Manage the active pane at the model level

package.json

@@ -50,7 +50,7 @@
     "temp": "0.5.0",
     "text-buffer": "0.12.0",
     "underscore-plus": "0.6.1",
-    "theorist": "~0.9.0",
+    "theorist": "~0.10.0",
     "delegato": "~0.4.0",
     "mixto": "~0.4.0"
   },

spec/pane-container-model-spec.coffee

@@ -11,6 +11,36 @@ describe "PaneContainerModel", ->
       expect(pane3A.focused).toBe true
 
       containerB = containerA.testSerialization()
-      [pane1A, pane2A, pane3A] = containerB.getPanes()
-      expect(pane3A.focusContext).toBe containerB.focusContext
-      expect(pane3A.focused).toBe true
+      [pane1B, pane2B, pane3B] = containerB.getPanes()
+      expect(pane3B.focusContext).toBe containerB.focusContext
+      expect(pane3B.focused).toBe true
+
+  describe "::activePane", ->
+    [container, pane1, pane2] = []
+
+    beforeEach ->
+      pane1 = new PaneModel
+      container = new PaneContainerModel(root: pane1)
+
+    it "references the first pane if no pane has been focused", ->
+      expect(container.activePane).toBe pane1
+      expect(pane1.active).toBe true
+
+    it "references the most recently focused pane", ->
+      pane2 = pane1.splitRight()
+      expect(container.activePane).toBe pane2
+      expect(pane1.active).toBe false
+      expect(pane2.active).toBe true
+      pane1.focus()
+      expect(container.activePane).toBe pane1
+      expect(pane1.active).toBe true
+      expect(pane2.active).toBe false
+
+    it "is reassigned to the next pane if the current active pane is unfocused and destroyed", ->
+      pane2 = pane1.splitRight()
+      pane2.blur()
+      pane2.destroy()
+      expect(container.activePane).toBe pane1
+      expect(pane1.active).toBe true
+      pane1.destroy()
+      expect(container.activePane).toBe null

spec/pane-model-spec.coffee

@@ -88,7 +88,8 @@ describe "PaneModel", ->
   describe "::removeItemAtIndex(index)", ->
     describe "when the removal of the item causes blur to be called on the pane model", ->
       it "remains focused if it was before the item was removed", ->
-        pane = new PaneModel(items: ["A", "B", "C"], focusContext: new FocusContext)
+        pane = new PaneModel(items: ["A", "B", "C"])
+        container = new PaneContainerModel(root: pane)
         pane.on 'item-removed', -> pane.blur()
         pane.focus()
         pane.removeItemAtIndex(0)

src/pane-axis-model.coffee

@@ -12,19 +12,14 @@ class PaneAxisModel extends Model
   Serializable.includeInto(this)
   Delegator.includeInto(this)
 
-  @delegatesMethod 'focusNextPane', toProperty: 'parent'
+  @delegatesProperty 'focusContext', toProperty: 'container'
 
-  @property 'focusContext'
-
-  constructor: ({@focusContext, @orientation, children}) ->
+  constructor: ({@container, @orientation, children}) ->
     @children = Sequence.fromArray(children ? [])
 
-    @subscribe @$focusContext, (focusContext) =>
-      child.focusContext = focusContext for child in @children
-
     @subscribe @children.onEach (child) =>
       child.parent = this
-      child.focusContext = @focusContext
+      child.container = @container
       @subscribe child, 'destroyed', => @removeChild(child)
 
     @subscribe @children.onRemoval (child) => @unsubscribe(child)
@@ -33,8 +28,8 @@ class PaneAxisModel extends Model
     @when @children.$length.becomesLessThan(1), 'destroy'
 
   deserializeParams: (params) ->
-    {focusContext} = params
-    params.children = params.children.map (childState) -> atom.deserializers.deserialize(childState, {focusContext})
+    {container} = params
+    params.children = params.children.map (childState) -> atom.deserializers.deserialize(childState, {container})
     params
 
   serializeParams: ->

src/pane-container-model.coffee

@@ -2,6 +2,7 @@
 Serializable = require 'serializable'
 {find} = require 'underscore-plus'
 FocusContext = require './focus-context'
+PaneModel = require './pane-model'
 
 module.exports =
 class PaneContainerModel extends Model
@@ -10,18 +11,23 @@ class PaneContainerModel extends Model
 
   @properties
     root: null
-    focusContext: -> new FocusContext
+    focusContext: null
+    activePane: null
 
   constructor: ->
     super
+
+    @focusContext ?= new FocusContext
+
     @subscribe @$root, (root) =>
       if root?
         root.parent = this
-        root.focusContext = @focusContext
+        root.container = this
+        @activePane ?= root if root instanceof PaneModel
 
   deserializeParams: (params) ->
-    params.focusContext ?= new FocusContext
-    params.root = atom.deserializers.deserialize(params.root, focusContext: params.focusContext)
+    @focusContext ?= params.focusContext ? new FocusContext
+    params.root = atom.deserializers.deserialize(params.root, container: this)
     params
 
   serializeParams: (params) ->
@@ -57,3 +63,12 @@ class PaneContainerModel extends Model
       true
     else
       false
+
+  makeNextPaneActive: ->
+    panes = @getPanes()
+    if panes.length > 1
+      currentIndex = panes.indexOf(@activePane)
+      nextIndex = (currentIndex + 1) % panes.length
+      @activePane = panes[nextIndex]
+    else
+      @activePane = null

src/pane-model.coffee

@@ -13,26 +13,38 @@ class PaneModel extends Model
   Focusable.includeInto(this)
 
   @properties
+    container: null
     activeItem: null
 
+  @behavior 'active', ->
+    @$container
+      .flatMapLatest((container) -> container?.$activePane)
+      .map((activePane) => activePane is this)
+      .distinctUntilChanged()
+
   constructor: (params) ->
     super
 
-    @focus() if params?.focused
-
     @items = Sequence.fromArray(params?.items ? [])
     @activeItem ?= @items[0]
 
+    @subscribe @$container, (container) =>
+      @focusContext = container?.focusContext
+
     @subscribe @items.onEach (item) =>
       if typeof item.on is 'function'
         @subscribe item, 'destroyed', => @removeItem(item)
 
     @subscribe @items.onRemoval (item, index) =>
-      @unsubscribe item
+      @unsubscribe item if typeof item.on is 'function'
       @emit 'item-removed', item, index
 
     @when @items.$length.becomesLessThan(1), 'destroy'
 
+    @when @$focused, => @makeActive()
+
+    @focus() if params?.focused
+
   serializeParams: ->
     items: compact(@items.map((item) -> item.serialize?()))
     activeItemUri: @activeItem?.getUri?()
@@ -46,6 +58,10 @@ class PaneModel extends Model
 
   getViewClass: -> Pane ?= require './pane'
 
+  isActive: -> @active
+
+  makeActive: -> @container.activePane = this
+
   getPanes: -> [this]
 
   # Public: Returns all contained views.
@@ -144,7 +160,10 @@ class PaneModel extends Model
   # Private: Called by model superclass
   destroyed: ->
     item.destroy?() for item in @items.slice()
-    @parent.focusNextPane() if @focused
+    if @focused
+      @container.focusNextPane()
+    else if @isActive()
+      @container.makeNextPaneActive()
 
   # Public: Prompt the user to save the given item.
   promptToSaveItem: (item) ->
@@ -223,7 +242,7 @@ class PaneModel extends Model
 
   split: (orientation, side, params) ->
     if @parent.orientation isnt orientation
-      @parent.replaceChild(this, new PaneAxisModel({orientation, children: [this]}))
+      @parent.replaceChild(this, new PaneAxisModel({@container, orientation, children: [this]}))
 
     newPane = new @constructor(params)
     switch side