From fa49f0f0c664f9661878937f45f5d813e4b7891a Mon Sep 17 00:00:00 2001
From: "David N. Welton" <davidw@dedasys.com>
Date: Fri, 4 Jun 2010 17:44:51 +0200
Subject: [PATCH] Retool to use gen_event instead of our own callback.

I don't know if it's really an improvement, but hey, it was kind of
fun to do, and this way we can have multiple callbacks fairly easily.
---
 src/twitter_stream.erl     | 53 ++++++++++++++++++++++++++++----------
 src/twitter_stream_sup.erl |  4 +--
 2 files changed, 41 insertions(+), 16 deletions(-)

diff --git a/src/twitter_stream.erl b/src/twitter_stream.erl
index 30e6113..dd3f106 100644
--- a/src/twitter_stream.erl
+++ b/src/twitter_stream.erl
@@ -33,8 +33,8 @@
 
 
 %% API
--export([start_link/2]).
--export([fetch/2]).
+-export([start_link/1]).
+-export([fetch/2, add_handler/1, add_handler/2]).
 
 %% gen_server callbacks
 -export([init/1, handle_call/3, handle_cast/2, handle_info/2,
@@ -55,8 +55,18 @@
 %% Function: start_link() -> {ok,Pid} | ignore | {error,Error}
 %% Description: Starts the server
 %%--------------------------------------------------------------------
-start_link(Url, Callback) ->
-    gen_server:start_link(?SERVER, ?MODULE, [Url, Callback], []).
+start_link(Url) ->
+    gen_server:start_link(?SERVER, ?MODULE, [Url], []).
+
+%% Add a handler to receive callbacks.
+
+add_handler(Handler) ->
+    gen_server:call(?MODULE, {add_handler, Handler}).
+
+%% Add a handler with its own eventmanager.
+
+add_handler(EventManager, Handler) ->
+    gen_server:call(?MODULE, {add_handler, EventManager, Handler}).
 
 
 %%====================================================================
@@ -70,10 +80,10 @@ start_link(Url, Callback) ->
 %%                         {stop, Reason}
 %% Description: Initiates the server
 %%--------------------------------------------------------------------
-init([Url, Callback]) ->
+init([Url]) ->
     {ok, EventMgr} = gen_event:start_link(),
     gen_server:cast(?MODULE, {fetch, Url, 1}),
-    {ok, #state{eventmgr = EventMgr, callback = Callback, sleep = 1, url = Url}}.
+    {ok, #state{eventmgr = [EventMgr], sleep = 1, url = Url}}.
 
 %%--------------------------------------------------------------------
 %% Function: %% handle_call(Request, From, State) -> {reply, Reply, State} |
@@ -85,6 +95,14 @@ init([Url, Callback]) ->
 %% Description: Handling call messages
 %%--------------------------------------------------------------------
 
+handle_call({add_handler, EventManager, _Handler}, _From, State) ->
+    EventManList = State#state.eventmgr ++ [EventManager],
+    {reply, ok, State#state{eventmgr = EventManList}};
+
+handle_call({add_handler, Handler}, _From, State) ->
+    ok = gen_event:add_handler(State#state.eventmgr, Handler, []),
+    {reply, ok, State};
+
 handle_call(_Request, _From, State) ->
     {reply, ok, State}.
 
@@ -136,10 +154,13 @@ handle_info({http, Rest}, State) ->
 	%% Ignore it if it's empty.
 	{_RequestId, stream, Data} when Data == <<"\r\n">> ->
 	    ok;
+
+	%% This is where we actually do something!
 	{_RequestId, stream, Data} ->
-	    %% Call the gen_event stuff...
-	    {M, F, A} = State#state.callback,
-	    spawn(M, F, [A ++ [fill_status_rec(mochijson2:decode(Data))]]);
+	    Tweet = fill_status_rec(mochijson2:decode(Data)),
+	    notify_all_managers(State, {tweet, Tweet});
+%	    {M, F, A} = State#state.callback,
+%	    spawn(M, F, [A ++ [Tweet]]);
 	%% end of streaming data - we just restart in this case,
 	%% because we want a never-ending stream.
 	{_RequestId, stream_end, Headers} ->
@@ -169,11 +190,6 @@ terminate(_Reason, _State) ->
 code_change(_OldVsn, State, _Extra) ->
     {ok, State}.
 
-%%--------------------------------------------------------------------
-%%% Internal functions
-%%--------------------------------------------------------------------
-
-
 %% 3 arg version expects url of the form http://user:password@stream.twitter.com/1/statuses/sample.json
 %% retry - number of times the stream is reconnected
 %% sleep - secs to sleep between retries.
@@ -244,3 +260,12 @@ fill_status_rec(Tweet) ->
       user = 		fill_user_rec(element(2, lists:keyfind(<<"user">>, 1, Data)))
      },
     Status.
+
+%% Cycle through the list of event managers and send the message to
+%% all of them.
+
+notify_all_managers(State, Message) ->
+    lists:foreach(fun(Manager) ->
+			  gen_event:notify(Manager, Message)
+		  end,
+		  State#state.eventmgr).
diff --git a/src/twitter_stream_sup.erl b/src/twitter_stream_sup.erl
index 090dad7..974c631 100644
--- a/src/twitter_stream_sup.erl
+++ b/src/twitter_stream_sup.erl
@@ -8,8 +8,8 @@
 
 %% returns the Spec for the supervisor (called by the
 %% supervisor:start_link above)
-init([Url, Callback]) ->
+init([Url]) ->
     Spec = [{twitter_stream,
-	     {twitter_stream, start_link, [Url, Callback]}, % this gets run via apply(M, F, A)
+	     {twitter_stream, start_link, [Url]}, % this gets run via apply(M, F, A)
 	     transient, 2000, worker, [twitter_stream]}],
     {ok, {{one_for_one, 10, 60}, Spec}}.