{-# LANGUAGE GeneralizedNewtypeDeriving #-}

-- | Example usage of this module:
--
-- > -- options.hs
-- >
-- > {-# LANGUAGE OverloadedStrings #-}
-- >
-- > import Turtle
-- >
-- > parser :: Parser (Text, Int)
-- > parser = (,) <$> optText "name" 'n' "Your first name"
-- >              <*> optInt  "age"  'a' "Your current age"
-- >
-- > main = do
-- >     (name, age) <- options "Greeting script" parser
-- >     echo (format ("Hello there, "%s) name)
-- >     echo (format ("You are "%d%" years old") age)
--
-- > $ ./options --name John --age 42
-- > Hello there, John
-- > You are 42 years old
--
-- > $ ./options --help
-- > Greeting script
-- >
-- > Usage: options (-n|--name NAME) (-a|--age AGE)
-- >
-- > Available options:
-- >  -h,--help                Show this help text
-- >  --name NAME              Your first name
-- >  --age AGE                Your current age

module Turtle.Options
    ( -- * Types
      Parser
    , ArgName
    , ShortName
    , Description
    , HelpMessage

      -- * Flag-based option parsers
    , switch
    , optText
    , optInt
    , optInteger
    , optDouble
    , optPath
    , optRead
    , opt

    -- * Positional argument parsers
    , argText
    , argInt
    , argInteger
    , argDouble
    , argPath
    , argRead
    , arg

      -- * Consume parsers
    , options

    ) where

import Data.Monoid
import Data.Foldable
import Data.String (IsString)
import Text.Read (readMaybe)
import Data.Text (Text)
import qualified Data.Text as Text
import Data.Optional
import Control.Applicative
import Control.Monad.IO.Class
import Filesystem.Path.CurrentOS (FilePath, fromText)
import Options.Applicative (Parser)
import qualified Options.Applicative as Opts
import qualified Options.Applicative.Types as Opts
import Prelude hiding (FilePath)

-- | Parse the given options from the command line
options :: MonadIO io => Description -> Parser a -> io a
options desc parser = liftIO
    $ Opts.execParser
    $ Opts.info (Opts.helper <*> parser)
                (Opts.header (Text.unpack (getDescription desc)))

{-| The name of a command-line argument

    This is used to infer the long name and metavariable for the command line
    flag.  For example, an `ArgName` of @\"name\"@ will create a @--name@ flag
    with a @NAME@ metavariable
-}
newtype ArgName = ArgName { getArgName :: Text }
    deriving (IsString)

-- | The short one-character abbreviation for a flag (i.e. @-n@)
type ShortName = Char

{-| A brief description of what your program does

    This description will appear in the header of the @--help@ output
-}
newtype Description = Description { getDescription :: Text }
    deriving (IsString)

{-| A helpful message explaining what a flag does

    This will appear in the @--help@ output
-}
newtype HelpMessage = HelpMessage { getHelpMessage :: Text }
    deriving (IsString)

{-| This parser returns `True` if the given flag is set and `False` if the
    flag is absent
-}
switch
    :: ArgName
    -> ShortName
    -> Optional HelpMessage
    -> Parser Bool
switch argName c helpMessage
   = Opts.switch
   $ (Opts.long . Text.unpack . getArgName) argName
  <> Opts.short c
  <> foldMap (Opts.help . Text.unpack . getHelpMessage) helpMessage

{- | Build a flag-based option parser for any type by providing a `Text`-parsing
     function
-}
opt :: (Text -> Maybe a)
    -> ArgName
    -> ShortName
    -> Optional HelpMessage
    -> Parser a
opt argParse argName c helpMessage
   = Opts.option (argParseToReadM argParse)
   $ Opts.metavar (Text.unpack (Text.toUpper (getArgName argName)))
  <> Opts.long (Text.unpack (getArgName argName))
  <> Opts.short c
  <> foldMap (Opts.help . Text.unpack . getHelpMessage) helpMessage

-- | Parse any type that implements `Read`
optRead :: Read a => ArgName -> ShortName -> Optional HelpMessage -> Parser a
optRead = opt (readMaybe . Text.unpack)

-- | Parse an `Int` as a flag-based option
optInt :: ArgName -> ShortName -> Optional HelpMessage -> Parser Int
optInt = optRead

-- | Parse an `Integer` as a flag-based option
optInteger :: ArgName -> ShortName -> Optional HelpMessage -> Parser Integer
optInteger = optRead

-- | Parse a `Double` as a flag-based option
optDouble :: ArgName -> ShortName -> Optional HelpMessage -> Parser Double
optDouble = optRead

-- | Parse a `Text` value as a flag-based option
optText :: ArgName -> ShortName -> Optional HelpMessage -> Parser Text
optText = opt Just

-- | Parse a `FilePath` value as a flag-based option
optPath :: ArgName -> ShortName -> Optional HelpMessage -> Parser FilePath
optPath argName short msg = fmap fromText (optText argName short msg)

{- | Build a positional argument parser for any type by providing a
    `Text`-parsing function
-}
arg :: (Text -> Maybe a)
    -> ArgName
    -> Optional HelpMessage
    -> Parser a
arg argParse argName helpMessage
   = Opts.argument (argParseToReadM argParse)
   $ Opts.metavar (Text.unpack (Text.toUpper (getArgName argName)))
  <> foldMap (Opts.help . Text.unpack . getHelpMessage) helpMessage

-- | Parse any type that implements `Read` as a positional argument
argRead :: Read a => ArgName -> Optional HelpMessage -> Parser a
argRead = arg (readMaybe . Text.unpack)

-- | Parse an `Int` as a positional argument
argInt :: ArgName -> Optional HelpMessage -> Parser Int
argInt = argRead

-- | Parse an `Integer` as a positional argument
argInteger :: ArgName -> Optional HelpMessage -> Parser Integer
argInteger = argRead

-- | Parse a `Double` as a positional argument
argDouble :: ArgName -> Optional HelpMessage -> Parser Double
argDouble = argRead

-- | Parse a `Text` as a positional argument
argText :: ArgName -> Optional HelpMessage -> Parser Text
argText = arg Just

-- | Parse a `FilePath` as a positional argument
argPath :: ArgName -> Optional HelpMessage -> Parser FilePath
argPath argName msg = fmap fromText (argText argName msg)

argParseToReadM :: (Text -> Maybe a) -> Opts.ReadM a
argParseToReadM f = do
    s <- Opts.readerAsk
    case f (Text.pack s) of
        Just a -> return a
        Nothing -> Opts.readerAbort Opts.ShowHelpText