{-# LANGUAGE DeriveGeneric, DeriveAnyClass #-}
{-# LANGUAGE OverloadedStrings #-}
{-# OPTIONS_HADDOCK show-extensions #-}

-- | This module contains the definition of the structure -- 'Printout' -- used to represent the content of a job
module Thermoprint.Printout
       ( Printout(..)
       , Paragraph(..)
       , Chunk(..)
       , Block(..)
       , Line( HSpace
             , SpaceSep
             )
       , text, cotext
       , prop_text
       ) where

import Data.Sequence (Seq, (|>), (<|))

import Data.Text.Lazy (Text)

import Data.ByteString.Lazy (ByteString)

import GHC.Generics (Generic)
import Control.DeepSeq (NFData)

import Test.QuickCheck.Arbitrary (Arbitrary(..), CoArbitrary, genericShrink)
import Test.QuickCheck.Modifiers (NonNegative(..))
import Test.QuickCheck.Gen (oneof, suchThat)
import Test.QuickCheck.Instances
import Test.QuickCheck (forAll, Property)


import qualified Data.Text.Lazy as TL (split, null, pack, filter, intercalate, map)
import Data.Char (isSpace)

import Data.Monoid (Monoid(..), (<>))

import Data.List (dropWhile, dropWhileEnd, groupBy, genericLength, genericReplicate)

import Data.Sequence as Seq (fromList, null, singleton)

import Data.Function (on)

import Data.Foldable (toList)


-- | A 'Printout' is a sequence of visually seperated 'Paragraph's
type Printout = Seq Paragraph

-- | A 'Paragraph' is a non-seperated sequence of 'Chunk's
type Paragraph = Seq Chunk

-- | We introduce both 'Chunk' and 'Paragraph' mainly to allow 'Raw'.
-- 
-- Were we to disallow 'Raw', 'Block' would be identical to 'Paragraph'
data Chunk = Cooked Block -- ^ text semantically structured to be rendered in accordance with the display format of printer
           | Raw ByteString -- ^ direct instructions to the printer
           deriving (Generic, NFData, Show, CoArbitrary)

-- | 'Block' is the entry point for our structured document format
data Block = Line Line -- ^ a single 'Line' of text
           | VSpace Integer -- ^ vertical space of height equivalent to 'Integer' lines
           | NewlSep (Seq Block) -- ^ A sequence of 'Block's seperated by newlines
           deriving (Generic, NFData, Show, CoArbitrary)

{- | A 'Line' is one of:

  * a single word
  * horizontal space equivalent to the width of 'Integer' `em`.
  * a sequence of words seperated by spaces

We don't export all constructors and instead encourage the use of 'text'.
-} 
data Line = Word Text
          | HSpace Integer
          | SpaceSep (Seq Line)
          deriving (Generic, NFData, Show, CoArbitrary)

instance Monoid Block where
  mempty = NewlSep mempty
  x@(NewlSep xs) `mappend` y@(NewlSep ys)
    | Seq.null xs = y
    | Seq.null ys = x
    | otherwise = NewlSep (xs <> ys)
  (NewlSep xs) `mappend` y = NewlSep (xs |> y)
  x `mappend` (NewlSep ys) = NewlSep (x <| ys)
  x `mappend` y = NewlSep $ Seq.fromList [x, y]

instance Monoid Line where
  mempty = SpaceSep mempty
  x@(SpaceSep xs) `mappend` y@(SpaceSep ys)
    | Seq.null xs = y
    | Seq.null ys = x
    | otherwise = SpaceSep (xs <> ys)
  (SpaceSep xs) `mappend` y = SpaceSep (xs |> y)
  x `mappend` (SpaceSep ys) = SpaceSep (x <| ys)
  x `mappend` y = SpaceSep $ Seq.fromList [x, y]


text :: Text -> Either Block Line
-- ^ Smart constructor for 'Line'/'Block' which maps word and line boundaries (as determined by 'isSpace' and '(== '\n')' respectively) to the structure of 'Block' and 'Line'.
--
-- Since we are unwilling to duplicate the list of chars from 'isSpace' we cannot reasonably determine a width for the various whitespace 'Char's.
-- Thus they are all weighted equally as having width 1 `em`.
text t = case splitLines t of
  [] -> Right mempty
  [Line x] -> Right x
  xs -> Left $ mconcat xs
  where
    splitLines :: Text -> [Block]
    splitLines t = map toBlock
                   . groupBy ((==) `on` TL.null)
                   $ TL.split (== '\n') t
    splitWords :: Text -> [Line]
    splitWords t = map toLine
                   . groupBy ((==) `on` TL.null)
                   $ TL.split isSpace t
    toBlock [] = mempty
    toBlock xs@(x:_)
      | TL.null x = VSpace $ genericLength xs - 1
      | otherwise = mconcat . map (Line . mconcat . splitWords) $ xs
    toLine [] = mempty
    toLine xs@(x:_)
      | TL.null x = HSpace $ genericLength xs - 1
      | otherwise = mconcat . map Word $ xs
    list :: b -> (a -> [a] -> b) -> [a] -> b
    list c _ [] = c
    list _ f (x:xs) = f x xs

cotext :: Block -> Text
-- ^ inverse of
-- @
--   either id Line . `text`
-- @
cotext (VSpace n) = TL.pack . genericReplicate (n - 1) $ '\n'
cotext (NewlSep xs) =  TL.intercalate "\n" . map cotext . toList $ xs
cotext (Line x) = cotext' x
  where            
    cotext' (Word x) = x
    cotext' (HSpace n) = TL.pack . genericReplicate (n - 1) $ ' '
    cotext' (SpaceSep xs) = TL.intercalate " " . map cotext' . toList $ xs

prop_text :: Property
-- ^ prop> cotext . either id Line . `text` $ x = x
--
-- Where 'x' is restricted to those `TL.Text` which do not contain whitespace besides ' ' and '\n'.
prop_text = forAll (TL.map normSpace <$> arbitrary) $ \x -> (cotext . either id Line . text $ x) == x
  where
    normSpace c
      | isSpace c
      , c `elem` keep = c
      | isSpace c = ' ' -- We have to do this because all whitespace gets interpreted as width 1
      | otherwise = c
    keep = [' ', '\n']

-- | We don't test 'Raw' 'Chunk's
instance Arbitrary Chunk where
  shrink = genericShrink
  arbitrary = Cooked <$> arbitrary

instance Arbitrary Block where
  shrink = genericShrink
  arbitrary = oneof [ Line <$> arbitrary
                    , VSpace . getNonNegative <$> arbitrary
                    , NewlSep <$> arbitrary
                    ]

instance Arbitrary Line where
  shrink = genericShrink
  arbitrary = oneof [ Word . TL.filter (not . isSpace) <$> arbitrary -- 'isSpace '\n' == True'
                    , HSpace . getNonNegative <$> arbitrary
                    , SpaceSep <$> arbitrary
                    ]