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

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

Conversion of markdown-formatted plain text to 'Pandoc' document.
-}
module Text.Pandoc.Readers.Markdown ( 
                                     readMarkdown 
                                    ) where

import Data.List ( findIndex, sortBy )
import Text.ParserCombinators.Pandoc
import Text.Pandoc.Definition
import Text.Pandoc.Readers.LaTeX ( rawLaTeXInline, rawLaTeXEnvironment )
import Text.Pandoc.Shared 
import Text.Pandoc.Readers.HTML ( rawHtmlInline, rawHtmlBlock, 
                                  anyHtmlBlockTag, anyHtmlInlineTag )
import Text.Pandoc.HtmlEntities ( decodeEntities )
import Text.Regex ( matchRegex, mkRegex )
import Text.ParserCombinators.Parsec

-- | Read markdown from an input string and return a Pandoc document.
readMarkdown :: ParserState -> String -> Pandoc
readMarkdown = readWith parseMarkdown

-- | Parse markdown string with default options and print result (for testing).
testString :: String -> IO ()
testString = testStringWith parseMarkdown 

--
-- Constants and data structure definitions
--

spaceChars = " \t"
endLineChars = "\n"
labelStart = '['
labelEnd = ']'
labelSep = ':'
srcStart = '('
srcEnd = ')'
imageStart = '!'
noteStart = '^'
codeStart = '`'
codeEnd = '`'
emphStart = '*'
emphEnd = '*'
emphStartAlt = '_'
emphEndAlt = '_'
autoLinkStart = '<'
autoLinkEnd = '>'
mathStart = '$'
mathEnd = '$'
bulletListMarkers = "*+-"
orderedListDelimiters = ".)"
escapeChar = '\\'
hruleChars = "*-_"
quoteChars = "'\""
atxHChar = '#'
titleOpeners = "\"'("
setextHChars = ['=','-']
blockQuoteChar = '>'
hyphenChar = '-'

-- treat these as potentially non-text when parsing inline:
specialChars = [escapeChar, labelStart, labelEnd, emphStart, emphEnd,
                emphStartAlt, emphEndAlt, codeStart, codeEnd, autoLinkEnd,
                autoLinkStart, mathStart, mathEnd, imageStart, noteStart,
                hyphenChar]

--
-- auxiliary functions
--

-- | Skip a single endline if there is one.
skipEndline = option Space endline

indentSpaces = do
  state <- getState
  let tabStop = stateTabStop state
  oneOfStrings [ "\t", (replicate tabStop ' ') ] <?> "indentation"

skipNonindentSpaces = do
  state <- getState
  let tabStop = stateTabStop state
  choice (map (\n -> (try (count n (char ' ')))) (reverse [0..(tabStop - 1)]))

--
-- document structure
--

titleLine = try (do
  char '%'
  skipSpaces
  line <- manyTill inline newline
  return line)

authorsLine = try (do
  char '%'
  skipSpaces
  authors <- sepEndBy (many1 (noneOf ",;\n")) (oneOf ",;")
  newline
  return (map removeLeadingTrailingSpace authors))

dateLine = try (do
  char '%'
  skipSpaces
  date <- many (noneOf "\n")
  newline
  return (removeTrailingSpace date))

titleBlock = try (do
  title <- option [] titleLine
  author <- option [] authorsLine
  date <- option "" dateLine
  option "" blanklines
  return (title, author, date))

-- | Returns the number assigned to a Note block
numberOfNote :: Block -> Int
numberOfNote (Note ref _) = (read ref) 
numberOfNote _ = 0 

parseMarkdown = do
  updateState (\state -> state { stateParseRaw = True }) 
  -- need to parse raw HTML, since markdown allows it
  (title, author, date) <- option ([],[],"") titleBlock
  blocks <- parseBlocks
  let blocks' = filter (/= Null) blocks
  state <- getState
  let keys = reverse $ stateKeyBlocks state
  let notes = reverse $ stateNoteBlocks state
  let sortedNotes = sortBy (\x y -> compare (numberOfNote x) 
                           (numberOfNote y)) notes
  return (Pandoc (Meta title author date) (blocks' ++ sortedNotes ++ keys))

--
-- parsing blocks
--

parseBlocks = do
  result <- manyTill block eof
  return result

block = choice [ codeBlock, note, referenceKey, header, hrule, list, 
                 blockQuote, rawHtmlBlocks, rawLaTeXEnvironment, para,
                 plain, blankBlock, nullBlock ] <?> "block"

--
-- header blocks
--

header = choice [ setextHeader, atxHeader ] <?> "header"

atxHeader = try (do
  lead <- many1 (char atxHChar)
  skipSpaces
  txt <- manyTill inline atxClosing
  return (Header (length lead) (normalizeSpaces txt)))

atxClosing = try (do
  skipMany (char atxHChar)
  skipSpaces
  newline
  option "" blanklines)

setextHeader = choice $ 
               map (\x -> setextH x) (enumFromTo 1 (length setextHChars))

setextH n = try (do
  txt <- many1 (do {notFollowedBy newline; inline})
  endline
  many1 (char (setextHChars !! (n-1)))
  skipSpaces
  newline
  option "" blanklines
  return (Header n (normalizeSpaces txt)))

--
-- hrule block
--

hruleWith chr = try (do
  skipSpaces
  char chr
  skipSpaces
  char chr
  skipSpaces
  char chr
  skipMany (oneOf (chr:spaceChars))
  newline
  option "" blanklines
  return HorizontalRule)

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

--
-- code blocks
--

indentedLine = try (do
  indentSpaces
  result <- manyTill anyChar newline
  return (result ++ "\n"))

-- two or more indented lines, possibly separated by blank lines
indentedBlock = try (do 
  res1 <- indentedLine
  blanks <- many blankline 
  res2 <- choice [indentedBlock, indentedLine]
  return (res1 ++ blanks ++ res2))

codeBlock = do
  result <- choice [indentedBlock, indentedLine]
  option "" blanklines
  return (CodeBlock (stripTrailingNewlines result))

--
-- note block
--

rawLine = try (do
  notFollowedBy' blankline
  notFollowedBy' noteMarker
  contents <- many1 nonEndline
  end <- option "" (do
                      newline
                      option "" indentSpaces
                      return "\n")
  return (contents ++ end))

rawLines = do
    lines <- many1 rawLine
    return (concat lines)

note = try (do
  ref <- noteMarker
  char ':'
  skipSpaces
  skipEndline
  raw <- sepBy rawLines (try (do {blankline; indentSpaces}))
  option "" blanklines
  -- parse the extracted text, which may contain various block elements:
  state <- getState
  let parsed = case runParser parseBlocks 
                    (state {stateParserContext = BlockQuoteState}) "block" 
                    ((joinWithSep "\n" raw) ++ "\n\n") of
                       Left err     -> error $ "Raw block:\n" ++ show raw ++
                                       "\nError:\n" ++ show err
                       Right result -> result 
  let identifiers = stateNoteIdentifiers state
  case (findIndex (== ref) identifiers) of
    Just n  -> updateState (\s -> s {stateNoteBlocks = 
               (Note (show (n+1)) parsed):(stateNoteBlocks s)})
    Nothing -> updateState id 
  return Null)

--
-- block quotes
--

emacsBoxQuote = try (do
  string ",----"
  manyTill anyChar newline
  raw <- manyTill (try (do 
                          char '|'
                          option ' ' (char ' ')
                          result <- manyTill anyChar newline
                          return result))
                   (string "`----")
  manyTill anyChar newline
  option "" blanklines
  return raw)

emailBlockQuoteStart = try (do
  skipNonindentSpaces
  char blockQuoteChar
  option ' ' (char ' ')
  return "> ")

emailBlockQuote = try (do
  emailBlockQuoteStart
  raw <- sepBy (many (choice [nonEndline, 
                              (try (do 
                                      endline
                                      notFollowedBy' emailBlockQuoteStart
                                      return '\n'))]))
               (try (do {newline; emailBlockQuoteStart}))
  newline <|> (do{ eof; return '\n' })
  option "" blanklines
  return raw)

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

--
-- list blocks
--

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

bulletListStart = try (do
  option ' ' newline -- if preceded by a Plain block in a list context
  skipNonindentSpaces
  notFollowedBy' hrule  -- because hrules start out just like lists
  oneOf bulletListMarkers
  spaceChar
  skipSpaces)

orderedListStart = try (do
  option ' ' newline -- if preceded by a Plain block in a list context
  skipNonindentSpaces
  many1 digit <|> count 1 letter
  oneOf orderedListDelimiters
  oneOf spaceChars
  skipSpaces)

-- parse a line of a list item (start = parser for beginning of list item)
listLine start = try (do
  notFollowedBy' start
  notFollowedBy blankline
  notFollowedBy' (do 
                    indentSpaces
                    many (spaceChar)
                    choice [bulletListStart, orderedListStart])
  line <- manyTill anyChar newline
  return (line ++ "\n"))

-- parse raw text for one list item, excluding start marker and continuations
rawListItem start = try (do
  start
  result <- many1 (listLine start)
  blanks <- many blankline
  return ((concat result) ++ blanks))

-- continuation of a list item - indented and separated by blankline 
-- or (in compact lists) endline.
-- note: nested lists are parsed as continuations
listContinuation start = try (do
  followedBy' indentSpaces
  result <- many1 (listContinuationLine start)
  blanks <- many blankline
  return ((concat result) ++ blanks))

listContinuationLine start = try (do
  notFollowedBy' blankline
  notFollowedBy' start
  option "" indentSpaces
  result <- manyTill anyChar newline
  return (result ++ "\n"))

listItem start = try (do 
  first <- rawListItem start
  rest <- many (listContinuation start)
  -- 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}) 
                    "block" raw of
                       Left err     -> error $ "Raw block:\n" ++ raw ++ 
                                       "\nError:\n" ++ show err
                       Right result -> result
          where raw = concat (first:rest) 
  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'))

--
-- paragraph block
--

para = try (do 
  result <- many1 inline
  newline
  choice [ (do 
              followedBy' (oneOfStrings [">", ",----"])
              return "" ), 
           blanklines ]  
  let result' = normalizeSpaces result
  return (Para result'))

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

-- 
-- raw html
--

rawHtmlBlocks = try (do
  htmlBlocks <- many1 rawHtmlBlock    
  let combined = concatMap (\(RawHtml str) -> str) htmlBlocks
  let combined' = if (last combined == '\n')
                     then init combined  -- strip extra newline 
                     else combined 
  return (RawHtml combined'))

-- 
-- reference key
--

referenceKey = try (do
  skipSpaces
  label <- reference
  char labelSep
  skipSpaces
  option ' ' (char autoLinkStart)
  src <- many (noneOf (titleOpeners ++ [autoLinkEnd] ++ endLineChars))
  option ' ' (char autoLinkEnd)
  tit <- option "" title 
  blanklines 
  return (Key label (Src (removeTrailingSpace src) tit))) 

-- 
-- inline
--

text = choice [ math, strong, emph, code2, code1, str, linebreak, tabchar, 
                whitespace, endline ] <?> "text"

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

special = choice [ noteRef, inlineNote, link, referenceLink, rawHtmlInline, 
                   autoLink, image ] <?> "link, inline html, note, or image"

escapedChar = escaped anyChar

ltSign = try (do
  notFollowedBy' rawHtmlBlocks -- don't return < if it starts html
  char '<'
  return (Str ['<']))

specialCharsMinusLt = filter (/= '<') specialChars

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

hyphens = try (do
  result <- many1 (char '-')
  if (length result) == 1
     then skipEndline   -- don't want to treat endline after hyphen as a space
     else do{ string ""; return Space }
  return (Str result))

-- parses inline code, between codeStart and codeEnd
code1 = try (do 
  char codeStart
  result <- many (noneOf [codeEnd])
  char codeEnd
  -- get rid of any internal newlines
  let result' = removeLeadingTrailingSpace $ joinWithSep " " $ lines result
  return (Code result'))

-- parses inline code, between 2 codeStarts and 2 codeEnds
code2 = try (do
  string [codeStart, codeStart]
  result <- manyTill anyChar (try (string [codeEnd, codeEnd]))
  let result' = removeLeadingTrailingSpace $ joinWithSep " " $ lines result
  -- get rid of any internal newlines
  return (Code result'))

mathWord = many1 (choice [ (noneOf (" \t\n\\" ++ [mathEnd])), 
                           (try (do
                                   c <- char '\\'
                                   notFollowedBy (char mathEnd)
                                   return c))])

math = try (do
  char mathStart
  notFollowedBy space
  words <- sepBy1 mathWord (many1 space)
  char mathEnd
  return (TeX ("$" ++ (joinWithSep " " words) ++ "$")))

emph = do
  result <- choice [ (enclosed (char emphStart) (char emphEnd) inline), 
                     (enclosed (char emphStartAlt) (char emphEndAlt) inline) ]
  return (Emph (normalizeSpaces result))

strong = do
  result <- choice [ (enclosed (count 2 (char emphStart)) 
                               (count 2 (char emphEnd)) inline), 
                     (enclosed (count 2 (char emphStartAlt)) 
                               (count 2 (char emphEndAlt)) inline) ]
  return (Strong (normalizeSpaces result))

whitespace = do
  many1 (oneOf spaceChars) <?> "whitespace"
  return Space

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

-- hard line break
linebreak = try (do
  oneOf spaceChars
  many1 (oneOf spaceChars) 
  endline
  return LineBreak )

nonEndline = noneOf endLineChars

str = do 
  result <- many1 ((noneOf (specialChars ++ spaceChars ++ endLineChars))) 
  return (Str (decodeEntities result))

-- an endline character that can be treated as a space, not a structural break
endline = try (do
  newline
  -- next line would allow block quotes without preceding blank line
  -- Markdown.pl does allow this, but there's a chance of a wrapped
  -- greater-than sign triggering a block quote by accident...
  -- notFollowedBy' (choice [emailBlockQuoteStart, string ",----"])  
  notFollowedBy blankline
  -- parse potential list-starts differently if in a list:
  st <- getState
  if (stateParserContext st) == ListItemState
     then do
            notFollowedBy' orderedListStart
            notFollowedBy' bulletListStart
     else option () pzero
  return Space)

--
-- links
--

-- a reference label for a link
reference = do
  char labelStart
  notFollowedBy (char noteStart)
  label <- manyTill inline (char labelEnd)
  return (normalizeSpaces label)

-- source for a link, with optional title
source = try (do 
  char srcStart
  option ' ' (char autoLinkStart)
  src <- many (noneOf ([srcEnd, autoLinkEnd] ++ titleOpeners))
  option ' ' (char autoLinkEnd)
  tit <- option "" title
  skipSpaces
  char srcEnd
  return (Src (removeTrailingSpace src) tit))

titleWith startChar endChar = try (do
  skipSpaces
  skipEndline  -- a title can be on the next line from the source
  skipSpaces
  char startChar
  tit <- manyTill (choice [ try (do {char '\\'; char endChar}), 
                            (noneOf (endChar:endLineChars)) ]) (char endChar) 
  let tit' = gsub "\"" "&quot;" tit
  return tit')

title = choice [ titleWith '(' ')', 
                 titleWith '"' '"', 
                 titleWith '\'' '\''] <?> "title"

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

explicitLink = try (do
  label <- reference
  src <- source 
  return (Link label src)) 

referenceLink = choice [referenceLinkDouble, referenceLinkSingle]

-- a link like [this][/url/]
referenceLinkDouble = try (do
  label <- reference
  skipSpaces
  skipEndline
  skipSpaces
  ref <- reference 
  return (Link label (Ref ref))) 

-- a link like [this]
referenceLinkSingle = try (do
  label <- reference
  return (Link label (Ref []))) 

-- a link <like.this.com>
autoLink = try (do
  notFollowedBy' anyHtmlBlockTag
  src <- between (char autoLinkStart) (char autoLinkEnd) 
         (many (noneOf (spaceChars ++ endLineChars ++ [autoLinkEnd])))
  case (matchRegex emailAddress src) of
    Just _  -> return (Link [Str src] (Src ("mailto:" ++ src) ""))
    Nothing -> return (Link [Str src] (Src src ""))) 

emailAddress = 
    mkRegex "([^@:/]+)@(([^.]+[.]?)*([^.]+))"  -- presupposes no whitespace

image = try (do
  char imageStart
  (Link label src) <- link
  return (Image label src)) 

noteMarker = try (do
  char labelStart
  char noteStart
  manyTill (noneOf " \t\n") (char labelEnd))

noteRef = try (do
  ref <- noteMarker
  state <- getState
  let identifiers = (stateNoteIdentifiers state) ++ [ref] 
  updateState (\st -> st {stateNoteIdentifiers = identifiers})
  return (NoteRef (show (length identifiers))))

inlineNote = try (do
  char noteStart
  char labelStart
  contents <- manyTill inline (char labelEnd)
  state <- getState
  let identifiers = stateNoteIdentifiers state
  let ref = show $ (length identifiers) + 1
  let noteBlocks = stateNoteBlocks state
  updateState (\st -> st {stateNoteIdentifiers = (identifiers ++ [ref]),
                          stateNoteBlocks = 
                               (Note ref [Para contents]):noteBlocks})
  return (NoteRef ref))