Add persistence module

This will allow us to save the last chapter the user read, thus making it easier to track progress.

Implement persistence module

saveLastRead saves the chapter after each new one is read and writes it to xdgdata

app/Persistence.hs

@@ -1,4 +1,40 @@
-module Persistence where
+module Persistence 
+    ( saveLastRead
+    , loadLastRead 
+    ) where
 
--- TODO: Add book state persistence
+import System.Directory (getXdgDirectory, XdgDirectory(XdgData), createDirectoryIfMissing)
+import System.FilePath ((</>))
+import qualified Data.Text as T
+import qualified Data.Text.IO as TIO
+import Control.Exception (try, SomeException)
+import Text.Read (readMaybe)
 
+saveLastRead :: FilePath -> Int -> IO ()
+saveLastRead bPath chapterIdx = do
+    dataDir <- getXdgDirectory XdgData "svitak"
+    createDirectoryIfMissing True dataDir
+    
+    let configFile = dataDir </> "last_read.txt"
+    -- Line 1 = Path, Line 2 = Index
+    let content = T.pack bPath <> T.pack "\n" <> T.pack (show chapterIdx)
+    
+    TIO.writeFile configFile content
+    putStrLn $ "Progress saved to: " ++ configFile
+
+loadLastRead :: IO (Maybe (FilePath, Int))
+loadLastRead = do
+  dataDir <- getXdgDirectory XdgData "svitak"
+  let configFile = dataDir </> "last_read.txt"
+
+  result <- try (TIO.readFile configFile) :: IO (Either SomeException T.Text)
+  
+  case result of
+    Left _ -> pure Nothing
+    Right content -> do
+      let linesOfFile = T.lines content
+      case linesOfFile of
+        [path, idxStr] 
+          | Just idx <- readMaybe (T.unpack idxStr) -> 
+              pure $ Just (T.unpack path, idx)
+        _ -> pure Nothing

app/UI.hs

@@ -12,7 +12,8 @@ import Control.Monad.Reader (runReaderT)
 import Data.IORef (newIORef, readIORef, writeIORef)
 import Text.HTML.TagSoup (renderTags)
 
-import EpubParser (EpubEnv, resolveSpine, getChapter)
+import EpubParser (EpubEnv, resolveSpine, getChapter, bookPath)
+import Persistence (saveLastRead, loadLastRead)
 
 runApp :: EpubEnv -> IO ()
 runApp env = do
@@ -20,7 +21,7 @@ runApp env = do
     app <- Gtk.applicationNew (Just "com.svitak.reader.v2") []
 
     _ <- Gtk.on app #activate $ do
-        putStrLn "DEBUG: App Activated"
+        putStrLn "App Activated"
         
         -- Setup window
         window <- Gtk.applicationWindowNew app
@@ -34,30 +35,40 @@ runApp env = do
         -- Get the spine
         spine <- runReaderT resolveSpine env
         let totalChapters = length spine
-        putStrLn $ "DEBUG: Spine loaded. Total chapters: " ++ show totalChapters
+        putStrLn $ "Spine loaded. Total chapters: " ++ show totalChapters
 
         if totalChapters == 0 
            then putStrLn "ERROR: This book has no chapters!" 
            else do
                 currentIndex <- newIORef 0
 
-
                 let loadChapter index = do
                         let maxIdx = totalChapters - 1
                         let safeIdx = max 0 (min index maxIdx)
-                        
+
+                        -- Save state after every chapter
                         writeIORef currentIndex safeIdx
-                        putStrLn $ "DEBUG: Loading Chapter " ++ show (safeIdx + 1)
+                        putStrLn $ "Loading Chapter " ++ show (safeIdx + 1)
+                        saveLastRead (bookPath env) safeIdx
                         
                         let filename = spine !! safeIdx
                         tags <- runReaderT (getChapter filename) env
                         
                         let htmlContent = renderTags tags
+
                         -- Load HTML
                         WebKit.webViewLoadHtml webView htmlContent (Just "file:///")
 
-                -- Load the first chapter
-                loadChapter 0
+                -- If there's no state saved then load the first chapter
+                maybeSaved <- loadLastRead
+
+                case maybeSaved of
+                  Just (path, index)
+                    | path == bookPath env -> loadChapter index
+                    | otherwise            -> loadChapter 0
+
+                  Nothing -> loadChapter 0
+                  
 
                 -- Setup keyboard input
                 keyController <- Gtk.eventControllerKeyNew