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Java idiomatic client for Google Cloud Firestore.
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/*
 * Copyright 2017 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.cloud.firestore;

import java.util.Objects;
import javax.annotation.Nonnull;

/**
 * A DocumentChange represents a change to the documents matching a query. It contains the document
 * affected and a the type of change that occurred (added, modifed, or removed).
 */
public class DocumentChange {
  /** An enumeration of snapshot diff types. */
  public enum Type {
    /** Indicates a new document was added to the set of documents matching the query. */
    ADDED,
    /** Indicates a document within the query was modified. */
    MODIFIED,
    /**
     * Indicates a document within the query was removed (either deleted or no longer matches the
     * query.
     */
    REMOVED
  }

  private final Type type;

  private final QueryDocumentSnapshot document;

  /** The index in the old snapshot, after processing all previous changes. */
  private final int oldIndex;

  /** The index in the new snapshot, after processing all previous changes. */
  private final int newIndex;

  DocumentChange(QueryDocumentSnapshot document, Type type, int oldIndex, int newIndex) {
    this.type = type;
    this.document = document;
    this.oldIndex = oldIndex;
    this.newIndex = newIndex;
  }

  @Nonnull
  public Type getType() {
    return type;
  }

  /**
   * Returns the newly added or modified document if this DocumentChange is for an updated document.
   * Returns the deleted document if this document change represents a removal.
   *
   * @return A snapshot of the new data (for Type.ADDED or Type.MODIFIED) or the removed data (for
   *     Type.REMOVED).
   */
  @Nonnull
  public QueryDocumentSnapshot getDocument() {
    return document;
  }

  /**
   * The index of the changed document in the result set immediately prior to this DocumentChange
   * (specifically, supposing that all prior DocumentChange objects have been applied). Returns -1
   * for 'added' events.
   */
  public int getOldIndex() {
    return oldIndex;
  }

  /**
   * The index of the changed document in the result set immediately after this DocumentChange
   * (specifically, supposing that all prior DocumentChange objects and the current DocumentChange
   * object have been applied). Returns -1 for 'removed' events.
   */
  public int getNewIndex() {
    return newIndex;
  }

  /**
   * Returns true if this DocumentChange is equal to the provided object.
   *
   * @param obj The object to compare against.
   * @return Whether this DocumentChange is equal to the provided object.
   */
  @Override
  public boolean equals(Object obj) {
    if (this == obj) {
      return true;
    }
    if (obj == null || getClass() != obj.getClass()) {
      return false;
    }
    DocumentChange that = (DocumentChange) obj;
    return oldIndex == that.oldIndex
        && newIndex == that.newIndex
        && type == that.type
        && Objects.equals(document, that.document);
  }

  @Override
  public int hashCode() {
    return Objects.hash(type, document, oldIndex, newIndex);
  }
}