/*
 * Copyright 2012-2017 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.autoconfigure.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.context.annotation.Conditional;
import org.springframework.core.env.Environment;

/**
 * {@link Conditional} that checks if the specified properties have a specific value. By
 * default the properties must be present in the {@link Environment} and
 * <strong>not</strong> equal to {@code false}. The {@link #havingValue()} and
 * {@link #matchIfMissing()} attributes allow further customizations.
 *
 * <p>
 * The {@link #havingValue} attribute can be used to specify the value that the property
 * should have. The table below shows when a condition matches according to the property
 * value and the {@link #havingValue()} attribute:
 *
 * <table summary="having values" border="1">
 * <tr>
 * <th>Property Value</th>
 * <th>{@code havingValue=""}</th>
 * <th>{@code havingValue="true"}</th>
 * <th>{@code havingValue="false"}</th>
 * <th>{@code havingValue="foo"}</th>
 * </tr>
 * <tr>
 * <td>{@code "true"}</td>
 * <td>yes</td>
 * <td>yes</td>
 * <td>no</td>
 * <td>no</td>
 * </tr>
 * <tr>
 * <td>{@code "false"}</td>
 * <td>no</td>
 * <td>no</td>
 * <td>yes</td>
 * <td>no</td>
 * </tr>
 * <tr>
 * <td>{@code "foo"}</td>
 * <td>yes</td>
 * <td>no</td>
 * <td>no</td>
 * <td>yes</td>
 * </tr>
 * </table>
 *
 * <p>
 * If the property is not contained in the {@link Environment} at all, the
 * {@link #matchIfMissing()} attribute is consulted. By default missing attributes do not
 * match.
 *
 * @author Maciej Walkowiak
 * @author Stephane Nicoll
 * @author Phillip Webb
 * @since 1.1.0
 */
@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.TYPE, ElementType.METHOD })
@Documented
@Conditional(OnPropertyCondition.class)
public @interface ConditionalOnProperty {

	/**
	 * Alias for {@link #name()}.
	 * @return the names
	 */
	String[] value() default {};

	/**
	 * A prefix that should be applied to each property. The prefix automatically ends
	 * with a dot if not specified.
	 * @return the prefix
	 */
	String prefix() default "";

	/**
	 * The name of the properties to test. If a prefix has been defined, it is applied to
	 * compute the full key of each property. For instance if the prefix is
	 * {@code app.config} and one value is {@code my-value}, the fully key would be
	 * {@code app.config.my-value}
	 * <p>
	 * Use the dashed notation to specify each property, that is all lower case with a "-"
	 * to separate words (e.g. {@code my-long-property}).
	 * @return the names
	 */
	String[] name() default {};

	/**
	 * The string representation of the expected value for the properties. If not
	 * specified, the property must <strong>not</strong> be equals to {@code false}.
	 * @return the expected value
	 */
	String havingValue() default "";

	/**
	 * Specify if the condition should match if the property is not set. Defaults to
	 * {@code false}.
	 * @return if should match if the property is missing
	 */
	boolean matchIfMissing() default false;

}
