-- |The CommandLine module handles parsing of the command-line options. -- It should more or less be a black box, providing Main with only the -- information it requires. module CommandLine ( heartbeat, help_set, help_text, from_email_address, to_email_address, parse_errors, parse_usernames ) where import Data.Maybe (isJust, isNothing) import System.Console.GetOpt import System.Environment (getArgs) -- |A record containing values for all available options. data Options = Options { opt_heartbeat :: Maybe Int, opt_help :: Bool, opt_from :: Maybe String, opt_to :: Maybe String } -- |Constructs an instance of Options, with each of its members set to -- default values. default_options :: Options default_options = Options { opt_heartbeat = Just 600, opt_help = False, opt_from = Nothing, opt_to = Nothing } -- |The options list that we construct associates a function with each -- option. This function is responsible for updating an Options record -- with the appropriate value. -- -- For more information and an example of this idiom, see, -- -- -- options :: [OptDescr (Options -> IO Options)] options = [ Option ['h'][] (NoArg set_help) "Prints this help message.", Option ['n'][] (ReqArg set_heartbeat "heartbeat") "How many seconds to wait between polling.", Option ['t'][] (ReqArg set_to "email_address") "Send tweets TO email_address.", Option ['f'][] (ReqArg set_from "email_address") "Send tweets FROM email_address." ] -- | Attempt to parse an 'Int' from a 'String'. This is just a 'Maybe' -- wrapper around 'reads'. parse_int :: String -> Maybe Int parse_int s = case (reads s) of [(n,_)] -> Just n _ -> Nothing set_heartbeat :: String -> Options -> IO Options set_heartbeat arg opts = do let new_heartbeat = parse_int arg return opts { opt_heartbeat = new_heartbeat } set_help :: Options -> IO Options set_help opts = do return opts { opt_help = True } set_to :: String -> Options -> IO Options set_to arg opts = do return opts { opt_to = Just arg } set_from :: String -> Options -> IO Options set_from arg opts = do return opts { opt_from = Just arg } -- The usage header. usage :: String usage = "Usage: twat [-n heartbeat] [-t to_address] [-f from_address] [username2, [username3]...]" -- The usage header, and all available flags (as generated by GetOpt) help_text :: String help_text = usageInfo usage options -- Return a list of options. parse_options :: IO Options parse_options = do argv <- getArgs let (actions, _, _) = getOpt Permute options argv -- This will execute each of the functions contained in our options -- list, one after another, on a default_options record. The end -- result should be an Options instance with all of its members set -- correctly. opts <- foldl (>>=) (return default_options) actions return opts -- | A list of parse errors relating to the heartbeat. heartbeat_errors :: IO [String] heartbeat_errors = do hb <- heartbeat if (isNothing hb) then return ["\"heartbeat\" does not appear to be an integer."] else return [] -- |Parse errors relating to the list of usernames. username_errors :: IO [String] username_errors = do argv <- getArgs let (_, usernames, _) = getOpt Permute options argv if (null usernames) then return ["no usernames provided."] else return [] -- |Parse errors relating to the "To" address. to_errors :: IO [String] to_errors = do toaddr <- to_email_address fromaddr <- from_email_address if (isNothing toaddr) && (isJust fromaddr) then return ["\"from\" address specified without \"to\" address."] else return [] -- |Parse errors relating to the "From" address. from_errors :: IO [String] from_errors = do toaddr <- to_email_address fromaddr <- from_email_address if (isJust toaddr) && (isNothing fromaddr) then return ["\"to\" address specified without \"from\" address."] else return [] -- |Format an error message for printing. format_error :: String -> String format_error err = "ERROR: " ++ err ++ "\n" -- |Return a list of all parse errors. parse_errors :: IO [String] parse_errors = do argv <- getArgs let (_, _, errors) = getOpt Permute options argv errs_heartbeat <- heartbeat_errors errs_username <- username_errors errs_to <- to_errors errs_from <- from_errors return $ map format_error (errors ++ errs_heartbeat ++ errs_username ++ errs_to ++ errs_from) -- |Was the "help" option passed on the command line? help_set :: IO Bool help_set = do opts <- parse_options return (opt_help opts) -- |What's the heartbeat? heartbeat :: IO (Maybe Int) heartbeat = do opts <- parse_options return (opt_heartbeat opts) -- |What "To" address was given on the command line? to_email_address :: IO (Maybe String) to_email_address = do opts <- parse_options return (opt_to opts) -- |What "From" address was given on the command line? from_email_address :: IO (Maybe String) from_email_address = do opts <- parse_options return (opt_from opts) -- |What usernames were passed on the command line? parse_usernames :: IO [String] parse_usernames = do argv <- getArgs let (_, usernames, _) = getOpt Permute options argv return usernames