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()})
 	}
 
@@ -258,13 +262,16 @@ func (h *Handler) GetReadingProgress(c echo.Context) error {
 		UserID:  pgtype.UUID{Bytes: userUUID, Valid: true},
 	})
 	if err != nil {
-		// If no progress found, return default
-		return c.JSON(http.StatusOK, map[string]interface{}{
-			"ebook_id":     ebookIdStr,
-			"user_id":      userID,
-			"current_page": 0,
-			"total_pages":  nil,
-		})
+		if err == pgx.ErrNoRows {
+			// If no progress found, return default
+			return c.JSON(http.StatusOK, map[string]interface{}{
+				"ebook_id":     ebookIdStr,
+				"user_id":      userID,
+				"current_page": 0,
+				"total_pages":  nil,
+			})
+		}
+		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
 	}
 
 	return c.JSON(http.StatusOK, progress)
@@ -338,8 +345,11 @@ func (h *Handler) GetEbookRating(c echo.Context) error {
 		UserID:  pgtype.UUID{Bytes: userUUID, Valid: true},
 	})
 	if err != nil {
-		// If no rating found, return 404
-		return c.JSON(http.StatusNotFound, map[string]string{"error": "rating not found"})
+		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)