implement POST message creation

db/fake_db.go

@@ -45,3 +45,51 @@ func ExecDB(db_name string) map[string]interface{} {
 
 	return result
 }
+
+func WriteDB(db_name string, data interface{}) error {
+	var filePath string
+
+	switch db_name {
+	case "users":
+		filePath = "./test_data/users.json"
+	case "messages":
+		filePath = "./test_data/messages.json"
+	default:
+		return fmt.Errorf("invalid database name: %s", db_name)
+	}
+
+	jsonData, err := json.MarshalIndent(data, "", "  ")
+	if err != nil {
+		return fmt.Errorf("error marshaling data to JSON: %v", err)
+	}
+
+	err = os.WriteFile(filePath, jsonData, 0644)
+	if err != nil {
+		return fmt.Errorf("error writing to file: %v", err)
+	}
+
+	fmt.Printf("Successfully wrote to %s DB\n", db_name)
+	return nil
+}
+
+func AddUser(user map[string]interface{}) error {
+	currentData := ExecDB("users")
+	if currentData == nil {
+		return fmt.Errorf("error reading users database")
+	}
+
+	users := currentData["users"].([]interface{})
+	users = append(users, user)
+	return WriteDB("users", users)
+}
+
+func AddMessage(message map[string]interface{}) error {
+	currentData := ExecDB("messages")
+	if currentData == nil {
+		return fmt.Errorf("error reading messages database")
+	}
+
+	messages := currentData["messages"].([]interface{})
+	messages = append(messages, message)
+	return WriteDB("messages", messages)
+}