const std = @import("std");

pub const Pixel = packed struct(u32) {
	blue: u8,
	green: u8,
	red: u8,
	_padding: u8 = 0x0,
};

pub const Canvas = struct {
	const Self = @This();

	width: u32,
	height: u32,
	buffer: []volatile Pixel,

	pub fn fill(self: *const Canvas, pixel: Pixel) void {
		@memset(self.buffer, pixel);
	}

	fn gaussian_mean(values: [9]u32) u32 {
		return (values[0] +     values[1] * 2 + values[2] +
		        values[3] * 2 + values[4] * 8 + values[5] * 2 +
		        values[6] +     values[7] * 2 + values[8]) / 20;
	}

	pub fn set_with_anti_aliasing(self: *const Canvas, x: u32, y: u32) void {
		var neighbors_red: [9]u32 = undefined;
		var neighbors_green: [9]u32 = undefined;
		var neighbors_blue: [9]u32 = undefined;

		for (0..3) |h| {
			for (0..3) |w| {
				const pixel = self.buffer[(y + 1 - h) * self.width + x + 1 - w];
				neighbors_red[w + 3 * h] = pixel.red;
				neighbors_green[w + 3 * h] = pixel.green;
				neighbors_blue[w + 3 * h] = pixel.blue;
			}
		}

		self.buffer[x + (y * self.width)] = .{
			.red = @intCast(Self.gaussian_mean(neighbors_red)),
			.green = @intCast(Self.gaussian_mean(neighbors_green)),
			.blue = @intCast(Self.gaussian_mean(neighbors_blue)),
		};
	}
};

pub const Box = struct {
	const Self = @This();

	x: u32,
	y: u32,
	width: u32,
	height: u32,
	color: Pixel,
	radius: u32 = 0,

	fn render_rect(
		self: *const Self,
		x: u32,
		y: u32,
		width: u32,
		height: u32,
		canvas: *const Canvas
	) void {
		if (x >= canvas.width or y >= canvas.height) {
			return;
		}

		const x_end = @min(x + width, canvas.width);
		const y_end = @min(y + height, canvas.height);

		for (y..y_end) |yp| {
			const offset = yp * canvas.width;
			@memset(
				canvas.buffer[(offset + x)..(offset + x_end)],
				self.color
			);
		}
	}

	pub fn render(self: *const Self, canvas: *const Canvas) void {
		if (self.radius == 0) {
			self.render_rect(self.x, self.y, self.width, self.height, canvas);
			return;
		}

		const radius = @min(self.radius, self.width / 2, self.height / 2);
		const core_width = self.width - 2 * radius;
		const core_height = self.height - 2 * radius;

		self.render_rect(
			self.x + radius,
			self.y,
			core_width,
			radius,
			canvas
		);

		self.render_rect(
			self.x + radius,
			self.y + radius + core_height,
			core_width,
			radius,
			canvas
		);

		self.render_rect(
			self.x,
			self.y + radius,
			self.width,
			core_height,
			canvas
		);

		for (0..radius) |yp| {
			const width: u32 = @intFromFloat(std.math.round(
				@as(f64, @floatFromInt(radius)) *
				@cos(std.math.asin(
						@as(f64, @floatFromInt(yp)) / @as(f64, @floatFromInt(radius))
				))
			));
			const spacing = radius - width;

			var offset = ((radius - yp) + self.y) * canvas.width + self.x + spacing;
			@memset(
				canvas.buffer[offset..offset + width],
				self.color
			);

			offset = ((radius - yp) + self.y) * canvas.width + self.x + core_width + radius;
			@memset(
				canvas.buffer[offset..offset + width],
				self.color
			);

			offset = (yp + self.y + radius + core_height) * canvas.width + self.x + spacing;
			@memset(
				canvas.buffer[offset..offset + width],
				self.color
			);

			offset = (yp + self.y + radius + core_height) * canvas.width + self.x + core_width + radius;
			@memset(
				canvas.buffer[offset..offset + width],
				self.color
			);
		}

		for (0..radius) |yp| {
			const width: u32 = @intFromFloat(std.math.round(
				@as(f64, @floatFromInt(radius)) *
				@cos(std.math.asin(
						@as(f64, @floatFromInt(yp)) / @as(f64, @floatFromInt(radius))
				))
			));

			const spacing = radius - width;

			canvas.set_with_anti_aliasing(
				self.x + spacing,
				@intCast(self.y + radius - yp),
			);

			canvas.set_with_anti_aliasing(
				self.x + spacing - 1,
				@intCast(self.y + radius - yp),
			);

			canvas.set_with_anti_aliasing(
				self.x + core_width + radius + width,
				@intCast(self.y + radius - yp),
			);

			canvas.set_with_anti_aliasing(
				self.x + spacing,
				@intCast(self.y + yp + radius + core_height),
			);

			canvas.set_with_anti_aliasing(
				self.x + core_width + radius + width,
				@intCast(self.y +  yp + radius + core_height),
			);
		}

		for (0..core_width) |w| {
			canvas.set_with_anti_aliasing(@intCast(self.x + radius + w), self.y);
			canvas.set_with_anti_aliasing(@intCast(self.x + radius + w), self.y + self.height);
		}

		for (0..core_height) |h| {
			canvas.set_with_anti_aliasing(self.x, @intCast(self.y + radius + h));
			canvas.set_with_anti_aliasing(self.x + self.width, @intCast(self.y + radius + h));
		}
	}
};