1 files changed, 77 insertions, 15 deletions

diff --git a/lib/handler_stack.coffee b/lib/handler_stack.coffee
index 858f2ec9..76d835b7 100644
--- a/lib/handler_stack.coffee
+++ b/lib/handler_stack.coffee
@@ -1,37 +1,99 @@
 root = exports ? window
 
-class root.HandlerStack
+class HandlerStack
 
   constructor: ->
+    @debug = false
+    @eventNumber = 0
     @stack = []
     @counter = 0
 
-  genId: -> @counter = ++@counter & 0xffff
+    # A handler should return this value to immediately discontinue bubbling and pass the event on to the
+    # underlying page.
+    @stopBubblingAndTrue = new Object()
 
-  # Adds a handler to the stack. Returns a unique ID for that handler that can be used to remove it later.
+    # A handler should return this value to indicate that the event has been consumed, and no further
+    # processing should take place.  The event does not propagate to the underlying page.
+    @stopBubblingAndFalse = new Object()
+
+    # A handler should return this value to indicate that bubbling should be restarted.  Typically, this is
+    # used when, while bubbling an event, a new mode is pushed onto the stack.
+    @restartBubbling = new Object()
+
+  # Adds a handler to the top of the stack. Returns a unique ID for that handler that can be used to remove it
+  # later.
   push: (handler) ->
-    handler.id = @genId()
+    handler._name ||= "anon-#{@counter}"
     @stack.push handler
-    handler.id
+    handler.id = ++@counter
+
+  # As above, except the new handler is added to the bottom of the stack.
+  unshift: (handler) ->
+    handler._name ||= "anon-#{@counter}"
+    handler._name += "/unshift"
+    @stack.unshift handler
+    handler.id = ++@counter
 
-  # Called whenever we receive a key event. Each individual handler has the option to stop the event's
-  # propagation by returning a falsy value.
+  # Called whenever we receive a key or other event. Each individual handler has the option to stop the
+  # event's propagation by returning a falsy value, or stop bubbling by returning @stopBubblingAndFalse or
+  # @stopBubblingAndTrue.
   bubbleEvent: (type, event) ->
-    for i in [(@stack.length - 1)..0] by -1
-      handler = @stack[i]
-      # We need to check for existence of handler because the last function call may have caused the release
-      # of more than one handler.
-      if handler && handler[type]
+    @eventNumber += 1
+    # We take a copy of the array in order to avoid interference from concurrent removes (for example, to
+    # avoid calling the same handler twice, because elements have been spliced out of the array by remove).
+    for handler in @stack[..].reverse()
+      # A handler may have been removed (handler.id == null), so check.
+      if handler?.id and handler[type]
         @currentId = handler.id
-        passThrough = handler[type].call(@, event)
-        if not passThrough
-          DomUtils.suppressEvent(event)
+        result = handler[type].call @, event
+        @logResult type, event, handler, result if @debug
+        if not result
+          DomUtils.suppressEvent event  if @isChromeEvent event
           return false
+        return true if result == @stopBubblingAndTrue
+        return false if result == @stopBubblingAndFalse
+        return @bubbleEvent type, event if result == @restartBubbling
     true
 
   remove: (id = @currentId) ->
     for i in [(@stack.length - 1)..0] by -1
       handler = @stack[i]
       if handler.id == id
+        # Mark the handler as removed.
+        handler.id = null
         @stack.splice(i, 1)
         break
+
+  # The handler stack handles chrome events (which may need to be suppressed) and internal (pseudo) events.
+  # This checks whether the event at hand is a chrome event.
+  isChromeEvent: (event) ->
+    event?.preventDefault? or event?.stopImmediatePropagation?
+
+  # Convenience wrappers.  Handlers must return an approriate value.  These are wrappers which handlers can
+  # use to always return the same value.  This then means that the handler itself can be implemented without
+  # regard to its return value.
+  alwaysContinueBubbling: (handler) ->
+    handler()
+    true
+
+  neverContinueBubbling: (handler) ->
+    handler()
+    false
+
+  # Debugging.
+  logResult: (type, event, handler, result) ->
+    # FIXME(smblott).  Badge updating is too noisy, so we filter it out.  However, we do need to look at how
+    # many badge update events are happening.  It seems to be more than necessary. We also filter out
+    # registerKeyQueue as unnecessarily noisy and not particularly helpful.
+    return if type in [ "updateBadge", "registerKeyQueue" ]
+    label =
+      switch result
+        when @stopBubblingAndTrue then "stop/true"
+        when @stopBubblingAndFalse then "stop/false"
+        when @restartBubbling then "rebubble"
+        when true then "continue"
+    label ||= if result then "continue/truthy" else "suppress"
+    console.log "#{@eventNumber}", type, handler._name, label
+
+root.HandlerStack = HandlerStack
+root.handlerStack = new HandlerStack()