Add GET /user/:userId/allowance/:allowanceId (#50)

Reviewed-on: #50

backend/main.go

@@ -106,6 +106,49 @@ func getUserAllowance(c *gin.Context) {
 	c.IndentedJSON(http.StatusOK, allowances)
 }
 
+func getUserAllowanceById(c *gin.Context) {
+	userIdStr := c.Param("userId")
+	allowanceIdStr := c.Param("allowanceId")
+
+	userId, err := strconv.Atoi(userIdStr)
+	if err != nil {
+		log.Printf(ErrInvalidUserID+": %v", err)
+		c.JSON(http.StatusBadRequest, gin.H{"error": ErrInvalidUserID})
+		return
+	}
+
+	allowanceId, err := strconv.Atoi(allowanceIdStr)
+	if err != nil {
+		log.Printf("Invalid allowance ID: %v", err)
+		c.JSON(http.StatusBadRequest, gin.H{"error": "Invalid allowance ID"})
+		return
+	}
+
+	exists, err := db.UserExists(userId)
+	if err != nil {
+		log.Printf(ErrCheckingUserExist, err)
+		c.JSON(http.StatusInternalServerError, gin.H{"error": ErrInternalServerError})
+		return
+	}
+	if !exists {
+		c.JSON(http.StatusNotFound, gin.H{"error": ErrUserNotFound})
+		return
+	}
+
+	allowance, err := db.GetUserAllowanceById(userId, allowanceId)
+	if errors.Is(err, mysqlite.ErrNoRows) {
+		c.JSON(http.StatusNotFound, gin.H{"error": "Allowance not found"})
+		return
+	}
+	if err != nil {
+		log.Printf("Error getting allowance: %v", err)
+		c.JSON(http.StatusInternalServerError, gin.H{"error": ErrInternalServerError})
+		return
+	}
+
+	c.IndentedJSON(http.StatusOK, allowance)
+}
+
 func createUserAllowance(c *gin.Context) {
 	userIdStr := c.Param("userId")
 	userId, err := strconv.Atoi(userIdStr)
@@ -363,6 +406,7 @@ func start(ctx context.Context, config *ServerConfig) {
 	router.GET("/api/user/:userId/history", getHistory)
 	router.GET("/api/user/:userId/allowance", getUserAllowance)
 	router.POST("/api/user/:userId/allowance", createUserAllowance)
+	router.GET("/api/user/:userId/allowance/:allowanceId", getUserAllowanceById)
 	router.DELETE("/api/user/:userId/allowance/:allowanceId", deleteUserAllowance)
 	router.POST("/api/tasks", createTask)
 	router.GET("/api/tasks", getTasks)