Add back LTask

package.yaml

@@ -37,7 +37,7 @@ dependencies:
   #- transformers
   #- unix
   #- unordered-containers
-  #- vector
+- vector
   #- vty
 # tests
 - hspec

src/TaskMachine/LTask.hs

@@ -0,0 +1,63 @@
+-- | A way to store the 'Task's that preserves the original task order.
+--
+-- A @LTask@ stores a number representing its original position in addition to the 'Task' itself.
+-- To restore the original order, the @LTask@s are sorted by this number.
+-- When sorting this way, any @LTask@s created using 'lTask' are appended at the end.
+--
+-- LTasks can be deleted from any part of the list, but only appended to the end.
+--
+-- LTasks from different 'fromTasks' calls should /not/ be mixed together.
+
+module TaskMachine.LTask
+  ( LTask
+  , lTask
+  , toTask
+  , fromTasks
+  , toTasks
+  , sortLTasks
+  , loadLTasks
+  , saveLTasks
+  ) where
+
+import           Data.Function
+import           Data.List
+
+import qualified Data.Vector      as V
+import           Text.Megaparsec
+
+import           TaskMachine.Task
+
+data Position = Old Integer | New
+  deriving (Eq, Show, Ord)
+
+data LTask = LTask
+  { lPosition :: Position
+  , lRealTask :: Task
+  } deriving (Show)
+
+lTask :: Task -> LTask
+lTask = LTask New
+
+toTask :: LTask -> Task
+toTask = lRealTask
+
+fromTasks :: [Task] -> [LTask]
+fromTasks = zipWith LTask (map Old [1..])
+
+toTasks :: [LTask] -> [Task]
+toTasks = map toTask . sortLTasks
+
+sortLTasks :: [LTask] -> [LTask]
+sortLTasks = sortBy (compare `on` lPosition)
+
+loadLTasks :: FilePath -> IO (Either String (V.Vector LTask))
+loadLTasks file = do
+  content <- readFile file
+  case parse pTasks file content of
+    Right taskList  -> pure $ Right $ V.fromList $ fromTasks taskList
+    Left parseError -> pure $ Left $ show parseError
+
+saveLTasks :: V.Vector LTask -> FilePath -> IO ()
+saveLTasks ltasks file = do
+  let text = formatTasks $ toTasks $ V.toList ltasks
+  writeFile file text