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
   5 module CommandLine
   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_help  :: Bool,
  22                          opt_from :: Maybe String,
  23                          opt_to :: Maybe String }
  24
  25
  26 -- This constructs an instance of Options, with each of its members
  27 -- set to default values.
  28 default_options :: Options
  29 default_options = Options { opt_help = False,
  30                             opt_from = Nothing,
  31                             opt_to = Nothing }
  32
  33
  34 -- The options list that we construct associates a function with each
  35 -- option. This function is responsible for updating an Options record
  36 -- with the appropriate value.
  37 --
  38 -- For more information and an example of this idiom, see,
  39 --
  40 -- http://www.haskell.org/haskellwiki/High-level_option_handling_with_GetOpt
  41 --
  42 options :: [OptDescr (Options -> IO Options)]
  43 options =
  44   [ Option ['h'][] (NoArg set_help) "Prints this help message.",
  45     Option ['t'][] (ReqArg set_to "email_address") "Send tweets TO email_address.",
  46     Option ['f'][] (ReqArg set_from "email_address") "Send tweets FROM email_address."
  47   ]
  48
  49
  50 set_help :: Options -> IO Options
  51 set_help opts = do
  52   return opts { opt_help = True }
  53
  54 set_to :: String -> Options -> IO Options
  55 set_to arg opts = do
  56   return opts { opt_to = Just arg }
  57
  58 set_from :: String -> Options -> IO Options
  59 set_from arg opts = do
  60   return opts { opt_from = Just arg }
  61
  62
  63 -- The usage header.
  64 usage :: String
  65 usage = "Usage: twat [-t to_address] [-f from_address] <username1> [username2, [username3]...]"
  66
  67
  68 -- The usage header, and all available flags (as generated by GetOpt)
  69 help_text :: String
  70 help_text = usageInfo usage options
  71
  72
  73 -- Return a list of options.
  74 parse_options :: IO Options
  75 parse_options = do
  76   argv <- getArgs
  77   let (actions, _, _) = getOpt Permute options argv
  78
  79   -- This will execute each of the functions contained in our options
  80   -- list, one after another, on a default_options record. The end
  81   -- result should be an Options instance with all of its members set
  82   -- correctly.
  83   opts <- foldl (>>=) (return default_options) actions
  84
  85   return opts
  86
  87
  88 username_errors :: IO [String]
  89 username_errors = do
  90   argv <- getArgs
  91   let (_, usernames, _) = getOpt Permute options argv
  92
  93   if (null usernames)
  94     then return ["No usernames provided."]
  95     else return []
  96
  97
  98 to_errors :: IO [String]
  99 to_errors = do
 100   toaddr <- to_email_address
 101   fromaddr <- from_email_address
 102   if (isNothing toaddr) && (isJust fromaddr)
 103     then return ["\"From\" address specified without \"To\" address."]
 104     else return []
 105
 106 from_errors :: IO [String]
 107 from_errors = do
 108   toaddr <- to_email_address
 109   fromaddr <- from_email_address
 110   if (isJust toaddr) && (isNothing fromaddr)
 111     then return ["\"To\" address specified without \"From\" address."]
 112     else return []
 113
 114
 115 format_error :: String -> String
 116 format_error err = "ERROR: " ++ err ++ "\n"
 117
 118
 119 -- Return a list of errors.
 120 parse_errors :: IO [String]
 121 parse_errors = do
 122   argv <- getArgs
 123   let (_, _, errors) = getOpt Permute options argv
 124   errs_username <- username_errors
 125   errs_to <- to_errors
 126   errs_from <- from_errors
 127   return $ map format_error (errors ++ errs_username ++ errs_to ++ errs_from)
 128
 129 -- Is the help option set?
 130 help_set :: IO Bool
 131 help_set = do
 132     opts <- parse_options
 133     return (opt_help opts)
 134
 135
 136 to_email_address :: IO (Maybe String)
 137 to_email_address = do
 138     opts <- parse_options
 139     return (opt_to opts)
 140
 141 from_email_address :: IO (Maybe String)
 142 from_email_address = do
 143     opts <- parse_options
 144     return (opt_from opts)
 145
 146
 147 parse_usernames :: IO [String]
 148 parse_usernames = do
 149   argv <- getArgs
 150   let (_, usernames, _) = getOpt Permute options argv
 151   return usernames