-- ldgallery - A static generator which turns a collection of tagged
--             pictures into a searchable web gallery.
--
-- Copyright (C) 2019-2020  Pacien TRAN-GIRARD
--
-- This program is free software: you can redistribute it and/or modify
-- it under the terms of the GNU Affero General Public License as
-- published by the Free Software Foundation, either version 3 of the
-- License, or (at your option) any later version.
--
-- This program is distributed in the hope that it will be useful,
-- but WITHOUT ANY WARRANTY; without even the implied warranty of
-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-- GNU Affero General Public License for more details.
--
-- You should have received a copy of the GNU Affero General Public License
-- along with this program.  If not, see <https://www.gnu.org/licenses/>.

module Input
  ( decodeYamlFile
  , Sidecar(..)
  , InputTree(..), readInputTree
  ) where


import GHC.Generics (Generic)
import Control.Exception (Exception, AssertionFailed(..), throw, throwIO)
import Control.Monad.IO.Class (MonadIO, liftIO)
import Data.Function ((&))
import Data.Maybe (catMaybes)
import Data.Bool (bool)
import Data.List (find)
import Data.Yaml (ParseException, decodeFileEither)
import Data.Aeson (FromJSON)
import System.FilePath (isExtensionOf, dropExtension)
import System.Directory (doesFileExist)

import Files


data LoadException = LoadException String ParseException deriving Show
instance Exception LoadException

decodeYamlFile :: (MonadIO m, FromJSON a) => FileName -> m a
decodeYamlFile path =
  liftIO $ Data.Yaml.decodeFileEither path
  >>= either (throwIO . LoadException path) return


-- | Tree representing the input from the input directory.
data InputTree =
    InputFile
      { path :: Path
      , sidecar :: Sidecar }
    | InputDir
      { path :: Path
      , dirThumbnailPath :: Maybe Path
      , items :: [InputTree] }
  deriving Show

data Sidecar = Sidecar
  { title :: Maybe String
  , date :: Maybe String
  , description :: Maybe String
  , tags :: Maybe [String]
  } deriving (Generic, FromJSON, Show)

emptySidecar :: Sidecar
emptySidecar = Sidecar
  { title = Nothing
  , date = Nothing
  , description = Nothing
  , tags = Nothing }

sidecarExt :: String
sidecarExt = "yaml"

readSidecarFile :: FilePath -> IO Sidecar
readSidecarFile filepath =
  doesFileExist filepath
  >>= bool (return Nothing) (decodeYamlFile filepath)
  >>= return . maybe emptySidecar id


readInputTree :: AnchoredFSNode -> IO InputTree
readInputTree (AnchoredFSNode _ File{}) =
  throw $ AssertionFailed "Input directory is a file"
readInputTree (AnchoredFSNode anchor root@Dir{}) = mkDirNode root
  where
    mkInputNode :: FSNode -> IO (Maybe InputTree)
    mkInputNode file@File{path} | not $ isSidecar file =
      readSidecarFile (localPath $ anchor /> path <.> sidecarExt)
      >>= return . InputFile path
      >>= return . Just
    mkInputNode File{} = return Nothing
    mkInputNode dir@Dir{} = mkDirNode dir >>= return . Just

    mkDirNode :: FSNode -> IO InputTree
    mkDirNode File{} = throw $ AssertionFailed "Input directory is a file"
    mkDirNode Dir{path, items} =
      mapM mkInputNode items
      >>= return . catMaybes
      >>= return . InputDir path (findThumbnail items)

    isSidecar :: FSNode -> Bool
    isSidecar Dir{} = False
    isSidecar File{path} =
      fileName path
      & (maybe False $ isExtensionOf sidecarExt)

    isThumbnail :: FSNode -> Bool
    isThumbnail Dir{} = False
    isThumbnail File{path} =
      fileName path
      & fmap dropExtension
      & (maybe False ("thumbnail" ==))

    findThumbnail :: [FSNode] -> Maybe Path
    findThumbnail = (fmap Files.path) . (find isThumbnail)