feat: Add the count aggregate function (#972)

* Files copied over

* implementation of aggregate queries.

* Checkout index.ts previous version

* src seems to be error free

* optional parameters

* replace with recognized type

* protos generated

* old package.json

* aggregation query request

* Commit so I can revert

* Revert "aggregation query request"

This reverts commit 0f2bd32.

* Revert "Revert "aggregation query request""

This reverts commit 1733072.

* Added a parser

* Comment out filters

* Fixed parser

* Add info

* more tests, adding alias

* use deep strict equal instead

* Work on passing in buffered input.

* Convert to buffer

* Add alias

* Add the aggregate function

* change test descriptions

* Add a unit test

* Revert "Files copied over"

This reverts commit fe55548.

# Conflicts:
#	src/index.ts

* Revert "protos generated"

This reverts commit 1b21ec2.

* Eliminate comments

* Add new line

* Change upTo

* Change maximum name to upTo

* upTo relabelled from maximum

* remove import

* ran the linter

* improve code readability

* move self equals this

* change header

* Revert "change header"

This reverts commit b3ea976.

* Add a header

* change the unit test

* Architecture changes

* Getting closer

* Add the right parsing

* TODO message

* Remove and add array over for aggregate fields

* unit test and count function

* fix unit test as result of new changes

* linting fix

* Added a test for encoding using a count function

* lint fix

* removed upTo

* merge

* undid local changes to package.json

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* Update src/aggregate.ts

Co-authored-by: Ruy Adorno <ruyadorno@google.com>

* per reviewer

* refactor and rename some methods

* Add run method to aggregate query

* test update and return value change

* compare aggregate results

* createAggregationQuery

* linter and header fix

* TODOs

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* Remove autogenerated comment

* count aggregation with limit filter tests

* lint fix

* Commented functions and classes

Co-authored-by: Eric Schmidt <em.schmidt78@gmail.com>
Co-authored-by: Eric Schmidt <erschmid@google.com>
Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>
Co-authored-by: Ruy Adorno <ruyadorno@google.com>
Co-authored-by: Kristen O'Leary <kaoleary@google.com>

src/aggregate.ts

@@ -0,0 +1,160 @@
+// Copyright 2023 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
+//
+//     https://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.
+
+import {Query} from './index';
+import {RunQueryOptions, RunQueryResponse} from './query';
+import {RequestCallback} from './request';
+const AGGREGATE_QUERY = Symbol('AGGREGATE_QUERY');
+
+/**
+ * An AggregateQuery is a class that can be used to obtain results from an
+ * aggregate query request.
+ *
+ * @see {@link https://cloud.google.com/datastore/docs/aggregation-queries| Aggregation queries Reference}
+ *
+ * @class
+ */
+class AggregateQuery {
+  type = AGGREGATE_QUERY;
+  aggregations: Array<AggregateField>;
+  query: Query | undefined;
+
+  /**
+   * Build an AggregateQuery object.
+   *
+   * @param {Query} query
+   */
+  constructor(query: Query) {
+    this.query = query;
+    this.aggregations = [];
+  }
+
+  /**
+   * Add a `count` aggregate query to the list of aggregations.
+   *
+   * @param {string} alias
+   * @returns {AggregateQuery}
+   */
+  count(alias: string): AggregateQuery {
+    this.aggregations.push(AggregateField.count().alias(alias));
+    return this;
+  }
+
+  /**
+   * Add a custom aggregation to the list of aggregations.
+   *
+   * @param {AggregateField} aggregation
+   * @returns {AggregateQuery}
+   */
+  addAggregation(aggregation: AggregateField): AggregateQuery {
+    this.aggregations.push(aggregation);
+    return this;
+  }
+
+  /**
+   * Add a list of custom aggregations to the list of aggregations.
+   *
+   * @param {AggregateField[]} aggregation
+   * @returns {AggregateQuery}
+   */
+  addAggregations(aggregations: AggregateField[]): AggregateQuery {
+    for (const aggregation of aggregations) {
+      this.aggregations.push(aggregation);
+    }
+    return this;
+  }
+
+  /**
+   * Run the aggregation query and return the results.
+   *
+   * @param {RunQueryOptions | RequestCallback} [optionsOrCallback]
+   * @param {function} cb The callback function.
+   * @returns {void | Promise<RunQueryResponse>}
+   */
+  run(
+    optionsOrCallback?: RunQueryOptions | RequestCallback,
+    cb?: RequestCallback
+  ): void | Promise<RunQueryResponse> {
+    const options =
+      typeof optionsOrCallback === 'object' ? optionsOrCallback : {};
+    const callback =
+      typeof optionsOrCallback === 'function' ? optionsOrCallback : cb!;
+    const scope = this.query!.scope;
+    const runAggregationQuery = scope!.runAggregationQuery.bind(scope);
+    return runAggregationQuery(this, options, callback);
+  }
+
+  /**
+   * Get the proto for the list of aggregations.
+   *
+   */
+  // eslint-disable-next-line
+  toProto(): any {
+    return this.aggregations.map(aggregation => aggregation.toProto());
+  }
+}
+
+/**
+ * An AggregateField is a class that contains data that defines an aggregation.
+ *
+ */
+abstract class AggregateField {
+  alias_?: string;
+
+  /**
+   * Gets a copy of the Count aggregate field.
+   *
+   * @returns {Count}
+   */
+  static count(): Count {
+    return new Count();
+  }
+
+  /**
+   * Gets a copy of the Count aggregate field.
+   *
+   * @param {string} alias The label used in the results to describe this
+   * aggregate field when a query is run.
+   * @returns {AggregateField}
+   */
+  alias(alias: string): AggregateField {
+    this.alias_ = alias;
+    return this;
+  }
+
+  /**
+   * Gets the proto for the aggregate field.
+   *
+   */
+  // eslint-disable-next-line
+  abstract toProto(): any;
+}
+
+/**
+ * A Count is a class that contains data that defines a Count aggregation.
+ *
+ */
+class Count extends AggregateField {
+  // eslint-disable-next-line
+  /**
+   * Gets the proto for the count aggregate field.
+   *
+   */
+  toProto(): any {
+    const count = Object.assign({});
+    return Object.assign({count}, this.alias_ ? {alias: this.alias_} : null);
+  }
+}
+
+export {AggregateField, AggregateQuery, AGGREGATE_QUERY};

src/index.ts

@@ -64,6 +64,7 @@ import {
 import {Transaction} from './transaction';
 import {promisifyAll} from '@google-cloud/promisify';
 import {google} from '../protos/protos';
+import {AggregateQuery} from './aggregate';
 
 const {grpc} = new GrpcClient();
 
@@ -509,6 +510,15 @@ class Datastore extends DatastoreRequest {
     this.auth = new GoogleAuth(this.options);
   }
 
+  /**
+   * Create an aggregation query from a Query.
+   *
+   * @param {Query} query A Query object.
+   */
+  createAggregationQuery(query: Query): AggregateQuery {
+    return new AggregateQuery(query);
+  }
+
   /**
    * Export entities from this project to a Google Cloud Storage bucket.
    *
@@ -1797,10 +1807,12 @@ class Datastore extends DatastoreRequest {
  */
 promisifyAll(Datastore, {
   exclude: [
+    'createAggregationQuery',
     'double',
     'isDouble',
     'geoPoint',
     'getProjectId',
+    'getSharedQueryOptions',
     'isGeoPoint',
     'index',
     'int',

src/query.ts

@@ -21,6 +21,7 @@ import {Entity} from './entity';
 import {Transaction} from './transaction';
 import {CallOptions} from 'google-gax';
 import {RunQueryStreamOptions} from '../src/request';
+import {AggregateField, AggregateQuery} from './aggregate';
 
 export type Operator =
   | '='
@@ -572,6 +573,8 @@ export interface RunQueryCallback {
 
 export type RunQueryResponse = [Entity[], RunQueryInfo];
 
+export type RunAggregateQueryResponse = any;
+
 export interface RunQueryInfo {
   endCursor?: string;
   moreResults?: