1 {
		@inline(memory.copy, Color, top_cursor, top_start_idx, @bitcast(width))
	}

	return surface
}