Initial view implementation (fix #3).

packages/xo-collection/package.json

@@ -21,6 +21,8 @@
   ],
   "dependencies": {
     "babel-runtime": "^5",
+    "lodash.bind": "^3.1.0",
+    "lodash.callback": "^3.1.1",
     "lodash.foreach": "^3.0.2",
     "make-error": "^1.0.0"
   },

packages/xo-collection/src/view.example.js

@@ -0,0 +1,40 @@
+import Collection from './'
+import View from './view'
+
+const users = new Collection()
+users.getId = (user) => user.name
+
+const activeUsers = new View(users, 'active')
+activeUsers.on('add', console.log)
+activeUsers.on('update', console.log)
+activeUsers.on('remove', console.log)
+
+users.add({
+  name: 'bob'
+})
+
+users.add({
+  name: 'clara',
+  active: true
+})
+
+users.add({
+  name: 'ophelia'
+})
+
+users.add({
+  name: 'Steve',
+  active: true
+})
+
+setTimeout(function () {
+  console.log('-----')
+
+  users.set({
+    name: 'ophelia',
+    active: true
+  })
+  users.set({
+    name: 'Steve'
+  })
+}, 10)

packages/xo-collection/src/view.js

@@ -0,0 +1,78 @@
+import bind from 'lodash.bind'
+import createCallback from 'lodash.callback'
+import forEach from 'lodash.foreach'
+
+import Collection from './'
+
+// ===================================================================
+
+export default class View extends Collection {
+  constructor (collection, predicate, thisArg) {
+    super()
+
+    this._collection = collection
+    this._predicate = createCallback(predicate, thisArg)
+
+    // Bound versions of listeners.
+    this._onAdd = bind(this._onAdd, this)
+    this._onUpdate = bind(this._onUpdate, this)
+    this._onRemove = bind(this._onRemove, this)
+
+    // Register listeners.
+    this._collection.on('add', this._onAdd)
+    this._collection.on('update', this._onUpdate)
+    this._collection.on('remove', this._onRemove)
+  }
+
+  destroy () {
+    this._collection.removeListener('add', this._onAdd)
+    this._collection.removeListener('update', this._onUpdate)
+    this._collection.removeListener('remove', this._onRemove)
+  }
+
+  add () {
+    throw new Error('a view is read only')
+  }
+
+  clear () {
+    throw new Error('a view is read only')
+  }
+
+  set () {
+    throw new Error('a view is read only')
+  }
+
+  update () {
+    throw new Error('a view is read only')
+  }
+
+  _onAdd (items) {
+    const {_predicate: predicate} = this
+
+    forEach(items, (value, key) => {
+      if (predicate(value, key, this)) {
+        super.add(key, value)
+      }
+    })
+  }
+
+  _onUpdate (items) {
+    const {_predicate: predicate} = this
+
+    forEach(items, (value, key) => {
+      if (predicate(value, key, this)) {
+        super.set(key, value)
+      } else if (super.has(key)) {
+        super.remove(key)
+      }
+    })
+  }
+
+  _onRemove (items) {
+    forEach(items, (value, key) => {
+      if (super.has(key)) {
+        super.remove(key)
+      }
+    })
+  }
+}