fix: #7 large EPUB parsing performance

src/NexusReader.Infrastructure/Services/EpubService.cs

@@ -46,34 +46,29 @@ public class EpubService : IEpubService
                 return Result.Fail($"EPUB file at '{fullPath}' is not accessible or does not exist.");
             }
 
-            EpubBook book;
+            using var bookRef = await EpubReader.OpenBookAsync(fullPath);
-            try 
+            var readingOrder = bookRef.GetReadingOrder();
-            {
-                book = await EpubReader.ReadBookAsync(fullPath);
-            }
-            catch (Exception ex)
-            {
-                return Result.Fail(new Error($"Failed to parse EPUB file. It might be corrupted or in use. Path: {fullPath}").CausedBy(ex));
-            }
-            var blocks = new List<ContentBlock>();
-            int totalWordCount = 0;
-            int blockCounter = 0;
 
-            if (book.ReadingOrder == null || !book.ReadingOrder.Any())
+            if (readingOrder == null || !readingOrder.Any())
             {
                 return Result.Fail("The EPUB has no readable content files in ReadingOrder.");
             }
 
             // Ensure index is within bounds
-            if (chapterIndex < 0 || chapterIndex >= book.ReadingOrder.Count)
+            if (chapterIndex < 0 || chapterIndex >= readingOrder.Count)
             {
                 chapterIndex = 0; // Default to first chapter
             }
 
-            var chapter = book.ReadingOrder[chapterIndex];
+            var chapterRef = readingOrder[chapterIndex];
-            var chapterTitle = chapter.FilePath ?? $"Chapter {chapterIndex + 1}";
+            var chapterTitle = chapterRef.FilePath ?? $"Chapter {chapterIndex + 1}";
+            var chapterContent = await chapterRef.ReadContentAsTextAsync();
 
-            var paragraphs = ExtractParagraphs(chapter.Content);
+            var blocks = new List<ContentBlock>();
+            int totalWordCount = 0;
+            int blockCounter = 0;
+
+            var paragraphs = ExtractParagraphs(chapterContent);
             foreach (var p in paragraphs)
             {
                 var sanitizedContent = SanitizeParagraph(p);
@@ -99,7 +94,7 @@ public class EpubService : IEpubService
                 blocks.Add(CreateAiTrigger($"trigger-{blockCounter++}"));
             }
 
-            return Result.Ok(new ReaderPageViewModel(blocks, chapterIndex, book.ReadingOrder.Count, chapterTitle));
+            return Result.Ok(new ReaderPageViewModel(blocks, chapterIndex, readingOrder.Count, chapterTitle));
         }
         catch (Exception ex)
         {