/**
 * @tags: [requires_fcv_50]
 *
 * Test the extension to the mongos `hello` command by which clients
 * that have arrived through a load balancer affirm that they are
 * compatible with the way mongos handles load-balanced clients.
 * See `src/mongo/s/load_balancing_support.h`.
 */
(() => {
    "use strict";

    load('jstests/libs/fail_point_util.js');

    /**
     * The whole ShardingTest is restarted just to get a fresh connection.
     * Obviously this could be accomplished much more efficiently.
     */
    var runInShardingTest = (func) => {
        var st = new ShardingTest({shards: 1, mongos: 1});
        try {
            func(st.s0.getDB("admin"));
        } finally {
            st.stop();
        }
    };

    var doHello = (admin, {lbConnection, lbHello, expectServiceId}) => {
        if (lbConnection)
            assert.commandWorked(admin.adminCommand(
                {configureFailPoint: 'clientIsFromLoadBalancer', mode: 'alwaysOn'}));
        try {
            var helloDoc = {};
            if (lbHello)
                helloDoc['loadBalanced'] = true;
            return admin.runCommand("hello", helloDoc);
        } finally {
            assert.commandWorked(
                admin.adminCommand({configureFailPoint: 'clientIsFromLoadBalancer', mode: 'off'}));
        }
    };

    var assertServiceId = (res) => {
        assert.commandWorked(res);
        assert(res.hasOwnProperty("serviceId"),
               "serviceId missing from hello response:" + tojson(res));
        assert(res.serviceId.isObjectId, "res.serviceId = " + tojson(res.serviceId));
    };

    var assertNoServiceId = (res) => {
        assert.commandWorked(res);
        assert(!res.hasOwnProperty("serviceId"), "res.serviceId = " + tojson(res.serviceId));
    };

    /*
     * The ordinary baseline non-load-balanced case.
     */
    runInShardingTest((admin) => {
        // Before getting started, confirm that the feature is enabled.
        assert(admin.adminCommand({getParameter: 1, featureFlagLoadBalancer: 1})
                   .featureFlagLoadBalancer.value,
               'featureFlagLoadBalancer should be enabled for this test');

        jsTestLog("Initial hello command");
        assertNoServiceId(doHello(admin, {}));
        jsTestLog("Non-initial hello command");
        assertNoServiceId(doHello(admin, {}));
    });

    /*
     * Good case: client arrived via load balancer, and load balancing declared by client.
     * The load balancing `serviceId` reporting applies only to the initial hello.
     * The `loadBalanced` option is ignored in subsequent `hello` commands.
     */
    runInShardingTest((admin) => {
        assertServiceId(doHello(admin, {lbConnection: true, lbHello: true}));
        assertNoServiceId(doHello(admin, {lbConnection: true, lbHello: true}));
    });

    /*
     * Client did not arrive via load-balancer, but load balancing support declared by client.
     * We tolerate the `isLoadBalanced` option but ignore it.
     */
    runInShardingTest((admin) => {
        assertNoServiceId(doHello(admin, {lbHello: true}));
    });

    /*
     * Client arrived via load balancer, but load balancing support was not declared by client.
     * This is an error that should result in a disconnection.
     */
    runInShardingTest((admin) => {
        var res = doHello(admin, {lbConnection: true});
        assert.commandFailedWithCode(res, ErrorCodes.LoadBalancerSupportMismatch);
    });
})();
