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src/TaskMachine/LTask.hs

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+-- | A way to store the 'Task's that preserves the original task order.
+
+module TaskMachine.LTask
+  ( LTask(..)
+  , fromTasks
+  , loadLTasks
+  , saveLTasks
+  ) where
+
+import Data.List
+import Data.Function
+
+import qualified Data.Vector         as V
+import           Text.Megaparsec
+
+import           TaskMachine.Todotxt
+
+-- | A "ListTask" for use in the task list
+data LTask = LTask
+  { ltaskNumber :: Integer
+  -- ^ Sort by this number to get the original order of the tasks
+  , ltaskTask   :: Task
+  -- ^ The 'Task' itself
+  } deriving (Show)
+
+fromTasks :: [Task] -> [LTask]
+fromTasks = zipWith LTask [1..]
+
+loadLTasks :: FilePath -> IO (Either String (V.Vector LTask))
+loadLTasks file = do
+  content <- readFile file
+  case parseTasks file content of
+    Right tasks     -> pure $ Right $ V.fromList $ fromTasks tasks
+    Left parseError -> pure $ Left $ show parseError
+
+saveLTasks :: V.Vector LTask -> FilePath -> IO ()
+saveLTasks ltasks file = do
+  let tasks = map ltaskTask $ sortBy (compare `on` ltaskNumber) $ V.toList ltasks
+      text = unlines $ map formatTask tasks
+  writeFile file text