var ModExpression = module.exports = (function(){
	// CONSTRUCTOR
	/** A $mod pipeline expression. @see evaluate **/
	var klass = function ModExpression(){
		if(arguments.length !== 0) throw new Error("zero args expected");
		base.call(this);
	}, base = require("./NaryExpression"), proto = klass.prototype = Object.create(base.prototype, {constructor:{value:klass}});

	// DEPENDENCIES
	var Value = require("../Value");

	// PROTOTYPE MEMBERS
	proto.getOpName = function getOpName(){
		return "$mod";
	};

	proto.addOperand = function addOperand(expr) {
		this.checkArgLimit(2);
		base.prototype.addOperand.call(this, expr);
	};

	/** 
	* Takes an array that contains a pair of numbers and returns the remainder of the first number divided by the second number. 
	**/
	proto.evaluate = function evaluate(doc){
		this.checkArgCount(2);
		var left = this.operands[0].evaluate(doc),
			right = this.operands[1].evaluate(doc);
		if(left instanceof Date || right instanceof Date) throw new Error("$mod does not support dates; code 16374");

		// pass along jstNULLs and Undefineds
		if(left === undefined || left === null) return left;
		if(right === undefined || right === null) return right;

		// ensure we aren't modding by 0
		right = Value.coerceToDouble(right);
		if(right === 0) return undefined;

		left = Value.coerceToDouble(left);
		return left % right;
	};

	return klass;
})();