module System.Sifflet.Paths
       (findDataFile, copyLibFile, readLibFile)
       where

import Control.Monad (unless)
import System.Directory (doesFileExist, copyFile)
import System.FilePath (replaceDirectory)

-- Cabal-generated paths module tells where a datafile
-- _should_ be, but not necessarily where it is,
-- if the installed files have been relocated.

import Paths_sifflet_lib (getDataFileName)

import Graphics.UI.Sifflet.Types (VPUI(..))
import Graphics.UI.Sifflet.GtkUtil (showErrorMessage)

-- | Try to find the original of a datafile that is part of the
-- sifflet library.  
-- These are usually files like sifflet.scm or sifflet.py that provide 
-- Sifflet support for the target language when exporting.
-- First try the directory where Cabal would have installed data files.
-- This may fail if Sifflet has been installed (or portably installed)
-- on Windows into a non-standard location; in that case, also try
-- the directory from which sifflet.exe was launched.

findDataFile :: VPUI -> FilePath -> IO (Maybe FilePath)
findDataFile vpui fileBaseName = do
  -- path1 is where it should be;
  -- path2 is where it might be on Windows.
  path1 <- getDataFileName fileBaseName
  let path2 = replaceDirectory fileBaseName (vpuiInitialDir vpui)
      -- There's surely a name for this type of search,
      -- which simply returns the first item in the list
      -- for which a predicate `returns` True (m True):
      search [] = return Nothing
      search (path:paths) = do
        fileExists <- doesFileExist path
        if fileExists
          then return $ Just path
          else search paths
  search [path1, path2]
  
-- | Try to copy a library file (such as sifflet.py or Sifflet.java)
-- to the same directory where an export file is being written,
-- if it doesn't already exist there.
-- Show a warning message if the library file cannot be found.
copyLibFile :: VPUI -> FilePath -> FilePath -> IO ()
copyLibFile vpui libFileName dest = do
    mLibFilePath <- findDataFile vpui libFileName
    destExists <- doesFileExist dest
    unless destExists $ do
      case mLibFilePath of
        Nothing ->
          showErrorMessage $ "Sifflet could not locate the file " ++ 
          libFileName ++ "\n" ++
          "Please copy it from the Sifflet installation directory to " ++
          "the same directory into which you are saving the export file.\n"
        Just libFileSource ->
          copyFile libFileSource dest
                
-- | Get the contents of a library file (such as sifflet.scm) 
-- so you can insert it into the file being exported.
-- If the file cannot be found, display an error message and
-- return the empty string.
readLibFile :: VPUI -> FilePath -> FilePath -> IO String
readLibFile vpui libFileName exportFile = do
  mLibFilePath <- findDataFile vpui libFileName
  case mLibFilePath of
    Nothing -> do
      showErrorMessage $ "Sifflet could not locate the file " ++ 
        libFileName ++ "\n" ++
        "Please find it in the Sifflet installation directory " ++
        "and insert its contents into " ++ exportFile ++ "\n"
      return ""
    Just libFilePath ->
      readFile libFilePath