content: // Protocol Buffers - Google's data interchange format
  // Copyright 2008 Google Inc.  All rights reserved.
  // https://developers.google.com/protocol-buffers/
  //
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are
  // met:
  //
  //     * Redistributions of source code must retain the above copyright
  // notice, this list of conditions and the following disclaimer.
  //     * Redistributions in binary form must reproduce the above
  // copyright notice, this list of conditions and the following disclaimer
  // in the documentation and/or other materials provided with the
  // distribution.
  //     * Neither the name of Google Inc. nor the names of its
  // contributors may be used to endorse or promote products derived from
  // this software without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  package com.google.protobuf;
  
  import com.google.protobuf.Internal.ProtobufList;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  
  /**
   * Utility class that aids in properly manipulating list fields for either the lite or full runtime.
   */
  abstract class ListFieldSchema {
    // Disallow construction.
    private ListFieldSchema() {}
  
    private static final ListFieldSchema FULL_INSTANCE = new ListFieldSchemaFull();
    private static final ListFieldSchema LITE_INSTANCE = new ListFieldSchemaLite();
  
    abstract <L> List<L> mutableListAt(Object msg, long offset);
  
    abstract void makeImmutableListAt(Object msg, long offset);
  
    abstract <L> void mergeListsAt(Object msg, Object otherMsg, long offset);
  
    static ListFieldSchema full() {
      return FULL_INSTANCE;
    }
  
    static ListFieldSchema lite() {
      return LITE_INSTANCE;
    }
  
    /** Implementation for the full runtime. */
    private static final class ListFieldSchemaFull extends ListFieldSchema {
  
      private static final Class<?> UNMODIFIABLE_LIST_CLASS =
          Collections.unmodifiableList(Collections.emptyList()).getClass();
  
      @Override
      <L> List<L> mutableListAt(Object message, long offset) {
        return mutableListAt(message, offset, AbstractProtobufList.DEFAULT_CAPACITY);
      }
  
      @Override
      void makeImmutableListAt(Object message, long offset) {
        List<?> list = (List<?>) UnsafeUtil.getObject(message, offset);
        Object immutable = null;
        if (list instanceof LazyStringList) {
          immutable = ((LazyStringList) list).getUnmodifiableView();
        } else if (UNMODIFIABLE_LIST_CLASS.isAssignableFrom(list.getClass())) {
          // already immutable
          return;
        } else if (list instanceof PrimitiveNonBoxingCollection && list instanceof ProtobufList) {
          if (((ProtobufList<?>) list).isModifiable()) {
            ((ProtobufList<?>) list).makeImmutable();
          }
          return;
        } else {
          immutable = Collections.unmodifiableList((List<?>) list);
        }
        UnsafeUtil.putObject(message, offset, immutable);
      }
  
      @SuppressWarnings("unchecked")
      private static <L> List<L> mutableListAt(Object message, long offset, int additionalCapacity) {
        List<L> list = getList(message, offset);
        if (list.isEmpty()) {
          if (list instanceof LazyStringList) {
            list = (List<L>) new LazyStringArrayList(additionalCapacity);
          } else if (list instanceof PrimitiveNonBoxingCollection && list instanceof ProtobufList) {
            list = ((ProtobufList<L>) list).mutableCopyWithCapacity(additionalCapacity);
          } else {
            list = new ArrayList<L>(additionalCapacity);
          }
          UnsafeUtil.putObject(message, offset, list);
        } else if (UNMODIFIABLE_LIST_CLASS.isAssignableFrom(list.getClass())) {
          ArrayList<L> newList = new ArrayList<L>(list.size() + additionalCapacity);
          newList.addAll(list);
          list = newList;
          UnsafeUtil.putObject(message, offset, list);
        } else if (list instanceof UnmodifiableLazyStringList) {
          LazyStringArrayList newList = new LazyStringArrayList(list.size() + additionalCapacity);
          newList.addAll((UnmodifiableLazyStringList) list);
          list = (List<L>) newList;
          UnsafeUtil.putObject(message, offset, list);
        } else if (list instanceof PrimitiveNonBoxingCollection
            && list instanceof ProtobufList
            && !((ProtobufList<L>) list).isModifiable()) {
          list = ((ProtobufList<L>) list).mutableCopyWithCapacity(list.size() + additionalCapacity);
          UnsafeUtil.putObject(message, offset, list);
        }
        return list;
      }
  
      @Override
      <E> void mergeListsAt(Object msg, Object otherMsg, long offset) {
        List<E> other = getList(otherMsg, offset);
        List<E> mine = mutableListAt(msg, offset, other.size());
  
        int size = mine.size();
        int otherSize = other.size();
        if (size > 0 && otherSize > 0) {
          mine.addAll(other);
        }
  
        List<E> merged = size > 0 ? mine : other;
        UnsafeUtil.putObject(msg, offset, merged);
      }
  
      @SuppressWarnings("unchecked")
      static <E> List<E> getList(Object message, long offset) {
        return (List<E>) UnsafeUtil.getObject(message, offset);
      }
    }
  
    /** Implementation for the lite runtime. */
    private static final class ListFieldSchemaLite extends ListFieldSchema {
  
      @Override
      <L> List<L> mutableListAt(Object message, long offset) {
        ProtobufList<L> list = getProtobufList(message, offset);
        if (!list.isModifiable()) {
          int size = list.size();
          list =
              list.mutableCopyWithCapacity(
                  size == 0 ? AbstractProtobufList.DEFAULT_CAPACITY : size * 2);
          UnsafeUtil.putObject(message, offset, list);
        }
        return list;
      }
  
      @Override
      void makeImmutableListAt(Object message, long offset) {
        ProtobufList<?> list = getProtobufList(message, offset);
        list.makeImmutable();
      }
  
      @Override
      <E> void mergeListsAt(Object msg, Object otherMsg, long offset) {
        ProtobufList<E> mine = getProtobufList(msg, offset);
        ProtobufList<E> other = getProtobufList(otherMsg, offset);
  
        int size = mine.size();
        int otherSize = other.size();
        if (size > 0 && otherSize > 0) {
          if (!mine.isModifiable()) {
            mine = mine.mutableCopyWithCapacity(size + otherSize);
          }
          mine.addAll(other);
        }
  
        ProtobufList<E> merged = size > 0 ? mine : other;
        UnsafeUtil.putObject(msg, offset, merged);
      }
  
      @SuppressWarnings("unchecked")
      static <E> ProtobufList<E> getProtobufList(Object message, long offset) {
        return (ProtobufList<E>) UnsafeUtil.getObject(message, offset);
      }
    }
  }
  