/*
 * 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 static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;

import com.google.common.collect.HashMultimap;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Multimap;
import com.google.inject.Binder;
import com.google.inject.Key;
import com.google.inject.Module;
import com.google.inject.Provides;
import com.google.inject.TypeLiteral;
import com.google.inject.spi.InjectionPoint;
import com.google.inject.spi.Message;
import com.google.inject.spi.ModuleAnnotatedMethodScanner;
import com.google.inject.util.Modules;
import java.lang.annotation.Annotation;
import java.lang.reflect.Member;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

Creates bindings to methods annotated with @Provides. Use the scope and binding annotations on the provider method to configure the binding. 
Author:
crazybob@google.com (Bob Lee), jessewilson@google.com (Jesse Wilson)/**
 * Creates bindings to methods annotated with {@literal @}{@link Provides}. Use the scope and
 * binding annotations on the provider method to configure the binding.
 *
 * @author crazybob@google.com (Bob Lee)
 * @author jessewilson@google.com (Jesse Wilson)
 */
public final class ProviderMethodsModule implements Module {
  private final Object delegate;
  private final TypeLiteral<?> typeLiteral;
  private final boolean skipFastClassGeneration;
  private final ModuleAnnotatedMethodScanner scanner;

  private ProviderMethodsModule(
      Object delegate, boolean skipFastClassGeneration, ModuleAnnotatedMethodScanner scanner) {
    this.delegate = checkNotNull(delegate, "delegate");
    this.typeLiteral = TypeLiteral.get(getDelegateModuleClass());
    this.skipFastClassGeneration = skipFastClassGeneration;
    this.scanner = scanner;
  }

  
Returns a module which creates bindings for provider methods from the given module. /** Returns a module which creates bindings for provider methods from the given module. */
  public static Module forModule(Module module) {
    return forObject(module, false, ProvidesMethodScanner.INSTANCE);
  }

  
Returns a module which creates bindings methods in the module that match the scanner. /** Returns a module which creates bindings methods in the module that match the scanner. */
  public static Module forModule(Object module, ModuleAnnotatedMethodScanner scanner) {
    return forObject(module, false, scanner);
  }

  
Returns a module which creates bindings for provider methods from the given object. This is
useful notably for GIN
This will skip bytecode generation for provider methods, since it is assumed that callers
are only interested in Module metadata.
/**
   * Returns a module which creates bindings for provider methods from the given object. This is
   * useful notably for <a href="http://code.google.com/p/google-gin/">GIN</a>
   *
   * <p>This will skip bytecode generation for provider methods, since it is assumed that callers
   * are only interested in Module metadata.
   */
  public static Module forObject(Object object) {
    return forObject(object, true, ProvidesMethodScanner.INSTANCE);
  }

  private static Module forObject(
      Object object, boolean skipFastClassGeneration, ModuleAnnotatedMethodScanner scanner) {
    // avoid infinite recursion, since installing a module always installs itself
    if (object instanceof ProviderMethodsModule) {
      return Modules.EMPTY_MODULE;
    }

    return new ProviderMethodsModule(object, skipFastClassGeneration, scanner);
  }

  public Class<?> getDelegateModuleClass() {
    return isStaticModule() ? (Class<?>) delegate : delegate.getClass();
  }

  private boolean isStaticModule() {
    return delegate instanceof Class;
  }

  @Override
  public void configure(Binder binder) {
    for (ProviderMethod<?> providerMethod : getProviderMethods(binder)) {
      providerMethod.configure(binder);
    }
  }

  public List<ProviderMethod<?>> getProviderMethods(Binder binder) {
    List<ProviderMethod<?>> result = null;
    List<MethodAndAnnotation> methodsAndAnnotations = null;
    // The highest class in the type hierarchy that contained a provider method definition.
    Class<?> superMostClass = getDelegateModuleClass();
    for (Class<?> c = superMostClass; c != Object.class && c != null; c = c.getSuperclass()) {
      for (Method method : DeclaredMembers.getDeclaredMethods(c)) {
        Annotation annotation = getAnnotation(binder, method);
        if (annotation != null) {
          if (isStaticModule()
              && !Modifier.isStatic(method.getModifiers())
              && !Modifier.isAbstract(method.getModifiers())) {
            binder
                .skipSources(ProviderMethodsModule.class)
                .addError(
                    "%s is an instance method, but a class literal was passed. Make this method"
                        + " static or pass an instance of the module instead.",
                    method);
            continue;
          }
          if (result == null) {
            result = new ArrayList<>();
            methodsAndAnnotations = new ArrayList<>();
          }

          ProviderMethod<Object> providerMethod = createProviderMethod(binder, method, annotation);
          if (providerMethod != null) {
            result.add(providerMethod);
          }
          methodsAndAnnotations.add(new MethodAndAnnotation(method, annotation));
          superMostClass = c;
        }
      }
    }
    if (result == null) {
      // We didn't find anything
      return ImmutableList.of();
    }
    // We have found some provider methods, now we need to check if any were overridden.
    // We do this as a separate pass to avoid calculating all the signatures when there are no
    // provides methods, or when all provides methods are defined in a single class.
    Multimap<Signature, Method> methodsBySignature = null;
    // We can stop scanning when we see superMostClass, since no superclass method can override
    // a method in a subclass.  Corrollary, if superMostClass == getDelegateModuleClass(), there can
    // be no overrides of a provides method.
    for (Class<?> c = getDelegateModuleClass(); c != superMostClass; c = c.getSuperclass()) {
      for (Method method : c.getDeclaredMethods()) {
        if (((method.getModifiers() & (Modifier.PRIVATE | Modifier.STATIC)) == 0)
            && !method.isBridge()
            && !method.isSynthetic()) {
          if (methodsBySignature == null) {
            methodsBySignature = HashMultimap.create();
          }
          methodsBySignature.put(new Signature(typeLiteral, method), method);
        }
      }
    }
    if (methodsBySignature != null) {
      // we have found all the signatures and now need to identify if any were overridden
      // In the worst case this will have O(n^2) in the number of @Provides methods, but that is
      // only assuming that every method is an override, in general it should be very quick.
      for (MethodAndAnnotation methodAndAnnotation : methodsAndAnnotations) {
        Method method = methodAndAnnotation.method;
        Annotation annotation = methodAndAnnotation.annotation;

        for (Method matchingSignature :
            methodsBySignature.get(new Signature(typeLiteral, method))) {
          // matching signature is in the same class or a super class, therefore method cannot be
          // overridding it.
          if (matchingSignature.getDeclaringClass().isAssignableFrom(method.getDeclaringClass())) {
            continue;
          }
          // now we know matching signature is in a subtype of method.getDeclaringClass()
          if (overrides(matchingSignature, method)) {
            String annotationString =
                annotation.annotationType() == Provides.class
                    ? "@Provides"
                    : "@" + annotation.annotationType().getCanonicalName();
            binder.addError(
                "Overriding "
                    + annotationString
                    + " methods is not allowed."
                    + "\n\t"
                    + annotationString
                    + " method: %s\n\toverridden by: %s",
                method,
                matchingSignature);
            break;
          }
        }
      }
    }
    return result;
  }

  private static class MethodAndAnnotation {
    final Method method;
    final Annotation annotation;

    MethodAndAnnotation(Method method, Annotation annotation) {
      this.method = method;
      this.annotation = annotation;
    }
  }

  
Returns the annotation that is claimed by the scanner, or null if there is none. /** Returns the annotation that is claimed by the scanner, or null if there is none. */
  private Annotation getAnnotation(Binder binder, Method method) {
    if (method.isBridge() || method.isSynthetic()) {
      return null;
    }
    Annotation annotation = null;
    for (Class<? extends Annotation> annotationClass : scanner.annotationClasses()) {
      Annotation foundAnnotation = method.getAnnotation(annotationClass);
      if (foundAnnotation != null) {
        if (annotation != null) {
          binder.addError(
              "More than one annotation claimed by %s on method %s."
                  + " Methods can only have one annotation claimed per scanner.",
              scanner, method);
          return null;
        }
        annotation = foundAnnotation;
      }
    }
    return annotation;
  }

  private static final class Signature {
    final Class<?>[] parameters;
    final String name;
    final int hashCode;

    Signature(TypeLiteral<?> typeLiteral, Method method) {
      this.name = method.getName();
      // We need to 'resolve' the parameters against the actual class type in case this method uses
      // type parameters.  This is so we can detect overrides of generic superclass methods where
      // the subclass specifies the type parameter.  javac implements these kinds of overrides via
      // bridge methods, but we don't want to give errors on bridge methods (but rather the target
      // of the bridge).
      List<TypeLiteral<?>> resolvedParameterTypes = typeLiteral.getParameterTypes(method);
      this.parameters = new Class<?>[resolvedParameterTypes.size()];
      int i = 0;
      for (TypeLiteral<?> type : resolvedParameterTypes) {
        parameters[i] = type.getRawType();
      }
      this.hashCode = name.hashCode() + 31 * Arrays.hashCode(parameters);
    }

    @Override
    public boolean equals(Object obj) {
      if (obj instanceof Signature) {
        Signature other = (Signature) obj;
        return other.name.equals(name) && Arrays.equals(parameters, other.parameters);
      }
      return false;
    }

    @Override
    public int hashCode() {
      return hashCode;
    }
  }

  
Returns true if a overrides b, assumes that the signatures match /** Returns true if a overrides b, assumes that the signatures match */
  private static boolean overrides(Method a, Method b) {
    // See JLS section 8.4.8.1
    int modifiers = b.getModifiers();
    if (Modifier.isPublic(modifiers) || Modifier.isProtected(modifiers)) {
      return true;
    }
    if (Modifier.isPrivate(modifiers)) {
      return false;
    }
    // b must be package-private
    return a.getDeclaringClass().getPackage().equals(b.getDeclaringClass().getPackage());
  }

  private <T> ProviderMethod<T> createProviderMethod(
      Binder binder, Method method, Annotation annotation) {
    binder = binder.withSource(method);
    Errors errors = new Errors(method);

    // prepare the parameter providers
    InjectionPoint point = InjectionPoint.forMethod(method, typeLiteral);
    @SuppressWarnings("unchecked") // Define T as the method's return type.
    TypeLiteral<T> returnType = (TypeLiteral<T>) typeLiteral.getReturnType(method);
    Key<T> key = getKey(errors, returnType, method, method.getAnnotations());
    try {
      key = scanner.prepareMethod(binder, annotation, key, point);
    } catch (Throwable t) {
      binder.addError(t);
    }

    if (Modifier.isAbstract(method.getModifiers())) {
      checkState(
          key == null,
          "%s returned a non-null key (%s) for %s. prepareMethod() must return null for abstract"
              + " methods",
          scanner,
          key,
          method);
      return null;
    } else {
      checkState(
          key != null,
          "%s returned a null key for %s. prepareMethod() can only return null for abstract"
              + " methods",
          scanner,
          method);
    }

    Class<? extends Annotation> scopeAnnotation =
        Annotations.findScopeAnnotation(errors, method.getAnnotations());
    for (Message message : errors.getMessages()) {
      binder.addError(message);
    }

    return ProviderMethod.create(
        key,
        method,
        isStaticModule() ? null : delegate,
        ImmutableSet.copyOf(point.getDependencies()),
        scopeAnnotation,
        skipFastClassGeneration,
        annotation);
  }

  <T> Key<T> getKey(Errors errors, TypeLiteral<T> type, Member member, Annotation[] annotations) {
    Annotation bindingAnnotation = Annotations.findBindingAnnotation(errors, member, annotations);
    return bindingAnnotation == null ? Key.get(type) : Key.get(type, bindingAnnotation);
  }

  @Override
  public boolean equals(Object o) {
    return o instanceof ProviderMethodsModule
        && ((ProviderMethodsModule) o).delegate == delegate
        && ((ProviderMethodsModule) o).scanner == scanner;
  }

  @Override
  public int hashCode() {
    return delegate.hashCode();
  }
}