class Tube {	
	#maxLevels;
	#colors;
	
	constructor(levels)
	{
		this.#maxLevels = levels;
		this.#colors = [];
	}
	
	addColorLayer(color)
	{
		if (this.isFull()) return false;
		
		this.#colors.push(color);
		return true;
	}
	
	removeColorLayer()
	{
		if (this.isEmpty()) return null;
		
		return this.#colors.pop();
	}
	
	drain()
	{
		this.#colors = [];
	}
	
	height()
	{
		return this.#maxLevels;
	}
	
	isFull()
	{
		return this.#colors.length == this.#maxLevels;
	}
	
	isEmpty()
	{
		return this.#colors.length == 0;
	}
	
	remainingSpace()
	{
		return this.#maxLevels - this.#colors.length;
	}
	
	getColorAtLevel(index)
	{
		if (index < 0 || index >= this.#colors.length) return null;
		
		return this.#colors[index].toString();
	}
	
	peekTopColor()
	{
		let length = this.#colors.length;
		
		return this.getColorAtLevel(length-1);
	}

	isComplete()
	{
		if (this.remainingSpace() != 1) return false;
		
		let reference = this.#colors[0];
		
		for (let i = 1; i < this.#colors.length; i++)
		{
			if (this.#colors[i] != reference)
			{
				return false;
			}
		}
		
		return true;
	}
}