{-# LANGUAGE GeneralizedNewtypeDeriving, TypeSynonymInstances, TemplateHaskell, RecordWildCards  #-}

module Cake.Core (
  -- * Patterns and rules.
  Rule,
  P, (==>),
  
  -- * High-level interface
  Act,             
  cake,
  need,           
  list,
  -- * Mid-level interface
  produce,
  use,
  -- * Low-level interface
  debug,
  distill,
  cut,
  shielded,
  Question(..),
  Answer(..),
  -- * Re-exports
  module Control.Applicative,
  ) where

import Data.Digest.Pure.MD5
-- import Data.Digest.OpenSSL.MD5 -- "nano-md5" -- md5sum

import qualified Data.ByteString.Lazy as B
import System.Directory
import System.FilePath
import Control.Applicative
import Control.Monad (when)
import Control.Monad.RWS hiding (put,get)
import qualified Control.Monad.RWS as RWS
import qualified Parsek
import Parsek (completeResults, parse, Parser)
import qualified Data.Map as M
import qualified Data.Set as S
import Data.Binary hiding (put,get)
import System.Exit
import Control.Arrow (second,first)

import Data.DeriveTH
import Data.Binary
import System.IO

data Question = FileContents FilePath 
              | Listing FilePath String
              | Custom [String]
--              | Option [String]
              deriving (Eq, Ord)
$( derive makeBinary ''Question )             
                         
data Answer = Stamp (Maybe MD5Digest) 
            | Text [String]
            deriving (Eq, Show)
$( derive makeBinary ''Answer )             

instance Show Question where
    show (FileContents f) = "{"++f++"}"
    show (Listing f ext) = "("++f++"/*"++ext++")"
    show (Custom c) = show c

type DB = M.Map Question Answer
type Produced = S.Set FilePath      

type P = Parser Char

-- | Rules map names of files to actions building them.
type Rule = P (Act ()) 
type State = (Produced,Status)
type Written = Dual DB -- take the dual so the writer overwrites old entries in the DB.
data Context = Context {ctxHandle :: Handle, ctxRule :: Rule, ctxDB :: DB, ctxProducing :: [Question]}
newtype Act a = Act (RWST Context Written State IO a)
  deriving (Functor, Applicative, Monad, MonadIO, MonadState State, MonadWriter Written, MonadReader Context)
-- Take the dual here so that new info overwrites old.

data Status = Clean | Dirty 
            deriving Eq
  
instance Applicative P where
  (<*>) = ap
  pure = return

instance Alternative P where
  (<|>) = (Parsek.<|>)
  empty = Parsek.pzero

                     
(==>) :: P x -> (x -> Act a) -> Rule
p ==> a = (\s -> do a s;return ()) <$> p


databaseFile = ".cake"
logFile = ".cake.log"


-- | Run an action in the context of a set of rules.
cake :: Rule -> Act () -> IO ()
cake rule action = do
  e <- doesFileExist databaseFile 
  oldDB <- if e 
    then decodeFile databaseFile
    else return $ M.empty
  newDB <- runAct rule oldDB action
  putStrLn $ "Database is:"
  forM_ (M.assocs newDB) $ \(k,v) ->
    putStrLn $ (show k) ++ " => " ++ (show v)
  encodeFile databaseFile newDB


produced :: FilePath -> Act Bool
produced f = do 
  (ps,_) <- RWS.get
  return $ f `S.member` ps

distill :: Question -> Act Answer -> Act Answer
distill q act = local modCx $ do
  debug $ "Starting to answer"
  db <- ctxDB <$> ask
  let a0 = M.lookup q db
  a1 <- shielded act
  tell (Dual $ M.singleton q a1)
  when (Just a1 /= a0) $ do
    clobber
    debug $ "Question has not the same answer"
  return a1
 where modCx (Context {..}) = Context {ctxProducing = q:ctxProducing,..}    


produce :: FilePath -> Act () -> Act ()
produce f a = do
  p <- produced f -- Do nothing if the file is already produced.
  when (not p) $ do
     distill (FileContents f) $ 
       do e <- liftIO $ doesFileExist f
          when (not e) clobber 
          a
          modify $ first $ S.insert f 
          -- remember that the file has been produced already
          fileStamp f
     return ()

-- | List directory contents by extension
list directory extension = do 
  Text x <- distill (Listing directory extension) $ do
   files <- filter (filt . takeExtension) <$> liftIO (getDirectoryContents directory)
   return $ Text (map (directory </>) files)
  return x
 where filt = if null extension then const True else (== '.':extension)


-- | Mark that a file is used. Do not chase dependencies on this file
-- though.
use f = do
  distill (FileContents f) (fileStamp f)
  

-- | Run the argument in a clean context, and do not clobber the state
-- even if the argument does that.  To use when the construction of
-- the argument actually does not depend on the previous questions
-- asked, and the constructed thing is "atomic" for the environment.

-- NOTE: This can be used only when the purpose of the argument (why
-- we call it) is known -- for example we already have determined that
-- another goal depends on what we're going to perform. The dirty flag
-- must be set independently in the context if the produced object is
-- not present.
shielded :: Act a -> Act a
shielded a = do 
  (ps,s) <- RWS.get
  RWS.put (ps,Clean)
  x <- a
  (ps',_) <- RWS.get
  RWS.put (ps',s)
  return x

runAct :: Rule -> DB -> Act () -> IO DB
runAct r db (Act act) = do 
  h <- openFile logFile WriteMode
  (_a,Dual db) <- evalRWST act (Context h r db []) (S.empty,Clean)
  hClose h
  return db    

findRule :: FilePath -> Act (Maybe (Act ()))
findRule f = do
  r <- ctxRule <$> ask
  let rs = parse r completeResults f
  case rs of
    Right [x] -> return (Just x)
    Right _ -> fail $ "More than one rule for file " ++ f
    Left e -> do 
      debug $ "No rule for file: " ++ f
      -- debug $ "Parser says: " ++ show e
      return Nothing
     
debug :: String -> Act ()           
debug x = do 
  h <- ctxHandle <$> ask
  ps <- ctxProducing <$> ask
  (_,s) <- RWS.get
  let st = case s of
              Clean -> "O"
              Dirty -> "X"
  liftIO $ hPutStrLn h $ "cake: " ++ st ++ " "++ concat (map (++": ") $ reverse $ map show ps) ++ x 

{-
runQuery :: Question -> IO Answer          
runQuery (Listing directory extension) = do
  files <- filter (filt . takeExtension) <$> getDirectoryContents directory
  return $ Text (map (directory </>) files)
 where filt = if null extension then const True else (== '.':extension)
  
runQuery (Stamp f) = fileStamp f
-}

fileStamp f = liftIO $ do
  e <- doesFileExist f
  Stamp <$> if e 
    then Just <$> md5 <$> B.readFile f
    else return Nothing

clobber = RWS.modify $ second $ const Dirty

cut x = do
  (_,s) <- RWS.get
  case s of
    Clean -> debug $ "Clean state; skipping."
    Dirty -> x

-- | Try to build a file using known rules; then mark it as used.
need :: FilePath -> Act ()
need f = do
  debug $ "Need: " ++ f
  r <- findRule f
  case r of      
    Nothing -> do 
      e <- liftIO $ doesFileExist f
      when (not e) $ fail $ "No rule to create " ++ f
      debug $ "using existing file"
      use f
      return ()
    Just a -> a