googleapis
diff --git a/‎dev/src/reference.ts‎
Lines changed: 323 additions & 2 deletions b/‎dev/src/reference.ts‎
Lines changed: 323 additions & 2 deletions
@@ -15,7 +15,7 @@
  */
 
 import * as firestore from '@google-cloud/firestore';
-import {Duplex, Transform} from 'stream';
+import {Duplex, Readable, Transform} from 'stream';
 import * as deepEqual from 'fast-deep-equal';
 
 import * as protos from '../protos/firestore_v1_proto_api';
@@ -55,7 +55,6 @@ import {
 } from './validate';
 import {DocumentWatch, QueryWatch} from './watch';
 import {validateDocumentData, WriteBatch, WriteResult} from './write-batch';
-
 import api = protos.google.firestore.v1;
 
 /**
@@ -1599,6 +1598,27 @@ export class Query<T = firestore.DocumentData> implements firestore.Query<T> {
     return new Query(this._firestore, options);
   }
 
+  /**
+   * Returns a query that counts the documents in the result set of this
+   * query.
+   *
+   * The returned query, when executed, counts the documents in the result set
+   * of this query without actually downloading the documents.
+   *
+   * Using the returned query to count the documents is efficient because only
+   * the final count, not the documents' data, is downloaded. The returned
+   * query can even count the documents if the result set would be
+   * prohibitively large to download entirely (e.g. thousands of documents).
+   *
+   * @return a query that counts the documents in the result set of this
+   * query. The count can be retrieved from `snapshot.data().count`, where
+   * `snapshot` is the `AggregateQuerySnapshot` resulting from running the
+   * returned query.
+   */
+  count(): AggregateQuery<{count: firestore.AggregateField<number>}> {
+    return new AggregateQuery(this, {count: {}});
+  }
+
   /**
    * Returns true if this `Query` is equal to the provided value.
    *
@@ -2832,6 +2852,307 @@ export class CollectionReference<T = firestore.DocumentData>
   }
 }
 
+/**
+ * A query that calculates aggregations over an underlying query.
+ */
+export class AggregateQuery<T extends firestore.AggregateSpec>
+  implements firestore.AggregateQuery<T>
+{
+  /**
+   * @private
+   * @internal
+   *
+   * @param _query The query whose aggregations will be calculated by this
+   * object.
+   * @param _aggregates The aggregations that will be performed by this query.
+   */
+  constructor(
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    private readonly _query: Query<any>,
+    private readonly _aggregates: T
+  ) {}
+
+  /** The query whose aggregations will be calculated by this object. */
+  get query(): firestore.Query<unknown> {
+    return this._query;
+  }
+
+  /**
+   * Executes this query.
+   *
+   * @return A promise that will be resolved with the results of the query.
+   */
+  get(): Promise<AggregateQuerySnapshot<T>> {
+    return this._get();
+  }
+
+  /**
+   * Internal get() method that accepts an optional transaction id.
+   *
+   * @private
+   * @internal
+   * @param {bytes=} transactionId A transaction ID.
+   */
+  _get(transactionId?: Uint8Array): Promise<AggregateQuerySnapshot<T>> {
+    // Capture the error stack to preserve stack tracing across async calls.
+    const stack = Error().stack!;
+
+    return new Promise((resolve, reject) => {
+      const stream = this._stream(transactionId);
+      stream.on('error', err => {
+        reject(wrapError(err, stack));
+      });
+      stream.once('data', result => {
+        stream.destroy();
+        resolve(result);
+      });
+      stream.on('end', () => {
+        reject('No AggregateQuery results');
+      });
+    });
+  }
+
+  /**
+   * Internal streaming method that accepts an optional transaction ID.
+   *
+   * @private
+   * @internal
+   * @param transactionId A transaction ID.
+   * @returns A stream of document results.
+   */
+  _stream(transactionId?: Uint8Array): Readable {
+    const tag = requestTag();
+    const firestore = this._query.firestore;
+
+    const stream: Transform = new Transform({
+      objectMode: true,
+      transform: (proto: api.IRunAggregationQueryResponse, enc, callback) => {
+        if (proto.result) {
+          const readTime = Timestamp.fromProto(proto.readTime!);
+          const data = this.decodeResult(proto.result);
+          callback(
+            undefined,
+            new AggregateQuerySnapshot<T>(this, readTime, data)
+          );
+        } else {
+          callback(Error('RunAggregationQueryResponse is missing result'));
+        }
+      },
+    });
+
+    firestore
+      .initializeIfNeeded(tag)
+      .then(async () => {
+        // `toProto()` might throw an exception. We rely on the behavior of an
+        // async function to convert this exception into the rejected Promise we
+        // catch below.
+        const request = this.toProto(transactionId);
+
+        let streamActive: Deferred<boolean>;
+        do {
+          streamActive = new Deferred<boolean>();
+          const backendStream = await firestore.requestStream(
+            'runAggregationQuery',
+            /* bidirectional= */ false,
+            request,
+            tag
+          );
+          stream.on('close', () => {
+            backendStream.resume();
+            backendStream.end();
+          });
+          backendStream.on('error', err => {
+            backendStream.unpipe(stream);
+            // If a non-transactional query failed, attempt to restart.
+            // Transactional queries are retried via the transaction runner.
+            if (
+              !transactionId &&
+              !isPermanentRpcError(err, 'runAggregationQuery')
+            ) {
+              logger(
+                'AggregateQuery._stream',
+                tag,
+                'AggregateQuery failed with retryable stream error:',
+                err
+              );
+              streamActive.resolve(/* active= */ true);
+            } else {
+              logger(
+                'AggregateQuery._stream',
+                tag,
+                'AggregateQuery failed with stream error:',
+                err
+              );
+              stream.destroy(err);
+              streamActive.resolve(/* active= */ false);
+            }
+          });
+          backendStream.resume();
+          backendStream.pipe(stream);
+        } while (await streamActive.promise);
+      })
+      .catch(e => stream.destroy(e));
+
+    return stream;
+  }
+
+  /**
+   * Internal method to decode values within result.
+   * @private
+   */
+  private decodeResult(
+    proto: api.IAggregationResult
+  ): firestore.AggregateSpecData<T> {
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const data: any = {};
+    const fields = proto.aggregateFields;
+    if (fields) {
+      const serializer = this._query.firestore._serializer!;
+      for (const prop of Object.keys(fields)) {
+        if (this._aggregates[prop] === undefined) {
+          throw new Error(
+            `Unexpected alias [${prop}] in result aggregate result`
+          );
+        }
+        data[prop] = serializer.decodeValue(fields[prop]);
+      }
+    }
+    return data;
+  }
+
+  /**
+   * Internal method for serializing a query to its RunAggregationQuery proto
+   * representation with an optional transaction id.
+   *
+   * @private
+   * @internal
+   * @returns Serialized JSON for the query.
+   */
+  toProto(transactionId?: Uint8Array): api.IRunAggregationQueryRequest {
+    const queryProto = this._query.toProto();
+    //TODO(tomandersen) inspect _query to build request - this is just hard
+    // coded count right now.
+    const runQueryRequest: api.IRunAggregationQueryRequest = {
+      parent: queryProto.parent,
+      structuredAggregationQuery: {
+        structuredQuery: queryProto.structuredQuery,
+        aggregations: [
+          {
+            alias: 'count',
+            count: {},
+          },
+        ],
+      },
+    };
+
+    if (transactionId instanceof Uint8Array) {
+      runQueryRequest.transaction = transactionId;
+    }
+
+    return runQueryRequest;
+  }
+
+  /**
+   * Compares this object with the given object for equality.
+   *
+   * This object is considered "equal" to the other object if and only if
+   * `other` performs the same aggregations as this `AggregateQuery` and
+   * the underlying Query of `other` compares equal to that of this object
+   * using `Query.isEqual()`.
+   *
+   * @param other The object to compare to this object for equality.
+   * @return `true` if this object is "equal" to the given object, as
+   * defined above, or `false` otherwise.
+   */
+  isEqual(other: firestore.AggregateQuery<T>): boolean {
+    if (this === other) {
+      return true;
+    }
+    if (!(other instanceof AggregateQuery)) {
+      return false;
+    }
+    if (!this.query.isEqual(other.query)) {
+      return false;
+    }
+    return deepEqual(this._aggregates, other._aggregates);
+  }
+}
+
+/**
+ * The results of executing an aggregation query.
+ */
+export class AggregateQuerySnapshot<T extends firestore.AggregateSpec>
+  implements firestore.AggregateQuerySnapshot<T>
+{
+  /**
+   * @private
+   * @internal
+   *
+   * @param _query The query that was executed to produce this result.
+   * @param _readTime The time this snapshot was read.
+   * @param _data The results of the aggregations performed over the underlying
+   * query.
+   */
+  constructor(
+    private readonly _query: AggregateQuery<T>,
+    private readonly _readTime: Timestamp,
+    private readonly _data: firestore.AggregateSpecData<T>
+  ) {}
+
+  /** The query that was executed to produce this result. */
+  get query(): firestore.AggregateQuery<T> {
+    return this._query;
+  }
+
+  /** The time this snapshot was read. */
+  get readTime(): firestore.Timestamp {
+    return this._readTime;
+  }
+
+  /**
+   * Returns the results of the aggregations performed over the underlying
+   * query.
+   *
+   * The keys of the returned object will be the same as those of the
+   * `AggregateSpec` object specified to the aggregation method, and the
+   * values will be the corresponding aggregation result.
+   *
+   * @returns The results of the aggregations performed over the underlying
+   * query.
+   */
+  data(): firestore.AggregateSpecData<T> {
+    return this._data;
+  }
+
+  /**
+   * Compares this object with the given object for equality.
+   *
+   * Two `AggregateQuerySnapshot` instances are considered "equal" if they
+   * have the same data and their underlying queries compare "equal" using
+   * `AggregateQuery.isEqual()`.
+   *
+   * @param other The object to compare to this object for equality.
+   * @return `true` if this object is "equal" to the given object, as
+   * defined above, or `false` otherwise.
+   */
+  isEqual(other: firestore.AggregateQuerySnapshot<T>): boolean {
+    if (this === other) {
+      return true;
+    }
+    if (!(other instanceof AggregateQuerySnapshot)) {
+      return false;
+    }
+    // Since the read time is different on every read, we explicitly ignore all
+    // document metadata in this comparison, just like
+    // `DocumentSnapshot.isEqual()` does.
+    if (!this.query.isEqual(other.query)) {
+      return false;
+    }
+
+    return deepEqual(this._data, other._data);
+  }
+}
+
 /**
  * Validates the input string as a field order direction.
  *