mungedb-aggregate/lib/pipeline/expressions/CondExpression.js

"use strict";

/**
 * $cond expression;  @see evaluate
 * @class CondExpression
 * @namespace mungedb-aggregate.pipeline.expressions
 * @module mungedb-aggregate
 * @constructor
 **/
var CondExpression = module.exports = function CondExpression(vars) {
    this.nargs = 3;
    this.pCond = this.evaluateInternal(vars);
    this.idx = this.pCond.coerceToBool() ? 1 : 2;

    if (arguments.length !== 3) throw new Error("three args expected");
    base.call(this);
}, klass = CondExpression,
    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 "$cond";
};

klass.parse = function parse(expr, vps) {
    this.checkArgLimit(3);

    // if not an object, return;
    if (typeof(expr) !== Object)
		return Expression.parse(expr, vps);

    // verify
    if (Expression.parseOperand(expr) !== "$cond")
		throw new Error("Invalid expression");

    var ret = new CondExpression();

    var ex = Expression.parseObject(expr);
    var args = Expression.parseOperand(expr, vps);
    if (args[0] !== "if")
		throw new Error("Missing 'if' parameter to $cond");
    if (args[1] !== "then")
		throw new Error("Missing 'then' parameter to $cond");
    if (args[2] !== "else")
		throw new Error("Missing 'else' parameter to $cond");


    return ret;
};

/**
 * Use the $cond operator with the following syntax:  { $cond: [ <boolean-expression>, <true-case>, <false-case> ] }
 * @method evaluate
 **/
proto.evaluateInternal = function evaluateInternal(vars) {
		var pCond1 = this.operands[0].evaluateInternal(vars);

		this.idx = 0;
		if (pCond1.coerceToBool()) {
			this.idx = 1;
		} else {
			this.idx = 2;
		}

		return this.operands[this.idx].evaluateInternal(vars);
};

/** Register Expression */
Expression.registerExpression("$cond", klass.parse);