src/Main.hs

   1 module Main
   2 where
   3
   4 import Control.Concurrent (forkIO, threadDelay)
   5 import Control.Monad (forever, when)
   6 import System.Exit (ExitCode(..), exitWith)
   7 import System.IO (hPutStrLn, stderr)
   8
   9 import CommandLine
  10 import ExitCodes
  11 import Mail
  12 import Twitter.Http
  13 import Twitter.Status
  14 import Twitter.User
  15
  16
  17 -- |The length of all calls to sleep (or threadDelay), in seconds.
  18 heartbeat :: Int
  19 heartbeat = 600
  20
  21 -- |A wrapper around threadDelay which takes seconds instead of
  22 -- microseconds as its argument.
  23 thread_sleep :: Int -> IO ()
  24 thread_sleep seconds = do
  25   let microseconds = seconds * (10 ^ (6 :: Int))
  26   threadDelay microseconds
  27
  28
  29 -- |Given a 'Message' and a 'Status', update that message's body and
  30 -- subject with the information contained in the status. Returns the
  31 -- updated message.
  32 message_from_status :: Message -> Status -> Message
  33 message_from_status message status =
  34     message { subject = "Twat: " ++ (screen_name (user status)),
  35               body    = (pretty_print status) }
  36
  37
  38 -- |This is the main recursive loop. It takes a username, a
  39 -- latest_status_id, and optionally a 'Message' as arguments. The
  40 -- latest_status_id is the last status (that we know of) to be posted
  41 -- to username's Twitter account. If we find any newer statuses when
  42 -- we check, they are printed and optionally emailed (if a 'Message'
  43 -- was supplied). Then, the process repeats.
  44 recurse :: String -> Integer -> (Maybe Message) -> IO ()
  45 recurse username latest_status_id maybe_message = do
  46     thread_sleep heartbeat
  47     xmldata <- get_user_new_statuses username latest_status_id
  48
  49     -- Parsing an empty result can blow up. Just pretend there are
  50     -- no new statuses in that case.
  51     let new_statuses = case xmldata of
  52                          Just xml -> parse_statuses xml
  53                          Nothing  -> []
  54
  55     case (length new_statuses) of
  56       0 ->
  57         recurse username latest_status_id maybe_message
  58       _ -> do
  59         let new_latest_status_id = get_max_status_id new_statuses
  60         mapM (putStrLn . pretty_print) new_statuses
  61
  62         case maybe_message of
  63           Nothing -> do
  64              recurse username new_latest_status_id maybe_message
  65              return ()
  66           Just message -> do
  67              let messages = map (message_from_status message) new_statuses
  68              sendmail_results <- mapM sendmail messages
  69              mapM print_sendmail_result sendmail_results
  70              recurse username new_latest_status_id maybe_message
  71              return ()
  72
  73
  74 -- |Try continually to download username's timeline, and determine the
  75 -- latest status id to be posted once we have done so.
  76 get_latest_status_id :: String -> IO Integer
  77 get_latest_status_id username = do
  78   xmldata <- get_user_timeline username
  79
  80   let initial_statuses = case xmldata of
  81                            Just xml -> parse_statuses xml
  82                            Nothing -> []
  83
  84   case (length initial_statuses) of
  85     0 -> do
  86       -- If the HTTP part barfs, try again after a while.
  87       putStrLn ("Couldn't retrieve " ++ username ++ "'s timeline. Retrying...")
  88       thread_sleep heartbeat
  89       get_latest_status_id username
  90     _ -> return (get_max_status_id initial_statuses)
  91
  92
  93
  94 -- |This function wraps two steps. First, we need to find the latest
  95 -- status id posted by username. Once we have that, we can begin the
  96 -- recursive loop that checks for updates forever. The message
  97 -- argument is optional and is passed to recurse in case the updates
  98 -- should be emailed.
  99 run_twat :: Maybe Message -> String -> IO ()
 100 run_twat message username = do
 101   latest_status_id <- get_latest_status_id username
 102   recurse username latest_status_id message
 103   return ()
 104
 105
 106 -- |The main function just parses the command-line arguments and then
 107 -- forks off calls to 'run_twat' for each supplied username. After
 108 -- forking, main loops forever.
 109 main :: IO ()
 110 main = do
 111   errors <- parse_errors
 112
 113   -- If there  were errors parsing the command-line options,
 114   -- print them and exit.
 115   when (not (null errors)) $ do
 116       hPutStrLn stderr (concat errors)
 117       putStrLn help_text
 118       exitWith (ExitFailure exit_args_parse_failed)
 119
 120   -- Next, check to see if the 'help' option was passed to the
 121   -- program. If it was, display the help, and exit successfully.
 122   help_opt_set <- help_set
 123   when help_opt_set $ do
 124       putStrLn help_text
 125       exitWith ExitSuccess
 126
 127   usernames <- parse_usernames
 128
 129   -- If we have both a "To" and "From" address, we'll create a
 130   -- message object to be passed to all of our threads.
 131   to_address <- to_email_address
 132   from_address <- from_email_address
 133   let message = case to_address of
 134                   Nothing -> Nothing
 135                   Just toaddr ->
 136                       case from_address of
 137                         Nothing -> Nothing
 138                         Just fromaddr ->
 139                             Just (Message { headers = [],
 140                                             body = "",
 141                                             subject = "",
 142                                             to = toaddr,
 143                                             from = fromaddr })
 144
 145   -- Execute run_twat on each username in a new thread.
 146   mapM (forkIO . (run_twat message)) usernames
 147
 148   forever $ do
 149     -- This thread (the one executing main) doesn't do anything,
 150     -- but when it terminates, so do all the threads we forked.
 151     -- As a result, we need to keep this thread on life support.
 152     thread_sleep heartbeat
 153
 154   return ()