Enhance error handling in ebook handlers

- Add pgx.ErrNoRows checks in GetEbook and GetReadingProgress
- Improve error handling in GetEbookRating with proper status codes
- Return consistent error responses across all endpoints
- Add missing pgx import for proper error comparison

internal/handlers/ebook.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/google/uuid"
+	"github.com/jackc/pgx/v5"
 	"github.com/jackc/pgx/v5/pgtype"
 	"github.com/labstack/echo/v4"
 )
@@ -107,6 +108,9 @@ func (h *Handler) GetEbook(c echo.Context) error {
 
 	ebook, err := h.db.GetEbook(c.Request().Context(), pgtype.UUID{Bytes: id, Valid: true})
 	if err != nil {
+		if err == pgx.ErrNoRows {
+			return c.JSON(http.StatusNotFound, map[string]string{"error": "ebook not found"})
+		}
 		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
 	}
 
@@ -258,6 +262,7 @@ func (h *Handler) GetReadingProgress(c echo.Context) error {
 		UserID:  pgtype.UUID{Bytes: userUUID, Valid: true},
 	})
 	if err != nil {
+		if err == pgx.ErrNoRows {
 			// If no progress found, return default
 			return c.JSON(http.StatusOK, map[string]interface{}{
 				"ebook_id":     ebookIdStr,
@@ -266,6 +271,8 @@ func (h *Handler) GetReadingProgress(c echo.Context) error {
 				"total_pages":  nil,
 			})
 		}
+		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
+	}
 
 	return c.JSON(http.StatusOK, progress)
 }
@@ -338,9 +345,12 @@ func (h *Handler) GetEbookRating(c echo.Context) error {
 		UserID:  pgtype.UUID{Bytes: userUUID, Valid: true},
 	})
 	if err != nil {
+		if err == pgx.ErrNoRows {
 			// If no rating found, return 404
 			return c.JSON(http.StatusNotFound, map[string]string{"error": "rating not found"})
 		}
+		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
+	}
 
 	return c.JSON(http.StatusOK, rating)
 }