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Java idiomatic client for Google Cloud Datastore.
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/*
 * Copyright 2015 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.datastore;

import static com.google.cloud.datastore.Validator.validateKind;
import static com.google.cloud.datastore.Validator.validateNamespace;
import static com.google.cloud.datastore.Validator.validateProjectId;

import com.google.common.base.MoreObjects;
import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableList;
import java.io.Serializable;
import java.util.LinkedList;
import java.util.List;
import java.util.Objects;

/** Base class for keys. */
public abstract class BaseKey implements Serializable {

  private static final long serialVersionUID = -5897863400209818325L;

  private final String projectId;
  private final String namespace;
  private final String databaseId;
  private final ImmutableList path;

  /**
   * Base class for key builders.
   *
   * @param  the key builder.
   */
  public abstract static class Builder> {

    String projectId = "";
    String namespace = "";
    String databaseId = "";
    String kind;
    final List ancestors;

    private static final int MAX_PATH = 100;

    Builder(String projectId) {
      this.projectId = validateProjectId(projectId);
      ancestors = new LinkedList<>();
    }

    Builder(String projectId, String kind) {
      this(projectId);
      this.kind = validateKind(kind);
    }

    Builder(BaseKey copyFrom) {
      projectId = copyFrom.getProjectId();
      namespace = copyFrom.getNamespace();
      databaseId = copyFrom.getDatabaseId();
      ancestors = new LinkedList<>(copyFrom.getAncestors());
      kind = copyFrom.getKind();
    }

    @SuppressWarnings("unchecked")
    B self() {
      return (B) this;
    }

    /** Adds an ancestor for this key. */
    public B addAncestor(PathElement ancestor) {
      Preconditions.checkState(ancestors.size() < MAX_PATH, "path can have at most 100 elements");
      ancestors.add(ancestor);
      return self();
    }

    /** Adds the provided ancestors to the key. */
    public B addAncestors(PathElement ancestor, PathElement... other) {
      return addAncestors(ImmutableList.builder().add(ancestor).add(other).build());
    }

    /** Adds the provided ancestors to the key. */
    public B addAncestors(Iterable ancestors) {
      ImmutableList list = ImmutableList.copyOf(ancestors);
      Preconditions.checkState(
          this.ancestors.size() + list.size() < MAX_PATH, "path can have at most 100 elements");
      this.ancestors.addAll(list);
      return self();
    }

    /** Sets the kind of the key. */
    public B setKind(String kind) {
      this.kind = validateKind(kind);
      return self();
    }

    /** Sets the project ID of the key. */
    public B setProjectId(String projectId) {
      this.projectId = validateProjectId(projectId);
      return self();
    }

    /** Sets the namespace of the key. */
    public B setNamespace(String namespace) {
      this.namespace = validateNamespace(namespace);
      return self();
    }

    /** Sets the database id of the key. */
    public B setDatabaseId(String databaseId) {
      this.databaseId = databaseId;
      return self();
    }

    protected abstract BaseKey build();
  }

  BaseKey(String projectId, String namespace, ImmutableList path) {
    this(projectId, namespace, "", path);
  }

  BaseKey(String projectId, String namespace, String databaseId, ImmutableList path) {
    Preconditions.checkArgument(!path.isEmpty(), "Path must not be empty");
    this.projectId = projectId;
    this.namespace = namespace;
    this.databaseId = databaseId;
    this.path = path;
  }

  /** Returns the key's projectId. */
  public String getProjectId() {
    return projectId;
  }

  /** Returns the key's namespace or {@code null} if not provided. */
  public String getNamespace() {
    return namespace;
  }

  public String getDatabaseId() {
    return databaseId;
  }

  /** Returns an immutable list with the key's ancestors. */
  public List getAncestors() {
    return getPath().subList(0, getPath().size() - 1);
  }

  /** Returns an immutable list of the key's path (ancestors + self). */
  List getPath() {
    return path;
  }

  PathElement getLeaf() {
    return getPath().get(getPath().size() - 1);
  }

  /** Returns the key's kind. */
  public String getKind() {
    return getLeaf().getKind();
  }

  abstract BaseKey getParent();

  @Override
  public String toString() {
    return MoreObjects.toStringHelper(this)
        .add("projectId", projectId)
        .add("namespace", namespace)
        .add("databaseId", databaseId)
        .add("path", path)
        .toString();
  }

  @Override
  public int hashCode() {
    return Objects.hash(getProjectId(), getNamespace(), getDatabaseId(), getPath());
  }

  @Override
  public boolean equals(Object obj) {
    if (obj == this) {
      return true;
    }
    if (!(obj instanceof BaseKey)) {
      return false;
    }
    BaseKey other = (BaseKey) obj;
    return Objects.equals(getProjectId(), other.getProjectId())
        && Objects.equals(getNamespace(), other.getNamespace())
        && Objects.equals(getDatabaseId(), other.getDatabaseId())
        && Objects.equals(getPath(), other.getPath());
  }

  com.google.datastore.v1.Key toPb() {
    com.google.datastore.v1.Key.Builder keyPb = com.google.datastore.v1.Key.newBuilder();
    com.google.datastore.v1.PartitionId.Builder partitionIdPb =
        com.google.datastore.v1.PartitionId.newBuilder();
    partitionIdPb.setProjectId(projectId);
    partitionIdPb.setDatabaseId(databaseId);
    partitionIdPb.setNamespaceId(namespace);
    keyPb.setPartitionId(partitionIdPb.build());
    for (PathElement pathEntry : path) {
      keyPb.addPath(pathEntry.toPb());
    }
    return keyPb.build();
  }
}