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// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
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package org.apache.juneau.internal;

import static org.apache.juneau.common.internal.ThrowableUtils.*;
import static org.apache.juneau.internal.CollectionUtils.*;

import java.lang.annotation.*;
import java.lang.reflect.*;
import java.util.*;
import java.util.stream.*;

/**
 * Annotation utilities.
 *
 * See Also:

 * 
 */
public class AnnotationUtils {

	/**
	 * Checks if two annotations are equal using the criteria for equality presented in the {@link Annotation#equals(Object)} API docs.
	 *
	 * @param a1 the first Annotation to compare, {@code null} returns {@code false} unless both are {@code null}
	 * @param a2 the second Annotation to compare, {@code null} returns {@code false} unless both are {@code null}
	 * @return {@code true} if the two annotations are {@code equal} or both {@code null}
	 */
	public static boolean equals(Annotation a1, Annotation a2) {
		if (a1 == a2)
			return true;
		if (a1 == null || a2 == null)
			return false;

		Class t1 = a1.annotationType();
		Class t2 = a2.annotationType();

		if (! t1.equals(t2))
			return false;

		boolean b= getAnnotationMethods(t1)
			.anyMatch(x -> ! memberEquals(x.getReturnType(), safeSupplier(()->x.invoke(a1)), safeSupplier(()->x.invoke(a2))));
		if (b)
			return false;

		return true;
	}

	/**
	 * Generate a hash code for the given annotation using the algorithm presented in the {@link Annotation#hashCode()} API docs.
	 *
	 * @param a the Annotation for a hash code calculation is desired, not {@code null}
	 * @return the calculated hash code
	 * @throws RuntimeException if an {@code Exception} is encountered during annotation member access
	 * @throws IllegalStateException if an annotation method invocation returns {@code null}
	 */
	public static int hashCode(Annotation a) {
		return getAnnotationMethods(a.annotationType())
			.mapToInt(x -> hashMember(x.getName(), safeSupplier(()->x.invoke(a))))
			.sum();
	}

	private static Stream getAnnotationMethods(Class type) {
		return alist(type.getDeclaredMethods())
			.stream()
			.filter(x -> x.getParameterCount() == 0 && x.getDeclaringClass().isAnnotation())
		;
	}

	private static int hashMember(String name, Object value) {
		int part1 = name.hashCode() * 127;
		if (value == null)
			return part1;
		if (value.getClass().isArray())
			return part1 ^ arrayMemberHash(value.getClass().getComponentType(), value);
		if (value instanceof Annotation)
			return part1 ^ hashCode((Annotation) value);
		return part1 ^ value.hashCode();
	}

	private static boolean memberEquals(Class type, Object o1, Object o2) {
		if (o1 == o2)
			return true;
		if (o1 == null || o2 == null)
			return false;
		if (type.isArray())
			return arrayMemberEquals(type.getComponentType(), o1, o2);
		if (type.isAnnotation())
			return equals((Annotation) o1, (Annotation) o2);
		return o1.equals(o2);
	}

	private static boolean arrayMemberEquals(Class componentType, Object o1, Object o2) {
		if (componentType.isAnnotation())
			return annotationArrayMemberEquals((Annotation[]) o1, (Annotation[]) o2);
		if (componentType.equals(Byte.TYPE))
			return Arrays.equals((byte[]) o1, (byte[]) o2);
		if (componentType.equals(Short.TYPE))
			return Arrays.equals((short[]) o1, (short[]) o2);
		if (componentType.equals(Integer.TYPE))
			return Arrays.equals((int[]) o1, (int[]) o2);
		if (componentType.equals(Character.TYPE))
			return Arrays.equals((char[]) o1, (char[]) o2);
		if (componentType.equals(Long.TYPE))
			return Arrays.equals((long[]) o1, (long[]) o2);
		if (componentType.equals(Float.TYPE))
			return Arrays.equals((float[]) o1, (float[]) o2);
		if (componentType.equals(Double.TYPE))
			return Arrays.equals((double[]) o1, (double[]) o2);
		if (componentType.equals(Boolean.TYPE))
			return Arrays.equals((boolean[]) o1, (boolean[]) o2);
		return Arrays.equals((Object[]) o1, (Object[]) o2);
	}

	private static boolean annotationArrayMemberEquals(Annotation[] a1, Annotation[] a2) {
		if (a1.length != a2.length)
			return false;
		for (int i = 0; i < a1.length; i++)
			if (! equals(a1[i], a2[i]))
				return false;
		return true;
	}

	private static int arrayMemberHash(Class componentType, Object o) {
		if (componentType.equals(Byte.TYPE))
			return Arrays.hashCode((byte[]) o);
		if (componentType.equals(Short.TYPE))
			return Arrays.hashCode((short[]) o);
		if (componentType.equals(Integer.TYPE))
			return Arrays.hashCode((int[]) o);
		if (componentType.equals(Character.TYPE))
			return Arrays.hashCode((char[]) o);
		if (componentType.equals(Long.TYPE))
			return Arrays.hashCode((long[]) o);
		if (componentType.equals(Float.TYPE))
			return Arrays.hashCode((float[]) o);
		if (componentType.equals(Double.TYPE))
			return Arrays.hashCode((double[]) o);
		if (componentType.equals(Boolean.TYPE))
			return Arrays.hashCode((boolean[]) o);
		return Arrays.hashCode((Object[]) o);
	}
}