-- 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 ( 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_help :: Bool, opt_from :: Maybe String, opt_to :: Maybe String } -- This constructs an instance of Options, with each of its members -- set to default values. default_options :: Options default_options = Options { 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, -- -- http://www.haskell.org/haskellwiki/High-level_option_handling_with_GetOpt -- options :: [OptDescr (Options -> IO Options)] options = [ Option ['h'][] (NoArg set_help) "Prints this help message.", Option ['t'][] (ReqArg set_to "email_address") "Send tweets TO email_address.", Option ['f'][] (ReqArg set_from "email_address") "Send tweets FROM email_address." ] 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 [-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 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 [] 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 [] 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_error :: String -> String format_error err = "ERROR: " ++ err ++ "\n" -- Return a list of errors. parse_errors :: IO [String] parse_errors = do argv <- getArgs let (_, _, errors) = getOpt Permute options argv errs_username <- username_errors errs_to <- to_errors errs_from <- from_errors return $ map format_error (errors ++ errs_username ++ errs_to ++ errs_from) -- Is the help option set? help_set :: IO Bool help_set = do opts <- parse_options return (opt_help opts) to_email_address :: IO (Maybe String) to_email_address = do opts <- parse_options return (opt_to opts) from_email_address :: IO (Maybe String) from_email_address = do opts <- parse_options return (opt_from opts) parse_usernames :: IO [String] parse_usernames = do argv <- getArgs let (_, usernames, _) = getOpt Permute options argv return usernames