src/CommandLine.hs

   1 -- |The CommandLine module handles parsing of the command-line options.
   2 -- It should more or less be a black box, providing Main with only the
   3 -- information it requires.
   4 module CommandLine
   5 ( heartbeat,
   6   help_set,
   7   help_text,
   8   from_email_address,
   9   to_email_address,
  10   parse_errors,
  11   parse_usernames
  12 ) where
  13
  14 import Data.Maybe (isJust, isNothing)
  15 import System.Console.GetOpt
  16 import System.Environment (getArgs)
  17
  18
  19
  20 -- |A record containing values for all available options.
  21 data Options = Options { opt_heartbeat :: Maybe Int,
  22                          opt_help  :: Bool,
  23                          opt_from :: Maybe String,
  24                          opt_to :: Maybe String }
  25
  26
  27 -- |Constructs an instance of Options, with each of its members set to
  28 -- default values.
  29 default_options :: Options
  30 default_options = Options { opt_heartbeat = Just 600,
  31                             opt_help = False,
  32                             opt_from = Nothing,
  33                             opt_to = Nothing }
  34
  35
  36 -- |The options list that we construct associates a function with each
  37 -- option. This function is responsible for updating an Options record
  38 -- with the appropriate value.
  39 --
  40 -- For more information and an example of this idiom, see,
  41 --
  42 -- <http://www.haskell.org/haskellwiki/High-level_option_handling_with_GetOpt>
  43 --
  44 options :: [OptDescr (Options -> IO Options)]
  45 options =
  46   [ Option ['h'][] (NoArg set_help) "Prints this help message.",
  47     Option ['n'][] (ReqArg set_heartbeat "heartbeat") "How many seconds to wait between polling.",
  48     Option ['t'][] (ReqArg set_to "email_address") "Send tweets TO email_address.",
  49     Option ['f'][] (ReqArg set_from "email_address") "Send tweets FROM email_address."
  50   ]
  51
  52
  53 -- | Attempt to parse an 'Int' from a 'String'. This is just a 'Maybe'
  54 --   wrapper around 'reads'.
  55 parse_int :: String -> Maybe Int
  56 parse_int s =
  57   case (reads s) of
  58     [(n,_)]   -> Just n
  59     _         -> Nothing
  60
  61 set_heartbeat :: String -> Options -> IO Options
  62 set_heartbeat arg opts = do
  63   let new_heartbeat = parse_int arg
  64   return opts { opt_heartbeat = new_heartbeat }
  65
  66 set_help :: Options -> IO Options
  67 set_help opts = do
  68   return opts { opt_help = True }
  69
  70 set_to :: String -> Options -> IO Options
  71 set_to arg opts = do
  72   return opts { opt_to = Just arg }
  73
  74 set_from :: String -> Options -> IO Options
  75 set_from arg opts = do
  76   return opts { opt_from = Just arg }
  77
  78
  79 -- The usage header.
  80 usage :: String
  81 usage = "Usage: twat [-n heartbeat] [-t to_address] [-f from_address] <username1> [username2, [username3]...]"
  82
  83
  84 -- The usage header, and all available flags (as generated by GetOpt)
  85 help_text :: String
  86 help_text = usageInfo usage options
  87
  88
  89 -- Return a list of options.
  90 parse_options :: IO Options
  91 parse_options = do
  92   argv <- getArgs
  93   let (actions, _, _) = getOpt Permute options argv
  94
  95   -- This will execute each of the functions contained in our options
  96   -- list, one after another, on a default_options record. The end
  97   -- result should be an Options instance with all of its members set
  98   -- correctly.
  99   opts <- foldl (>>=) (return default_options) actions
 100
 101   return opts
 102
 103
 104 -- | A list of parse errors relating to the heartbeat.
 105 heartbeat_errors :: IO [String]
 106 heartbeat_errors = do
 107   hb <- heartbeat
 108   if (isNothing hb)
 109     then return ["\"heartbeat\" does not appear to be an integer."]
 110     else return []
 111
 112 -- |Parse errors relating to the list of usernames.
 113 username_errors :: IO [String]
 114 username_errors = do
 115   argv <- getArgs
 116   let (_, usernames, _) = getOpt Permute options argv
 117
 118   if (null usernames)
 119     then return ["no usernames provided."]
 120     else return []
 121
 122
 123 -- |Parse errors relating to the "To" address.
 124 to_errors :: IO [String]
 125 to_errors = do
 126   toaddr <- to_email_address
 127   fromaddr <- from_email_address
 128   if (isNothing toaddr) && (isJust fromaddr)
 129     then return ["\"from\" address specified without \"to\" address."]
 130     else return []
 131
 132
 133 -- |Parse errors relating to the "From" address.
 134 from_errors :: IO [String]
 135 from_errors = do
 136   toaddr <- to_email_address
 137   fromaddr <- from_email_address
 138   if (isJust toaddr) && (isNothing fromaddr)
 139     then return ["\"to\" address specified without \"from\" address."]
 140     else return []
 141
 142
 143 -- |Format an error message for printing.
 144 format_error :: String -> String
 145 format_error err = "ERROR: " ++ err ++ "\n"
 146
 147
 148 -- |Return a list of all parse errors.
 149 parse_errors :: IO [String]
 150 parse_errors = do
 151   argv <- getArgs
 152   let (_, _, errors) = getOpt Permute options argv
 153   errs_heartbeat <- heartbeat_errors
 154   errs_username <- username_errors
 155   errs_to <- to_errors
 156   errs_from <- from_errors
 157   return $ map format_error (errors ++
 158                              errs_heartbeat ++
 159                              errs_username ++
 160                              errs_to ++
 161                              errs_from)
 162
 163 -- |Was the "help" option passed on the command line?
 164 help_set :: IO Bool
 165 help_set = do
 166     opts <- parse_options
 167     return (opt_help opts)
 168
 169 -- |What's the heartbeat?
 170 heartbeat :: IO (Maybe Int)
 171 heartbeat = do
 172   opts <- parse_options
 173   return (opt_heartbeat opts)
 174
 175 -- |What "To" address was given on the command line?
 176 to_email_address :: IO (Maybe String)
 177 to_email_address = do
 178     opts <- parse_options
 179     return (opt_to opts)
 180
 181 -- |What "From" address was given on the command line?
 182 from_email_address :: IO (Maybe String)
 183 from_email_address = do
 184     opts <- parse_options
 185     return (opt_from opts)
 186
 187
 188 -- |What usernames were passed on the command line?
 189 parse_usernames :: IO [String]
 190 parse_usernames = do
 191   argv <- getArgs
 192   let (_, usernames, _) = getOpt Permute options argv
 193   return usernames