/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

package org.apache.skywalking.apm.toolkit.trace;

import java.lang.annotation.ElementType;
import java.lang.annotation.Repeatable;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Tag the current active span with key {@link #key()} and value {@link #value()}, if there is no active span, this
 * annotation takes no effect.
 *
 * @see Tags
 */
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Repeatable(Tags.class)
public @interface Tag {
    /**
     * @return the key of the tag to be injected into the current active span
     */
    String key();

    /**
     * @return the value of the tag to be injected into the current active span, in the form of the customized
     * enhancement rules, for more information, refer to <a href="https://github.com/apache/skywalking-java/blob/master/docs/en/setup/service-agent/java-agent/Customize-enhance-trace.md#how-to-configure">Customize-enhance-trace.md#how-to-configure</a>
     */
    String value();
}
