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/*
 * Copyright 2017-2020 original 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
 *
 * https://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 io.micronaut.http.annotation;

import io.micronaut.context.annotation.AliasFor;
import io.micronaut.core.bind.annotation.Bindable;

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

import static java.lang.annotation.RetentionPolicy.RUNTIME;

/**
 * An annotation that can be applied to method arguments to indicate that the method argument is bound to an HTTP request attribute
 *   This can also be used in conjunction with @RequestAttributes to list attributes on a client class that will always be applied
 *   Note: Request attributes are intended for internal data sharing only, and are not attached to the outbound request.
 *
 * The following example demonstrates usage at the type level to declare default values to pass in the request when using the {@code Client} annotation;
 *
 *  * @RequestAttribute(name = "X-Username", value = "Freddy"),
 * @RequestAttribute(name = "X-MyParam", value = "${foo.bar}")
 * @Client('/users')
 * interface UserClient {
 *
 * }
 * 
 *
 * When declared as a binding annotation the {@code @RequestAttribute} annotation is declared on each parameter to be bound:
 *
 *  * @Get('/user')
 * User get(@RequestAttribute('X-Username') String username, @RequestAttribute('X-MyParam') String myparam) {
 *    return new User(username, myparam);
 * }
 * 
 *
 * @author Ahmed Lafta
 * @since 1.0
 */
@Documented
@Retention(RUNTIME)
@Target({ElementType.PARAMETER, ElementType.TYPE, ElementType.METHOD, ElementType.ANNOTATION_TYPE}) // this can be either type or param
@Repeatable(value = RequestAttributes.class)
@Bindable
public @interface RequestAttribute {

    /**
     * If used as a bound parameter, this is the attribute name. If used on a class level this is value and not the attribute name.
     * @return The name of the attribute, otherwise it is inferred from the parameter name
     */
    @AliasFor(annotation = Bindable.class, member = "value")
    String value() default "";

    /**
     * If used on a class level with @RequestAttributes this is the attribute name and value is the value.
     * @return name of header when using with @RequestAttributes
     */
    @AliasFor(annotation = Bindable.class, member = "value")
    String name() default "";

    /**
     * @see Bindable#defaultValue()
     * @return The default value
     */
    @AliasFor(annotation = Bindable.class, member = "defaultValue")
    String defaultValue() default "";

}