Add child event methods to PaneAxis

This eliminates our reliance on the Sequence object for informing us
of changes

package.json

@@ -26,7 +26,7 @@
     "coffee-script": "1.7.0",
     "coffeestack": "0.7.0",
     "delegato": "^1",
-    "emissary": "^1.2.2",
+    "emissary": "^1.3.0",
     "event-kit": "0.0.0",
     "first-mate": "^2.0.5",
     "fs-plus": "^2.2.6",

src/pane-axis-view.coffee

@@ -1,11 +1,17 @@
+{CompositeDisposable} = require 'event-kit'
 {View} = require './space-pen-extensions'
 PaneView = null
 
 module.exports =
 class PaneAxisView extends View
   initialize: (@model) ->
-    @onChildAdded(child) for child in @model.children
-    @subscribe @model.children, 'changed', @onChildrenChanged
+    @subscriptions = new CompositeDisposable
+
+    @onChildAdded({child, index}) for child, index in @model.getChildren()
+
+    @subscriptions.add @model.onDidAddChild(@onChildAdded)
+    @subscriptions.add @model.onDidRemoveChild(@onChildRemoved)
+    @subscriptions.add @model.onDidReplaceChild(@onChildReplaced)
 
   afterAttach: ->
     @container = @closest('.panes').view()
@@ -14,19 +20,22 @@ class PaneAxisView extends View
     viewClass = model.getViewClass()
     model._view ?= new viewClass(model)
 
-  onChildrenChanged:  ({index, removedValues, insertedValues}) =>
+  onChildReplaced:  ({index, oldChild, newChild}) =>
     focusedElement = document.activeElement if @hasFocus()
-    @onChildRemoved(child, index) for child in removedValues
-    @onChildAdded(child, index + i) for child, i in insertedValues
+    @onChildRemoved({child: oldChild, index})
+    @onChildAdded({child: newChild, index})
     focusedElement?.focus() if document.activeElement is document.body
 
-  onChildAdded: (child, index) =>
+  onChildAdded: ({child, index}) =>
     view = @viewForModel(child)
     @insertAt(index, view)
 
-  onChildRemoved: (child) =>
+  onChildRemoved: ({child}) =>
     view = @viewForModel(child)
     view.detach()
     PaneView ?= require './pane-view'
     if view instanceof PaneView and view.model.isDestroyed()
       @container?.trigger 'pane:removed', [view]
+
+  beforeRemove: ->
+    @subscriptions.dispose()

src/pane-axis.coffee

@@ -1,4 +1,5 @@
 {Model} = require 'theorist'
+{Emitter} = require 'event-kit'
 {flatten} = require 'underscore-plus'
 Serializable = require 'serializable'
 
@@ -11,6 +12,7 @@ class PaneAxis extends Model
   Serializable.includeInto(this)
 
   constructor: ({@container, @orientation, children}) ->
+    @emitter = new Emitter
     @children = []
     if children?
       @addChild(child) for child in children
@@ -30,45 +32,53 @@ class PaneAxis extends Model
     else
       PaneRowView ?= require './pane-row-view'
 
+  getChildren: -> @children.slice()
+
   getPanes: ->
     flatten(@children.map (child) -> child.getPanes())
 
-  addChild: (child, index=@children.length) ->
-    @children.splice(index, 0, child)
-    @childAdded(child)
+  onDidAddChild: (fn) ->
+    @emitter.on 'did-add-child', fn
 
-  removeChild: (child) ->
+  onDidRemoveChild: (fn) ->
+    @emitter.on 'did-remove-child', fn
+
+  onDidReplaceChild: (fn) ->
+    @emitter.on 'did-replace-child', fn
+
+  addChild: (child, index=@children.length) ->
+    child.parent = this
+    child.container = @container
+    @subscribe child, 'destroyed', => @removeChild(child)
+    @children.splice(index, 0, child)
+    @emitter.emit 'did-add-child', {child, index}
+
+  removeChild: (child, replacing=false) ->
     index = @children.indexOf(child)
     throw new Error("Removing non-existent child") if index is -1
+    @unsubscribe child
     @children.splice(index, 1)
-    @childRemoved(child)
-    @reparentLastChild() if @children.length < 2
+    @emitter.emit 'did-remove-child', {child, index}
+    @reparentLastChild() if not replacing and @children.length < 2
 
   replaceChild: (oldChild, newChild) ->
+    @unsubscribe oldChild
+    newChild.parent = this
+    newChild.container = @container
+    @subscribe newChild, 'destroyed', => @removeChild(newChild)
+
     index = @children.indexOf(oldChild)
-    throw new Error("Replacing non-existent child") if index is -1
     @children.splice(index, 1, newChild)
-    @childRemoved(oldChild)
-    @childAdded(newChild)
+    @emitter.emit 'did-replace-child', {oldChild, newChild, index}
 
   insertChildBefore: (currentChild, newChild) ->
     index = @children.indexOf(currentChild)
-    @children.splice(index, 0, newChild)
-    @childAdded(newChild)
+    @addChild(newChild, index)
 
   insertChildAfter: (currentChild, newChild) ->
     index = @children.indexOf(currentChild)
-    @children.splice(index + 1, 0, newChild)
-    @childAdded(newChild)
+    @addChild(newChild, index + 1)
 
   reparentLastChild: ->
     @parent.replaceChild(this, @children[0])
     @destroy()
-
-  childAdded: (child) ->
-    child.parent = this
-    child.container = @container
-    @subscribe child, 'destroyed', => @removeChild(child)
-
-  childRemoved: (child) ->
-    @unsubscribe child