/*
 * Copyright (C) 2008 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.common.base.Objects;
import com.google.common.collect.ImmutableSet;
import com.google.inject.Binder;
import com.google.inject.Exposed;
import com.google.inject.Key;
import com.google.inject.PrivateBinder;
import com.google.inject.Provides;
import com.google.inject.internal.InternalProviderInstanceBindingImpl.InitializationTiming;
import com.google.inject.internal.util.StackTraceElements;
import com.google.inject.spi.BindingTargetVisitor;
import com.google.inject.spi.Dependency;
import com.google.inject.spi.HasDependencies;
import com.google.inject.spi.ProviderInstanceBinding;
import com.google.inject.spi.ProviderWithExtensionVisitor;
import com.google.inject.spi.ProvidesMethodBinding;
import com.google.inject.spi.ProvidesMethodTargetVisitor;
import java.lang.annotation.Annotation;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Set;

A provider that invokes a method and returns its result.
Author:
jessewilson@google.com (Jesse Wilson)/**
 * A provider that invokes a method and returns its result.
 *
 * @author jessewilson@google.com (Jesse Wilson)
 */
public abstract class ProviderMethod<T> extends InternalProviderInstanceBindingImpl.CyclicFactory<T>
    implements HasDependencies, ProvidesMethodBinding<T>, ProviderWithExtensionVisitor<T> {

  
Creates a ProviderMethod. 
Unless skipFastClassGeneration is set, this will use FastClass to invoke the actual method, since it is significantly faster. However, this will fail if the method is private or protected, since fastclass is subject to java access policies. /**
   * Creates a {@link ProviderMethod}.
   *
   * <p>Unless {@code skipFastClassGeneration} is set, this will use {@link
   * net.sf.cglib.reflect.FastClass} to invoke the actual method, since it is significantly faster.
   * However, this will fail if the method is {@code private} or {@code protected}, since fastclass
   * is subject to java access policies.
   */
  static <T> ProviderMethod<T> create(
      Key<T> key,
      Method method,
      Object instance,
      ImmutableSet<Dependency<?>> dependencies,
      Class<? extends Annotation> scopeAnnotation,
      boolean skipFastClassGeneration,
      Annotation annotation) {
    int modifiers = method.getModifiers();
    /*if[AOP]*/
    if (!skipFastClassGeneration) {
      try {
        net.sf.cglib.reflect.FastClass fc = BytecodeGen.newFastClassForMember(method);
        if (fc != null) {
          return new FastClassProviderMethod<T>(
              key, fc, method, instance, dependencies, scopeAnnotation, annotation);
        }
      } catch (net.sf.cglib.core.CodeGenerationException e) {
        /* fall-through */
      }
    }
    /*end[AOP]*/

    if (!Modifier.isPublic(modifiers)
        || !Modifier.isPublic(method.getDeclaringClass().getModifiers())) {
      method.setAccessible(true);
    }

    return new ReflectionProviderMethod<T>(
        key, method, instance, dependencies, scopeAnnotation, annotation);
  }

  protected final Object instance;
  protected final Method method;

  private final Key<T> key;
  private final Class<? extends Annotation> scopeAnnotation;
  private final ImmutableSet<Dependency<?>> dependencies;
  private final boolean exposed;
  private final Annotation annotation;

  
Set by initialize(InjectorImpl, Errors) so it is always available prior to injection. /**
   * Set by {@link #initialize(InjectorImpl, Errors)} so it is always available prior to injection.
   */
  private SingleParameterInjector<?>[] parameterInjectors;

  
Params:
method – the method to invoke. It's return type must be the same type as key./** @param method the method to invoke. It's return type must be the same type as {@code key}. */
  private ProviderMethod(
      Key<T> key,
      Method method,
      Object instance,
      ImmutableSet<Dependency<?>> dependencies,
      Class<? extends Annotation> scopeAnnotation,
      Annotation annotation) {
    // We can be safely initialized eagerly since our bindings must exist statically and it is an
    // error for them not to.
    super(InitializationTiming.EAGER);
    this.key = key;
    this.scopeAnnotation = scopeAnnotation;
    this.instance = instance;
    this.dependencies = dependencies;
    this.method = method;
    this.exposed = method.isAnnotationPresent(Exposed.class);
    this.annotation = annotation;
  }

  @Override
  public Key<T> getKey() {
    return key;
  }

  @Override
  public Method getMethod() {
    return method;
  }

  // exposed for GIN
  public Object getInstance() {
    return instance;
  }

  @Override
  public Object getEnclosingInstance() {
    return instance;
  }

  @Override
  public Annotation getAnnotation() {
    return annotation;
  }

  public void configure(Binder binder) {
    binder = binder.withSource(method);

    if (scopeAnnotation != null) {
      binder.bind(key).toProvider(this).in(scopeAnnotation);
    } else {
      binder.bind(key).toProvider(this);
    }

    if (exposed) {
      // the cast is safe 'cause the only binder we have implements PrivateBinder. If there's a
      // misplaced @Exposed, calling this will add an error to the binder's error queue
      ((PrivateBinder) binder).expose(key);
    }
  }

  @Override
  void initialize(InjectorImpl injector, Errors errors) throws ErrorsException {
    parameterInjectors = injector.getParametersInjectors(dependencies.asList(), errors);
  }

  @Override
  protected T doProvision(InternalContext context, Dependency<?> dependency)
      throws InternalProvisionException {
    try {
      T t = doProvision(SingleParameterInjector.getAll(context, parameterInjectors));
      if (t == null && !dependency.isNullable()) {
        InternalProvisionException.onNullInjectedIntoNonNullableDependency(getMethod(), dependency);
      }
      return t;
    } catch (IllegalAccessException e) {
      throw new AssertionError(e);
    } catch (InvocationTargetException userException) {
      Throwable cause = userException.getCause() != null ? userException.getCause() : userException;
      throw InternalProvisionException.errorInProvider(cause).addSource(getSource());
    }
  }

  
Extension point for our subclasses to implement the provisioning strategy. /** Extension point for our subclasses to implement the provisioning strategy. */
  abstract T doProvision(Object[] parameters)
      throws IllegalAccessException, InvocationTargetException;

  @Override
  public Set<Dependency<?>> getDependencies() {
    return dependencies;
  }

  @Override
  @SuppressWarnings("unchecked")
  public <B, V> V acceptExtensionVisitor(
      BindingTargetVisitor<B, V> visitor, ProviderInstanceBinding<? extends B> binding) {
    if (visitor instanceof ProvidesMethodTargetVisitor) {
      return ((ProvidesMethodTargetVisitor<T, V>) visitor).visit(this);
    }
    return visitor.visit(binding);
  }

  @Override
  public String toString() {
    String annotationString = annotation.toString();
    // Show @Provides w/o the com.google.inject prefix.
    if (annotation.annotationType() == Provides.class) {
      annotationString = "@Provides";
    } else if (annotationString.endsWith("()")) {
      // Remove the common "()" suffix if there are no values.
      annotationString = annotationString.substring(0, annotationString.length() - 2);
    }
    return annotationString + " " + StackTraceElements.forMember(method);
  }

  @Override
  public boolean equals(Object obj) {
    if (obj instanceof ProviderMethod) {
      ProviderMethod<?> o = (ProviderMethod<?>) obj;
      return method.equals(o.method)
          && Objects.equal(instance, o.instance)
          && annotation.equals(o.annotation);
    } else {
      return false;
    }
  }

  @Override
  public int hashCode() {
    // Avoid calling hashCode on 'instance', which is a user-object
    // that might not be expecting it.
    // (We need to call equals, so we do.  But we can avoid hashCode.)
    return Objects.hashCode(method, annotation);
  }

  /*if[AOP]*/
  
A ProviderMethod implementation that uses FastClass.invoke to invoke the provider method. /**
   * A {@link ProviderMethod} implementation that uses {@link net.sf.cglib.reflect.FastClass#invoke}
   * to invoke the provider method.
   */
  private static final class FastClassProviderMethod<T> extends ProviderMethod<T> {
    final net.sf.cglib.reflect.FastClass fastClass;
    final int methodIndex;

    FastClassProviderMethod(
        Key<T> key,
        net.sf.cglib.reflect.FastClass fc,
        Method method,
        Object instance,
        ImmutableSet<Dependency<?>> dependencies,
        Class<? extends Annotation> scopeAnnotation,
        Annotation annotation) {
      super(key, method, instance, dependencies, scopeAnnotation, annotation);
      this.fastClass = fc;
      this.methodIndex = fc.getMethod(method).getIndex();
    }

    @SuppressWarnings("unchecked")
    @Override
    public T doProvision(Object[] parameters)
        throws IllegalAccessException, InvocationTargetException {
      return (T) fastClass.invoke(methodIndex, instance, parameters);
    }
  }
  /*end[AOP]*/

  
A ProviderMethod implementation that invokes the method using normal java reflection. /**
   * A {@link ProviderMethod} implementation that invokes the method using normal java reflection.
   */
  private static final class ReflectionProviderMethod<T> extends ProviderMethod<T> {
    ReflectionProviderMethod(
        Key<T> key,
        Method method,
        Object instance,
        ImmutableSet<Dependency<?>> dependencies,
        Class<? extends Annotation> scopeAnnotation,
        Annotation annotation) {
      super(key, method, instance, dependencies, scopeAnnotation, annotation);
    }

    @SuppressWarnings("unchecked")
    @Override
    T doProvision(Object[] parameters) throws IllegalAccessException, InvocationTargetException {
      return (T) method.invoke(instance, parameters);
    }
  }
}