index.js

var _ = require('underscore');
var Backbone = require('backbone');
var proxyCollection = require('backbone-collection-proxy');
var createFilter = require('./src/create-filter.js');

// Beware of `this`
// All of the following functions are meant to be called in the context
// of the FilteredCollection object, but are not public functions.

function invalidateCache() {
  this._filterResultCache = {};
}

function invalidateCacheForFilter(filterName) {
  for (var cid in this._filterResultCache) {
    if (this._filterResultCache.hasOwnProperty(cid)) {
      delete this._filterResultCache[cid][filterName];
    }
  }
}

function addFilter(filterName, filterObj) {
  // If we've already had a filter of this name, we need to invalidate
  // any and all of the cached results
  if (this._filters[filterName]) {
    invalidateCacheForFilter.call(this, filterName);
  }

  this._filters[filterName] = filterObj;
  this.trigger('filtered:add', filterName);
}

function removeFilter(filterName) {
  delete this._filters[filterName];
  invalidateCacheForFilter.call(this, filterName);
  this.trigger('filtered:remove', filterName);
}

function execFilterOnModel(model) {
  if (!this._filterResultCache[model.cid]) {
    this._filterResultCache[model.cid] = {};
  }

  var cache = this._filterResultCache[model.cid];

  for (var filterName in this._filters) {
    if (this._filters.hasOwnProperty(filterName)) {
      // if we haven't already calculated this, calculate it and cache
      if (!cache.hasOwnProperty(filterName)) {
        cache[filterName] = this._filters[filterName].fn(model);
      }
      if (!cache[filterName]) {
        return false;
      }
    }
  }
  return true;
}

function execFilter() {
  var filtered = [];

  // Filter the collection
  if (this._superset) {
    filtered = this._superset.filter(_.bind(execFilterOnModel, this));
  }

  this._collection.reset(filtered);
  this.length = this._collection.length;
}

function onAddChange(model) {
  // reset the cached results
  this._filterResultCache[model.cid] = {};

  if (execFilterOnModel.call(this, model)) {
    if (!this._collection.get(model.cid)) {
      var index = this.superset().indexOf(model);

      // Find the index at which to insert the model in the
      // filtered collection by finding the index of the
      // previous non-filtered model in the filtered collection
      var filteredIndex = null;
      for (var i = index - 1; i >= 0; i -= 1) {
        if (this.contains(this.superset().at(i))) {
          filteredIndex = this.indexOf(this.superset().at(i)) + 1;
          break;
        }
      }
      filteredIndex = filteredIndex || 0;

      this._collection.add(model, { at: filteredIndex });
    }
  } else {
    if (this._collection.get(model.cid)) {
      this._collection.remove(model);
    }
  }
  this.length = this._collection.length;
}

// This fires on 'change:[attribute]' events. We only want to
// remove this model if it fails the test, but not add it if
// it does. If we remove it, it will prevent the 'change'
// events from being forwarded, and if we add it, it will cause
// an unneccesary 'change' event to be forwarded without the
// 'change:[attribute]' that goes along with it.
function onModelAttributeChange(model) {
  // reset the cached results
  this._filterResultCache[model.cid] = {};

  if (!execFilterOnModel.call(this, model)) {
    if (this._collection.get(model.cid)) {
      this._collection.remove(model);
    }
  }
}

function onAll(eventName, model, value) {
  if (eventName.slice(0, 7) === "change:") {
    onModelAttributeChange.call(this, arguments[1]);
  }
}

function onModelRemove(model) {
  if (this.contains(model)) {
    this._collection.remove(model);
  }
  this.length = this._collection.length;
}

function Filtered(superset) {
  // Save a reference to the original collection
  this._superset = superset;

  // The idea is to keep an internal backbone collection with the filtered
  // set, and expose limited functionality.
  this._collection = new Backbone.Collection(superset.toArray());
  proxyCollection(this._collection, this);

  // Set up the filter data structures
  this.resetFilters();

  this.listenTo(this._superset, 'reset sort', execFilter);
  this.listenTo(this._superset, 'add change', onAddChange);
  this.listenTo(this._superset, 'remove', onModelRemove);
  this.listenTo(this._superset, 'all', onAll);
}

var methods = {

  defaultFilterName: '__default',

  filterBy: function(filterName, filter) {
    // Allow the user to skip the filter name if they're only using one filter
    if (!filter) {
      filter = filterName;
      filterName = this.defaultFilterName;
    }

    addFilter.call(this, filterName, createFilter(filter));

    execFilter.call(this);
    return this;
  },

  removeFilter: function(filterName) {
    if (!filterName) {
      filterName = this.defaultFilterName;
    }

    removeFilter.call(this, filterName);

    execFilter.call(this);
    return this;
  },

  resetFilters: function() {
    this._filters = {};
    invalidateCache.call(this);

    this.trigger('filtered:reset');

    execFilter.call(this);
    return this;
  },

  superset: function() {
    return this._superset;
  },

  refilter: function(arg) {
    if (typeof arg === "object" && arg.cid) {
      // is backbone model, refilter that one
      onAddChange.call(this, arg);
    } else {
      // refilter everything
      invalidateCache.call(this);
      execFilter.call(this);
    }

    return this;
  },

  getFilters: function() {
    return  _.keys(this._filters);
  },

  hasFilter: function(name) {
    return _.contains(this.getFilters(), name);
  },

  destroy: function() {
    this.stopListening();
    this._collection.reset([]);
    this._superset = this._collection;
    this.length = 0;

    this.trigger('filtered:destroy');
  }

};

// Build up the prototype
_.extend(Filtered.prototype, methods, Backbone.Events);

module.exports = Filtered;