At the model layer: Focus next pane when a focused pane is destroyed

This incorporates the Focusable mixin into PaneModel and ensures that
all panes in the same pane container share a single focus context.

spec/pane-model-spec.coffee

@@ -80,7 +80,7 @@ describe "PaneModel", ->
 
     it "focuses the new pane, even if the current pane isn't focused", ->
       expect(pane1.focused).toBe false
-      pane2 = pane1.split()
+      pane2 = pane1.splitRight()
       expect(pane2.focused).toBe true
 
   describe "::destroy()", ->
@@ -110,3 +110,13 @@ describe "PaneModel", ->
         expect(container.root.children).toEqual [pane1, pane2]
         pane2.destroy()
         expect(container.root).toBe pane1
+
+    describe "if the pane is focused", ->
+      it "shifts focus to the next pane", ->
+        pane2 = pane1.splitRight()
+        pane3 = pane2.splitRight()
+        pane2.focus()
+        expect(pane2.focused).toBe true
+        expect(pane3.focused).toBe false
+        pane2.destroy()
+        expect(pane3.focused).toBe true

src/pane-axis-model.coffee

@@ -1,4 +1,6 @@
 {Model, Sequence} = require 'theorist'
+{flatten} = require 'underscore-plus'
+Delegator = require 'delegato'
 Serializable = require 'serializable'
 
 PaneRow = null
@@ -8,15 +10,24 @@ module.exports =
 class PaneAxisModel extends Model
   atom.deserializers.add(this)
   Serializable.includeInto(this)
+  Delegator.includeInto(this)
+
+  @delegatesMethod 'focusNextPane', toProperty: 'parent'
+
+  @property 'focusContext'
 
   constructor: ({@orientation, children}) ->
     @children = Sequence.fromArray(children ? [])
 
-    @children.onEach (child) =>
+    @subscribe @$focusContext, (focusContext) =>
+      child.focusContext = focusContext for child in @children
+
+    @subscribe @children.onEach (child) =>
       child.parent = this
+      child.focusContext = @focusContext
       @subscribe child, 'destroyed', => @removeChild(child)
 
-    @children.onRemoval (child) => @unsubscribe(child)
+    @subscribe @children.onRemoval (child) => @unsubscribe(child)
 
     @when @children.$length.becomesLessThan(2), 'reparentLastChild'
     @when @children.$length.becomesLessThan(1), 'destroy'
@@ -34,6 +45,9 @@ class PaneAxisModel extends Model
     else
       PaneRow ?= require './pane-row'
 
+  getPanes: ->
+    flatten(@children.map (child) -> child.getPanes())
+
   addChild: (child, index=@children.length) ->
     @children.splice(index, 0, child)
 

src/pane-container-model.coffee

@@ -1,5 +1,7 @@
 {Model} = require 'theorist'
 Serializable = require 'serializable'
+{find} = require 'underscore-plus'
+FocusContext = require './focus-context'
 
 module.exports =
 class PaneContainerModel extends Model
@@ -8,10 +10,13 @@ class PaneContainerModel extends Model
 
   @properties
     root: null
+    focusContext: -> new FocusContext
 
   constructor: ->
     super
-    @subscribe @$root, (root) => root?.parent = this
+    @subscribe @$root.filterDefined(), (root) =>
+      root.parent = this
+      root.focusContext = @focusContext
 
   deserializeParams: (params) ->
     params.root = atom.deserializers.deserialize(params.root)
@@ -23,3 +28,30 @@ class PaneContainerModel extends Model
   replaceChild: (oldChild, newChild) ->
     throw new Error("Replacing non-existent child") if oldChild isnt @root
     @root = newChild
+
+  getPanes: ->
+    @root?.getPanes() ? []
+
+  getFocusedPane: ->
+    find @getPanes(), (pane) -> pane.focused
+
+  focusNextPane: ->
+    panes = @getPanes()
+    if panes.length > 1
+      currentIndex = panes.indexOf(@getFocusedPane())
+      nextIndex = (currentIndex + 1) % panes.length
+      panes[nextIndex].focus()
+      true
+    else
+      false
+
+  focusPreviousPane: ->
+    panes = @getPanes()
+    if panes.length > 1
+      currentIndex = panes.indexOf(@getFocusedPane())
+      previousIndex = currentIndex - 1
+      previousIndex = panes.length - 1 if previousIndex < 0
+      panes[previousIndex].focus()
+      true
+    else
+      false

src/pane-model.coffee

@@ -3,17 +3,18 @@
 {Model} = require 'theorist'
 Serializable = require 'serializable'
 PaneAxisModel = require './pane-axis-model'
+Focusable = require './focusable'
 Pane = null
 
 module.exports =
 class PaneModel extends Model
   atom.deserializers.add(this)
   Serializable.includeInto(this)
+  Focusable.includeInto(this)
 
   @properties
     items: -> []
     activeItem: null
-    focused: false
 
   constructor: ->
     super
@@ -32,11 +33,7 @@ class PaneModel extends Model
 
   getViewClass: -> Pane ?= require './pane'
 
-  focus: ->
-    @focused = true
-
-  blur: ->
-    @focused = false
+  getPanes: -> [this]
 
   # Public: Returns all contained views.
   getItems: ->
@@ -132,6 +129,10 @@ class PaneModel extends Model
   destroyInactiveItems: ->
     @destroyItem(item) for item in @getItems() when item isnt @activeItem
 
+  # Private: Called by model superclass
+  destroyed: ->
+    @parent.focusNextPane() if @focused
+
   # Public: Prompt the user to save the given item.
   promptToSaveItem: (item) ->
     return true unless item.shouldPromptToSave?()
@@ -211,8 +212,10 @@ class PaneModel extends Model
     if @parent.orientation isnt orientation
       @parent.replaceChild(this, new PaneAxisModel({orientation, children: [this]}))
 
-    newPane = new @constructor(extend({focused: true}, params))
+    newPane = new @constructor(params)
     switch side
       when 'before' then @parent.insertChildBefore(this, newPane)
       when 'after' then @parent.insertChildAfter(this, newPane)
+
+    newPane.focus()
     newPane