feat(opds): add on-the-fly KEPUB conversion for downloads

- Integrate conversion service with OPDS handler
- Convert EPUB to KEPUB format on download request
- Cache converted files to reduce processing time
- Support per-device catalog with format availability
- Maintain backward compatibility with existing downloads

internal/handlers/opds.go

@@ -3,6 +3,8 @@ package handlers
 import (
 	"bookmann/internal/database"
 	"bookmann/internal/opds"
+	"bookmann/internal/services"
+	"context"
 	"crypto/rand"
 	"encoding/hex"
 	"fmt"
@@ -19,12 +21,18 @@ import (
 )
 
 type OPDSHandler struct {
-	db *database.Queries
+	db                *database.Queries
+	conversionService interface {
+		ConvertEPUBToKEPUB(ctx context.Context, mediaItemID pgtype.UUID, epubPath string) (*services.ConvertedKEPUB, error)
+	}
 }
 
-func NewOPDSHandler(db *database.Queries) *OPDSHandler {
+func NewOPDSHandler(db *database.Queries, conversionService interface {
+	ConvertEPUBToKEPUB(ctx context.Context, mediaItemID pgtype.UUID, epubPath string) (*services.ConvertedKEPUB, error)
+}) *OPDSHandler {
 	return &OPDSHandler{
-		db: db,
+		db:                db,
+		conversionService: conversionService,
 	}
 }
 
@@ -382,11 +390,11 @@ func (h *OPDSHandler) DownloadBook(c echo.Context) error {
 	mimeType := ""
 
 	if format == "kepub" {
-		// Check for pre-converted KEPUB
 		kepubFormat, err := h.db.GetMediaItemFormatByType(c.Request().Context(), database.GetMediaItemFormatByTypeParams{
 			MediaItemID: pgtype.UUID{Bytes: bookUUID, Valid: true},
 			FormatType:  "kepub",
 		})
+
 		if err == nil && kepubFormat.FilePath.Valid {
 			filePath = kepubFormat.FilePath.String
 			if kepubFormat.FileSha256.Valid {
@@ -396,10 +404,19 @@ func (h *OPDSHandler) DownloadBook(c echo.Context) error {
 				mimeType = kepubFormat.MimeType.String
 			}
 		} else {
-			// Fall back to EPUB (no on-the-fly conversion for now)
-			filePath = mediaItem.FilePath
-			if mediaItem.MimeType.Valid {
-				mimeType = mediaItem.MimeType.String
+			if h.conversionService != nil {
+				converted, err := h.conversionService.ConvertEPUBToKEPUB(c.Request().Context(), pgtype.UUID{Bytes: bookUUID, Valid: true}, mediaItem.FilePath)
+				if err != nil {
+					return c.JSON(http.StatusInternalServerError, map[string]string{"error": fmt.Sprintf("KEPUB conversion failed: %v", err)})
+				}
+				filePath = converted.Path
+				fileSha256 = converted.SHA256
+				mimeType = "application/vnd.kobo+xml+zip"
+			} else {
+				filePath = mediaItem.FilePath
+				if mediaItem.MimeType.Valid {
+					mimeType = mediaItem.MimeType.String
+				}
 			}
 		}
 	} else if format == "pdf" {
@@ -451,11 +468,10 @@ func (h *OPDSHandler) DownloadBook(c echo.Context) error {
 	c.Response().Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=\"%s\"", filename))
 	c.Response().Header().Set("X-Bookmann-UUID", bookUUID.String())
 
-	if fileSha256 != "" {
-		c.Response().Header().Set("X-Bookmann-SHA256", fileSha256)
-	}
 	if format == "kepub" && fileSha256 != "" {
 		c.Response().Header().Set("X-Bookmann-KEPUB-SHA256", fileSha256)
+	} else if fileSha256 != "" {
+		c.Response().Header().Set("X-Bookmann-SHA256", fileSha256)
 	}
 
 	// Stream file