/**
 * Copyright (C) 2006 Google Inc.
 * <p>
 * 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
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * 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.apache.struts2.inject;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.ArrayList;
import java.util.List;

/**
 * Context of a dependency construction. Used to manage circular references.
 *
 * @author crazybob@google.com (Bob Lee)
 */
class ConstructionContext<T> {

    T currentReference;
    boolean constructing;

    List<DelegatingInvocationHandler<T>> invocationHandlers;

    T getCurrentReference() {
        return currentReference;
    }

    void removeCurrentReference() {
        this.currentReference = null;
    }

    void setCurrentReference(T currentReference) {
        this.currentReference = currentReference;
    }

    boolean isConstructing() {
        return constructing;
    }

    void startConstruction() {
        this.constructing = true;
    }

    void finishConstruction() {
        this.constructing = false;
        invocationHandlers = null;
    }

    Object createProxy(Class<? super T> expectedType) {
        // TODO: if I create a proxy which implements all the interfaces of
        // the implementation type, I'll be able to get away with one proxy
        // instance (as opposed to one per caller).

        if (!expectedType.isInterface()) {
            throw new DependencyException(expectedType.getName() + " is not an interface.");
        }

        if (invocationHandlers == null) {
            invocationHandlers = new ArrayList<>();
        }

        DelegatingInvocationHandler<T> invocationHandler = new DelegatingInvocationHandler<>();
        invocationHandlers.add(invocationHandler);

        return Proxy.newProxyInstance(
                expectedType.getClassLoader(),
                new Class[]{expectedType},
                invocationHandler
        );
    }

    void setProxyDelegates(T delegate) {
        if (invocationHandlers != null) {
            for (DelegatingInvocationHandler<T> invocationHandler : invocationHandlers) {
                invocationHandler.setDelegate(delegate);
            }
        }
    }

    static class DelegatingInvocationHandler<T> implements InvocationHandler {

        T delegate;

        public Object invoke(Object proxy, Method method, Object[] args)
                throws Throwable {
            if (delegate == null) {
                throw new IllegalStateException(
                        "Not finished constructing. Please don't call methods on this"
                                + " object until the caller's construction is complete.");
            }

            try {
                return method.invoke(delegate, args);
            } catch (IllegalAccessException | IllegalArgumentException e) {
                throw new RuntimeException(e);
            } catch (InvocationTargetException e) {
                throw e.getTargetException();
            }
        }

        void setDelegate(T delegate) {
            this.delegate = delegate;
        }
    }
}
