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

"use strict";

/**
 * internal expression for coercing things to booleans
 * @class CoerceToBoolExpression
 * @namespace mungedb-aggregate.pipeline.expressions
 * @module mungedb-aggregate
 * @constructor
 */
var CoerceToBoolExpression = module.exports = function CoerceToBoolExpression(theExpression){
	if (arguments.length !== 1) throw new Error(klass.name + ": expected args: expr");
	this.expression = theExpression;
	base.call(this);
}, klass = CoerceToBoolExpression, base = require("./Expression"), proto = klass.prototype = Object.create(base.prototype, {constructor:{value:klass}});

var Value = require("../Value"),
	AndExpression = require("./AndExpression"),
	OrExpression = require("./OrExpression"),
	NotExpression = require("./NotExpression"),
	Expression = require("./Expression");

klass.create = function create(expression) {
	var newExpr = new CoerceToBoolExpression(expression);
	return newExpr;
};

proto.optimize = function optimize() {
	// optimize the operand
	this.expression = this.expression.optimize();

	// if the operand already produces a boolean, then we don't need this
	// LATER - Expression to support a "typeof" query?
	var expr = this.expression;
	if (expr instanceof AndExpression ||
			expr instanceof OrExpression ||
			expr instanceof NotExpression ||
			expr instanceof CoerceToBoolExpression)
		return expr;
	return this;
};

proto.addDependencies = function addDependencies(deps, path) {
	this.expression.addDependencies(deps);
};

proto.evaluateInternal = function evaluateInternal(vars) {
	var result = this.expression.evaluateInternal(vars);
	return Value.coerceToBool(result);
};

proto.serialize = function serialize(explain) {
	// When not explaining, serialize to an $and expression. When parsed, the $and expression
	// will be optimized back into a ExpressionCoerceToBool.
	var name = explain ? "$coerceToBool" : "$and",
		obj = {};
	obj[name] = [this.expression.serialize(explain)];
	return obj;
};