// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd

package com.google.protobuf;

import com.google.protobuf.Descriptors.Descriptor;
import com.google.protobuf.Descriptors.FieldDescriptor;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

/**
 * A table of known extensions, searchable by name or field number. When parsing a protocol message
 * that might have extensions, you must provide an {@code ExtensionRegistry} in which you have
 * registered any extensions that you want to be able to parse. Otherwise, those extensions will
 * just be treated like unknown fields.
 *
 * <p>For example, if you had the {@code .proto} file:
 *
 * <pre>
 * option java_class = "MyProto";
 *
 * message Foo {
 *   extensions 1000 to max;
 * }
 *
 * extend Foo {
 *   optional int32 bar;
 * }
 * </pre>
 *
 * Then you might write code like:
 *
 * <pre>
 * ExtensionRegistry registry = ExtensionRegistry.newInstance();
 * registry.add(MyProto.bar);
 * MyProto.Foo message = MyProto.Foo.parseFrom(input, registry);
 * </pre>
 *
 * <p>Background:
 *
 * <p>You might wonder why this is necessary. Two alternatives might come to mind. First, you might
 * imagine a system where generated extensions are automatically registered when their containing
 * classes are loaded. This is a popular technique, but is bad design; among other things, it
 * creates a situation where behavior can change depending on what classes happen to be loaded. It
 * also introduces a security vulnerability, because an unprivileged class could cause its code to
 * be called unexpectedly from a privileged class by registering itself as an extension of the right
 * type.
 *
 * <p>Another option you might consider is lazy parsing: do not parse an extension until it is first
 * requested, at which point the caller must provide a type to use. This introduces a different set
 * of problems. First, it would require a mutex lock any time an extension was accessed, which would
 * be slow. Second, corrupt data would not be detected until first access, at which point it would
 * be much harder to deal with it. Third, it could violate the expectation that message objects are
 * immutable, since the type provided could be any arbitrary message class. An unprivileged user
 * could take advantage of this to inject a mutable object into a message belonging to privileged
 * code and create mischief.
 *
 * @author kenton@google.com Kenton Varda
 */
public class ExtensionRegistry extends ExtensionRegistryLite {
  /** Construct a new, empty instance. */
  public static ExtensionRegistry newInstance() {
    return new ExtensionRegistry();
  }

  /** Get the unmodifiable singleton empty instance. */
  public static ExtensionRegistry getEmptyRegistry() {
    return EMPTY_REGISTRY;
  }

  /** Returns an unmodifiable view of the registry. */
  @Override
  public ExtensionRegistry getUnmodifiable() {
    return new ExtensionRegistry(this);
  }

  /** A (Descriptor, Message) pair, returned by lookup methods. */
  public static final class ExtensionInfo {
    /** The extension's descriptor. */
    public final FieldDescriptor descriptor;

    /**
     * A default instance of the extension's type, if it has a message type. Otherwise, {@code
     * null}.
     */
    public final Message defaultInstance;

    private ExtensionInfo(final FieldDescriptor descriptor) {
      this.descriptor = descriptor;
      defaultInstance = null;
    }

    private ExtensionInfo(final FieldDescriptor descriptor, final Message defaultInstance) {
      this.descriptor = descriptor;
      this.defaultInstance = defaultInstance;
    }
  }

  /** Deprecated. Use {@link #findImmutableExtensionByName(String)} instead. */
  @Deprecated
  public ExtensionInfo findExtensionByName(final String fullName) {
    return findImmutableExtensionByName(fullName);
  }

  /**
   * Find an extension for immutable APIs by fully-qualified field name, in the proto namespace.
   * i.e. {@code result.descriptor.fullName()} will match {@code fullName} if a match is found.
   *
   * @return Information about the extension if found, or {@code null} otherwise.
   */
  public ExtensionInfo findImmutableExtensionByName(final String fullName) {
    return immutableExtensionsByName.get(fullName);
  }

  /**
   * Find an extension for mutable APIs by fully-qualified field name, in the proto namespace. i.e.
   * {@code result.descriptor.fullName()} will match {@code fullName} if a match is found.
   *
   * @return Information about the extension if found, or {@code null} otherwise.
   */
  @Deprecated
  public ExtensionInfo findMutableExtensionByName(final String fullName) {
    return mutableExtensionsByName.get(fullName);
  }

  /** Deprecated. Use {@link #findImmutableExtensionByNumber(Descriptors.Descriptor, int)} */
  @Deprecated
  public ExtensionInfo findExtensionByNumber(
      final Descriptor containingType, final int fieldNumber) {
    return findImmutableExtensionByNumber(containingType, fieldNumber);
  }

  /**
   * Find an extension by containing type and field number for immutable APIs.
   *
   * @return Information about the extension if found, or {@code null} otherwise.
   */
  public ExtensionInfo findImmutableExtensionByNumber(
      final Descriptor containingType, final int fieldNumber) {
    return immutableExtensionsByNumber.get(new DescriptorIntPair(containingType, fieldNumber));
  }

  /**
   * Find an extension by containing type and field number for mutable APIs.
   *
   * @return Information about the extension if found, or {@code null} otherwise.
   */
  @Deprecated
  public ExtensionInfo findMutableExtensionByNumber(
      final Descriptor containingType, final int fieldNumber) {
    return mutableExtensionsByNumber.get(new DescriptorIntPair(containingType, fieldNumber));
  }

  /**
   * Find all extensions for mutable APIs by fully-qualified name of extended class. Note that this
   * method is more computationally expensive than getting a single extension by name or number.
   *
   * @return Information about the extensions found, or {@code null} if there are none.
   */
  @Deprecated
  public Set<ExtensionInfo> getAllMutableExtensionsByExtendedType(final String fullName) {
    HashSet<ExtensionInfo> extensions = new HashSet<ExtensionInfo>();
    for (DescriptorIntPair pair : mutableExtensionsByNumber.keySet()) {
      if (pair.descriptor.getFullName().equals(fullName)) {
        extensions.add(mutableExtensionsByNumber.get(pair));
      }
    }
    return extensions;
  }

  /**
   * Find all extensions for immutable APIs by fully-qualified name of extended class. Note that
   * this method is more computationally expensive than getting a single extension by name or
   * number.
   *
   * @return Information about the extensions found, or {@code null} if there are none.
   */
  public Set<ExtensionInfo> getAllImmutableExtensionsByExtendedType(final String fullName) {
    HashSet<ExtensionInfo> extensions = new HashSet<ExtensionInfo>();
    for (DescriptorIntPair pair : immutableExtensionsByNumber.keySet()) {
      if (pair.descriptor.getFullName().equals(fullName)) {
        extensions.add(immutableExtensionsByNumber.get(pair));
      }
    }
    return extensions;
  }

  /** Add an extension from a generated file to the registry. */
  public void add(final Extension<?, ?> extension) {
    if (extension.getExtensionType() != Extension.ExtensionType.IMMUTABLE
        && extension.getExtensionType() != Extension.ExtensionType.MUTABLE) {
      // do not support other extension types. ignore
      return;
    }
    add(newExtensionInfo(extension), extension.getExtensionType());
  }

  /** Add an extension from a generated file to the registry. */
  public void add(final GeneratedMessage.GeneratedExtension<?, ?> extension) {
    add((Extension<?, ?>) extension);
  }

  static ExtensionInfo newExtensionInfo(final Extension<?, ?> extension) {
    if (extension.getDescriptor().getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
      if (extension.getMessageDefaultInstance() == null) {
        throw new IllegalStateException(
            "Registered message-type extension had null default instance: "
                + extension.getDescriptor().getFullName());
      }
      return new ExtensionInfo(
          extension.getDescriptor(), (Message) extension.getMessageDefaultInstance());
    } else {
      return new ExtensionInfo(extension.getDescriptor(), null);
    }
  }

  /** Add a non-message-type extension to the registry by descriptor. */
  public void add(final FieldDescriptor type) {
    if (type.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
      throw new IllegalArgumentException(
          "ExtensionRegistry.add() must be provided a default instance when "
              + "adding an embedded message extension.");
    }
    ExtensionInfo info = new ExtensionInfo(type, null);
    add(info, Extension.ExtensionType.IMMUTABLE);
    add(info, Extension.ExtensionType.MUTABLE);
  }

  /** Add a message-type extension to the registry by descriptor. */
  public void add(final FieldDescriptor type, final Message defaultInstance) {
    if (type.getJavaType() != FieldDescriptor.JavaType.MESSAGE) {
      throw new IllegalArgumentException(
          "ExtensionRegistry.add() provided a default instance for a non-message extension.");
    }
      add(new ExtensionInfo(type, defaultInstance), Extension.ExtensionType.IMMUTABLE);
  }

  // =================================================================
  // Private stuff.

  private ExtensionRegistry() {
    this.immutableExtensionsByName = new HashMap<String, ExtensionInfo>();
    this.mutableExtensionsByName = new HashMap<String, ExtensionInfo>();
    this.immutableExtensionsByNumber = new HashMap<DescriptorIntPair, ExtensionInfo>();
    this.mutableExtensionsByNumber = new HashMap<DescriptorIntPair, ExtensionInfo>();
  }

  private ExtensionRegistry(ExtensionRegistry other) {
    super(other);
    this.immutableExtensionsByName = Collections.unmodifiableMap(other.immutableExtensionsByName);
    this.mutableExtensionsByName = Collections.unmodifiableMap(other.mutableExtensionsByName);
    this.immutableExtensionsByNumber =
        Collections.unmodifiableMap(other.immutableExtensionsByNumber);
    this.mutableExtensionsByNumber = Collections.unmodifiableMap(other.mutableExtensionsByNumber);
  }

  private final Map<String, ExtensionInfo> immutableExtensionsByName;
  private final Map<String, ExtensionInfo> mutableExtensionsByName;
  private final Map<DescriptorIntPair, ExtensionInfo> immutableExtensionsByNumber;
  private final Map<DescriptorIntPair, ExtensionInfo> mutableExtensionsByNumber;

  ExtensionRegistry(boolean empty) {
    super(EMPTY_REGISTRY_LITE);
    this.immutableExtensionsByName = Collections.<String, ExtensionInfo>emptyMap();
    this.mutableExtensionsByName = Collections.<String, ExtensionInfo>emptyMap();
    this.immutableExtensionsByNumber = Collections.<DescriptorIntPair, ExtensionInfo>emptyMap();
    this.mutableExtensionsByNumber = Collections.<DescriptorIntPair, ExtensionInfo>emptyMap();
  }

  static final ExtensionRegistry EMPTY_REGISTRY = new ExtensionRegistry(true);

  private void add(final ExtensionInfo extension, final Extension.ExtensionType extensionType) {
    if (!extension.descriptor.isExtension()) {
      throw new IllegalArgumentException(
          "ExtensionRegistry.add() was given a FieldDescriptor for a regular "
              + "(non-extension) field.");
    }

    Map<String, ExtensionInfo> extensionsByName;
    Map<DescriptorIntPair, ExtensionInfo> extensionsByNumber;
    switch (extensionType) {
      case IMMUTABLE:
        extensionsByName = immutableExtensionsByName;
        extensionsByNumber = immutableExtensionsByNumber;
        break;
      case MUTABLE:
        extensionsByName = mutableExtensionsByName;
        extensionsByNumber = mutableExtensionsByNumber;
        break;
      default:
        // Ignore the unknown supported type.
        return;
    }

    extensionsByName.put(extension.descriptor.getFullName(), extension);
    extensionsByNumber.put(
        new DescriptorIntPair(
            extension.descriptor.getContainingType(), extension.descriptor.getNumber()),
        extension);

    final FieldDescriptor field = extension.descriptor;
    if (field.getContainingType().getOptions().getMessageSetWireFormat()
        && field.getType() == FieldDescriptor.Type.MESSAGE
        && field.isOptional()
        && field.getExtensionScope() == field.getMessageType()) {
      // This is an extension of a MessageSet type defined within the extension
      // type's own scope.  For backwards-compatibility, allow it to be looked
      // up by type name.
      extensionsByName.put(field.getMessageType().getFullName(), extension);
    }
  }

  /** A (GenericDescriptor, int) pair, used as a map key. */
  private static final class DescriptorIntPair {
    private final Descriptor descriptor;
    private final int number;

    DescriptorIntPair(final Descriptor descriptor, final int number) {
      this.descriptor = descriptor;
      this.number = number;
    }

    @Override
    public int hashCode() {
      return descriptor.hashCode() * ((1 << 16) - 1) + number;
    }

    @Override
    public boolean equals(final Object obj) {
      if (!(obj instanceof DescriptorIntPair)) {
        return false;
      }
      final DescriptorIntPair other = (DescriptorIntPair) obj;
      return descriptor == other.descriptor && number == other.number;
    }
  }
}
