{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE UndecidableInstances #-}
module Symantic.Document.Plain where

import Data.Bool
import Data.Char (Char)
import Data.Eq (Eq(..))
import Data.Foldable (foldr)
import Data.Function (($), (.), id)
import Data.Functor ((<$>))
import Data.Maybe (Maybe(..))
import Data.Monoid (Monoid(..))
import Data.Ord (Ord(..), Ordering(..))
import Data.Semigroup (Semigroup(..))
import Data.String (String, IsString(..))
import Data.Text (Text)
import GHC.Natural (minusNatural,quotRemNatural)
import Numeric.Natural (Natural)
import Prelude (fromIntegral, Num(..))
import System.Console.ANSI
import Text.Show (Show(..), showString, showParen)
import qualified Data.List as List
import qualified Data.Text.Lazy as TL

import Symantic.Document.API

-- * Type 'Plain'
-- | Church encoded for performance concerns.
-- Kind like 'ParsecT' in @megaparsec@ but a little bit different
-- due to the use of 'PlainFit' for implementing 'breakingSpace' correctly
-- when in the left hand side of ('<>').
-- Prepending is done using continuation, like in a difference list.
newtype Plain d = Plain
 { unPlain ::
     {-curr-}PlainInh ->
     {-curr-}PlainState d ->
     {-ok-}( ({-prepend-}(d->d), {-new-}PlainState d) -> PlainFit d) ->
     PlainFit d
     -- NOTE: equivalent to:
     -- ReaderT PlainInh (StateT (PlainState d) (Cont (PlainFit d))) (d->d)
 }

runPlain :: Monoid d => Plain d -> d
runPlain x =
	unPlain x
	 defPlainInh
	 defPlainState
	 {-k-}(\(px,_sx) fits _overflow ->
		-- NOTE: if px fits, then appending mempty fits
		fits (px mempty) )
	 {-fits-}id
	 {-overflow-}id

-- ** Type 'PlainState'
data PlainState d = PlainState
 { plainState_buffer          :: ![PlainChunk d]
 , plainState_bufferStart     :: !Column
 , plainState_bufferWidth     :: !Width
 , plainState_removableIndent :: !Indent
   -- ^ The amount of 'Indent' added by 'breakspace'
   -- that can be removed by breaking the 'space' into a 'newline'.
 } deriving (Show)

defPlainState :: PlainState d
defPlainState = PlainState
 { plainState_buffer          = mempty
 , plainState_bufferStart     = 0
 , plainState_bufferWidth     = 0
 , plainState_removableIndent = 0
 }

-- ** Type 'PlainInh'
data PlainInh = PlainInh
 { plainInh_width   :: !(Maybe Column)
 , plainInh_justify :: !Bool
 , plainInh_indent  :: !Width
 } deriving (Show)

defPlainInh :: PlainInh
defPlainInh = PlainInh
 { plainInh_width   = Nothing
 , plainInh_justify = False
 , plainInh_indent  = 0
 }

-- ** Type 'PlainFit'
-- | Double continuation to qualify the returned document
-- as fitting or overflowing the given 'plainInh_width'.
-- It's like @('Bool',d)@ in a normal style
-- (a non continuation-passing-style).
type PlainFit d = {-fits-}(d -> d) ->
                  {-overflow-}(d -> d) ->
                  d

-- ** Type 'PlainChunk'
data PlainChunk d
 =   PlainChunk_Ignored d
     -- ^ Ignored by the justification but kept in place.
     -- Used for instance to put ANSI sequences.
 |   PlainChunk_Word (Word d)
 |   PlainChunk_Spaces Width
     -- ^ 'spaces' preserved to be interleaved
     -- correctly with 'PlainChunk_Ignored'.
instance Show d => Show (PlainChunk d) where
	showsPrec p x =
		showParen (p>10) $
		case x of
		 PlainChunk_Ignored d ->
			showString "Z " .
			showsPrec 11 d
		 PlainChunk_Word (Word d) ->
			showString "W " .
			showsPrec 11 d
		 PlainChunk_Spaces s ->
			showString "S " .
			showsPrec 11 s
instance Lengthable d => Lengthable (PlainChunk d) where
	length = \case
	 PlainChunk_Ignored{} -> 0
	 PlainChunk_Word d -> length d
	 PlainChunk_Spaces s -> s
	nullLength = \case
	 PlainChunk_Ignored{} -> True
	 PlainChunk_Word d -> nullLength d
	 PlainChunk_Spaces s -> s == 0
instance DocFrom [SGR] d => DocFrom [SGR] (PlainChunk d) where
	docFrom sgr = PlainChunk_Ignored (docFrom sgr)

runPlainChunk :: Spaceable d => PlainChunk d -> d
runPlainChunk = \case
 PlainChunk_Ignored d -> d
 PlainChunk_Word (Word d) -> d
 PlainChunk_Spaces s -> spaces s

instance Semigroup d => Semigroup (Plain d) where
	Plain x <> Plain y = Plain $ \inh st k ->
		x inh st $ \(px,sx) ->
			y inh sx $ \(py,sy) ->
				k (px.py,sy)
instance Monoid d => Monoid (Plain d) where
	mempty = Plain $ \_inh st k -> k (id,st)
	mappend = (<>)
instance (Spaceable d) => Spaceable (Plain d) where
	newline = Plain $ \inh st k ->
		k(\next ->
			(if plainInh_justify inh then joinLine inh st else mempty) <>
			newline<>spaces (plainInh_indent inh)<>next
		 , st
			 { plainState_bufferStart      = plainInh_indent inh
			 , plainState_bufferWidth      = 0
			 , plainState_buffer           = mempty
			 }
		 )
	space = spaces 1
	spaces n = Plain $ \inh st@PlainState{..} k fits overflow ->
		let newWidth = plainState_bufferStart + plainState_bufferWidth + n in
		if plainInh_justify inh
		then
			let newState =
				case plainState_buffer of
				 PlainChunk_Spaces s:bs -> st
					 { plainState_buffer      = PlainChunk_Spaces (s+n):bs
					 }
				 _ -> st
					 { plainState_buffer      = PlainChunk_Spaces n:plainState_buffer
					 , plainState_bufferWidth = plainState_bufferWidth + 1
					 }
			in
			case plainInh_width inh of
			 Just width | width < newWidth ->
				overflow $ k (id{-(d<>)-}, newState) fits overflow
			 _ -> k (id{-(d<>)-}, newState) fits overflow
		else
			let newState = st
				 { plainState_bufferWidth = plainState_bufferWidth + n
				 } in
			case plainInh_width inh of
			 Just width | width < newWidth ->
				overflow $ k ((spaces n <>), newState) fits fits
			 _ -> k ((spaces n <>), newState) fits overflow
instance (DocFrom (Word s) d, Semigroup d, Lengthable s) => DocFrom (Word s) (Plain d) where
	docFrom s = Plain $ \inh st@PlainState{..} k fits overflow ->
		let wordLen = length s in
		if wordLen <= 0
		then k (id,st) fits overflow
		else
			let newBufferWidth = plainState_bufferWidth + wordLen in
			let newWidth = plainState_bufferStart + newBufferWidth in
			if plainInh_justify inh
			then
				let newState = st
					 { plainState_buffer =
						PlainChunk_Word (Word (docFrom s)) :
						plainState_buffer
					 , plainState_bufferWidth = newBufferWidth
					 } in
				case plainInh_width inh of
				 Just width | width < newWidth ->
					overflow $ k (id, newState) fits overflow
				 _ -> k (id, newState) fits overflow
			else
				let newState = st
					 { plainState_bufferWidth = newBufferWidth
					 } in
				case plainInh_width inh of
				 Just width | width < newWidth ->
					overflow $ k ((docFrom s <>), newState) fits fits
				 _ -> k ((docFrom s <>), newState) fits overflow
instance (DocFrom (Word s) d, Lengthable s, Spaceable d, Splitable s) =>
         DocFrom (Line s) (Plain d) where
	docFrom =
		mconcat .
		List.intersperse breakspace .
		(docFrom <$>) .
		words .
		unLine
instance Spaceable d => Indentable (Plain d) where
	align p = Plain $ \inh st ->
		let currInd = plainState_bufferStart st + plainState_bufferWidth st in
		unPlain p inh{plainInh_indent=currInd} st
	incrIndent i p = Plain $ \inh ->
		unPlain p inh{plainInh_indent = plainInh_indent inh + i}
	setIndent i p = Plain $ \inh ->
		unPlain p inh{plainInh_indent=i}
	fill m p = Plain $ \inh0 st0 ->
		let col0 = plainState_bufferStart st0 + plainState_bufferWidth st0 in
		let p1 = Plain $ \inh1 st1 ->
			let col1 = plainState_bufferStart st1 + plainState_bufferWidth st1 in
			let w | col0 <= col1 = col1`minusNatural`col0
			      | otherwise    = col0`minusNatural`col1 in
			unPlain
			 (if w<=m
				then spaces (m`minusNatural`w)
				else mempty)
			 inh1 st1
		in
		unPlain (p <> p1) inh0 st0
	breakfill m p = Plain $ \inh0 st0 ->
		let col0 = plainState_bufferStart st0 + plainState_bufferWidth st0 in
		let p1 = Plain $ \inh1 st1 ->
			let col1 = plainState_bufferStart st1 + plainState_bufferWidth st1 in
			let w | col0 <= col1 = col1`minusNatural`col0
			      | otherwise    = col0`minusNatural`col1 in
			unPlain
			 (case w`compare`m of
				 LT -> spaces (m`minusNatural`w)
				 EQ -> mempty
				 GT -> setIndent (col0 + m) newline)
			 inh1 st1
		in
		unPlain (p <> p1) inh0 st0
instance Spaceable d => Justifiable (Plain d) where
	justify p = (<> flushLastLine) $ Plain $ \inh ->
		unPlain p inh{plainInh_justify=True}
		where
		flushLastLine :: Plain d
		flushLastLine = Plain $ \_inh st@PlainState{..} ok ->
			ok
			 ( (joinPlainLine (collapseSpaces <$> List.reverse plainState_buffer) <>)
			 , st
				 { plainState_bufferStart      = plainState_bufferStart + plainState_bufferWidth
				 , plainState_bufferWidth      = 0
				 , plainState_buffer           = mempty
				 }
			 )
		collapseSpaces = \case
		 PlainChunk_Spaces s -> PlainChunk_Spaces (if s > 0 then 1 else 0)
		 x -> x
instance (Spaceable d) => Wrappable (Plain d) where
	setWidth w p = Plain $ \inh ->
		unPlain p inh{plainInh_width=w}
	breakpoint = Plain $ \inh st k fits overflow ->
		let newlineInd = plainInh_indent inh in
		k
		 ( id
		 , st
			 { plainState_removableIndent  = newlineInd
			 }
		 )
		 fits
		 {-overflow-}(\_r ->
			unPlain newline inh st k
			 fits
			 {-overflow-}(
				if plainState_removableIndent st < newlineInd
				then overflow
				else fits
			 )
		 )
	breakspace = Plain $ \inh st k fits overflow ->
		let newlineInd = plainInh_indent inh in
		k
		 ( if plainInh_justify inh then id else (space <>)
		 , st
			 { plainState_buffer =
				case plainState_buffer st of
				 PlainChunk_Spaces s:bs -> PlainChunk_Spaces (s+1):bs
				 bs -> PlainChunk_Spaces 1:bs
			 , plainState_bufferWidth      = plainState_bufferWidth st + 1
			 , plainState_removableIndent  = newlineInd
			 }
		 )
		 fits
		 {-overflow-}(\_r ->
			unPlain newline inh st k
			 fits
			 {-overflow-}(
				if plainState_removableIndent st < newlineInd
				then overflow
				else fits
			 )
		 )
	breakalt x y = Plain $ \inh st k fits overflow ->
		unPlain x inh st k fits
		 {-overflow-}(\_r ->
			unPlain y inh st k fits overflow
		 )
-- String
instance (DocFrom (Word String) d, Spaceable d) =>
         DocFrom String (Plain d) where
	docFrom =
		mconcat .
		List.intersperse newline .
		(docFrom <$>) .
		lines
instance (DocFrom (Word String) d, Spaceable d) =>
         IsString (Plain d) where
	fromString = docFrom
-- Text
instance (DocFrom (Word Text) d, Spaceable d) =>
         DocFrom Text (Plain d) where
	docFrom =
		mconcat .
		List.intersperse newline .
		(docFrom <$>) .
		lines
instance (DocFrom (Word TL.Text) d, Spaceable d) =>
         DocFrom TL.Text (Plain d) where
	docFrom =
		mconcat .
		List.intersperse newline .
		(docFrom <$>) .
		lines
-- Char
instance (DocFrom (Word Char) d, Spaceable d) =>
         DocFrom Char (Plain d) where
	docFrom ' '  = breakspace
	docFrom '\n' = newline
	docFrom c    = docFrom (Word c)


instance (DocFrom [SGR] d, Semigroup d) => DocFrom [SGR] (Plain d) where
	docFrom sgr = Plain $ \inh st k ->
		if plainInh_justify inh
		then k (id, st {plainState_buffer = PlainChunk_Ignored (docFrom sgr) : plainState_buffer st})
		else k ((docFrom sgr <>), st)

joinLine ::
 Spaceable d =>
 PlainInh -> PlainState d -> d
joinLine PlainInh{..} PlainState{..} =
	case plainInh_width of
	 Nothing -> joinPlainLine $ List.reverse plainState_buffer
	 Just width ->
		if width < plainState_bufferStart
		|| width < plainInh_indent
		then joinPlainLine $ List.reverse plainState_buffer
		else
			let wordCount =
				foldr (\c acc -> acc + case c of
				 PlainChunk_Word{} -> 1
				 _ -> 0) 0 plainState_buffer in
			let bufferWidth =
				-- NOTE: compress all separated spaces into a single one.
				if wordCount == 0
				then 0
				else
					let spaceCount = foldr
						 (\c acc ->
							acc + case c of
							 PlainChunk_Ignored{} -> 0
							 PlainChunk_Word{} -> 0
							 PlainChunk_Spaces s -> s)
						 0 plainState_buffer in
					(plainState_bufferWidth`minusNatural`spaceCount) +
					(wordCount`minusNatural`1) in
			let adjustedWidth =
				max bufferWidth $
					min
					(width`minusNatural`plainState_bufferStart)
					(width`minusNatural`plainInh_indent) in
			unLine $ padPlainLineInits adjustedWidth
			 (bufferWidth,wordCount,List.reverse plainState_buffer)

-- | @('justifyPadding' a b)@ returns the padding lengths
-- to reach @(a)@ in @(b)@ pads,
-- using the formula: @(a '==' m'*'(q '+' q'+'1) '+' ('r'-'m)'*'(q'+'1) '+' (b'-'r'-'m)'*'q)@
-- where @(q+1)@ and @(q)@ are the two padding lengths used and @(m = min (b-r) r)@.
--
-- A simple implementation of 'justifyPadding' could be:
-- @
-- 'justifyPadding' a b =
--   'join' ('List.replicate' m [q,q'+'1])
--   <> ('List.replicate' (r'-'m) (q'+'1)
--   <> ('List.replicate' ((b'-'r)'-'m) q
--   where
--   (q,r) = a`divMod`b
--   m = 'min' (b-r) r
-- @
justifyPadding :: Natural -> Natural -> [Natural]
justifyPadding a b = go r (b-r) -- NOTE: r >= 0 && b-r >= 0 due to 'divMod'
	where
	(q,r) = a`quotRemNatural`b
	
	go 0  bmr = List.replicate (fromIntegral bmr) q    -- when min (b-r) r == b-r
	go rr 0   = List.replicate (fromIntegral rr) (q+1) -- when min (b-r) r == r
	go rr bmr = q:(q+1) : go (rr`minusNatural`1) (bmr`minusNatural`1)

padPlainLineInits ::
 Spaceable d =>
 Width -> (Natural, Natural, [PlainChunk d]) -> Line d
padPlainLineInits width (lineLen,wordCount,line) = Line $
	if width <= lineLen
		-- The gathered line reached or overreached the width,
		-- hence no padding id needed.
	|| wordCount <= 1
		-- The case width <= lineLen && wordCount == 1
		-- can happen if first word's length is < width
		-- but second word's len is >= width.
	then joinPlainLine line
	else
		-- Share the missing spaces as evenly as possible
		-- between the words of the line.
		padPlainLine line $ justifyPadding (width-lineLen) (wordCount-1)

joinPlainLine :: Monoid d => Spaceable d => [PlainChunk d] -> d
joinPlainLine = mconcat . (runPlainChunk <$>)

padPlainLine :: Spaceable d => [PlainChunk d] -> [Width] -> d
padPlainLine = go
	where
	go (w:ws) lls@(l:ls) =
		case w of
		 PlainChunk_Spaces _s -> spaces (fromIntegral (l+1)) <> go ws ls
		 _ -> runPlainChunk w <> go ws lls
	go (w:ws) [] = runPlainChunk w <> go ws []
	go [] _ls = mempty