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package com.google.protobuf;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

Equivalent to ExtensionRegistry but supports only "lite" types. 
If all of your types are lite types, then you only need to use ExtensionRegistryLite. Similarly, if all your types are regular types, then you only need 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. 
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:
  Extended type     Inner type    Extension         Use registry
  =======================================================================
  lite              lite          lite              ExtensionRegistryLite
  lite              regular       lite              ExtensionRegistry
  regular           regular       regular           ExtensionRegistry
  all other combinations                            not supported

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/**
 * 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;

  // short circuit the ExtensionRegistryFactory via assumevalues trickery
  @SuppressWarnings("JavaOptionalSuggestions")
  private static boolean doFullRuntimeInheritanceCheck = true;

  // 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.
This may be an ExtensionRegistry if the full (non-Lite) proto libraries are available. /**
   * 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 doFullRuntimeInheritanceCheck
        ? ExtensionRegistryFactory.create()
        : new ExtensionRegistryLite();
  }

  private static volatile ExtensionRegistryLite emptyRegistry;

  
Get the unmodifiable singleton empty instance of either ExtensionRegistryLite or 
ExtensionRegistry (if the full (non-Lite) proto libraries are available). /**
   * 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 =
                  doFullRuntimeInheritanceCheck
                      ? ExtensionRegistryFactory.createEmpty()
                      : EMPTY_REGISTRY_LITE;
        }
      }
    }
    return result;
  }


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

  
Find an extension by containing type and field number.
Returns:
Information about the extension if found, or null otherwise./**
   * 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. /** 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. GeneratedExtension. /**
   * 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 (doFullRuntimeInheritanceCheck && 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. /** 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;
    }
  }
}