/*
 * Copyright (C) 2011 Google Inc.
 *
 * 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
 *
 * http://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 com.google.inject.internal;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.inject.internal.ProvisionListenerStackCallback.ProvisionCallback;
import com.google.inject.spi.Dependency;
import javax.inject.Provider;

Base class for InternalFactories that are used by Providers, to handle circular dependencies.
Author:
sameb@google.com (Sam Berlin)/**
 * Base class for InternalFactories that are used by Providers, to handle circular dependencies.
 *
 * @author sameb@google.com (Sam Berlin)
 */
abstract class ProviderInternalFactory<T> implements InternalFactory<T> {

  protected final Object source;

  ProviderInternalFactory(Object source) {
    this.source = checkNotNull(source, "source");
  }

  protected T circularGet(
      final Provider<? extends T> provider,
      InternalContext context,
      final Dependency<?> dependency,
      /* @Nullable */ ProvisionListenerStackCallback<T> provisionCallback)
      throws InternalProvisionException {
    final ConstructionContext<T> constructionContext = context.getConstructionContext(this);

    // We have a circular reference between constructors. Return a proxy.
    if (constructionContext.isConstructing()) {
      Class<?> expectedType = dependency.getKey().getTypeLiteral().getRawType();
      // TODO: if we can't proxy this object, can we proxy the other object?
      @SuppressWarnings("unchecked")
      T proxyType = (T) constructionContext.createProxy(context.getInjectorOptions(), expectedType);
      return proxyType;
    }

    // Optimization: Don't go through the callback stack if no one's listening.
    constructionContext.startConstruction();
    try {
      if (provisionCallback == null) {
        return provision(provider, dependency, constructionContext);
      } else {
        return provisionCallback.provision(
            context,
            new ProvisionCallback<T>() {
              @Override
              public T call() throws InternalProvisionException {
                return provision(provider, dependency, constructionContext);
              }
            });
      }
    } finally {
      constructionContext.removeCurrentReference();
      constructionContext.finishConstruction();
    }
  }

  
Provisions a new instance. Subclasses should override this to catch exceptions & rethrow as
ErrorsExceptions.
/**
   * Provisions a new instance. Subclasses should override this to catch exceptions & rethrow as
   * ErrorsExceptions.
   */
  protected T provision(
      Provider<? extends T> provider,
      Dependency<?> dependency,
      ConstructionContext<T> constructionContext)
      throws InternalProvisionException {
    T t = provider.get();
    if (t == null && !dependency.isNullable()) {
      InternalProvisionException.onNullInjectedIntoNonNullableDependency(source, dependency);
    }
    constructionContext.setProxyDelegates(t);
    return t;
  }
}