-----------------------------------------------------------------------------
--
-- Module      :  Parser
-- Copyright   :  (c) Phil Freeman 2014
-- License     :  MIT
--
-- Maintainer  :  Phil Freeman <paf31@cantab.net>
-- Stability   :  experimental
-- Portability :
--
-- |
-- Parser for PSCI.
--
-----------------------------------------------------------------------------

module Parser
  ( parseCommand
  ) where

import Prelude hiding (lex)

import Data.Char (isSpace)
import Data.List (intercalate)

import Control.Applicative hiding (many)

import Text.Parsec hiding ((<|>))

import qualified Language.PureScript as P
import Language.PureScript.Parser.Common (mark, same)

import qualified Directive as D
import Types

-- |
-- Parses PSCI metacommands or expressions input from the user.
--
parseCommand :: String -> Either String Command
parseCommand cmdString =
  case cmdString of
    (':' : cmd) -> parseDirective cmd
    _ -> parseRest psciCommand cmdString

parseRest :: P.TokenParser a -> String -> Either String a
parseRest p s = either (Left . show) Right $ do
  ts <- P.lex "" s
  P.runTokenParser "" (p <* eof) ts

psciCommand :: P.TokenParser Command
psciCommand = choice (map try parsers)
  where
  parsers =
    [ psciLet
    , psciImport
    , psciOtherDeclaration
    , psciExpression
    ]

trim :: String -> String
trim = trimEnd . trimStart

trimStart :: String -> String
trimStart = dropWhile isSpace

trimEnd :: String -> String
trimEnd = reverse . trimStart . reverse

parseDirective :: String -> Either String Command
parseDirective cmd =
  case D.directivesFor' dstr of
    [(d, _)] -> commandFor d
    []       -> Left "Unrecognized directive. Type :? for help."
    ds       -> Left ("Ambiguous directive. Possible matches: " ++
                  intercalate ", " (map snd ds) ++ ". Type :? for help.")
  where
  (dstr, arg) = break isSpace cmd

  commandFor d = case d of
    Help    -> return ShowHelp
    Quit    -> return QuitPSCi
    Reset   -> return ResetState
    Browse  -> BrowseModule <$> parseRest P.moduleName arg
    Load    -> return $ LoadFile (trim arg)
    Foreign -> return $ LoadForeign (trim arg)
    Show    -> ShowInfo <$> parseReplQuery' (trim arg)
    Type    -> TypeOf <$> parseRest P.parseValue arg
    Kind    -> KindOf <$> parseRest P.parseType arg

-- |
-- Parses expressions entered at the PSCI repl.
--
psciExpression :: P.TokenParser Command
psciExpression = Expression <$> P.parseValue

-- |
-- PSCI version of @let@.
-- This is essentially let from do-notation.
-- However, since we don't support the @Eff@ monad,
-- we actually want the normal @let@.
--
psciLet :: P.TokenParser Command
psciLet = Decls <$> (P.reserved "let" *> P.indented *> manyDecls)
  where
  manyDecls :: P.TokenParser [P.Declaration]
  manyDecls = mark (many1 (same *> P.parseLocalDeclaration))

-- | Imports must be handled separately from other declarations, so that
-- :show import works, for example.
psciImport :: P.TokenParser Command
psciImport = Import <$> P.parseImportDeclaration'

-- | Any other declaration that we don't need a 'special case' parser for
-- (like let or import declarations).
psciOtherDeclaration :: P.TokenParser Command
psciOtherDeclaration = Decls . (:[]) <$> do
  decl <- discardPositionInfo <$> P.parseDeclaration
  if acceptable decl
    then return decl
    else fail "this kind of declaration is not supported in psci"

discardPositionInfo :: P.Declaration -> P.Declaration
discardPositionInfo (P.PositionedDeclaration _ _ d) = d
discardPositionInfo d = d

acceptable :: P.Declaration -> Bool
acceptable P.DataDeclaration{} = True
acceptable P.TypeSynonymDeclaration{} = True
acceptable P.ExternDeclaration{} = True
acceptable P.ExternDataDeclaration{} = True
acceptable P.ExternInstanceDeclaration{} = True
acceptable P.TypeClassDeclaration{} = True
acceptable P.TypeInstanceDeclaration{} = True
acceptable _ = False

parseReplQuery' :: String -> Either String ReplQuery
parseReplQuery' str =
  case parseReplQuery str of
    Nothing -> Left ("Don't know how to show " ++ str ++ ". Try one of: " ++
                      intercalate ", " replQueryStrings ++ ".")
    Just query -> Right query