module Command.Watch
    ( watch
    ) where

import           Control.Concurrent.Chan (Chan, newChan, readChan)
import           Data.List               (isSuffixOf)
import           Data.Time.Clock         (UTCTime, getCurrentTime)
import qualified System.FilePath         as FP
import qualified System.FSNotify         as FSN

import           Command.Compile         (compileIO)
import           Common                  (waspSays)
import qualified Common
import qualified Lib
import           StrongPath              (Abs, Dir, Path, (</>))
import qualified StrongPath              as SP


-- TODO: Another possible problem: on re-generation, wasp re-generates a lot of files, even those that should not
--   be generated again, since it is not smart enough yet to know which files do not need to be regenerated.
--   This can trigger `npm start` processes to reload multiple times, once for each file!
--   `nodemon` specifically has --delay option which says how long it should wait before restarting,
--   and it's default value is 1 second, so it will restart only once if all file changes happen in one second interval.
--   We could play in the future with increasing this delay. Nodemon can also be manually restarted with `rs` so
--   that could also be useful -> if we could do only manual restarting and not have it restart on its own, we could
--   have tigther control over it. But do we need nodemon at all then hm :)?
-- TODO: Idea: Read .gitignore file, and ignore everything from it. This will then also cover the
--   .wasp dir, and users can easily add any custom stuff they want ignored. But, we also have to
--   be ready for the case when there is no .gitignore, that could be possible.
-- | Forever listens for any file changes in waspProjectDir, and if there is a change,
--   compiles Wasp source files in waspProjectDir and regenerates files in outDir.
watch :: Path Abs (Dir Common.WaspProjectDir) -> Path Abs (Dir Lib.ProjectRootDir) -> IO ()
watch waspProjectDir outDir = FSN.withManager $ \mgr -> do
    currentTime <- getCurrentTime
    chan <- newChan
    _ <- FSN.watchDirChan mgr (SP.toFilePath waspProjectDir) eventFilter chan
    _ <- FSN.watchTreeChan mgr (SP.toFilePath $ waspProjectDir </> Common.extCodeDirInWaspProjectDir) eventFilter chan
    listenForEvents chan currentTime
  where
      listenForEvents :: Chan FSN.Event -> UTCTime -> IO ()
      listenForEvents chan lastCompileTime = do
          event <- readChan chan
          let eventTime = FSN.eventTime event
          if eventTime < lastCompileTime
              -- | If event happened before last compilation started, skip it.
              then listenForEvents chan lastCompileTime
              else do
                  currentTime <- getCurrentTime
                  recompile
                  listenForEvents chan currentTime

      recompile :: IO ()
      recompile = do
          waspSays "Recompiling on file change..."
          compilationResult <- compileIO waspProjectDir outDir
          case compilationResult of
              Left err -> waspSays $ "Recompilation on file change failed: " ++ err
              Right () -> waspSays "Recompilation on file change succeeded."
          return ()

      -- TODO: This is a hardcoded approach to ignoring most of the common tmp files that editors
      --   create next to the source code. Bad thing here is that users can't modify this,
      --   so better approach would be probably to use information from .gitignore instead, or
      --   maybe combining the two somehow.
      eventFilter :: FSN.Event -> Bool
      eventFilter event =
          let filename = FP.takeFileName $ FSN.eventPath event
          in not (null filename)
             && not (take 2 filename == ".#") -- Ignore emacs lock files.
             && not (head filename == '#' && last filename == '#') -- Ignore emacs auto-save files.
             && not (last filename == '~') -- Ignore emacs and vim backup files.
             && not (head filename == '.' && ".swp" `isSuffixOf` filename) -- Ignore vim swp files.
             && not (head filename == '.' && ".un~" `isSuffixOf` filename) -- Ignore vim undo files.