content: // Protocol Buffers - Google's data interchange format
  // Copyright 2008 Google Inc.  All rights reserved.
  // https://developers.google.com/protocol-buffers/
  //
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  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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  package com.google.protobuf;
  
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.Map;
  
  /**
   * Equivalent to {@link ExtensionRegistry} but supports only "lite" types.
   *
   * <p>If all of your types are lite types, then you only need to use {@code ExtensionRegistryLite}.
   * Similarly, if all your types are regular types, then you only need {@link ExtensionRegistry}.
   * Typically it does not make sense to mix the two, since if you have any regular types in your
   * program, you then require the full runtime and lose all the benefits of the lite runtime, so you
   * might as well make all your types be regular types. However, in some cases (e.g. when depending
   * on multiple third-party libraries where one uses lite types and one uses regular), you may find
   * yourself wanting to mix the two. In this case things get more complicated.
   *
   * <p>There are three factors to consider: Whether the type being extended is lite, whether the
   * embedded type (in the case of a message-typed extension) is lite, and whether the extension
   * itself is lite. Since all three are declared in different files, they could all be different.
   * Here are all the combinations and which type of registry to use:
   *
   * <pre>
   *   Extended type     Inner type    Extension         Use registry
   *   =======================================================================
   *   lite              lite          lite              ExtensionRegistryLite
   *   lite              regular       lite              ExtensionRegistry
   *   regular           regular       regular           ExtensionRegistry
   *   all other combinations                            not supported
   * </pre>
   *
   * <p>Note that just as regular types are not allowed to contain lite-type fields, they are also not
   * allowed to contain lite-type extensions. This is because regular types must be fully accessible
   * via reflection, which in turn means that all the inner messages must also support reflection. On
   * the other hand, since regular types implement the entire lite interface, there is no problem with
   * embedding regular types inside lite types.
   *
   * @author kenton@google.com Kenton Varda
   */
  public class ExtensionRegistryLite {
  
    // Set true to enable lazy parsing feature for MessageSet.
    //
    // TODO(xiangl): Now we use a global flag to control whether enable lazy
    // parsing feature for MessageSet, which may be too crude for some
    // applications. Need to support this feature on smaller granularity.
    private static volatile boolean eagerlyParseMessageSets = false;
  
    // Visible for testing.
    static final String EXTENSION_CLASS_NAME = "com.google.protobuf.Extension";
  
    /* @Nullable */
    static Class<?> resolveExtensionClass() {
      try {
        return Class.forName(EXTENSION_CLASS_NAME);
      } catch (ClassNotFoundException e) {
        // See comment in ExtensionRegistryFactory on the potential expense of this.
        return null;
      }
    }
  
    /* @Nullable */
    private static final Class<?> extensionClass = resolveExtensionClass();
  
    public static boolean isEagerlyParseMessageSets() {
      return eagerlyParseMessageSets;
    }
  
    public static void setEagerlyParseMessageSets(boolean isEagerlyParse) {
      eagerlyParseMessageSets = isEagerlyParse;
    }
  
    /**
     * Construct a new, empty instance.
     *
     * <p>This may be an {@code ExtensionRegistry} if the full (non-Lite) proto libraries are
     * available.
     */
    public static ExtensionRegistryLite newInstance() {
      return ExtensionRegistryFactory.create();
    }
  
    private static volatile ExtensionRegistryLite emptyRegistry;
  
    /**
     * Get the unmodifiable singleton empty instance of either ExtensionRegistryLite or {@code
     * ExtensionRegistry} (if the full (non-Lite) proto libraries are available).
     */
    public static ExtensionRegistryLite getEmptyRegistry() {
      ExtensionRegistryLite result = emptyRegistry;
      if (result == null) {
        synchronized (ExtensionRegistryLite.class) {
          result = emptyRegistry;
          if (result == null) {
            result = emptyRegistry = ExtensionRegistryFactory.createEmpty();
          }
        }
      }
      return result;
    }
  
  
    /** Returns an unmodifiable view of the registry. */
    public ExtensionRegistryLite getUnmodifiable() {
      return new ExtensionRegistryLite(this);
    }
  
    /**
     * Find an extension by containing type and field number.
     *
     * @return Information about the extension if found, or {@code null} otherwise.
     */
    @SuppressWarnings("unchecked")
    public <ContainingType extends MessageLite>
        GeneratedMessageLite.GeneratedExtension<ContainingType, ?> findLiteExtensionByNumber(
            final ContainingType containingTypeDefaultInstance, final int fieldNumber) {
      return (GeneratedMessageLite.GeneratedExtension<ContainingType, ?>)
          extensionsByNumber.get(new ObjectIntPair(containingTypeDefaultInstance, fieldNumber));
    }
  
    /** Add an extension from a lite generated file to the registry. */
    public final void add(final GeneratedMessageLite.GeneratedExtension<?, ?> extension) {
      extensionsByNumber.put(
          new ObjectIntPair(extension.getContainingTypeDefaultInstance(), extension.getNumber()),
          extension);
    }
  
    /**
     * Add an extension from a lite generated file to the registry only if it is a non-lite extension
     * i.e. {@link GeneratedMessageLite.GeneratedExtension}.
     */
    public final void add(ExtensionLite<?, ?> extension) {
      if (GeneratedMessageLite.GeneratedExtension.class.isAssignableFrom(extension.getClass())) {
        add((GeneratedMessageLite.GeneratedExtension<?, ?>) extension);
      }
      if (ExtensionRegistryFactory.isFullRegistry(this)) {
        try {
          this.getClass().getMethod("add", extensionClass).invoke(this, extension);
        } catch (Exception e) {
          throw new IllegalArgumentException(
              String.format("Could not invoke ExtensionRegistry#add for %s", extension), e);
        }
      }
    }
  
    // =================================================================
    // Private stuff.
  
    // Constructors are package-private so that ExtensionRegistry can subclass
    // this.
  
    ExtensionRegistryLite() {
      this.extensionsByNumber =
          new HashMap<ObjectIntPair, GeneratedMessageLite.GeneratedExtension<?, ?>>();
    }
  
    static final ExtensionRegistryLite EMPTY_REGISTRY_LITE = new ExtensionRegistryLite(true);
  
    ExtensionRegistryLite(ExtensionRegistryLite other) {
      if (other == EMPTY_REGISTRY_LITE) {
        this.extensionsByNumber = Collections.emptyMap();
      } else {
        this.extensionsByNumber = Collections.unmodifiableMap(other.extensionsByNumber);
      }
    }
  
    private final Map<ObjectIntPair, GeneratedMessageLite.GeneratedExtension<?, ?>>
        extensionsByNumber;
  
    ExtensionRegistryLite(boolean empty) {
      this.extensionsByNumber = Collections.emptyMap();
    }
  
    /** A (Object, int) pair, used as a map key. */
    private static final class ObjectIntPair {
      private final Object object;
      private final int number;
  
      ObjectIntPair(final Object object, final int number) {
        this.object = object;
        this.number = number;
      }
  
      @Override
      public int hashCode() {
        return System.identityHashCode(object) * ((1 << 16) - 1) + number;
      }
  
      @Override
      public boolean equals(final Object obj) {
        if (!(obj instanceof ObjectIntPair)) {
          return false;
        }
        final ObjectIntPair other = (ObjectIntPair) obj;
        return object == other.object && number == other.number;
      }
    }
  }
  