{-# LANGUAGE AllowAmbiguousTypes   #-}
{-# LANGUAGE ConstraintKinds       #-}
{-# LANGUAGE DataKinds             #-}
{-# LANGUAGE DeriveLift            #-}
{-# LANGUAGE DerivingStrategies    #-}
{-# LANGUAGE FlexibleContexts      #-}
{-# LANGUAGE FlexibleInstances     #-}
{-# LANGUAGE LambdaCase            #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE NamedFieldPuns        #-}
{-# LANGUAGE OverloadedStrings     #-}
{-# LANGUAGE ScopedTypeVariables   #-}
{-# LANGUAGE TemplateHaskell       #-}
{-# LANGUAGE TupleSections         #-}
{-# LANGUAGE TypeApplications      #-}
{-# LANGUAGE TypeFamilies          #-}
{- HLINT ignore "Reduce duplication" -}
module Auth.Biscuit.Datalog.Parser
  ( block
  , check
  , fact
  , predicate
  , rule
  , verifier
  -- these are only exported for testing purposes
  , checkParser
  , expressionParser
  , policyParser
  , predicateParser
  , ruleParser
  , termParser
  , verifierParser
  , HasParsers
  , HasTermParsers
  ) where

import           Control.Applicative            (liftA2, optional, (<|>))
import qualified Control.Monad.Combinators.Expr as Expr
import           Data.Attoparsec.Text
import           Data.ByteString                (ByteString)
import           Data.ByteString.Base16         as Hex
import           Data.Char                      (isSpace)
import           Data.Either                    (partitionEithers)
import           Data.Foldable                  (fold)
import           Data.Functor                   (void, ($>))
import qualified Data.Set                       as Set
import           Data.Text                      (Text, pack, unpack)
import           Data.Text.Encoding             (encodeUtf8)
import           Data.Time                      (UTCTime, defaultTimeLocale,
                                                 parseTimeM)
import           Data.Void                      (Void)
import           Instances.TH.Lift              ()
import           Language.Haskell.TH
import           Language.Haskell.TH.Quote
import           Language.Haskell.TH.Syntax     (Lift)

import           Auth.Biscuit.Datalog.AST

class ConditionalParse a v where
  ifPresent :: String -> Parser a -> Parser v

instance ConditionalParse a Void where
  ifPresent name _ = fail $ name <> " is not available in this context"

instance ConditionalParse m m where
  ifPresent _ p = p

class SetParser (inSet :: IsWithinSet) (ctx :: ParsedAs) where
  parseSet :: Parser (SetType inSet ctx)

instance SetParser 'WithinSet ctx where
  parseSet = fail "nested sets are forbidden"

instance SetParser 'NotWithinSet 'QuasiQuote where
  parseSet = Set.fromList <$> (char '[' *> commaList0 termParser <* char ']')

instance SetParser 'NotWithinSet 'RegularString where
  parseSet = Set.fromList <$> (char '[' *> commaList0 termParser <* char ']')

type HasTermParsers inSet pof ctx =
  ( ConditionalParse (SliceType 'QuasiQuote)                   (SliceType ctx)
  , ConditionalParse (VariableType 'NotWithinSet 'InPredicate) (VariableType inSet pof)
  , SetParser inSet ctx
  )
type HasParsers pof ctx = HasTermParsers 'NotWithinSet pof ctx

-- | Parser for an identifier (predicate name, variable name, symbol name, …)
nameParser :: Parser Text
nameParser = takeWhile1 $ inClass "a-zA-Z0-9_"

delimited :: Parser x
          -> Parser y
          -> Parser a
          -> Parser a
delimited before after p = before *> p <* after

parens :: Parser a -> Parser a
parens = delimited (char '(') (skipSpace *> char ')')

commaList :: Parser a -> Parser [a]
commaList p =
  sepBy1 p (skipSpace *> char ',')

commaList0 :: Parser a -> Parser [a]
commaList0 p =
  sepBy p (skipSpace *> char ',')

predicateParser :: HasParsers pof ctx => Parser (Predicate' pof ctx)
predicateParser = do
  skipSpace
  name <- nameParser
  skipSpace
  terms <- parens (commaList termParser)
  pure Predicate{name,terms}

unary :: HasParsers 'InPredicate ctx => Parser (Expression' ctx)
unary = choice
  [ unaryParens
  , unaryNegate
  , unaryLength
  ]

unaryParens :: HasParsers 'InPredicate ctx => Parser (Expression' ctx)
unaryParens = do
  skipSpace
  _ <- char '('
  skipSpace
  e <- expressionParser
  skipSpace
  _ <- char ')'
  pure $ EUnary Parens e

unaryNegate :: HasParsers 'InPredicate ctx => Parser (Expression' ctx)
unaryNegate = do
  skipSpace
  _ <- char '!'
  skipSpace
  EUnary Negate <$> expressionParser

unaryLength :: HasParsers 'InPredicate ctx => Parser (Expression' ctx)
unaryLength = do
  skipSpace
  e <- choice
         [ EValue <$> termParser
         , unaryParens
         ]
  skipSpace
  _ <- string ".length()"
  pure $ EUnary Length e

exprTerm :: HasParsers 'InPredicate ctx => Parser (Expression' ctx)
exprTerm = choice
  [ unary
  , EValue <$> termParser
  ]

methodParser :: HasParsers 'InPredicate ctx => Parser (Expression' ctx)
methodParser = do
  e1 <- exprTerm
  _ <- char '.'
  method <- choice
    [ Contains     <$ string "contains"
    , Intersection <$ string "intersection"
    , Union        <$ string "union"
    , Prefix       <$ string "starts_with"
    , Suffix       <$ string "ends_with"
    , Regex        <$ string "matches"
    ]
  _ <- char '('
  skipSpace
  e2 <- expressionParser
  skipSpace
  _ <- char ')'
  pure $ EBinary method e1 e2

expressionParser :: HasParsers 'InPredicate ctx => Parser (Expression' ctx)
expressionParser = Expr.makeExprParser (methodParser <|> exprTerm) table

table :: HasParsers 'InPredicate ctx
      => [[Expr.Operator Parser (Expression' ctx)]]
table = [ [ binary  "*" Mul
          , binary  "/" Div
          ]
        , [ binary  "+" Add
          , binary  "-" Sub
          ]
        , [ binary  "<=" LessOrEqual
          , binary  ">=" GreaterOrEqual
          , binary  "<"  LessThan
          , binary  ">"  GreaterThan
          , binary  "==" Equal
          ]
        , [ binary  "&&" And
          , binary  "||" Or
          ]
        ]

binary :: HasParsers 'InPredicate ctx
       => Text
       -> Binary
       -> Expr.Operator Parser (Expression' ctx)
binary name op = Expr.InfixL  (EBinary op <$ (skipSpace *> string name))

hexBsParser :: Parser ByteString
hexBsParser = do
  void $ string "hex:"
  (digits, "") <- Hex.decode . encodeUtf8 <$> takeWhile1 (inClass "0-9a-fA-F")
  pure digits

litStringParser :: Parser Text
litStringParser =
  let regularChars = takeTill (inClass "\"\\")
      escaped = choice
        [ string "\\n" $> "\n"
        , string "\\\"" $> "\""
        , string "\\\\"  $> "\\"
        ]
      str = do
        f <- regularChars
        r <- optional (liftA2 (<>) escaped str)
        pure $ f <> fold r
   in char '"' *> str <* char '"'

rfc3339DateParser :: Parser UTCTime
rfc3339DateParser =
  -- get all the chars until the end of the term
  -- a term can be terminated by
  --  - a space (before another delimiter)
  --  - a comma (before another term)
  --  - a closing paren (the end of a term list)
  --  - a closing bracket (the end of a set)
  let getDateInput = takeWhile1 (notInClass ", )];")
      parseDate = parseTimeM False defaultTimeLocale "%FT%T%Q%EZ"
   in parseDate . unpack =<< getDateInput

termParser :: forall inSet pof ctx
            . ( HasTermParsers inSet pof ctx
              )
           => Parser (ID' inSet pof ctx)
termParser = skipSpace *> choice
  [ Antiquote <$> ifPresent "slice" (Slice <$> (string "${" *> many1 letter <* char '}'))
  , Variable <$> ifPresent "var" (char '$' *> nameParser)
  , TermSet <$> parseSet @inSet @ctx
  , Symbol <$> (char '#' *> nameParser)
  , LBytes <$> hexBsParser
  , LDate <$> rfc3339DateParser
  , LInteger <$> signed decimal
  , LString <$> litStringParser
  , LBool <$> choice [ string "true"  $> True
                     , string "false" $> False
                     ]
  ]

-- | same as a predicate, but allows empty
-- | terms list
ruleHeadParser :: HasParsers 'InPredicate ctx => Parser (Predicate' 'InPredicate ctx)
ruleHeadParser = do
  skipSpace
  name <- nameParser
  skipSpace
  terms <- parens (commaList0 termParser)
  pure Predicate{name,terms}

ruleBodyParser :: HasParsers 'InPredicate ctx
               => Parser ([Predicate' 'InPredicate ctx], [Expression' ctx])
ruleBodyParser = do
  let predicateOrExprParser =
            Right <$> expressionParser
        <|> Left <$> predicateParser
  elems <- sepBy1 (skipSpace *> predicateOrExprParser)
                  (skipSpace *> char ',')
  pure $ partitionEithers elems

ruleParser :: HasParsers 'InPredicate ctx => Parser (Rule' ctx)
ruleParser = do
  rhead <- ruleHeadParser
  skipSpace
  void $ string "<-"
  (body, expressions) <- ruleBodyParser
  pure Rule{rhead, body, expressions}

queryParser :: HasParsers 'InPredicate ctx => Parser (Query' ctx)
queryParser =
  fmap (uncurry QueryItem) <$> sepBy1 ruleBodyParser (skipSpace *> asciiCI "or" <* satisfy isSpace)

checkParser :: HasParsers 'InPredicate ctx => Parser (Check' ctx)
checkParser = string "check if" *> queryParser

commentParser :: Parser ()
commentParser = do
  skipSpace
  _ <- string "//"
  _ <- skipWhile ((&&) <$> (/= '\r') <*> (/= '\n'))
  void $ choice [ void (char '\n')
                , void (string "\r\n")
                , endOfInput
                ]

blockElementParser :: HasParsers 'InPredicate ctx => Parser (BlockElement' ctx)
blockElementParser = choice
  [ BlockRule    <$> ruleParser <* skipSpace <* char ';'
  , BlockFact    <$> predicateParser <* skipSpace <* char ';'
  , BlockCheck   <$> checkParser <* skipSpace <* char ';'
  , BlockComment <$  commentParser
  ]

verifierElementParser :: HasParsers 'InPredicate ctx => Parser (VerifierElement' ctx)
verifierElementParser = choice
  [ VerifierPolicy  <$> policyParser <* skipSpace <* char ';'
  , BlockElement    <$> blockElementParser
  ]

verifierParser :: ( HasParsers 'InPredicate ctx
                  , HasParsers 'InFact ctx
                  , Show (VerifierElement' ctx)
                  )
               => Parser (Verifier' ctx)
verifierParser = do
  elems <- many1 (skipSpace *> verifierElementParser)
  pure $ foldMap elementToVerifier elems

blockParser :: ( HasParsers 'InPredicate ctx
               , HasParsers 'InFact ctx
               , Show (BlockElement' ctx)
               )
            => Parser (Block' ctx)
blockParser = do
  elems <- many1 (skipSpace *> blockElementParser)
  pure $ foldMap elementToBlock elems

policyParser :: HasParsers 'InPredicate ctx => Parser (Policy' ctx)
policyParser = do
  policy <- choice
              [ Allow <$ string "allow if"
              , Deny  <$ string "deny if"
              ]
  (policy, ) <$> queryParser

compileParser :: Lift a => Parser a -> String -> Q Exp
compileParser p str = case parseOnly p (pack str) of
  Right result -> [| result |]
  Left e       -> fail e

-- | Quasiquoter for a rule expression. You can reference haskell variables
-- like this: @${variableName}@.
--
-- You most likely want to directly use 'block' or 'verifier' instead.
rule :: QuasiQuoter
rule = QuasiQuoter
  { quoteExp = compileParser (ruleParser @'QuasiQuote)
  , quotePat = error "not supported"
  , quoteType = error "not supported"
  , quoteDec = error "not supported"
  }

-- | Quasiquoter for a predicate expression. You can reference haskell variables
-- like this: @${variableName}@.
--
-- You most likely want to directly use 'block' or 'verifier' instead.
predicate :: QuasiQuoter
predicate = QuasiQuoter
  { quoteExp = compileParser (predicateParser @'InPredicate @'QuasiQuote)
  , quotePat = error "not supported"
  , quoteType = error "not supported"
  , quoteDec = error "not supported"
  }

-- | Quasiquoter for a fact expression. You can reference haskell variables
-- like this: @${variableName}@.
--
-- You most likely want to directly use 'block' or 'verifier' instead.
fact :: QuasiQuoter
fact = QuasiQuoter
  { quoteExp = compileParser (predicateParser @'InFact @'QuasiQuote)
  , quotePat = error "not supported"
  , quoteType = error "not supported"
  , quoteDec = error "not supported"
  }

-- | Quasiquoter for a check expression. You can reference haskell variables
-- like this: @${variableName}@.
--
-- You most likely want to directly use 'block' or 'verifier' instead.
check :: QuasiQuoter
check = QuasiQuoter
  { quoteExp = compileParser (checkParser @'QuasiQuote)
  , quotePat = error "not supported"
  , quoteType = error "not supported"
  , quoteDec = error "not supported"
  }

-- | Quasiquoter for a block expression. You can reference haskell variables
-- like this: @${variableName}@.
--
-- A typical use of 'block' looks like this:
--
-- > [block|
-- >   resource(#authority, ${fileName});
-- >   rule($variable) <- fact($value), other_fact($value);
-- >   check if operation(#ambient, #read);
-- > |]
block :: QuasiQuoter
block = QuasiQuoter
  { quoteExp = compileParser (blockParser @'QuasiQuote)
  , quotePat = error "not supported"
  , quoteType = error "not supported"
  , quoteDec = error "not supported"
  }

-- | Quasiquoter for a verifier expression. You can reference haskell variables
-- like this: @${variableName}@.
--
-- A typical use of 'block' looks like this:
--
-- > [verifier|
-- >   current_time(#ambient, ${now});
-- >   allow if resource(#authority, "file1");
-- >   deny if true;
-- > |]
verifier :: QuasiQuoter
verifier = QuasiQuoter
  { quoteExp = compileParser (verifierParser @'QuasiQuote)
  , quotePat = error "not supported"
  , quoteType = error "not supported"
  , quoteDec = error "not supported"
  }