refactor!: disk-first zero-copy architecture with file-to-file cwebp conversion

BREAKING CHANGE: Complete refactoring of the conversion pipeline.

- Replace in-memory Page/PageContainer with disk-based PageFile struct
- Extract archives to temp directory instead of loading into memory
- Use cwebp InputFile/OutputFile for zero-copy file-to-file conversion
- Use cwebp -crop for splitting (no Go-side image decode needed)
- Check if already converted before extracting (fast pre-check)
- Remove oliamb/cutter dependency (replaced by cwebp -crop)
- Remove page_container.go (no longer needed)
- Add comprehensive tests with improved coverage

Co-authored-by: Belphemur <197810+Belphemur@users.noreply.github.com>

internal/cbz/cbz_creator.go

@@ -12,6 +12,8 @@ import (
 	"github.com/rs/zerolog/log"
 )
 
+// WriteChapterToCBZ creates a CBZ file from a Chapter by streaming page files
+// from disk directly into the zip archive. No image data is held in memory.
 func WriteChapterToCBZ(chapter *manga.Chapter, outputFilePath string) error {
 	log.Debug().
 		Str("chapter_file", chapter.FilePath).
@@ -20,8 +22,7 @@ func WriteChapterToCBZ(chapter *manga.Chapter, outputFilePath string) error {
 		Bool("is_converted", chapter.IsConverted).
 		Msg("Starting CBZ file creation")
 
-	// Create a new ZIP file
-	log.Debug().Str("output_path", outputFilePath).Msg("Creating output CBZ file")
+	// Create output file
 	zipFile, err := os.Create(outputFilePath)
 	if err != nil {
 		log.Error().Str("output_path", outputFilePath).Err(err).Msg("Failed to create CBZ file")
@@ -29,109 +30,88 @@ func WriteChapterToCBZ(chapter *manga.Chapter, outputFilePath string) error {
 	}
 	defer errs.Capture(&err, zipFile.Close, "failed to close .cbz file")
 
-	// Create a new ZIP writer
-	log.Debug().Str("output_path", outputFilePath).Msg("Creating ZIP writer")
+	// Create ZIP writer
 	zipWriter := zip.NewWriter(zipFile)
-	if err != nil {
-		log.Error().Str("output_path", outputFilePath).Err(err).Msg("Failed to create ZIP writer")
-		return err
-	}
 	defer errs.Capture(&err, zipWriter.Close, "failed to close .cbz writer")
 
-	// Write each page to the ZIP archive
-	log.Debug().Str("output_path", outputFilePath).Int("pages_to_write", len(chapter.Pages)).Msg("Writing pages to CBZ archive")
+	// Write each page to the archive by streaming from disk
 	for _, page := range chapter.Pages {
-		// Construct the file name for the page
 		var fileName string
 		if page.IsSplitted {
-			// Use the format page%03d-%02d for split pages
 			fileName = fmt.Sprintf("%04d-%02d%s", page.Index, page.SplitPartIndex, page.Extension)
 		} else {
-			// Use the format page%03d for non-split pages
 			fileName = fmt.Sprintf("%04d%s", page.Index, page.Extension)
 		}
 
 		log.Debug().
 			Str("output_path", outputFilePath).
 			Uint16("page_index", page.Index).
-			Bool("is_splitted", page.IsSplitted).
-			Uint16("split_part", page.SplitPartIndex).
 			Str("filename", fileName).
-			Uint64("size", page.Size).
+			Str("source", page.FilePath).
 			Msg("Writing page to CBZ archive")
 
-		// Create a new file in the ZIP archive
+		// Create file entry in the zip (Store method = no compression, images are already compressed)
 		fileWriter, err := zipWriter.CreateHeader(&zip.FileHeader{
 			Name:     fileName,
 			Method:   zip.Store,
 			Modified: time.Now(),
 		})
 		if err != nil {
-			log.Error().Str("output_path", outputFilePath).Str("filename", fileName).Err(err).Msg("Failed to create file in CBZ archive")
+			log.Error().Str("filename", fileName).Err(err).Msg("Failed to create file in CBZ archive")
 			return fmt.Errorf("failed to create file in .cbz: %w", err)
 		}
 
-		// Stream the page contents into the archive. This transparently
-		// handles pages staged on disk (see manga.Page.TempFilePath) so we
-		// never need to hold the whole chapter's contents in memory at once.
-		pageReader, err := page.Open()
+		// Stream the page file from disk into the archive
+		pageFile, err := os.Open(page.FilePath)
 		if err != nil {
-			log.Error().Str("output_path", outputFilePath).Str("filename", fileName).Err(err).Msg("Failed to open page contents")
-			return fmt.Errorf("failed to open page contents: %w", err)
+			log.Error().Str("filename", fileName).Str("source", page.FilePath).Err(err).Msg("Failed to open page file")
+			return fmt.Errorf("failed to open page file: %w", err)
 		}
 
-		bytesWritten, err := io.Copy(fileWriter, pageReader)
-		closeErr := pageReader.Close()
+		bytesWritten, err := io.Copy(fileWriter, pageFile)
+		closeErr := pageFile.Close()
 		if err != nil {
-			log.Error().Str("output_path", outputFilePath).Str("filename", fileName).Err(err).Msg("Failed to write page contents")
+			log.Error().Str("filename", fileName).Err(err).Msg("Failed to write page contents")
 			return fmt.Errorf("failed to write page contents: %w", err)
 		}
 		if closeErr != nil {
-			log.Error().Str("output_path", outputFilePath).Str("filename", fileName).Err(closeErr).Msg("Failed to close page contents reader")
-			return fmt.Errorf("failed to close page contents reader: %w", closeErr)
+			log.Error().Str("filename", fileName).Err(closeErr).Msg("Failed to close page file")
+			return fmt.Errorf("failed to close page file: %w", closeErr)
 		}
 
 		log.Debug().
-			Str("output_path", outputFilePath).
 			Str("filename", fileName).
 			Int64("bytes_written", bytesWritten).
 			Msg("Page written successfully")
 	}
 
-	// Optionally, write the ComicInfo.xml file if present
+	// Write ComicInfo.xml if present
 	if chapter.ComicInfoXml != "" {
-		log.Debug().Str("output_path", outputFilePath).Int("xml_size", len(chapter.ComicInfoXml)).Msg("Writing ComicInfo.xml to CBZ archive")
+		log.Debug().Str("output_path", outputFilePath).Msg("Writing ComicInfo.xml")
 		comicInfoWriter, err := zipWriter.CreateHeader(&zip.FileHeader{
 			Name:     "ComicInfo.xml",
 			Method:   zip.Deflate,
 			Modified: time.Now(),
 		})
 		if err != nil {
-			log.Error().Str("output_path", outputFilePath).Err(err).Msg("Failed to create ComicInfo.xml in CBZ archive")
 			return fmt.Errorf("failed to create ComicInfo.xml in .cbz: %w", err)
 		}
 
-		bytesWritten, err := comicInfoWriter.Write([]byte(chapter.ComicInfoXml))
+		_, err = comicInfoWriter.Write([]byte(chapter.ComicInfoXml))
 		if err != nil {
-			log.Error().Str("output_path", outputFilePath).Err(err).Msg("Failed to write ComicInfo.xml contents")
-			return fmt.Errorf("failed to write ComicInfo.xml contents: %w", err)
+			return fmt.Errorf("failed to write ComicInfo.xml: %w", err)
 		}
-		log.Debug().Str("output_path", outputFilePath).Int("bytes_written", bytesWritten).Msg("ComicInfo.xml written successfully")
-	} else {
-		log.Debug().Str("output_path", outputFilePath).Msg("No ComicInfo.xml to write")
 	}
 
+	// Set zip comment for converted chapters
 	if chapter.IsConverted {
-		convertedString := fmt.Sprintf("%s\nThis chapter has been converted by CBZOptimizer.", chapter.ConvertedTime)
-		log.Debug().Str("output_path", outputFilePath).Str("comment", convertedString).Msg("Setting CBZ comment for converted chapter")
-		err = zipWriter.SetComment(convertedString)
+		comment := fmt.Sprintf("%s\nThis chapter has been converted by CBZOptimizer.", chapter.ConvertedTime)
+		err = zipWriter.SetComment(comment)
 		if err != nil {
-			log.Error().Str("output_path", outputFilePath).Err(err).Msg("Failed to write CBZ comment")
 			return fmt.Errorf("failed to write comment: %w", err)
 		}
-		log.Debug().Str("output_path", outputFilePath).Msg("CBZ comment set successfully")
 	}
 
-	log.Debug().Str("output_path", outputFilePath).Msg("CBZ file creation completed successfully")
+	log.Debug().Str("output_path", outputFilePath).Msg("CBZ file creation completed")
 	return nil
 }