-- This file is part of Diohsc
-- Copyright (C) 2020 Martin Bays <mbays@sdf.org>
--
-- This program is free software: you can redistribute it and/or modify
-- it under the terms of version 3 of the GNU General Public License as
-- published by the Free Software Foundation, or any later version.
--
-- You should have received a copy of the GNU General Public License
-- along with this program.  If not, see http://www.gnu.org/licenses/.

{-# LANGUAGE CPP               #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE Safe              #-}

module TextGemini where

import           Control.Monad       (forM)
import           Control.Monad.State (State, evalState, gets, modify)
import           Data.Maybe          (catMaybes, isJust, mapMaybe)

import           ANSIColour

import qualified Data.Text.Lazy      as T
import           URI

data Link = Link { linkUri :: URIRef, linkDescription :: T.Text }
    deriving (Eq,Ord,Show)

data GeminiLine
    = TextLine T.Text
    | LinkLine { linkLineIndex :: Int, linkLineLink :: Link }
    | AltTextLine T.Text
    | PreformatToggleLine
    | PreformattedLine T.Text T.Text
    | HeadingLine Int T.Text
    | ItemLine T.Text
    | QuoteLine T.Text
    | ErrorLine T.Text
    deriving (Eq,Ord,Show)

newtype GeminiDocument = GeminiDocument { geminiDocumentLines :: [GeminiLine] }
    deriving (Eq,Ord,Show)

extractLinks :: GeminiDocument -> [Link]
extractLinks (GeminiDocument ls) = mapMaybe linkOfLine ls
    where
    linkOfLine (LinkLine _ link) = Just link
    linkOfLine _                 = Nothing

data PreOpt
    = PreOptAlt
    | PreOptPre
    | PreOptBoth
    deriving (Eq,Ord,Show)

showPreOpt :: PreOpt -> String
showPreOpt PreOptAlt  = "alt"
showPreOpt PreOptPre  = "pre"
showPreOpt PreOptBoth = "both"

data GemRenderOpts = GemRenderOpts
    { grOptsAnsi          :: Bool
    , grOptsPre           :: PreOpt
    , grOptsWrapWidth     :: Int
    , grOptsLinkDescFirst :: Bool
    } deriving (Eq,Ord,Show)

printGemDoc :: GemRenderOpts -> (URIRef -> T.Text) -> GeminiDocument -> [T.Text]
printGemDoc (GemRenderOpts ansi preOpt width linkDescFirst)
        showUri (GeminiDocument doc) = concatMap printLine doc
    where
    printLine (TextLine line) = wrapWith "" False $ stripControl line
    printLine (AltTextLine line)
        | preOpt == PreOptPre || T.null line = []
        | otherwise = (:[]) $ applyIf ansi withBoldStr "`` " <> stripControl line

    printLine PreformatToggleLine = []

    printLine (PreformattedLine alt line)
        | preOpt == PreOptAlt && not (T.null alt) = []
        | otherwise =
            -- We allow \t and CSI escape sequences in preformatted text only
            let sanitise = applyIf (not ansi) (stripCSI .) sanitiseForDisplay
            in (:[]) $ applyIf ansi ((resetCode <>) . withBoldStr) "` " <> sanitise line
    printLine (HeadingLine level line) =
        wrapWith (T.take (fromIntegral level) (T.repeat '#') <> " ") False
        . applyIf ansi
            ( applyIf (level /= 2) withUnderlineStr
            . applyIf (level < 3) withBoldStr ) $ stripControl line
    printLine (ItemLine line) = wrapWith "* " False $ stripControl line
    printLine (QuoteLine line) = wrapWith "> " True $ stripControl line
    printLine (ErrorLine line) = (:[]) $ applyIf ansi (withColourStr Red)
        "! Formatting error in text/gemini: " <> line
    printLine (LinkLine n (Link uri desc)) =
        wrapWith (T.pack $ '[' : show (n+1) ++ if n+1 < 10 then "]  " else "] ") False
            $ (if T.null desc then id
                else (if linkDescFirst then id else flip) (\a b -> a <> " " <> b)
                    $ applyIf ansi (withColourStr Cyan) (stripControl desc))
                (showUri uri)

    wrapWith :: T.Text -> Bool -> T.Text -> [T.Text]
    wrapWith pre onAll line =
        concat . zipWith prependHeader lineHeaders $ wrap (width - n) line
        where
            n = visibleLength pre
            lineHeaders = (pre:) . repeat $
                if onAll then pre else T.replicate (fromIntegral n) " "
            splitWordHeader = if n > 0 then "|" <> T.replicate (fromIntegral n - 1) " " else ""
            prependHeader header (l:ls) = header <> l : ((splitWordHeader <>) <$> ls)
            prependHeader _ [] = []

    wrap :: Int -> T.Text -> [[T.Text]]
    wrap wrapWidth line = wrap' [] "" 0 $ T.words line
        where
        maxWCWidth = 2
        ww = max maxWCWidth wrapWidth
        wrap' ls l _ [] = [ls <> [l] ]
        wrap' ls l n (w:ws) =
            let nw = visibleLength w
                l' = if T.null l then w else l <> " " <> w
                n' = n + nw + (if T.null l then 0 else 1)
            in if nw > ww && n + 1 < ww
                then let (a,b) = splitAtVisible ww l'
                    in wrap' (ls <> [a]) "" 0 $ b:ws
                else if n' > ww
                    then (ls <> [l]:) $ wrap' [] "" 0 $ w:ws
                    else wrap' ls l' n' ws


data GeminiParseState = GeminiParseState { numLinks :: Int, preformatted :: Maybe T.Text }

initialParseState :: GeminiParseState
initialParseState = GeminiParseState 0 Nothing

parseGemini :: T.Text -> GeminiDocument
parseGemini text = GeminiDocument . catMaybes $ evalState
        (forM (T.lines text) (parseLine . stripTrailingCR)) initialParseState
    where
    stripTrailingCR = T.dropWhileEnd (== '\r')
    parseLine :: T.Text -> State GeminiParseState (Maybe GeminiLine)
    parseLine line = do
        pre <- gets preformatted
        case T.take 1 line of
            "`" | T.take 3 line == "```", isJust pre ->  do
                modify $ \s -> s { preformatted = Nothing }
                return $ case T.strip $ T.drop 3 line of
                    "" -> Nothing
                    _ -> Just . ErrorLine $ "Illegal non-empty text after closing '```'"
                    -- ^The spec says we MUST ignore any text on a "```" line closing a preformatted
                    -- block. This seems like a gaping extensibility hole to me, so I'm interpreting it
                    -- as not disallowing an error message.
            "`" | T.take 3 line == "```" ->
                let alt = T.strip $ T.drop 3 line in do
                    modify $ \s -> s { preformatted = Just alt }
                    return . Just . AltTextLine $ alt
            _ | Just alt <- pre ->
                return . Just $ PreformattedLine alt line
            "=" | T.take 2 line == "=>" ->
                case parseLink . T.dropWhile isGemWhitespace $ T.drop 2 line of
                    Nothing -> return . Just . ErrorLine $ "Unparseable link line: " <> line
                    Just link -> do
                        n <- gets numLinks
                        modify $ \s -> s { numLinks = n + 1 }
                        return . Just $ LinkLine n link
            "#" | headers <- T.length . T.takeWhile (== '#') $ line,
                    headers > 0 && headers < 4 ->
                return . Just . HeadingLine (fromIntegral headers) .
                    T.dropWhile isGemWhitespace . T.dropWhile (== '#') $ line
            "*" | T.take 2 line == "* " ->
                return . Just . ItemLine $ T.drop 2 line
            ">" ->
                return . Just . QuoteLine $ T.drop 1 line
            _ ->
                return . Just $ TextLine line

    parseLink :: T.Text -> Maybe Link
    parseLink linkInfo =
        let uriText = T.takeWhile (not . isGemWhitespace) linkInfo
            desc = T.dropWhile isGemWhitespace . T.dropWhile (not . isGemWhitespace) $ linkInfo
        in (`Link` desc) <$> parseUriReference (
#ifdef IRILinks
        escapeIRI $
#endif
        T.unpack uriText)

    isGemWhitespace :: Char -> Bool
    isGemWhitespace = (`elem` (" \t"::String))