-----------------------------------------------------------------------------
-- |
-- Module      : System.Taffybar.Information.XDG.DesktopEntry
-- Copyright   : 2017 Ulf Jasper
-- License     : BSD3-style (see LICENSE)
--
-- Maintainer  : Ulf Jasper <ulf.jasper@web.de>
-- Stability   : unstable
-- Portability : unportable
--
-- Implementation of version 1.1 of the freedesktop "Desktop Entry
-- specification", see
-- https://specifications.freedesktop.org/desktop-entry-spec/desktop-entry-spec-1.1.html.
-----------------------------------------------------------------------------

module System.Taffybar.Information.XDG.DesktopEntry
  ( DesktopEntry(..)
  , deCommand
  , deComment
  , deHasCategory
  , deIcon
  , deName
  , deNoDisplay
  , deNotShowIn
  , deOnlyShowIn
  , existingDirs
  , getDefaultDataHome
  , getDirectoryEntry
  , getDirectoryEntryDefault
  , getXDGDataDirs
  , listDesktopEntries
  ) where

import           Control.Monad
import           Control.Monad.IO.Class
import           Control.Monad.Trans.Except
import           Data.Char
import qualified Data.ConfigFile as CF
import           Data.List
import           Data.Maybe
import qualified Data.Set as S
import           System.Directory
import           System.Environment
import           System.FilePath.Posix
import           System.Log.Logger
import           System.Posix.Files
import           Text.Printf

data DesktopEntryType = Application | Link | Directory
  deriving (Read, Show, Eq)

existingDirs :: [FilePath] -> IO [FilePath]
existingDirs  dirs = do
  exs <- mapM fileExist dirs
  return $ S.toList $ S.fromList $ map fst $ filter snd $ zip dirs exs

getDefaultDataHome :: IO FilePath
getDefaultDataHome = do
  h <- getHomeDirectory
  return $ h </> ".local" </> "share"

-- XXX: We really ought to use
-- https://hackage.haskell.org/package/directory-1.3.2.2/docs/System-Directory.html#v:getXdgDirectory
getXDGDataDirs :: IO [FilePath]
getXDGDataDirs = do
  dataHome <- lookupEnv "XDG_DATA_HOME" >>= maybe getDefaultDataHome return
  dataDirs <- map normalise . splitSearchPath . fromMaybe "" <$>
              lookupEnv "XDG_DATA_DIRS"
  nubBy equalFilePath <$>
        existingDirs (  dataHome:dataDirs
                     ++ ["/usr/local/share", "/usr/share"]
                     )

-- | Desktop Entry. All attributes (key-value-pairs) are stored in an
-- association list.
data DesktopEntry = DesktopEntry
  { deType :: DesktopEntryType
  , deFilename :: FilePath -- ^ unqualified filename, e.g. "taffybar.desktop"
  , deAttributes :: [(String, String)] -- ^ Key-value pairs
  } deriving (Read, Show, Eq)

-- | Determine whether the Category attribute of a desktop entry contains a
-- given value.
deHasCategory
  :: DesktopEntry -- ^ desktop entry
  -> String -- ^ category to be checked
  -> Bool
deHasCategory de cat =
  maybe False ((cat `elem`) . splitAtSemicolon) $
        lookup "Categories" (deAttributes de)

splitAtSemicolon :: String -> [String]
splitAtSemicolon = lines . map (\c -> if c == ';' then '\n' else c)

-- | Return the proper name of the desktop entry, depending on the list of
-- preferred languages.
deName
  :: [String] -- ^ Preferred languages
  -> DesktopEntry
  -> String
deName langs de = fromMaybe (deFilename de) $ deLocalisedAtt langs de "Name"

-- | Return the categories in which the entry shall be shown
deOnlyShowIn :: DesktopEntry -> [String]
deOnlyShowIn = maybe [] splitAtSemicolon . deAtt "OnlyShowIn"

-- | Return the categories in which the entry shall not be shown
deNotShowIn :: DesktopEntry -> [String]
deNotShowIn = maybe [] splitAtSemicolon . deAtt "NotShowIn"

-- | Return the value of the given attribute key
deAtt :: String -> DesktopEntry -> Maybe String
deAtt att = lookup att . deAttributes

-- | Return the Icon attribute
deIcon :: DesktopEntry -> Maybe String
deIcon = deAtt "Icon"

-- | Return True if the entry must not be displayed
deNoDisplay :: DesktopEntry -> Bool
deNoDisplay de = maybe False (("true" ==) . map toLower) $ deAtt "NoDisplay" de

deLocalisedAtt
  :: [String] -- ^ Preferred languages
  -> DesktopEntry
  -> String
  -> Maybe String
deLocalisedAtt langs de att =
  let localeMatches =
        mapMaybe (\l -> lookup (att ++ "[" ++ l ++ "]") (deAttributes de)) langs
  in if null localeMatches
       then lookup att $ deAttributes de
       else Just $ head localeMatches

-- | Return the proper comment of the desktop entry, depending on the list of
-- preferred languages.
deComment :: [String] -- ^ Preferred languages
          -> DesktopEntry
          -> Maybe String
deComment langs de = deLocalisedAtt langs de "Comment"

-- | Return the command defined by the given desktop entry.
-- TODO: should check  the dbus thing.
-- TODO: are there "field codes", i.e. %<char> things, that
deCommand :: DesktopEntry -> Maybe String
deCommand de =
  reverse . dropWhile (== ' ') . reverse . takeWhile (/= '%') <$>
  lookup "Exec" (deAttributes de)

-- | Return a list of all desktop entries in the given directory.
listDesktopEntries
  :: String -- ^ The extension to use in the search
  -> FilePath -- ^ The filepath at which to search
  -> IO [DesktopEntry]
listDesktopEntries extension dir = do
  let normalizedDir = normalise dir
  ex <- doesDirectoryExist normalizedDir
  if ex
  then do
    files <-
      map (normalizedDir </>) . filter (\v -> v /= "." && v /= "..") <$>
      getDirectoryContents dir
    entries <-
      (nub . catMaybes) <$>
      mapM readDesktopEntry (filter (extension `isSuffixOf`) files)
    subDirs <- filterM doesDirectoryExist files
    subEntries <- concat <$> mapM (listDesktopEntries extension) subDirs
    return $ entries ++ subEntries
  else return []

-- XXX: This function doesn't recurse, but `listDesktopEntries` does. Why?
-- Shouldn't they really share logic...
-- | Retrieve a desktop entry with a specific name.
getDirectoryEntry :: [FilePath] -> String -> IO (Maybe DesktopEntry)
getDirectoryEntry dirs name = do
  liftIO $ logM "System.Taffybar.Information.XDG.DesktopEntry" DEBUG $
           printf "Searching %s for %s" (show dirs) name
  exFiles <- filterM doesFileExist $ map ((</> name) . normalise) dirs
  if null exFiles
  then return Nothing
  else readDesktopEntry $ head exFiles

getDirectoryEntryDefault :: String -> IO (Maybe DesktopEntry)
getDirectoryEntryDefault entry =
  fmap (</> "applications") <$> getXDGDataDirs >>=
  flip getDirectoryEntry (printf "%s.desktop" entry)

-- | Main section of a desktop entry file.
sectionMain :: String
sectionMain = "Desktop Entry"

-- | Read a desktop entry from a file.
readDesktopEntry :: FilePath -> IO (Maybe DesktopEntry)
readDesktopEntry fp = do
  ex <- doesFileExist fp
  if ex
    then doReadDesktopEntry fp
    else do
      putStrLn $ "File does not exist: '" ++ fp ++ "'"
      return Nothing
  where
    doReadDesktopEntry :: FilePath -> IO (Maybe DesktopEntry)
    doReadDesktopEntry f = do
      eResult <-
        runExceptT $ do
          cp <- join $ liftIO $ CF.readfile CF.emptyCP f
          CF.items cp sectionMain
      case eResult of
        Left _ -> return Nothing
        Right r ->
          return $
          Just
            DesktopEntry
            { deType = maybe Application read (lookup "Type" r)
            , deFilename = f
            , deAttributes = r
            }