// Take IV: Explicitly handle mixins, provide a mixin for calling super when
// working with anonymous functions.
// Inspired by Prototype's Class class (http://prototypejs.org)
// Copyright (C) 2009-2010 by T.J. Crowder
// Licensed under the Creative Commons Attribution License 2.0 (UK)
// http://creativecommons.org/licenses/by/2.0/uk/
var Helper = (function(){
    var toStringProblematic,    // true if 'toString' may be missing from for..in
        valueOfProblematic;     // true if 'valueOf' may be missing from for..in

    // IE doesn't enumerate toString or valueOf; detect that (once) and
    // remember so makeClass can deal with it. We do this with an anonymous
    // function we don't keep a reference to to minimize what we keep
    // around when we're done.
    (function(){
        var name;

        toStringProblematic = valueOfProblematic = true;
        for (name in {toString: true, valueOf: true}) {
            if (name == 'toString') {
                toStringProblematic = false;
            }
            if (name == 'valueOf') {
                valueOfProblematic = false;
            }
        }
    })();

	// This function is used to create the prototype object for our generated
	// constructors if the class has a parent class. See makeConstructor for details.
	function protoCtor() { }

    // Build and return a constructor; we do this with a separate function
    // to minimize what the new constructor (a closure) closes over.
    function makeConstructor(base) {

        // Here's our basic constructor function (each class gets its own, a
        // new one of these is created every time makeConstructor is called).
        function ctor() {
            // Call the initialize method
            this.initialize.apply(this, arguments);
        }

		// If there's a base class, hook it up. We go indirectly through `protoCtor`
		// rather than simply doing "new base()" because calling `base` will call the base
		// class's `initialize` function, which we don't want to execute. We just want the
		// prototype.
		if (base) {
			protoCtor.prototype = base.prototype;
			ctor.prototype = new protoCtor();
			protoCtor.prototype = {};	// Don't leave a dangling reference
		}

        // Set the prototype's constructor property so `this.constructor` resolves
        // correctly
        ctor.prototype.constructor = ctor;

		// Flag up that this is a constructor (for mixin support)
        ctor._isConstructor = true;

		// Return the newly-constructed constructor
        return ctor;
    }

    // This function is used when a class doesn't have its own initialize
    // function; since it does nothing and can only appear on base classes,
    // all instances can share it.
    function defaultInitialize() {
    }

    // Get the names in a specification object, allowing for toString and
    // valueOf issues
    function getNames(members) {
        var names,      // The names of the properties in 'members'
            name,       // Each name
            nameIndex;  // Index into 'names'

        names = [];
        nameIndex = 0;
        for (name in members) {
            names[nameIndex++] = name;
        }
        if (toStringProblematic && typeof members.toString != 'undefined') {
            names[nameIndex++] = 'toString';
        }
        if (valueOfProblematic && typeof members.valueOf != 'undefined') {
            names[nameIndex++] = 'valueOf';
        }
        return names;
    }

    // makeClass: Our public "make a class" function.
    // Arguments:
    // - base: An optional constructor for the base class.
    // - ...:  One or more specification objects containing properties to
    //         put on our class as members; or functions that return
    //         specification objects. If a property is defined by more than one
    //         specification object, the last in the list wins.
    // Returns:
    //     A constructor function for instances of the class.
    //
    // Typical use will be just one specification object, but allow for more
    // in case the author is drawing members from multiple locations.
    function makeClass() {
        var base,       // Our base class (constructor function), if any
            argsIndex,  // Index of first unused argument in 'arguments'
            ctor,       // The constructor function we create and return
            members,    // Each members specification object
            names,      // The names of the properties in 'members'
            nameIndex,  // Index into 'names'
            name,       // Each name in 'names'
            value,      // The value for each name
            baseValue;  // The base class's value for the name

        // We use this index to keep track of the arguments we've consumed
        argsIndex = 0;

        // Do we have a base?
        if (typeof arguments[argsIndex] == 'function' &&
            arguments[argsIndex]._isConstructor) {
            // Yes
            base = arguments[argsIndex++];
        }

        // Get our constructor; this will hook up the base class's prototype
		// if there's a base class, and mark the new constructor as a constructor
        ctor = makeConstructor(base);

        // Assign the members from the specification object(s) to the prototype
        // Again, typically there's only spec object, but allow for more
        while (argsIndex < arguments.length) {
            // Get this specification object
            members = arguments[argsIndex++];
            if (typeof members == 'function') {
                members = members();
            }

            // Get all of its names
            names = getNames(members);

            // Copy the members
            for (nameIndex = names.length - 1; nameIndex >= 0; --nameIndex) {
                name = names[nameIndex];
                value = members[name];
                if (base && typeof value == 'function' && !value._isMixinFunction) {
                    baseValue = base.prototype[name];
                    if (typeof baseValue == 'function') {
                        value.$super = baseValue;
                    }
                }
                ctor.prototype[name] = value;
            }
        }

        // If there's no initialize function, provide one
        if (!('initialize' in ctor.prototype)) {
            // Note that this can only happen in base classes; in a derived
            // class, the check above will find the base class's version if the
            // subclass didn't define one.
            ctor.prototype.initialize = defaultInitialize;
        }

        // Return the constructor
        return ctor;
    }

    // makeMixin: Our public "make a mixin" function.
    // Arguments:
    // - ...:  One or more specification objects containing properties to
    //         put on our class as members; or functions that return
    //         specification objects. If a property is defined by more than one
    //         specification object, the last in the list wins.
    // Returns:
    //     A specification object containing all of the members, flagged as
    //     mixin members.
    function makeMixin() {
        var rv,         // Our return value
            argsIndex,  // Index of first unused argument in 'arguments'
            members,    // Each members specification object
            names,      // The names in each 'members'
            value;      // Each value as we copy it

        // Set up our return object
        rv = {};

        // Loop through the args (usually just one, but...)
        argsIndex = 0;
        while (argsIndex < arguments.length) {
            // Get this members specification object
            members = arguments[argsIndex++];
            if (typeof members == 'function') {
                members = members();
            }

            // Get its names
            names = getNames(members);

            // Copy its members, marking them as we go
            for (nameIndex = names.length - 1; nameIndex >= 0; --nameIndex) {
                name = names[nameIndex];
                value = members[name];
                if (typeof value == 'function') {
                    value._isMixinFunction = true;
                }
                rv[name] = value;
            }
        }

        // Return the consolidated, marked specification object
        return rv;
    }

    // Return our public members
    return {
        makeClass: makeClass,
        makeMixin: makeMixin
        };
})();