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.Time (getClockTime)
   8 import System.IO (hPutStrLn, stderr)
   9
  10 import CommandLine
  11 import ExitCodes
  12 import Mail
  13 import Twitter.Http
  14 import Twitter.Status
  15 import Twitter.User
  16
  17
  18 -- |The length of all calls to sleep (or threadDelay), in seconds.
  19 heartbeat :: Int
  20 heartbeat = 600
  21
  22 -- |A wrapper around threadDelay which takes seconds instead of
  23 -- microseconds as its argument.
  24 thread_sleep :: Int -> IO ()
  25 thread_sleep seconds = do
  26   let microseconds = seconds * (10 ^ (6 :: Int))
  27   threadDelay microseconds
  28
  29
  30 -- |Given a 'Message', 'Status', and date, update that message's body
  31 -- and subject with the information contained in the status. Adds a
  32 -- /Date: / header, and returns the updated message.
  33 message_from_status :: Message -> String -> Status -> Message
  34 message_from_status message date status =
  35     message { subject = "Twat: " ++ (screen_name (user status)),
  36               body    = (pretty_print status),
  37               headers = ((headers message) ++ ["Date: " ++ date])}
  38
  39
  40 -- |This is the main recursive loop. It takes a username, a
  41 -- latest_status_id, and optionally a 'Message' as arguments. The
  42 -- latest_status_id is the last status (that we know of) to be posted
  43 -- to username's Twitter account. If we find any newer statuses when
  44 -- we check, they are printed and optionally emailed (if a 'Message'
  45 -- was supplied). Then, the process repeats.
  46 recurse :: String -> Integer -> (Maybe Message) -> IO ()
  47 recurse username latest_status_id maybe_message = do
  48     thread_sleep heartbeat
  49     xmldata <- get_user_new_statuses username latest_status_id
  50
  51     -- Parsing an empty result can blow up. Just pretend there are
  52     -- no new statuses in that case.
  53     let new_statuses = case xmldata of
  54                          Just xml -> parse_statuses xml
  55                          Nothing  -> []
  56
  57     case (length new_statuses) of
  58       0 ->
  59         recurse username latest_status_id maybe_message
  60       _ -> do
  61         let new_latest_status_id = get_max_status_id new_statuses
  62         mapM (putStrLn . pretty_print) new_statuses
  63
  64         case maybe_message of
  65           Nothing -> do
  66              recurse username new_latest_status_id maybe_message
  67              return ()
  68           Just message -> do
  69              date <- getClockTime
  70              let messages = map (message_from_status message (show date)) new_statuses
  71              sendmail_results <- mapM sendmail messages
  72              mapM print_sendmail_result sendmail_results
  73              recurse username new_latest_status_id maybe_message
  74              return ()
  75
  76
  77 -- |Try continually to download username's timeline, and determine the
  78 -- latest status id to be posted once we have done so.
  79 get_latest_status_id :: String -> IO Integer
  80 get_latest_status_id username = do
  81   xmldata <- get_user_timeline username
  82
  83   let initial_statuses = case xmldata of
  84                            Just xml -> parse_statuses xml
  85                            Nothing -> []
  86
  87   case (length initial_statuses) of
  88     0 -> do
  89       -- If the HTTP part barfs, try again after a while.
  90       putStrLn ("Couldn't retrieve " ++ username ++ "'s timeline. Retrying...")
  91       thread_sleep heartbeat
  92       get_latest_status_id username
  93     _ -> return (get_max_status_id initial_statuses)
  94
  95
  96
  97 -- |This function wraps two steps. First, we need to find the latest
  98 -- status id posted by username. Once we have that, we can begin the
  99 -- recursive loop that checks for updates forever. The message
 100 -- argument is optional and is passed to recurse in case the updates
 101 -- should be emailed.
 102 run_twat :: Maybe Message -> String -> IO ()
 103 run_twat message username = do
 104   latest_status_id <- get_latest_status_id username
 105   recurse username latest_status_id message
 106   return ()
 107
 108
 109 -- |The main function just parses the command-line arguments and then
 110 -- forks off calls to 'run_twat' for each supplied username. After
 111 -- forking, main loops forever.
 112 main :: IO ()
 113 main = do
 114   errors <- parse_errors
 115
 116   -- If there  were errors parsing the command-line options,
 117   -- print them and exit.
 118   when (not (null errors)) $ do
 119       hPutStrLn stderr (concat errors)
 120       putStrLn help_text
 121       exitWith (ExitFailure exit_args_parse_failed)
 122
 123   -- Next, check to see if the 'help' option was passed to the
 124   -- program. If it was, display the help, and exit successfully.
 125   help_opt_set <- help_set
 126   when help_opt_set $ do
 127       putStrLn help_text
 128       exitWith ExitSuccess
 129
 130   usernames <- parse_usernames
 131
 132   -- If we have both a "To" and "From" address, we'll create a
 133   -- message object to be passed to all of our threads.
 134   to_address <- to_email_address
 135   from_address <- from_email_address
 136   let message = case to_address of
 137                   Nothing -> Nothing
 138                   Just toaddr ->
 139                       case from_address of
 140                         Nothing -> Nothing
 141                         Just fromaddr ->
 142                             Just (Message { headers = [],
 143                                             body = "",
 144                                             subject = "",
 145                                             to = toaddr,
 146                                             from = fromaddr })
 147
 148   -- Execute run_twat on each username in a new thread.
 149   mapM (forkIO . (run_twat message)) usernames
 150
 151   forever $ do
 152     -- This thread (the one executing main) doesn't do anything,
 153     -- but when it terminates, so do all the threads we forked.
 154     -- As a result, we need to keep this thread on life support.
 155     thread_sleep heartbeat
 156
 157   return ()