core/src/com/google/inject/internal/ProvisionListenerStackCallback.java

/**
 * 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 com.google.inject.Binding;
import com.google.inject.ProvisionException;
import com.google.inject.spi.DependencyAndSource;
import com.google.inject.spi.ProvisionListener;

import java.util.List;

/**
 * Intercepts provisions with a stack of listeners.
 *
 * @author sameb@google.com (Sam Berlin)
 */
final class ProvisionListenerStackCallback<T> {

  private static final ProvisionListener EMPTY_LISTENER[] = new ProvisionListener[0]; 
  private final ProvisionListener[] listeners;
  private final Binding<T> binding;

  public ProvisionListenerStackCallback(Binding<T> binding, List<ProvisionListener> listeners) {
    this.binding = binding;
    if (listeners.isEmpty()) {
      this.listeners = EMPTY_LISTENER;
    } else {
      this.listeners = listeners.toArray(new ProvisionListener[listeners.size()]);
    }
  }
  
  public boolean hasListeners() {
    return listeners.length > 0;
  }

  public T provision(Errors errors, InternalContext context, ProvisionCallback<T> callable)
      throws ErrorsException {
    Provision provision = new Provision(errors, context, callable);
    RuntimeException caught = null;
    try {
      provision.provision();
    } catch(RuntimeException t) {
      caught = t;
    }
    
    if (provision.exceptionDuringProvision != null) {
      throw provision.exceptionDuringProvision;
    } else if (caught != null) {
      Object listener = provision.erredListener != null ?
          provision.erredListener.getClass() : "(unknown)";
      throw errors
          .errorInUserCode(caught, "Error notifying ProvisionListener %s of %s.%n"
              + " Reason: %s", listener, binding.getKey(), caught)
          .toException();
    } else {
      return provision.result;
    }
  }

  // TODO(sameb): Can this be more InternalFactory-like?
  public interface ProvisionCallback<T> {
    public T call() throws ErrorsException;
  }

  private class Provision extends ProvisionListener.ProvisionInvocation<T> {

    final Errors errors;
    final InternalContext context;
    final ProvisionCallback<T> callable;
    int index = -1;
    T result;
    ErrorsException exceptionDuringProvision;
    ProvisionListener erredListener;

    public Provision(Errors errors, InternalContext context, ProvisionCallback<T> callable) {
      this.callable = callable;
      this.context = context;
      this.errors = errors;
    }

    @Override
    public T provision() {
      index++;
      if (index == listeners.length) {
        try {
          result = callable.call();
        } catch(ErrorsException ee) {
          exceptionDuringProvision = ee;
          throw new ProvisionException(errors.merge(ee.getErrors()).getMessages());
        }
      } else if (index < listeners.length) {
        int currentIdx = index;
        try {

          listeners[index].onProvision(this);
        } catch(RuntimeException re) {
          erredListener = listeners[currentIdx];
          throw re;
        }
        if (currentIdx == index) {
          // Our listener didn't provision -- do it for them.
          provision();
        }
      } else {
        throw new IllegalStateException("Already provisioned in this listener.");
      }
      return result;
    }
    
    @Override
    public Binding<T> getBinding() {
      // TODO(sameb): Because so many places cast directly to BindingImpl & subclasses,
      // we can't decorate this to prevent calling getProvider().get(), which means
      // if someone calls that they'll get strange errors.
      return binding;
    }
    
    @Override
    public List<DependencyAndSource> getDependencyChain() {
      return context.getDependencyChain();
    }
  }
}