"use strict";

/**
 * A $month pipeline expression.
 * @see evaluate
 * @class MonthExpression
 * @namespace mungedb-aggregate.pipeline.expressions
 * @module mungedb-aggregate
 * @constructor
 **/
var MonthExpression = module.exports = function MonthExpression() {
	base.call(this);
}, klass = MonthExpression,
	FixedArityExpression = require("./FixedArityExpressionT")(klass, 1),
	base = FixedArityExpression,
	proto = klass.prototype = Object.create(base.prototype, {
		constructor: {
			value: klass
		}
	});

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

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

/**
 * Takes a date and returns the month as a number between 1 and 12.
 * @method evaluate
 **/
proto.evaluateInternal = function evaluateInternal(vars) {
	var date = this.operands[0].evaluateInternal(vars);
	return date.getUTCMonth();
};

/** Register Expression */
Expression.registerExpression("$month", base.parse);