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

"use strict";

/**
 * The base class for all n-ary `Expression`s
 * @class NaryExpression
 * @namespace mungedb-aggregate.pipeline.expressions
 * @module mungedb-aggregate
 * @extends mungedb-aggregate.pipeline.expressions.Expression
 * @constructor
 **/
var Expression = require("./Expression");

var NaryExpression = module.exports = function NaryExpression(){
	if (arguments.length !== 0) throw new Error("zero args expected");
	this.operands = [];
	base.call(this);
}, klass = NaryExpression, base = Expression, proto = klass.prototype = Object.create(base.prototype, {constructor:{value:klass}});

klass.parseArguments = function(exprElement, vps) {
    var out = [];
    if(exprElement instanceof Array) {
        for(var ii = 0; ii < exprElement.length; ii++) {
            out.push(Expression.parseOperand(exprElement[ii], vps));
        }
    } else {
        out.push(Expression.parseOperand(exprElement, vps));
    }
    return out;
};


function partitionBy(fn, coll) {
    var ret = {pass:[],
               fail:[]};
    coll.forEach(function(x) {
        if(fn(x)) {
            ret.pass.push(x);
        } else {
            ret.fail.push(x);
        }
    });
    return ret;
}
// DEPENDENCIES
var ConstantExpression = require("./ConstantExpression");

// PROTOTYPE MEMBERS
proto.evaluate = undefined; // evaluate(doc){ ... defined by inheritor ... }

proto.getOpName = function getOpName(doc){
	throw new Error("NOT IMPLEMENTED BY INHERITOR");
};

proto.optimize = function optimize(){
    var n = this.operands.length,
        constantCount = 0;

    for(var ii = 0; ii < n; ii++) {
        if(this.operands[ii] instanceof ConstantExpression) {
            constantCount++;
        } else {
            this.operands[ii] = this.operands[ii].optimize();
        }
    }

    if(constantCount === n) {
        return new ConstantExpression(this.evaluateInternal({}));
    }

    if(!this.isAssociativeAndCommutative) {
        return this;
    }

    // Flatten and inline nested operations of the same type

    var similar = partitionBy(function(x){ return x.getOpName() === this.getOpName();}, this.operands);

    this.operands = similar.fail;
    similar.pass.forEach(function(x){
        this.operands.concat(x.operands);
    });

    // Partial constant folding

    var constantOperands = partitionBy(function(x) {return x instanceof ConstantExpression;}, this.operands);

    this.operands = constantOperands.pass;
    this.operands = [new ConstantExpression(this.evaluateInternal({}))].concat(constantOperands.fail);

    return this;
};

proto.addDependencies = function addDependencies(deps){
	for(var i = 0, l = this.operands.length; i < l; ++i)
		this.operands[i].addDependencies(deps);
};

/**
 * Add an operand to the n-ary expression.
 * @method addOperand
 * @param pExpression the expression to add
 **/
proto.addOperand = function addOperand(expr) {
	this.operands.push(expr);
};

proto.serialize = function serialize() {
    var ret = {}, subret = [];
    for(var ii = 0; ii < this.operands.length; ii++) {
        subret.push(this.operands[ii].serialize());
    }
    ret[this.getOpName()] = subret;
    return ret;
};