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/*******************************************************************
 * © 2019 SAP SE or an SAP affiliate company. All rights reserved. *
 *******************************************************************/
package com.sap.cds.reflect;

import java.util.Optional;
import java.util.function.Predicate;
import java.util.stream.Stream;

import com.google.common.annotations.Beta;

public interface CdsAnnotatable {

	/**
	 * Returns a sequential {@code Stream} over all {@link CdsAnnotation
	 * CdsAnnotation(s)} of this {@code CdsAnnotatable}.
	 *
	 * @return a sequential {@code Stream} over the {@code CdsAnnotation(s)}
	 */
	Stream> annotations();

	/**
	 * Returns an {@link Optional} wrapping a {@link CdsAnnotation}.
	 * 
	 * @param   the expected type of the annotation value
	 * @param name the name of the {@code CdsAnnotation}
	 * @return an {@code Optional} describing the {@code CdsAnnotation} with the
	 *         given name, or an empty {@code Optional} if there is no
	 *         {@code CdsAnnotation} with this name
	 */
	 Optional> findAnnotation(String name);

	/**
	 * Returns the value of the {@code CdsAnnotation} with the given name.
	 * 
	 * @param           the type of the annotation value
	 * @param name         the name of the {@code CdsAnnotation}
	 * @param defaultValue the value to be returned if there is no annotation
	 *                     present, may be null
	 * @return the value of the annotation, or {@code defaultValue} if there is no
	 *         annotation with the given name
	 */
	@SuppressWarnings("unchecked")
	default  T getAnnotationValue(String name, T defaultValue) {
		return (T) findAnnotation(name).map(CdsAnnotation::getValue).orElse(defaultValue);
	}

	/**
	 * Returns a {@link Predicate} to filter {@code CdsAnnotatable(s)} that have a
	 * {@link CdsAnnotation} with the given name.
	 * 
	 * @param annotation the name of the {@code CdsAnnotation}
	 * @return a {@link Predicate} filtering by annotations
	 */
	static Predicate byAnnotation(String annotation) {
		return a -> a.findAnnotation(annotation).isPresent();
	}

	@Beta
	default Optional getDoc() {
		return Optional.empty();
	}

}