/*
 *      backbone.shard.js.
 * 
 *      (c) 2013 Anton Shestakov.
 * 
 *      This extension to Backbone may be freely distributed
 *      under the MIT license:
 *      http://opensource.org/licenses/mit-license.php
 */
Backbone.Shard = function(options) {
    this._collection = options.collection;
    this._filter = options.filter;
    
    this.models = this._collection.filter(this._filter);
    
    this._collection
        .on('all', function(event, model) {
            if (event == 'change') {
                if (this._filter(model) && _(this.models).contains(model)) {
                    this.trigger.apply(this, arguments);
                }
                if (this._filter(model) && !_(this.models).contains(model)) {
                    this.models.push(model);
                    this.trigger('add', model);
                }
                if (!this._filter(model) && _(this.models).contains(model)) {
                    this.models = _.without(this.models, model);
                    this.trigger('remove', model);
                }
            } else if (/^change:/.test(event) && this._filter(model) && _(this.models).contains(model)) {
                this.trigger.apply(this, arguments);
            }
        }, this)
        .on('add', function(model) {
            if (this._filter(model) && !_(this.models).contains(model)) {
                this.models.push(model);
                this.trigger('add', model);
            }
        }, this)
        .on('remove', function(model) {
            if (this._filter(model) && _(this.models).contains(model)) {
                this.models = _.without(this.models, model);
                this.trigger('remove', model);
            }
        }, this)
        .on('reset', function() {
            this.models = this._collection.filter(this._filter);
            this.trigger('reset');
        }, this);
    
    this.initialize.apply(this, arguments);
};
_.extend(Backbone.Shard.prototype, Backbone.Events, {
    initialize: function() {},
    
    pluck: function(attr) {
        return _.map(this.models, function(model) { return model.get(attr); });
    }
});
// Underscore methods that we want to implement on the Shard.
var methods = ['forEach', 'each', 'map', 'collect', 'reduce', 'foldl',
    'inject', 'reduceRight', 'foldr', 'find', 'detect', 'filter', 'select',
    'reject', 'every', 'all', 'some', 'any', 'include', 'contains', 'invoke',
    'max', 'min', 'toArray', 'size', 'first', 'head', 'take', 'initial', 'rest',
    'tail', 'drop', 'last', 'without', 'indexOf', 'shuffle', 'lastIndexOf',
    'isEmpty', 'chain'];
// Mix in each Underscore method as a proxy to `Shard#models`.
_.each(methods, function(method) {
    Backbone.Shard.prototype[method] = function() {
        var args = Array.prototype.slice.call(arguments);
        args.unshift(this.models);
        return _[method].apply(_, args);
    };
});
// Underscore methods that take a property name as an argument.
var attributeMethods = ['groupBy', 'countBy', 'sortBy'];
// Use attributes instead of properties.
_.each(attributeMethods, function(method) {
    Backbone.Shard.prototype[method] = function(value, context) {
        var iterator = _.isFunction(value) ? value : function(model) {
            return model.get(value);
        };
        return _[method](this.models, iterator, context);
    };
});