class ProgressBar {
	constructor(taskCount) {
		this.taskCount=taskCount;
		this.completeCount=0;
		this.updateListeneres=[];
	}

	get percent() {
		return Math.floor(this.completeCount/this.taskCount*100);
	}

	get ready() {
		return this.completeCount==this.taskCount;
	}

	addUpdateListener(fn) {
		this.updateListeneres.push(fn.bind(this));
	}
	addReadyListener(fn) {
		this.updateListeneres.push(() => {
			if(this.ready) fn.bind(this)();
		});
	}

	update() {
		this.completeCount++;
		this.updateListeneres.forEach(l => l(this));
	}

	draw(canvas, bgColor='red', textColor='black') {
		let ctx=canvas.getContext('2d');
		ctx.clearRect(0, 0, canvas.width, canvas.height);
		ctx.fillStyle=bgColor;
		ctx.fillRect(0, 0, canvas.width*this.completeCount/this.taskCount, canvas.height);
		ctx.fillStyle=textColor;
		ctx.textAlign='center';
		ctx.textBaseline='middle';
		ctx.font=`${canvas.height/2}px 'Fira Code'`;
		ctx.fillText(this.percent+'%', canvas.width/2, canvas.height/2);
	}
}

return ProgressBar;