// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// https://developers.google.com/protocol-buffers/
//
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//
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package com.google.protobuf;

import java.util.AbstractList;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.RandomAccess;

An implementation of LazyStringList that wraps an ArrayList. Each element is one of String, ByteString, or byte[]. It caches the last one requested which is most likely the one needed next. This minimizes memory usage while satisfying the most common use cases. 
Note that this implementation is not synchronized. If multiple threads access
an ArrayList instance concurrently, and at least one of the threads modifies the list
structurally, it must be synchronized externally. (A structural modification is any
operation that adds or deletes one or more elements, or explicitly resizes the backing array;
merely setting the value of an element is not a structural modification.) This is typically
accomplished by synchronizing on some object that naturally encapsulates the list.
If the implementation is accessed via concurrent reads, this is thread safe. Conversions are
done in a thread safe manner. It's possible that the conversion may happen more than once if two
threads attempt to access the same element and the modifications were not visible to each other,
but this will not result in any corruption of the list or change in behavior other than
performance.
Author:
jonp@google.com (Jon Perlow)/**
 * An implementation of {@link LazyStringList} that wraps an ArrayList. Each element is one of
 * String, ByteString, or byte[]. It caches the last one requested which is most likely the one
 * needed next. This minimizes memory usage while satisfying the most common use cases.
 *
 * <p><strong>Note that this implementation is not synchronized.</strong> If multiple threads access
 * an <tt>ArrayList</tt> instance concurrently, and at least one of the threads modifies the list
 * structurally, it <i>must</i> be synchronized externally. (A structural modification is any
 * operation that adds or deletes one or more elements, or explicitly resizes the backing array;
 * merely setting the value of an element is not a structural modification.) This is typically
 * accomplished by synchronizing on some object that naturally encapsulates the list.
 *
 * <p>If the implementation is accessed via concurrent reads, this is thread safe. Conversions are
 * done in a thread safe manner. It's possible that the conversion may happen more than once if two
 * threads attempt to access the same element and the modifications were not visible to each other,
 * but this will not result in any corruption of the list or change in behavior other than
 * performance.
 *
 * @author jonp@google.com (Jon Perlow)
 */
public class LazyStringArrayList extends AbstractProtobufList<String>
    implements LazyStringList, RandomAccess {

  private static final LazyStringArrayList EMPTY_LIST = new LazyStringArrayList();

  static {
    EMPTY_LIST.makeImmutable();
  }

  static LazyStringArrayList emptyList() {
    return EMPTY_LIST;
  }

  // For compatibility with older runtimes.
  public static final LazyStringList EMPTY = EMPTY_LIST;

  private final List<Object> list;

  public LazyStringArrayList() {
    this(DEFAULT_CAPACITY);
  }

  public LazyStringArrayList(int initialCapacity) {
    this(new ArrayList<Object>(initialCapacity));
  }

  public LazyStringArrayList(LazyStringList from) {
    list = new ArrayList<Object>(from.size());
    addAll(from);
  }

  public LazyStringArrayList(List<String> from) {
    this(new ArrayList<Object>(from));
  }

  private LazyStringArrayList(ArrayList<Object> list) {
    this.list = list;
  }

  @Override
  public LazyStringArrayList mutableCopyWithCapacity(int capacity) {
    if (capacity < size()) {
      throw new IllegalArgumentException();
    }
    ArrayList<Object> newList = new ArrayList<Object>(capacity);
    newList.addAll(list);
    return new LazyStringArrayList(newList);
  }

  @Override
  public String get(int index) {
    Object o = list.get(index);
    if (o instanceof String) {
      return (String) o;
    } else if (o instanceof ByteString) {
      ByteString bs = (ByteString) o;
      String s = bs.toStringUtf8();
      if (bs.isValidUtf8()) {
        list.set(index, s);
      }
      return s;
    } else {
      byte[] ba = (byte[]) o;
      String s = Internal.toStringUtf8(ba);
      if (Internal.isValidUtf8(ba)) {
        list.set(index, s);
      }
      return s;
    }
  }

  @Override
  public int size() {
    return list.size();
  }

  @Override
  public String set(int index, String s) {
    ensureIsMutable();
    Object o = list.set(index, s);
    return asString(o);
  }

  @Override
  public void add(int index, String element) {
    ensureIsMutable();
    list.add(index, element);
    modCount++;
  }

  private void add(int index, ByteString element) {
    ensureIsMutable();
    list.add(index, element);
    modCount++;
  }

  private void add(int index, byte[] element) {
    ensureIsMutable();
    list.add(index, element);
    modCount++;
  }

  @Override
  public boolean addAll(Collection<? extends String> c) {
    // The default implementation of AbstractCollection.addAll(Collection)
    // delegates to add(Object). This implementation instead delegates to
    // addAll(int, Collection), which makes a special case for Collections
    // which are instances of LazyStringList.
    return addAll(size(), c);
  }

  @Override
  public boolean addAll(int index, Collection<? extends String> c) {
    ensureIsMutable();
    // When copying from another LazyStringList, directly copy the underlying
    // elements rather than forcing each element to be decoded to a String.
    Collection<?> collection =
        c instanceof LazyStringList ? ((LazyStringList) c).getUnderlyingElements() : c;
    boolean ret = list.addAll(index, collection);
    modCount++;
    return ret;
  }

  @Override
  public boolean addAllByteString(Collection<? extends ByteString> values) {
    ensureIsMutable();
    boolean ret = list.addAll(values);
    modCount++;
    return ret;
  }

  @Override
  public boolean addAllByteArray(Collection<byte[]> c) {
    ensureIsMutable();
    boolean ret = list.addAll(c);
    modCount++;
    return ret;
  }

  @Override
  public String remove(int index) {
    ensureIsMutable();
    Object o = list.remove(index);
    modCount++;
    return asString(o);
  }

  @Override
  public void clear() {
    ensureIsMutable();
    list.clear();
    modCount++;
  }

  @Override
  public void add(ByteString element) {
    ensureIsMutable();
    list.add(element);
    modCount++;
  }

  @Override
  public void add(byte[] element) {
    ensureIsMutable();
    list.add(element);
    modCount++;
  }

  @Override
  public Object getRaw(int index) {
    return list.get(index);
  }

  @Override
  public ByteString getByteString(int index) {
    Object o = list.get(index);
    ByteString b = asByteString(o);
    if (b != o) {
      list.set(index, b);
    }
    return b;
  }

  @Override
  public byte[] getByteArray(int index) {
    Object o = list.get(index);
    byte[] b = asByteArray(o);
    if (b != o) {
      list.set(index, b);
    }
    return b;
  }

  @Override
  public void set(int index, ByteString s) {
    setAndReturn(index, s);
  }

  private Object setAndReturn(int index, ByteString s) {
    ensureIsMutable();
    return list.set(index, s);
  }

  @Override
  public void set(int index, byte[] s) {
    setAndReturn(index, s);
  }

  private Object setAndReturn(int index, byte[] s) {
    ensureIsMutable();
    return list.set(index, s);
  }

  private static String asString(Object o) {
    if (o instanceof String) {
      return (String) o;
    } else if (o instanceof ByteString) {
      return ((ByteString) o).toStringUtf8();
    } else {
      return Internal.toStringUtf8((byte[]) o);
    }
  }

  private static ByteString asByteString(Object o) {
    if (o instanceof ByteString) {
      return (ByteString) o;
    } else if (o instanceof String) {
      return ByteString.copyFromUtf8((String) o);
    } else {
      return ByteString.copyFrom((byte[]) o);
    }
  }

  private static byte[] asByteArray(Object o) {
    if (o instanceof byte[]) {
      return (byte[]) o;
    } else if (o instanceof String) {
      return Internal.toByteArray((String) o);
    } else {
      return ((ByteString) o).toByteArray();
    }
  }

  @Override
  public List<?> getUnderlyingElements() {
    return Collections.unmodifiableList(list);
  }

  @Override
  public void mergeFrom(LazyStringList other) {
    ensureIsMutable();
    for (Object o : other.getUnderlyingElements()) {
      if (o instanceof byte[]) {
        byte[] b = (byte[]) o;
        // Byte array's content is mutable so they should be copied rather than
        // shared when merging from one message to another.
        list.add(Arrays.copyOf(b, b.length));
      } else {
        list.add(o);
      }
    }
  }

  private static class ByteArrayListView extends AbstractList<byte[]> implements RandomAccess {
    private final LazyStringArrayList list;

    ByteArrayListView(LazyStringArrayList list) {
      this.list = list;
    }

    @Override
    public byte[] get(int index) {
      return list.getByteArray(index);
    }

    @Override
    public int size() {
      return list.size();
    }

    @Override
    public byte[] set(int index, byte[] s) {
      Object o = list.setAndReturn(index, s);
      modCount++;
      return asByteArray(o);
    }

    @Override
    public void add(int index, byte[] s) {
      list.add(index, s);
      modCount++;
    }

    @Override
    public byte[] remove(int index) {
      Object o = list.remove(index);
      modCount++;
      return asByteArray(o);
    }
  }

  @Override
  public List<byte[]> asByteArrayList() {
    return new ByteArrayListView(this);
  }

  private static class ByteStringListView extends AbstractList<ByteString> implements RandomAccess {
    private final LazyStringArrayList list;

    ByteStringListView(LazyStringArrayList list) {
      this.list = list;
    }

    @Override
    public ByteString get(int index) {
      return list.getByteString(index);
    }

    @Override
    public int size() {
      return list.size();
    }

    @Override
    public ByteString set(int index, ByteString s) {
      Object o = list.setAndReturn(index, s);
      modCount++;
      return asByteString(o);
    }

    @Override
    public void add(int index, ByteString s) {
      list.add(index, s);
      modCount++;
    }

    @Override
    public ByteString remove(int index) {
      Object o = list.remove(index);
      modCount++;
      return asByteString(o);
    }
  }

  @Override
  public List<ByteString> asByteStringList() {
    return new ByteStringListView(this);
  }

  @Override
  public LazyStringList getUnmodifiableView() {
    if (isModifiable()) {
      return new UnmodifiableLazyStringList(this);
    }
    return this;
  }
}