module Text.HTML.TagSoup.HT.Parser.Combinator (
   Parser.T, Full, Emitting, Fallible, Plain,
   char, dropSpaces, getPos,
   many, many1, manyNull, many1Null, many0toN, many1toN,
   many1Satisfy, manySatisfy, readUntil,
   satisfy, string,
   emit, modifyEmission,
   eval, write, gets,
   withDefault, allowFail, allowEmit,
   Identity, runIdentity, )
  where


import qualified Text.XML.Basic.Position as Position
import qualified Text.HTML.TagSoup.HT.Parser.Status as Status
import qualified Text.HTML.TagSoup.HT.Parser.Stream as Stream

-- import Text.HTML.TagSoup.HT.Parser.Custom as Parser
import Text.HTML.TagSoup.HT.Parser.MTL as Parser

import Control.Monad (liftM, liftM2, guard, )
-- import Control.Monad.Trans (lift, )

import Data.Monoid (Monoid)

import Data.Char (isSpace)



type Full     input w = Parser.T input [w] Maybe
type Fallible input   = Parser.T input ()  Maybe
type Emitting input w = Parser.T input [w] Identity
type Plain    input   = Parser.T input ()  Identity


write :: Monad fail =>
   FilePath -> Parser.T input [w] fail () -> input -> fail [w]
write fileName p =
   liftM (\ ~(_,_,ws) -> ws) .
   run p .
   Status.Cons (Position.initialize fileName)

eval ::  Monad fail =>
   FilePath -> Parser.T input [w] fail a -> input -> fail a
eval fileName p =
   liftM (\ ~(x,_,_) -> x) .
   run p .
   Status.Cons (Position.initialize fileName)



getPos ::
   (Monoid output, Monad fail) =>
   Parser.T input output fail Position.T
getPos = gets Status.sourcePos

satisfy ::
   (Monoid output, Stream.C input) =>
   (Char -> Bool) -> Parser.T input output Maybe Char
satisfy p =
   do c <- nextChar
      if p c
        then return c
        else fail "character not matched"

-- | does never fail
many :: Monoid output =>
   Parser.T input output Maybe a -> Parser.T input output Identity [a]
many x =
   {- It is better to have 'force' at the place it is,
      instead of writing it to the recursive call,
      because 'x' can cause an infinite loop. -}
   withDefault (many1 x) (return [])

-- | fails when trying the sub-parser the first time or never
many1 :: Monoid output =>
   Parser.T input output Maybe a -> Parser.T input output Maybe [a]
many1 x = liftM2 (:) x (allowFail $ many x)


manyNull :: Monoid output =>
   Parser.T input output Maybe () -> Parser.T input output Identity ()
manyNull x =
   withDefault (many1Null x) (return ())

many1Null :: Monoid output =>
   Parser.T input output Maybe () -> Parser.T input output Maybe ()
many1Null x = x >> (allowFail $ manyNull x)


many0toN :: Monoid output =>
   Int -> Parser.T input output Maybe a -> Parser.T input output Identity [a]
many0toN n x =
   withDefault (guard (n>0) >> many1toN n x) (return [])

-- | condition: n>0, this will not be checked
many1toN :: Monoid output =>
   Int -> Parser.T input output Maybe a -> Parser.T input output Maybe [a]
many1toN n x = liftM2 (:) x (allowFail $ many0toN (pred n) x)


manySatisfy :: (Stream.C input) =>
   (Char -> Bool) -> Parser.T input [w] Identity String
manySatisfy =
   allowEmit . many . satisfy

many1Satisfy :: (Stream.C input) =>
   (Char -> Bool) -> Parser.T input [w] Maybe String
many1Satisfy =
   allowEmit . many1 . satisfy

dropSpaces :: (Stream.C input) =>
   Parser.T input [w] Identity ()
dropSpaces =
   manySatisfy isSpace >> return ()


char ::
   (Monoid output, Stream.C input) =>
   Char -> Parser.T input output Maybe Char
char c = satisfy (c==)

string :: (Stream.C input) =>
   String -> Parser.T input [w] Maybe String
string = allowEmit . mapM char


readUntil :: (Stream.C input) =>
   String -> Parser.T input [w] Identity (Bool,String)
readUntil pattern =
   let recourse =
          foldr withDefault (return (False,[])) $
          liftM (const (True,[])) (mapM char pattern) :
          (do c <- nextChar
              ~(found,str) <- allowFail recourse
              return (found,c:str)) :
          []
   in  allowEmit recourse
{-
runStateT (readUntil "-->") (Position.initialize "input", "<!-- comment --> other stuff")
-}



emit :: Monad fail =>
   w -> Parser.T input [w] fail ()
emit w = tell [w]

modifyEmission :: Monad fail =>
   ([w] -> [w]) -> Parser.T input [w] fail a -> Parser.T input [w] fail a
modifyEmission f = censor f