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node_modules/mongodb/src/operations/count_documents.ts

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+import type { Document } from '../bson';
+import type { Collection } from '../collection';
+import type { Server } from '../sdam/server';
+import type { ClientSession } from '../sessions';
+import type { Callback } from '../utils';
+import { AggregateOperation, AggregateOptions } from './aggregate';
+
+/** @public */
+export interface CountDocumentsOptions extends AggregateOptions {
+  /** The number of documents to skip. */
+  skip?: number;
+  /** The maximum amounts to count before aborting. */
+  limit?: number;
+}
+
+/** @internal */
+export class CountDocumentsOperation extends AggregateOperation<number> {
+  constructor(collection: Collection, query: Document, options: CountDocumentsOptions) {
+    const pipeline = [];
+    pipeline.push({ $match: query });
+
+    if (typeof options.skip === 'number') {
+      pipeline.push({ $skip: options.skip });
+    }
+
+    if (typeof options.limit === 'number') {
+      pipeline.push({ $limit: options.limit });
+    }
+
+    pipeline.push({ $group: { _id: 1, n: { $sum: 1 } } });
+
+    super(collection.s.namespace, pipeline, options);
+  }
+
+  override execute(
+    server: Server,
+    session: ClientSession | undefined,
+    callback: Callback<number>
+  ): void {
+    super.execute(server, session, (err, result) => {
+      if (err || !result) {
+        callback(err);
+        return;
+      }
+
+      // NOTE: We're avoiding creating a cursor here to reduce the callstack.
+      const response = result as unknown as Document;
+      if (response.cursor == null || response.cursor.firstBatch == null) {
+        callback(undefined, 0);
+        return;
+      }
+
+      const docs = response.cursor.firstBatch;
+      callback(undefined, docs.length ? docs[0].n : 0);
+    });
+  }
+}