/**
 * Verifies that the $collStats aggregation stage includes the shard and hostname for each output
 * document when run via mongoS, and that the former is absent when run on a non-shard mongoD.
 * @tags: [
 *   requires_sharding,
 * ]
 */
(function() {
"use strict";

const conn = MongoRunner.runMongod();
let testDB = conn.getDB(jsTestName());
let testColl = testDB.test;

// getHostName() doesn't include port, db.getMongo().host is 127.0.0.1:<port>
const hostName = (getHostName() + ":" + testDB.getMongo().host.split(":")[1]);

// Test that the shard field is absent and the host field is present when run on mongoD.
assert.eq(testColl
              .aggregate([
                  {$collStats: {latencyStats: {histograms: true}}},
                  {$group: {_id: {shard: "$shard", host: "$host"}}}
              ])
              .toArray(),
          [{_id: {host: hostName}}]);

MongoRunner.stopMongod(conn);

// Test that both shard and hostname are present for $collStats results on a sharded cluster.
const st = new ShardingTest({name: jsTestName(), shards: 2});

testDB = st.s.getDB(jsTestName());
testColl = testDB.test;

assert.commandWorked(testDB.dropDatabase());

// Enable sharding on the test database.
assert.commandWorked(testDB.adminCommand({enableSharding: testDB.getName()}));

// Shard 'testColl' on {_id: 'hashed'}. This will automatically presplit the collection and
// place chunks on each shard.
assert.commandWorked(
    testDB.adminCommand({shardCollection: testColl.getFullName(), key: {_id: "hashed"}}));

// Group $collStats result by $shard and $host to confirm that both fields are present.
assert.eq(testColl
              .aggregate([
                  {$collStats: {latencyStats: {histograms: true}}},
                  {$group: {_id: {shard: "$shard", host: "$host"}}},
                  {$sort: {_id: 1}}
              ])
              .toArray(),
          [
              {_id: {shard: st.shard0.shardName, host: st.rs0.getPrimary().host}},
              {_id: {shard: st.shard1.shardName, host: st.rs1.getPrimary().host}},
          ]);

st.stop();
})();