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diff --git a/compiler/src/Input.hs b/compiler/src/Input.hs
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+{-# LANGUAGE DuplicateRecordFields, DeriveGeneric, DeriveAnyClass #-}
+
+-- ldgallery - A static generator which turns a collection of tagged
+--             pictures into a searchable web gallery.
+--
+-- Copyright (C) 2019  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
+  ( Sidecar, title, date, description, tags
+  , InputTree(..), readInputTree
+  ) where
+
+
+import GHC.Generics (Generic)
+import Control.Exception (Exception, throwIO)
+import Control.Monad.IO.Class (MonadIO, liftIO)
+import Data.Function ((&))
+import Data.Maybe (mapMaybe, catMaybes)
+import Data.List (find)
+import Data.Yaml (ParseException, decodeFileEither)
+import Data.Aeson (FromJSON)
+import System.FilePath (isExtensionOf, dropExtension)
+
+import Files
+import Utils
+
+
+data LoadException = LoadException String ParseException deriving Show
+instance Exception LoadException
+
+decodeYamlFile :: (MonadIO m, FromJSON a) => Path -> m a
+decodeYamlFile path =
+  liftIO $ Data.Yaml.decodeFileEither fpath
+  >>= either (throwIO . LoadException fpath) return
+  where
+    fpath = localPath path
+
+
+-- | Tree representing the input from the input directory.
+data InputTree =
+    InputFile
+      { path :: Path
+      , sidecar :: Sidecar }
+    | InputDir
+      { path :: Path
+      , thumbnailPath :: 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)
+
+
+readInputTree :: AnchoredFSNode -> IO InputTree
+readInputTree (AnchoredFSNode anchor root@Dir{}) =
+  filterDir (neg isHidden) root & mkDirNode
+  where
+    mkInputNode :: FSNode -> IO (Maybe InputTree)
+    mkInputNode (File path@(filename:pathto)) | ".yaml" `isExtensionOf` filename =
+      decodeYamlFile (anchor /> path)
+      >>= return . InputFile ((dropExtension filename):pathto)
+      >>= return . Just
+    mkInputNode File{} = return Nothing
+    mkInputNode dir@Dir{} = mkDirNode dir >>= return . Just
+
+    mkDirNode :: FSNode -> IO InputTree
+    mkDirNode (Dir path items) =
+      mapM mkInputNode items
+      >>= return . catMaybes
+      >>= return . InputDir path (findThumbnail items)
+      where
+        findThumbnail :: [FSNode] -> Maybe Path
+        findThumbnail = (fmap nodePath) . (find matchThumbnail)
+
+        matchThumbnail :: FSNode -> Bool
+        matchThumbnail Dir{} = False
+        matchThumbnail (File (filename:_)) = (dropExtension filename) == "thumbnail"