"use strict";

/** 
 * A $toUpper pipeline expression.
 * @see evaluate 
 * @class ToUpperExpression
 * @namespace mungedb-aggregate.pipeline.expressions
 * @module mungedb-aggregate
 * @constructor
 **/
var ToUpperExpression = module.exports = function ToUpperExpression(){
	if (arguments.length !== 0) throw new Error("zero args expected");
	base.call(this);
}, klass = ToUpperExpression, 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 "$toUpper";
};

proto.addOperand = function addOperand(expr) {
	this.checkArgLimit(1);
	base.prototype.addOperand.call(this, expr);
};

/** 
* Takes a single string and converts that string to lowercase, returning the result. All uppercase letters become lowercase. 
**/
proto.evaluate = function evaluate(doc) {
	this.checkArgCount(1);
	var val = this.operands[0].evaluate(doc),
		str = Value.coerceToString(val);
	return str.toUpperCase();
};