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diff --git a/background_scripts/sync.coffee b/background_scripts/sync.coffee
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+
+#
+# * Sync.set() and Sync.clear() propagate local changes to chrome.storage.
+# * Sync.listener() listens for changes to chrome.storage and propagates those
+#   changes to localStorage and into vimium's internal state.
+# * Sync.pull() polls chrome.storage at startup, similarly propagating changes
+#   to localStorage and into vimium's internal state.
+#
+# Changes are propagated into vimium's state using the same mechanism that is
+# used when options are changed on the options page.
+#
+# The effect is best-effort synchronization of vimium options/settings between
+# chrome/vimium instances, whenever:
+#   - chrome is logged in to the user's Google account, and
+#   - chrome synchronization is enabled.
+#
+# NOTE:
+#   Values handled within this module are ALWAYS already JSON.stringifed, so
+#   they're always non-empty strings.
+#
+
+console.log ">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>"
+root = exports ? window
+root.Sync = Sync = 
+
+  # ##################
+  # constants
+
+  debug: true
+  storage: chrome.storage.sync
+  doNotSync: [ "settingsVersion", "previousVersion" ]
+
+  init: ->
+    chrome.storage.onChanged.addListener (changes, area) -> Sync.listener changes, area
+    @pull()
+    @log "Sync.init()"
+
+  # asynchronous fetch from synced storage, called at startup
+  pull: ->
+    @storage.get null, (items) ->
+      Sync.log "pull callback: #{Sync.callbackStatus()}"
+      if not chrome.runtime.lastError
+        for own key, value of items
+          Sync.storeAndPropagate key, value
+
+  # asynchronous message from synced storage
+  listener: (changes, area) ->
+    @log "listener: #{area}"
+    for own key, change of changes
+      @storeAndPropagate key, change.newValue
+  
+  # only ever called from asynchronous synced-storage callbacks (pull and listener)
+  storeAndPropagate: (key, value) ->
+    # must be JSON.stringifed or undefined
+    @checkHaveStringOrUndefined value
+    # ignore, if not accepting this key
+    if not @syncKey key
+       @log "callback ignoring: #{key}"
+       return
+    # ignore, if unchanged
+    if localStorage[key] == value
+       @log "callback unchanged: #{key}"
+       return
+
+    # ok: accept, store and propagate update
+    defaultValue = root.Settings.defaults[key]
+    defaultValueJSON = JSON.stringify(defaultValue) # could cache this to avoid repeated recalculation
+
+    if value && value != defaultValueJSON
+      # key/value has been changed to non-default value at remote instance
+      @log "callback set: #{key}=#{value}"
+      localStorage[key] = value
+      root.Settings.doPostUpdateHook key, JSON.parse(value)
+    else
+      # key has been reset to default value at remote instance
+      @log "callback clear: #{key}=#{value}"
+      delete localStorage[key]
+      root.Settings.doPostUpdateHook key, defaultValue
+
+  # only called synchronously from within vimium, never on a callback
+  # no need to propagate updates into the rest of vimium (because that will already have been handled externally)
+  set: (key, value) ->
+    # value must be JSON.stringifed
+    @checkHaveString value
+    if value
+      if @syncKey key
+        @storage.set @mkKeyValue(key,value), -> Sync.logCallback "DONE set", key
+        @log "set scheduled: #{key}=#{value}"
+    else
+      # unreachable? (because value is a JSON string)
+      @log "UNREACHABLE in Sync.set(): #{key}"
+      @clear key
+
+  # only called synchronously from within vimium, never on a callback
+  # no need to propagate updates into the rest of  vimium (because that will already have been handled by externally)
+  clear: (key) ->
+    if @syncKey key
+      @storage.remove key, -> Sync.logCallback "DONE clear", key
+      @log "clear scheduled: #{key}"
+
+  # ##################
+  # utilities 
+
+  syncKey: (key) ->
+    key not in @doNotSync
+
+  # there has to be a more elegant way to do this!
+  mkKeyValue: (key, value) ->
+    obj = {}
+    obj[key] = value
+    obj
+
+  # debugging messages
+  # disable these by setting root.Sync.debug to anything falsy
+  log: (msg) ->
+    console.log "sync debug: #{msg}" if @debug
+
+  logCallback: (where, key) ->
+    @log "#{where} callback: #{key} #{@callbackStatus()}"
+
+  callbackStatus: ->
+    if chrome.runtime.lastError then "ERROR: #{chrome.runtime.lastError.message}" else "(OK)"
+
+  checkHaveString: (thing) ->
+    if typeof(thing) != "string" or not thing
+      @log "sync.coffee: Yikes! this should be a non-empty string: #{typeof(thing)} #{thing}"
+
+  checkHaveStringOrUndefined: (thing) ->
+    if ( typeof(thing) != "string" and typeof(thing) != "undefined" ) or ( typeof(thing) == "string" and not thing )
+      @log "sync.coffee: Yikes! this should be a non-empty string or undefined: #{typeof(thing)} #{thing}"
+  
+  # end of Sync object
+  # ##################
+
+Sync.init()
+