Emit events when the active Stacktrace is changed.

Author: smashwilson

lib/stacktrace.coffee

@@ -1,4 +1,7 @@
 fs = require 'fs'
+
+{Emitter} = require 'emissary'
+
 jsSHA = require 'jssha'
 {chomp} = require 'line-chomper'
 traceParser = null
@@ -12,6 +15,9 @@ ACTIVE = null
 #
 class Stacktrace
 
+  # Turn the Stacktrace class into an emitter.
+  Emitter.extend this
+
   constructor: (@frames = [], @message = '') ->
 
   # Internal: Compute the SHA256 checksum of the normalized stacktrace.
@@ -45,11 +51,18 @@ class Stacktrace
   # Public: Mark this trace as the "active" one. The active trace is shown in the navigation view
   # and its frames are given a marker in an open {EditorView}.
   #
-  activate: -> ACTIVE = this
+  activate: ->
+    former = ACTIVE
+    ACTIVE = this
+    if former isnt ACTIVE
+      Stacktrace.emit 'active-changed', oldTrace: former, newTrace: ACTIVE
 
   # Public: Deactivate this trace if it's active.
   #
-  deactivate: -> ACTIVE = null if ACTIVE is this
+  deactivate: ->
+    if ACTIVE is this
+      ACTIVE = null
+      Stacktrace.emit 'active-changed', oldTrace: this, newTrace: null
 
   # Public: Parse zero to many Stacktrace instances from a corpus of text.
   #

spec/stacktrace-spec.coffee

@@ -79,6 +79,7 @@ describe 'Stacktrace', ->
       afterEach ->
         activated = Stacktrace.getActivated()
         activated.deactivate() if activated?
+        Stacktrace.off 'active-changed'
 
       it 'can be activated', ->
         trace.activate()
@@ -93,6 +94,14 @@ describe 'Stacktrace', ->
         trace.deactivate()
         expect(Stacktrace.getActivated()).toBeNull()
 
+      it 'broadcasts a "active-changed" event', ->
+        event = null
+        Stacktrace.on 'active-changed', (e) -> event = e
+
+        trace.activate()
+        expect(event.oldTrace).toBeNull()
+        expect(event.newTrace).toBe(trace)
+
 describe 'Frame', ->
   [frame] = []