export default class SpriteSheet {
	constructor(url, tilew, tileh, scale = 1) {
		this.url = url;
		this.tilew = tilew;
		this.tileh = tileh;
		this.scale = scale;

		this.definitions = {};
		this.waiting = [];

		this.ready = false;

		this.img = new Image();
		this.img.src = url;
		this.img.onload = () => {
			this.ready = true;
			this.waiting.forEach(f => f());
		};
		this.img.onerror = err => {
			console.error("Failed to load "+url+".");
		};
	}

	whenReady(fn) {
		if (this.ready) return fn();

		this.waiting.push(fn);
		return this;
	}

	define(name, x, y, w = this.tilew, h = this.tileh) {
		this.definitions[name] = null;

		this.whenReady(() => {
			let can = document.createElement("canvas");
			can.width = w * this.scale;
			can.height = h * this.scale;
			let ctx = can.getContext("2d");

			ctx.mozImageSmoothingEnabled = false;
			ctx.webkitImageSmoothingEnabled = false;
			ctx.msImageSmoothingEnabled = false;
			ctx.imageSmoothingEnabled = false;
			ctx.drawImage(
				this.img, x, y,
				w, h, 0, 0,
				w * this.scale, h * this.scale);

			this.definitions[name] = can;
		});
		return this;
	}

	defineTile(name, tx, ty) {
		return this.define(name, tx * this.tilew, ty * this.tileh);
	}

	draw(ctx, name, x, y, sx = 1, sy = 1) {
		let def = this.definitions[name];
		if (def === null) return;
		if (def === undefined) throw new Error("Undefined sprite: "+name);

		ctx.drawImage(
			def, x, y,
			def.width * sx,
			def.height * sy);
		return this;
	}

	drawTile(ctx, name, tx, ty, sx = 1, sy = 1) {
		this.draw(
			ctx, name,
			tx * this.tilew * this.scale, ty * this.tileh * this.scale,
			sx, sy);
		return this;
	}

	get tileWidth() {
		return this.tilew * this.scale;
	}
	get tileHeight() {
		return this.tileh * this.scale;
	}
}