"use strict";

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

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

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

/**
 * Takes a single string and converts that string to lowercase, returning the result. All uppercase letters become lowercase.
 **/
proto.evaluateInternal = function evaluateInternal(vars) {
	var val = this.operands[0].evaluateInternal(vars),
		str = Value.coerceToString(val);
	return str.toLowerCase();
};

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