/*
 * Copyright 2012-2019 the original author or authors.
 *
 * Licensed 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.springframework.boot.actuate.autoconfigure.endpoint.condition;

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

import org.springframework.boot.actuate.endpoint.annotation.Endpoint;
import org.springframework.boot.actuate.endpoint.annotation.EndpointExtension;
import org.springframework.context.annotation.Conditional;
import org.springframework.core.env.Environment;

/**
 * {@link Conditional} that checks whether an endpoint is exposed or not. Matches
 * according to the endpoint exposure configuration {@link Environment} properties. This
 * is designed as a companion annotation to {@link ConditionalOnEnabledEndpoint}.
 * <p>
 * For a given {@link Endpoint}, the condition will match if:
 * <ul>
 * <li>{@code "management.endpoints.web.exposure.*"} expose this endpoint</li>
 * <li>or if JMX is enabled and {@code "management.endpoints.jmx.exposure.*"} expose this
 * endpoint</li>
 * <li>or if the application is running on
 * {@link org.springframework.boot.cloud.CloudPlatform#CLOUD_FOUNDRY}</li>
 * </ul>
 *
 * When placed on a {@code @Bean} method, the endpoint defaults to the return type of the
 * factory method:
 *
 * <pre class="code">
 * &#064;Configuration
 * public class MyConfiguration {
 *
 *     &#064;ConditionalOnExposedEndpoint
 *     &#064;Bean
 *     public MyEndpoint myEndpoint() {
 *         ...
 *     }
 *
 * }</pre>
 * <p>
 * It is also possible to use the same mechanism for extensions:
 *
 * <pre class="code">
 * &#064;Configuration
 * public class MyConfiguration {
 *
 *     &#064;ConditionalOnExposedEndpoint
 *     &#064;Bean
 *     public MyEndpointWebExtension myEndpointWebExtension() {
 *         ...
 *     }
 *
 * }</pre>
 * <p>
 * In the sample above, {@code MyEndpointWebExtension} will be created if the endpoint is
 * enabled as defined by the rules above. {@code MyEndpointWebExtension} must be a regular
 * extension that refers to an endpoint, something like:
 *
 * <pre class="code">
 * &#064;EndpointWebExtension(endpoint = MyEndpoint.class)
 * public class MyEndpointWebExtension {
 *
 * }</pre>
 * <p>
 * Alternatively, the target endpoint can be manually specified for components that should
 * only be created when a given endpoint is enabled:
 *
 * <pre class="code">
 * &#064;Configuration
 * public class MyConfiguration {
 *
 *     &#064;ConditionalOnExposedEndpoint(endpoint = MyEndpoint.class)
 *     &#064;Bean
 *     public MyComponent myComponent() {
 *         ...
 *     }
 *
 * }</pre>
 *
 * @author Brian Clozel
 * @since 2.2.0
 * @see Endpoint
 * @see ConditionalOnEnabledEndpoint
 */
@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.METHOD, ElementType.TYPE })
@Documented
@Conditional(OnExposedEndpointCondition.class)
public @interface ConditionalOnExposedEndpoint {

	/**
	 * The endpoint type that should be checked. Inferred when the return type of the
	 * {@code @Bean} method is either an {@link Endpoint} or an {@link EndpointExtension}.
	 * @return the endpoint type to check
	 */
	Class<?> endpoint() default Void.class;

}
