/*
 * WorldEdit, a Minecraft world manipulation toolkit
 * Copyright (C) sk89q <http://www.sk89q.com>
 * Copyright (C) WorldEdit team and contributors
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

package com.sk89q.worldedit.util.eventbus;

import com.google.common.collect.HashMultimap;
import com.google.common.collect.Multimap;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.reflect.Method;

/**
 * A {@link SubscriberFindingStrategy} for collecting all event handler methods
 * that are marked with the {@link Subscribe} annotation.
 *
 * <p>Original for Guava, licensed under the Apache License, Version 2.0.</p>
 */
class AnnotatedSubscriberFinder implements SubscriberFindingStrategy {

    /**
     * {@inheritDoc}
     *
     * <p>
     * This implementation finds all methods marked with a {@link Subscribe}
     * annotation.
     * </p>
     */
    @Override
    public Multimap<Class<?>, EventHandler> findAllSubscribers(Object listener) {
        Multimap<Class<?>, EventHandler> methodsInListener = HashMultimap.create();
        Class<?> clazz = listener.getClass();
        while (clazz != null) {
            for (Method method : clazz.getMethods()) {
                Subscribe annotation = method.getAnnotation(Subscribe.class);
                method.setAccessible(true);

                if (annotation != null) {
                    Class<?>[] parameterTypes = method.getParameterTypes();
                    if (parameterTypes.length != 1) {
                        throw new IllegalArgumentException(
                                "Method " + method + " has @Subscribe annotation, but requires "
                                        + parameterTypes.length + " arguments. Event handler methods "
                                        + "must require a single argument."
                        );
                    }
                    Class<?> eventType = parameterTypes[0];
                    MethodHandle handle;
                    try {
                        handle = MethodHandles.publicLookup().unreflect(method);
                    } catch (IllegalAccessException e) {
                        throw new IllegalArgumentException("Method " + method + " failed to unreflect.", e);
                    }

                    EventHandler handler = new MethodHandleEventHandler(
                            annotation.priority(),
                            listener,
                            handle,
                            method.getName()
                    );
                    methodsInListener.put(eventType, handler);
                }
            }
            clazz = clazz.getSuperclass();
        }

        return methodsInListener;
    }

}
