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diff --git a/compiler/src/Caching.hs b/compiler/src/Caching.hs
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+++ b/compiler/src/Caching.hs
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+-- 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 Caching
+  ( Cache
+  , noCache
+  , ItemCache
+  , buildItemCache
+  , useCached
+  ) where
+
+
+import Control.Monad (when)
+import qualified Data.Map.Strict as Map
+import System.Directory (removePathForcibly, doesDirectoryExist, doesFileExist)
+
+import FileProcessors (FileProcessor)
+import Resource (GalleryItem(..), flattenGalleryTree)
+import Files
+
+
+type Cache a = FileProcessor a -> FileProcessor a
+
+
+noCache :: Cache a
+noCache processor itemPath resPath inputFsPath outputFsPath =
+  removePathForcibly outputFsPath
+  >> processor itemPath resPath inputFsPath outputFsPath
+
+
+type ItemCache = Path -> Maybe GalleryItem
+
+buildItemCache :: Maybe GalleryItem -> ItemCache
+buildItemCache cachedItems = lookupCache
+  where
+    withKey item = (webPath $ Resource.path item, item)
+    cachedItemList = maybe [] flattenGalleryTree cachedItems
+    cachedMap = Map.fromList (map withKey cachedItemList)
+    lookupCache path = Map.lookup (webPath path) cachedMap
+
+useCached :: ItemCache -> (GalleryItem -> a) -> Cache a
+useCached cache propGetter processor itemPath resPath inputFsPath outputFsPath =
+  do
+    isDir <- doesDirectoryExist outputFsPath
+    when isDir $ removePathForcibly outputFsPath
+
+    fileExists <- doesFileExist outputFsPath
+    if fileExists then
+      do
+        needUpdate <- isOutdated True inputFsPath outputFsPath
+        case (needUpdate, cache itemPath) of
+          (False, Just props) -> fromCache props
+          _ -> update
+    else
+      update
+
+  where
+    update = processor itemPath resPath inputFsPath outputFsPath
+    fromCache props =
+      putStrLn ("From cache:\t" ++ outputFsPath)
+      >> return (propGetter props)