{-# LANGUAGE OverloadedStrings #-}
module Distribution.Fields.ConfVar (parseConditionConfVar) where

import Distribution.Compat.CharParsing              (char, integral)
import Distribution.Compat.Prelude
import Distribution.Parsec                    (Parsec (..), runParsecParser, Position (..))
import Distribution.Parsec.FieldLineStream (fieldLineStreamFromBS)
import Distribution.Fields.Field                    (SectionArg (..))
import Distribution.Fields.ParseResult
import Distribution.Types.Condition
import Distribution.Types.ConfVar (ConfVar (..))
import Distribution.Version
       (anyVersion, earlierVersion, intersectVersionRanges, laterVersion, majorBoundVersion,
       mkVersion, noVersion, orEarlierVersion, orLaterVersion, thisVersion, unionVersionRanges,
       withinVersion)
import Prelude ()

import qualified Text.Parsec       as P
import qualified Text.Parsec.Error as P

-- | Parse @'Condition' 'ConfVar'@ from section arguments provided by parsec
-- based outline parser.
parseConditionConfVar :: [SectionArg Position] -> ParseResult (Condition ConfVar)
parseConditionConfVar args =
    -- The name of the input file is irrelevant, as we reformat the error message.
    case P.runParser (parser <* P.eof) () "<condition>" args of
        Right x  -> pure x
        Left err -> do
            -- Mangle the position to the actual one
            let ppos = P.errorPos err
            let epos = Position (P.sourceLine ppos) (P.sourceColumn ppos)
            let msg = P.showErrorMessages
                    "or" "unknown parse error" "expecting" "unexpected" "end of input"
                    (P.errorMessages err)
            parseFailure epos msg
            pure $ Lit True

type Parser = P.Parsec [SectionArg Position] ()

sepByNonEmpty :: Parser a -> Parser sep -> Parser (NonEmpty a)
sepByNonEmpty p sep = (:|) <$> p <*> many (sep *> p)

parser :: Parser (Condition ConfVar)
parser = condOr
  where
    condOr       = sepByNonEmpty condAnd (oper "||") >>= return . foldl1 COr
    condAnd      = sepByNonEmpty cond    (oper "&&") >>= return . foldl1 CAnd
    cond         = P.choice
         [ boolLiteral, parens condOr,  notCond, osCond, archCond, flagCond, implCond ]

    notCond      = CNot <$ oper "!" <*> cond

    boolLiteral  = Lit <$> boolLiteral'
    osCond       = Var . OS   <$ string "os"   <*> parens fromParsec
    flagCond     = Var . Flag <$ string "flag" <*> parens fromParsec
    archCond     = Var . Arch <$ string "arch" <*> parens fromParsec
    implCond     = Var        <$ string "impl" <*> parens implCond'

    implCond'    = Impl
        <$> fromParsec
        <*> P.option anyVersion versionRange

    version = fromParsec
    versionStar  = mkVersion <$> fromParsec' versionStar' <* oper "*"
    versionStar' = some (integral <* char '.')

    versionRange = expr
      where
        expr = foldl1 unionVersionRanges     <$> sepByNonEmpty term   (oper "||")
        term = foldl1 intersectVersionRanges <$> sepByNonEmpty factor (oper "&&")

        factor = P.choice
            $ parens expr
            : parseAnyVersion
            : parseNoVersion
            : parseWildcardRange
            : map parseRangeOp rangeOps

        parseAnyVersion    = anyVersion <$ string "-any"
        parseNoVersion     = noVersion  <$ string "-none"

        parseWildcardRange = P.try $ withinVersion <$ oper "==" <*> versionStar

        parseRangeOp (s,f) = P.try (f <$ oper s <*> version)
        rangeOps = [ ("<",  earlierVersion),
                     ("<=", orEarlierVersion),
                     (">",  laterVersion),
                     (">=", orLaterVersion),
                     ("^>=", majorBoundVersion),
                     ("==", thisVersion) ]

    -- Number token can have many dots in it: SecArgNum (Position 65 15) "7.6.1"
    identBS = tokenPrim $ \t -> case t of
        SecArgName _ s -> Just s
        _              -> Nothing

    boolLiteral' = tokenPrim $ \t -> case t of
        SecArgName _ s
            | s == "True"  -> Just True
            | s == "true"  -> Just True
            | s == "False" -> Just False
            | s == "false" -> Just False
        _                  -> Nothing

    string s = tokenPrim $ \t -> case t of
        SecArgName _ s' | s == s' -> Just ()
        _                         -> Nothing

    oper o = tokenPrim $ \t -> case t of
        SecArgOther _ o' | o == o' -> Just ()
        _                          -> Nothing

    parens = P.between (oper "(") (oper ")")

    tokenPrim = P.tokenPrim prettySectionArg updatePosition
    -- TODO: check where the errors are reported
    updatePosition x _ _ = x
    prettySectionArg = show

    fromParsec :: Parsec a => Parser a
    fromParsec = fromParsec' parsec

    fromParsec' p = do
        bs <- identBS
        let fls = fieldLineStreamFromBS bs
        either (fail . show) pure (runParsecParser p "<fromParsec'>" fls)
