Working prototype of crowdsourced hinting module.

Conflicts:
	common/static/coffee/src/logger.coffee

common/static/coffee/src/logger.coffee

@@ -1,8 +1,11 @@
 class @Logger
+
   # events we want sent to Segment.io for tracking
   SEGMENT_IO_WHITELIST = ["seq_goto", "seq_next", "seq_prev", "problem_check", "problem_reset", "problem_show", "problem_save"]
 
-  @log: (event_type, data) ->
+  # listeners[event_type][element] -> list of callbacks
+  listeners = {}
+  @log: (event_type, data, element = null) ->
     # Segment.io event tracking
     if event_type in SEGMENT_IO_WHITELIST
       # to avoid changing the format of data sent to our servers, we only massage it here
@@ -11,11 +14,36 @@ class @Logger
       else
         analytics.track event_type, data
 
+    # Check to see if we're listening for the event type.
+    if event_type of listeners
+      # Cool.  Do the elements also match?
+      # null element in the listener dictionary means any element will do.
+      # null element in the @log call means we don't know the element name.
+      if null of listeners[event_type]
+        # Make the callbacks.
+        for callback in listeners[event_type][null]
+          callback(event_type, data, element)
+      else if element of listeners[event_type]
+        for callback in listeners[event_type][element]
+          callback(event_type, data, element)
+
+    # Regardless of whether any callbacks were made, log this event.
     $.getWithPrefix '/event',
       event_type: event_type
       event: JSON.stringify(data)
       page: window.location.href
 
+  @listen: (event_type, element, callback) ->
+    # Add a listener.  If you want any element to trigger this listener,
+    # do element = null
+    if event_type not of listeners
+      listeners[event_type] = {}
+    if element not of listeners[event_type]
+      listeners[event_type][element] = [callback]
+    else
+      listeners[event_type][element].push callback
+
+
   @bind: ->
     window.onunload = ->
       $.ajaxWithPrefix