Add sync functionality

lib/google/calendar.rb

@@ -222,6 +222,39 @@ def events
       event_lookup()
     end
 
+    #
+    # Find all of the events associated with this calendar with the intention
+    # of future incremental syncing.
+    #
+    # This method is not useful if you do not store the returned next_sync_token.
+    #
+    #  Returns:
+    #   a hash with a next_sync_token plus an empty [:events] array if nothing found.
+    #   a hash with a next_sync_token plus an array with one element if only one event found.
+    #   a hash with a next_sync_token plus an array of events if many found.
+    #
+    def initial_sync
+      sync_event_lookup('', nil, nil)
+    end
+
+    #
+    # Find all new and updated events associated with this calendar using a
+    # sync_token. Use page tokens if the returned :events are paginated.
+    #
+    # This method is not useful if you do not store the returned
+    # next_sync_token if it does not equal the provided sync_token.
+    #
+    #  Returns:
+    #   a hash with a next_sync_token plus an empty [:events] array if nothing found.
+    #   a hash with a next_sync_token plus an array with one element if only one event found.
+    #   a hash with a next_sync_token plus an array of events if many found.
+    #   a hash with a next_sync_token and page_token, plus an array of events if many found.
+    #
+    def incremental_sync(sync_token: '', page_token: nil)
+      page_token_string = page_token == nil ? '' : "&pageToken=#{page_token}"
+      sync_event_lookup("?syncToken=#{sync_token}#{page_token_string}", sync_token, page_token)
+    end
+
     #
     # This is equivalent to running a search in the Google calendar web application.
     # Google does not provide a way to specify what attributes you would like to
@@ -476,6 +509,19 @@ def event_lookup(query_string = '') #:nodoc:
       end
     end
 
+    #
+    # Utility method used to centralize sync event lookup.
+    #
+    def sync_event_lookup(query_string = '', next_sync_token, next_page_token) #:nodoc:
+      begin
+        response = send_events_request(query_string, :get)
+        parsed_json = JSON.parse(response.body)
+        sync_events = Synchronize.synchronize_hash(parsed_json, self) || {}
+      rescue Google::HTTPNotFound
+        return { events: [], next_sync_token: next_sync_token, next_page_token: next_page_token }
+      end
+    end
+
     #
     # Utility method used to centralize event setup
     #

lib/google/synchronize.rb

@@ -0,0 +1,19 @@
+module Google
+  class Synchronize
+    #
+    # Convenience method used to build a hash for incremental sync.
+    # Includes events from a Google feed plus necessary synchronization tokens.
+    #
+    def self.synchronize_hash(response, calendar)
+      events = Event.build_from_google_feed(response, calendar)
+      unless events.empty?
+        events = events.length > 1 ? events : [events[0]]
+      end
+      result = { events: events }
+      result[:next_sync_token] = response['nextSyncToken'] if response['nextSyncToken']
+      result[:next_page_token] = response['nextPageToken'] if response['nextPageToken']
+
+      return result
+    end
+  end
+end

lib/google_calendar.rb

@@ -6,4 +6,5 @@ module Google
   require 'google/connection'
   require 'google/event'
   require 'google/freebusy'
+  require 'google/synchronize'
 end