.{math, memory} := @use("../../stn/src/lib.hb");
.{IVec2} := @use("rel:lib.hb")

Color := struct {b: u8, g: u8, r: u8, a: u8}
white := Color.(255, 255, 255, 255)
black := Color.(0, 0, 0, 255)
gray := Color.(127, 127, 127, 255)
red := Color.(0, 0, 205, 255)
green := Color.(0, 205, 0, 255)
yellow := Color.(0, 205, 205, 255)
blue := Color.(205, 0, 0, 255)
magenta := Color.(205, 0, 205, 255)
cyan := Color.(205, 205, 0, 255)
light_gray := Color.(229, 229, 229, 255)
light_red := Color.(0, 0, 255, 255)
light_green := Color.(0, 255, 0, 255)
light_yellow := Color.(0, 255, 255, 255)
light_blue := Color.(255, 0, 0, 255)
light_magenta := Color.(255, 0, 255, 255)
light_cyan := Color.(255, 255, 0, 255)

// fb_width := 1024
// fb_height := 768
// fb_pixels := fb_width * fb_height
// fb_bytes := fb_pixels << 2
copy_pixels := 0xC000 >> 2
// partitions := fb_pixels / copy_pixels
// total_pages := 1 + fb_bytes >> 12

ctx := @as(Context, idk)

Context := struct {
	fb: ^Color,
	bb: ^Color,
	buf: ^Color,
	width: int,
	height: int,
	partitions: int,
	pixels: int,
	bb_pages: int,
	double_buffer: bool,
}

init := fn(): void {
	width := @eca(int, 3, 6, "w\0", 2)
	height := @eca(int, 3, 6, "h\0", 2)
	// width := 1024
	// height := 768
	pixels := width * height
	bytes := pixels << 2
	partitions := pixels / copy_pixels
	pages := 1 + bytes >> 12
	back_buffer := create_back_buffer(pages)
	ctx = Context.{
		fb: @eca(^Color, 3, 6, "p\0", 2),
		bb: back_buffer,
		buf: back_buffer,
		width,
		height,
		partitions,
		pixels,
		bb_pages: pages,
		double_buffer: true,
	}
	return
}

doublebuffer := fn(enable: bool): void {
	if enable {
		ctx.buf = ctx.bb
	} else {
		ctx.buf = ctx.fb
	}
	ctx.double_buffer = enable
	return
}

create_back_buffer := fn(pages: int): ^Color {
	if pages <= 0xFF {
		return @bitcast(@inline(memory.request_page, pages))
	}
	ptr := @inline(memory.request_page, 255)
	remaining := pages - 0xFF
	loop if remaining <= 0 break else {
		if remaining < 0xFF {
			memory.request_page(remaining)
		} else {
			memory.request_page(0xFF)
		}
		remaining -= 0xFF
	}
	return @bitcast(ptr)
}

clear := fn(color: Color): void {
	cursor := ctx.buf
	boundary := cursor + 512
	loop if cursor == boundary break else {
		*cursor = color
		cursor += 1
	}
	boundary += 512 * 7
	loop if cursor == boundary break else {
		*@as(^[Color; 512], @bitcast(cursor)) = *@as(^[Color; 512], @bitcast(ctx.buf))
		cursor += 512
	}
	boundary += copy_pixels - 4096
	loop if cursor == boundary break else {
		*@as(^[Color; 4096], @bitcast(cursor)) = *@as(^[Color; 4096], @bitcast(ctx.buf))
		cursor += 4096
	}
	boundary += (ctx.partitions - 1) * copy_pixels
	loop if cursor == boundary break else {
		*@as(^[Color; copy_pixels], @bitcast(cursor)) = *@as(^[Color; copy_pixels], @bitcast(ctx.buf))
		cursor += @sizeof([u8; copy_pixels])
	}
	return
}

sync := fn(): void {
	if ctx.double_buffer {
		bb := ctx.buf
		fb := ctx.fb
		boundary := bb + ctx.pixels
		loop if bb == boundary break else {
			*@as(^[Color; copy_pixels], @bitcast(fb)) = *@as(^[Color; copy_pixels], @bitcast(bb))
			bb += copy_pixels
			fb += copy_pixels
		}
	}
	return
}

width := fn(): int {
	return ctx.width
}

height := fn(): int {
	return ctx.height
}

screenidx := fn(x: int, y: int): int {
	return x + ctx.width * y
}

put_pixel := fn(pos: IVec2, color: Color): void {
	*(ctx.buf + @inline(screenidx, pos.x, pos.y)) = color
	return
}

put_filled_rect := fn(pos: IVec2, tr: IVec2, color: Color): void {
	x := pos.x
	y := pos.y
	end := pos + tr
	loop if x == end.x break else {
		loop if y == end.y break else {
			*(ctx.buf + @inline(screenidx, x, y)) = color
			y += 1
		}
		x += 1
		y = pos.y
	}
	return
}

put_rect := fn(pos: IVec2, tr: IVec2, color: Color): void {
	x := pos.x
	y := pos.y
	end := pos + tr
	loop if y == end.y break else {
		*(ctx.buf + @inline(screenidx, x, y)) = color;
		*(ctx.buf + @inline(screenidx, x + tr.x, y)) = color
		y += 1
	}
	y = pos.y
	loop if x == end.x break else {
		*(ctx.buf + @inline(screenidx, x, y)) = color;
		*(ctx.buf + @inline(screenidx, x, y + tr.y)) = color
		x += 1
	}
	return
}

put_line_low := fn(p0: IVec2, p1: IVec2, color: Color): void {
	dx := p1.x - p0.x
	dy := p1.y - p0.y
	yi := 1
	if dy < 0 {
		yi = 0 - 1
		dy = 0 - dy
	}
	D := 2 * dy - dx
	y := p0.y
	x := p0.x
	loop if x == p1.x break else {
		*(ctx.buf + @inline(screenidx, x, y)) = color
		if D > 0 {
			y += yi
			D += 2 * (dy - dx)
		} else {
			D += 2 * dy
		}
		x += 1
	}
	return
}

put_line_high := fn(p0: IVec2, p1: IVec2, color: Color): void {
	dx := p1.x - p0.x
	dy := p1.y - p0.y
	xi := 1
	if dy < 0 {
		xi = 0 - 1
		dx = 0 - dx
	}
	D := 2 * dx - dy
	x := p0.x
	y := p0.y
	loop if y == p1.y break else {
		*(ctx.buf + @inline(screenidx, x, y)) = color
		if D > 0 {
			x += xi
			D += 2 * (dx - dy)
		} else {
			D += 2 * dx
		}
		y += 1
	}
	return
}

put_line := fn(p0: IVec2, p1: IVec2, color: Color): void {
	if @inline(math.abs, p1.y - p0.y) < @inline(math.abs, p1.x - p0.x) {
		if p0.x > p1.x {
			@inline(put_line_low, p1, p0, color)
		} else {
			@inline(put_line_low, p0, p1, color)
		}
	} else {
		if p0.y > p1.y {
			@inline(put_line_high, p1, p0, color)
		} else {
			@inline(put_line_high, p0, p1, color)
		}
	}
	return
}

set_height := fn(new: int): void {
	return
}

set_width := fn(new: int): void {
	return
}

dimensions := fn(): IVec2 {
	return .(ctx.width, ctx.height)
}

set_dimensions := fn(new: IVec2): void {
	return
}