{- |
   Module      : Text.Pandoc.Readers.RST 
   Copyright   : Copyright (C) 2006 John MacFarlane
   License     : GNU GPL, version 2 or above 

   Maintainer  : John MacFarlane <jgm at berkeley dot edu>
   Stability   : unstable
   Portability : portable

Conversion from reStructuredText to 'Pandoc' document.
-}
module Text.Pandoc.Readers.RST ( 
                                readRST
                               ) where
import Text.Pandoc.Definition
import Text.ParserCombinators.Pandoc
import Text.Pandoc.Shared 
import Text.Pandoc.Readers.HTML ( anyHtmlBlockTag, anyHtmlInlineTag )
import Text.Regex ( matchRegex, mkRegex )
import Text.ParserCombinators.Parsec
import Data.Maybe ( fromMaybe )
import List ( findIndex )
import Char ( toUpper )

-- | Parse reStructuredText string and return Pandoc document.
readRST :: ParserState -> String -> Pandoc
readRST = readWith parseRST

-- | Parse a string and print result (for testing).
testString :: String -> IO ()
testString = testStringWith parseRST

--
-- Constants and data structure definitions
---

bulletListMarkers = "*+-"
underlineChars = "!\"#$&'()*+,-./:;<=>?@[\\]^_`{|}~"

-- treat these as potentially non-text when parsing inline:
specialChars = "\\`|*_<>$:[-"

--
-- parsing documents
--

isAnonKeyBlock block = case block of
                         (Key [Str "_"] str) -> True
                         otherwise -> False

isNotAnonKeyBlock block = not (isAnonKeyBlock block)

isHeader1 :: Block -> Bool
isHeader1 (Header 1 _) = True
isHeader1 _ = False

isHeader2 :: Block -> Bool
isHeader2 (Header 2 _) = True
isHeader2 _ = False

-- | Promote all headers in a list of blocks.  (Part of
-- title transformation for RST.)
promoteHeaders :: Int -> [Block] -> [Block]
promoteHeaders num ((Header level text):rest) = 
    (Header (level - num) text):(promoteHeaders num rest)
promoteHeaders num (other:rest) = other:(promoteHeaders num rest)
promoteHeaders num [] = []

-- | If list of blocks starts with a header (or a header and subheader)
-- of level that are not found elsewhere, return it as a title and
-- promote all the other headers. 
titleTransform :: [Block]              -- ^ list of blocks
               -> ([Block], [Inline])  -- ^ modified list of blocks, title
titleTransform ((Header 1 head1):(Header 2 head2):rest) =  -- title subtitle
    if (any isHeader1 rest) || (any isHeader2 rest)
       then ((Header 1 head1):(Header 2 head2):rest, [])
       else ((promoteHeaders 2 rest), head1 ++ [Str ":", Space] ++ head2)
titleTransform ((Header 1 head1):rest) =       -- title, no subtitle
    if (any isHeader1 rest)
       then ((Header 1 head1):rest, [])
       else ((promoteHeaders 1 rest), head1)
titleTransform blocks = (blocks, [])

parseRST = do
  state <- getState
  input <- getInput
  blocks <- parseBlocks   -- first pass
  let anonymousKeys = filter isAnonKeyBlock blocks
  let blocks' = if (null anonymousKeys)
                   then blocks
                   else -- run parser again to fill in anonymous links...
                        case runParser parseBlocks 
                             (state { stateKeyBlocks = anonymousKeys }) 
                             "RST source, second pass" input of
                                Left err   -> error $ "\nError:\n" ++ show err
                                Right result -> 
                                  (filter isNotAnonKeyBlock result)
  let (blocks'', title) = if stateStandalone state
                             then titleTransform blocks'
                             else (blocks', [])
  state <- getState
  let authors = stateAuthors state
  let date = stateDate state
  let title' = if (null title) then (stateTitle state) else title
  return (Pandoc (Meta title' authors date) blocks'')

--
-- parsing blocks
--

parseBlocks = do
  result <- manyTill block eof
  return result

block = choice [ codeBlock, rawHtmlBlock, rawLaTeXBlock, blockQuote, 
                 referenceKey, imageBlock, unknownDirective, header,
                 hrule, list, fieldList, lineBlock, para, plain,
                 blankBlock, nullBlock ] <?> "block"

--
-- field list
--

fieldListItem = try (do
  char ':'
  name <- many1 alphaNum
  string ": "
  skipSpaces
  first <- manyTill anyChar newline
  rest <- many (do
                  notFollowedBy (char ':')
                  notFollowedBy blankline 
                  skipSpaces
                  manyTill anyChar newline )
  return (name, (joinWithSep " " (first:rest)))) 

fieldList = try (do
  items <- many1 fieldListItem
  blanklines
  let authors = case (lookup "Authors" items) of
                  Just auth -> [auth]
                  Nothing  -> map snd (filter (\(x,y) -> x == "Author") items)
  let date = case (lookup "Date" items) of
                  Just dat -> dat
                  Nothing  -> ""
  let title = case (lookup "Title" items) of
                  Just tit -> [Str tit]
                  Nothing  -> []
  let remaining = filter (\(x,y) -> (x /= "Authors") && (x /= "Author") && 
                  (x /= "Date") && (x /= "Title")) items
  let result = map (\(x,y) -> 
               Para [Strong [Str x], Str ":", Space, Str y]) remaining
  updateState (\st -> st { stateAuthors = authors, 
                           stateDate = date, 
                           stateTitle = title })
  return (BlockQuote result))

--
-- line block
--

lineBlockLine = try (do
  string "| "
  white <- many (oneOf " \t")
  line <- manyTill inline newline
  let line' = (if null white then [] else [Str white]) ++ line ++ [LineBreak]
  return line')

lineBlock = try (do
  lines <- many1 lineBlockLine
  blanklines
  return $ Para (concat lines))

--
-- paragraph block
--

para = choice [ paraBeforeCodeBlock, paraNormal ] <?> "paragraph"

codeBlockStart = try (do
  string "::"
  blankline
  blankline)

-- paragraph that ends in a :: starting a code block
paraBeforeCodeBlock = try (do
  result <- many1 (do {notFollowedBy' codeBlockStart; inline})
  followedBy' (string "::")
  return (Para (if (last result == Space)
                   then normalizeSpaces result
                   else (normalizeSpaces result) ++ [Str ":"])))

-- regular paragraph
paraNormal = try (do 
  result <- many1 inline
  newline
  blanklines
  let result' = normalizeSpaces result
  return (Para result'))

plain = do
  result <- many1 inline
  let result' = normalizeSpaces result
  return (Plain result')

--
-- image block
--

imageBlock = try (do
  string ".. image:: "
  src <- manyTill anyChar newline
  return (Plain [Image [Str "image"] (Src src "")]))

--
-- header blocks
--

header = choice [ doubleHeader, singleHeader ] <?> "header"

-- a header with lines on top and bottom
doubleHeader = try (do
  c <- oneOf underlineChars
  rest <- many (char c)  -- the top line
  let lenTop = length (c:rest)
  skipSpaces
  newline
  txt <- many1 (do {notFollowedBy blankline; inline})
  pos <- getPosition  
  let len = (sourceColumn pos) - 1
  if (len > lenTop) then fail "title longer than border" else (do {return ()})
  blankline              -- spaces and newline
  count lenTop (char c)  -- the bottom line
  blanklines
  -- check to see if we've had this kind of header before.  
  -- if so, get appropriate level.  if not, add to list.
  state <- getState
  let headerTable = stateHeaderTable state
  let (headerTable',level) = case findIndex (== DoubleHeader c) headerTable of
        Just ind -> (headerTable, ind + 1)
        Nothing -> (headerTable ++ [DoubleHeader c], (length headerTable) + 1)
  setState (state { stateHeaderTable = headerTable' })
  return (Header level (normalizeSpaces txt)))

-- a header with line on the bottom only
singleHeader = try (do 
  notFollowedBy' whitespace
  txt <- many1 (do {notFollowedBy blankline; inline})
  pos <- getPosition
  let len = (sourceColumn pos) - 1
  blankline
  c <- oneOf underlineChars
  rest <- count (len - 1) (char c)
  many (char c)
  blanklines
  state <- getState
  let headerTable = stateHeaderTable state
  let (headerTable',level) = case findIndex (== SingleHeader c) headerTable of
        Just ind -> (headerTable, ind + 1)
        Nothing -> (headerTable ++ [SingleHeader c], (length headerTable) + 1)
  setState (state { stateHeaderTable = headerTable' })
  return (Header level (normalizeSpaces txt)))

--
-- hrule block
--

hruleWith chr = try (do
  count 4 (char chr)
  skipMany (char chr)
  skipSpaces
  newline
  blanklines
  return HorizontalRule)

hrule = choice (map hruleWith underlineChars) <?> "hrule"

--
-- code blocks
--

-- read a line indented by a given string
indentedLine indents = try (do
  string indents
  result <- manyTill anyChar newline
  return (result ++ "\n"))

-- two or more indented lines, possibly separated by blank lines
-- if variable = True, then any indent will work, but it must be consistent through the block
-- if variable = False, indent should be one tab or equivalent in spaces
indentedBlock variable = try (do 
  state <- getState
  let tabStop = stateTabStop state
  indents <- if variable
                then many1 (oneOf " \t")
                else oneOfStrings ["\t", (replicate tabStop ' ')]
  firstline <- manyTill anyChar newline
  rest <- many (choice [ indentedLine indents, 
                         try (do 
                                b <- blanklines
                                l <- indentedLine indents
                                return (b ++ l))])
  option "" blanklines
  return (firstline ++ "\n" ++ (concat rest)))

codeBlock = try (do
  codeBlockStart
  result <- indentedBlock False
  -- the False means we want one tab stop indent on each line
  return (CodeBlock (stripTrailingNewlines result)))

--
-- raw html
--

rawHtmlBlock = try (do
  string ".. raw:: html"
  blanklines
  result <- indentedBlock True
  return (RawHtml result))

--
-- raw latex
--

rawLaTeXBlock = try (do
  string ".. raw:: latex"
  blanklines
  result <- indentedBlock True
  return (Para [(TeX result)]))

--
-- block quotes
--

blockQuote = try (do
  block <- indentedBlock True
  -- parse the extracted block, which may contain various block elements:
  state <- getState
  let parsed = case runParser parseBlocks 
                    (state {stateParserContext = BlockQuoteState}) 
                    "block" (block ++ "\n\n") of
                       Left err -> error $ "Raw block:\n" ++ show block ++ 
                                           "\nError:\n" ++ show err
                       Right result -> result
  return (BlockQuote parsed))

--
-- list blocks
--

list = choice [ bulletList, orderedList ] <?> "list"

-- parses bullet list start and returns its length (inc. following whitespace)
bulletListStart = try (do
  notFollowedBy' hrule  -- because hrules start out just like lists
  marker <- oneOf bulletListMarkers
  white <- many1 spaceChar
  let len = length (marker:white)
  return len) 

withPeriodSuffix parser = try (do
  a <- parser
  b <- char '.'
  return (a ++ [b]))

withParentheses parser = try (do
  a <- char '('
  b <- parser
  c <- char ')'
  return ([a] ++ b ++ [c]))

withRightParen parser = try (do
  a <- parser
  b <- char ')'
  return (a ++ [b]))

upcaseWord = map toUpper

romanNumeral = do
  let lowerNumerals = ["i", "ii", "iii", "iiii", "iv", "v", "vi",
                       "vii", "viii", "ix", "x", "xi", "xii", "xiii",
                       "xiv", "xv", "xvi", "xvii", "xviii", "xix", "xx",
                       "xxi", "xxii", "xxiii", "xxiv" ]
  let upperNumerals = map upcaseWord lowerNumerals
  result <- choice $ map string (lowerNumerals ++ upperNumerals)
  return result

orderedListEnumerator = choice [ many1 digit, 
                                 string "#", 
                                 count 1 letter, 
                                 romanNumeral ]

-- parses ordered list start and returns its length (inc following whitespace)
orderedListStart = try (do
  marker <- choice [ withPeriodSuffix orderedListEnumerator, 
                     withParentheses orderedListEnumerator, 
                     withRightParen orderedListEnumerator ]
  white <- many1 spaceChar
  let len = length (marker ++ white)
  return len)

-- parse a line of a list item
listLine markerLength = try (do
  notFollowedBy blankline
  indentWith markerLength
  line <- manyTill anyChar newline
  return (line ++ "\n"))

-- indent by specified number of spaces (or equiv. tabs)
indentWith num = do
  state <- getState
  let tabStop = stateTabStop state
  if (num < tabStop)
     then count num  (char ' ')
     else choice [ try (count num (char ' ')), 
                   (try (do {char '\t'; count (num - tabStop) (char ' ')})) ] 

-- parse raw text for one list item, excluding start marker and continuations
rawListItem start = try (do
  markerLength <- start
  firstLine <- manyTill anyChar newline
  restLines <- many (listLine markerLength)
  return (markerLength, (firstLine ++ "\n" ++ (concat restLines))))

-- continuation of a list item - indented and separated by blankline or 
-- (in compact lists) endline.  
-- Note: nested lists are parsed as continuations.
listContinuation markerLength = try (do
  blanks <- many1 blankline
  result <- many1 (listLine markerLength)
  return (blanks ++ (concat result)))

listItem start = try (do 
  (markerLength, first) <- rawListItem start
  rest <- many (listContinuation markerLength)
  blanks <- choice [ try (do 
                            b <- many blankline
                            followedBy' start
                            return b), 
                     many1 blankline ]  -- whole list must end with blank
  -- parsing with ListItemState forces markers at beginning of lines to
  -- count as list item markers, even if not separated by blank space.
  -- see definition of "endline"
  state <- getState
  let parsed = case runParser parseBlocks 
                    (state {stateParserContext = ListItemState}) "list item"
                    raw of
                      Left err     -> error $ "Raw:\n" ++ raw ++ 
                                              "\nError:\n" ++ show err
                      Right result -> result
          where raw = concat (first:rest) ++ blanks 
  return parsed)

orderedList = try (do
  items <- many1 (listItem orderedListStart)
  let items' = compactify items
  return (OrderedList items'))

bulletList = try (do
  items <- many1 (listItem bulletListStart)
  let items' = compactify items
  return (BulletList items'))

--
-- unknown directive (e.g. comment)
--

unknownDirective = try (do
  string ".. "
  manyTill anyChar newline
  many (do
          string "   "
          char ':'
          many1 (noneOf "\n:") 
          char ':'
          many1 (noneOf "\n")
          newline)
  option "" blanklines
  return Null)

-- 
-- reference key
--

referenceKey = choice [imageKey, anonymousKey, regularKeyQuoted, regularKey]

imageKey = try (do
  string ".. |"
  ref <- manyTill inline (char '|')
  skipSpaces
  string "image::"
  src <- manyTill anyChar newline
  return (Key (normalizeSpaces ref) 
              (Src (removeLeadingTrailingSpace src) "")))

anonymousKey = try (do
  choice [string ".. __:", string "__"]
  skipSpaces
  src <- manyTill anyChar newline
  state <- getState
  return (Key [Str "_"] (Src (removeLeadingTrailingSpace src) "")))

regularKeyQuoted = try (do
  string ".. _`"
  ref <- manyTill inline (string "`:")
  skipSpaces
  src <- manyTill anyChar newline
  return (Key (normalizeSpaces ref) 
              (Src (removeLeadingTrailingSpace src) "")))

regularKey = try (do
  string ".. _"
  ref <- manyTill inline (char ':')
  skipSpaces
  src <- manyTill anyChar newline
  return (Key (normalizeSpaces ref) 
              (Src (removeLeadingTrailingSpace src) "")))

 -- 
 -- inline
 --

text = choice [ strong, emph, code, str, tabchar, whitespace, 
                endline ] <?> "text"

inline = choice [ escapedChar, special, hyphens, text, symbol ] <?> "inline"

special = choice [ link, image ] <?> "link, inline html, or image"

hyphens = try (do
  result <- many1 (char '-')
  option Space endline 
  -- don't want to treat endline after hyphen or dash as a space
  return (Str result))

escapedChar = escaped anyChar

symbol = do 
  result <- oneOf specialChars
  return (Str [result])

-- parses inline code, between codeStart and codeEnd
code = try (do 
  string "``"
  result <- manyTill anyChar (string "``")
  let result' = removeLeadingTrailingSpace $ joinWithSep " " $ lines result
  return (Code result'))

emph = do
  result <- enclosed (char '*') (char '*') inline
  return (Emph (normalizeSpaces result))

strong = do
  result <- enclosed (string "**") (string "**") inline
  return (Strong (normalizeSpaces result))

whitespace = do
  many1 spaceChar <?> "whitespace"
  return Space

tabchar = do
  tab
  return (Str "\t")

str = do 
  notFollowedBy' oneWordReferenceLink
  result <- many1 (noneOf (specialChars ++ "\t\n "))
  return (Str result)

-- an endline character that can be treated as a space, not a structural break
endline = try (do
  newline
  notFollowedBy blankline
  -- parse potential list-starts at beginning of line differently in a list:
  st <- getState
  if ((stateParserContext st) == ListItemState)
     then notFollowedBy' (choice [orderedListStart, bulletListStart])
     else option () pzero
  return Space)

--
-- links
--

link = choice [explicitLink, referenceLink, autoLink, 
               oneWordReferenceLink] <?> "link"

explicitLink = try (do
  char '`'
  label <- manyTill inline (try (do {spaces; char '<'}))
  src <- manyTill (noneOf ">\n ") (char '>')
  skipSpaces
  string "`_"
  return (Link (normalizeSpaces label) 
               (Src (removeLeadingTrailingSpace src) ""))) 

anonymousLinkEnding = try (do
  char '_'
  state <- getState
  let anonKeys = stateKeyBlocks state
  -- if there's a list of anon key refs (from previous pass), pop one off.
  -- otherwise return an anon key ref for the next pass to take care of...
  case anonKeys of
    (Key [Str "_"] src):rest -> 
        do 
          setState (state { stateKeyBlocks = rest }) 
          return src
    otherwise -> return (Ref [Str "_"]))

referenceLink = try (do
  char '`'
  label <- manyTill inline (string "`_")
  src <- option (Ref []) anonymousLinkEnding
  return (Link (normalizeSpaces label) src)) 

oneWordReferenceLink = try (do
  label <- many1 alphaNum
  char '_'
  src <- option (Ref []) anonymousLinkEnding
  notFollowedBy alphaNum    -- because this_is_not a link
  return (Link [Str label] src)) 

uriScheme = oneOfStrings [ "http://", "https://", "ftp://", "file://", 
                           "mailto:", "news:", "telnet:" ]

uri = try (do
  scheme <- uriScheme
  identifier <- many1 (noneOf " \t\n")
  return (scheme ++ identifier))

autoURI = try (do
  src <- uri
  return (Link [Str src] (Src src "")))

emailChar = alphaNum <|> oneOf "-+_."

emailAddress = try (do
  firstLetter <- alphaNum
  restAddr <- many emailChar
  let addr = firstLetter:restAddr
  char '@'
  dom <- domain
  return (addr ++ '@':dom))

domainChar = alphaNum <|> char '-'

domain = try (do
  first <- many1 domainChar
  dom <- many1 (try (do{ char '.'; many1 domainChar }))
  return (joinWithSep "." (first:dom)))

autoEmail = try (do
  src <- emailAddress
  return (Link [Str src] (Src ("mailto:" ++ src) "")))

autoLink = autoURI <|> autoEmail

-- For now, we assume that all substitution references are for images.
image = try (do
  char '|'
  ref <- manyTill inline (char '|')
  return (Image (normalizeSpaces ref) (Ref ref)))