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 ( help_set,
   6   help_text,
   7   from_email_address,
   8   to_email_address,
   9   parse_errors,
  10   parse_usernames
  11 ) where
  12
  13 import Data.Maybe (isJust, isNothing)
  14 import System.Console.GetOpt
  15 import System.Environment (getArgs)
  16
  17
  18
  19 -- |A record containing values for all available options.
  20 data Options = Options { opt_help  :: Bool,
  21                          opt_from :: Maybe String,
  22                          opt_to :: Maybe String }
  23
  24
  25 -- |Constructs an instance of Options, with each of its members set to
  26 -- default values.
  27 default_options :: Options
  28 default_options = Options { opt_help = False,
  29                             opt_from = Nothing,
  30                             opt_to = Nothing }
  31
  32
  33 -- |The options list that we construct associates a function with each
  34 -- option. This function is responsible for updating an Options record
  35 -- with the appropriate value.
  36 --
  37 -- For more information and an example of this idiom, see,
  38 --
  39 -- <http://www.haskell.org/haskellwiki/High-level_option_handling_with_GetOpt>
  40 --
  41 options :: [OptDescr (Options -> IO Options)]
  42 options =
  43   [ Option ['h'][] (NoArg set_help) "Prints this help message.",
  44     Option ['t'][] (ReqArg set_to "email_address") "Send tweets TO email_address.",
  45     Option ['f'][] (ReqArg set_from "email_address") "Send tweets FROM email_address."
  46   ]
  47
  48
  49 set_help :: Options -> IO Options
  50 set_help opts = do
  51   return opts { opt_help = True }
  52
  53 set_to :: String -> Options -> IO Options
  54 set_to arg opts = do
  55   return opts { opt_to = Just arg }
  56
  57 set_from :: String -> Options -> IO Options
  58 set_from arg opts = do
  59   return opts { opt_from = Just arg }
  60
  61
  62 -- The usage header.
  63 usage :: String
  64 usage = "Usage: twat [-t to_address] [-f from_address] <username1> [username2, [username3]...]"
  65
  66
  67 -- The usage header, and all available flags (as generated by GetOpt)
  68 help_text :: String
  69 help_text = usageInfo usage options
  70
  71
  72 -- Return a list of options.
  73 parse_options :: IO Options
  74 parse_options = do
  75   argv <- getArgs
  76   let (actions, _, _) = getOpt Permute options argv
  77
  78   -- This will execute each of the functions contained in our options
  79   -- list, one after another, on a default_options record. The end
  80   -- result should be an Options instance with all of its members set
  81   -- correctly.
  82   opts <- foldl (>>=) (return default_options) actions
  83
  84   return opts
  85
  86
  87 -- |Parse errors relating to the list of usernames.
  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 -- |Parse errors relating to the "To" address.
  99 to_errors :: IO [String]
 100 to_errors = do
 101   toaddr <- to_email_address
 102   fromaddr <- from_email_address
 103   if (isNothing toaddr) && (isJust fromaddr)
 104     then return ["\"From\" address specified without \"To\" address."]
 105     else return []
 106
 107
 108 -- |Parse errors relating to the "From" address.
 109 from_errors :: IO [String]
 110 from_errors = do
 111   toaddr <- to_email_address
 112   fromaddr <- from_email_address
 113   if (isJust toaddr) && (isNothing fromaddr)
 114     then return ["\"To\" address specified without \"From\" address."]
 115     else return []
 116
 117
 118 -- |Format an error message for printing.
 119 format_error :: String -> String
 120 format_error err = "ERROR: " ++ err ++ "\n"
 121
 122
 123 -- |Return a list of all parse errors.
 124 parse_errors :: IO [String]
 125 parse_errors = do
 126   argv <- getArgs
 127   let (_, _, errors) = getOpt Permute options argv
 128   errs_username <- username_errors
 129   errs_to <- to_errors
 130   errs_from <- from_errors
 131   return $ map format_error (errors ++ errs_username ++ errs_to ++ errs_from)
 132
 133 -- |Was the "help" option passed on the command line?
 134 help_set :: IO Bool
 135 help_set = do
 136     opts <- parse_options
 137     return (opt_help opts)
 138
 139
 140 -- |What "To" address was given on the command line?
 141 to_email_address :: IO (Maybe String)
 142 to_email_address = do
 143     opts <- parse_options
 144     return (opt_to opts)
 145
 146 -- |What "From" address was given on the command line?
 147 from_email_address :: IO (Maybe String)
 148 from_email_address = do
 149     opts <- parse_options
 150     return (opt_from opts)
 151
 152
 153 -- |What usernames were passed on the command line?
 154 parse_usernames :: IO [String]
 155 parse_usernames = do
 156   argv <- getArgs
 157   let (_, usernames, _) = getOpt Permute options argv
 158   return usernames