// Test that $collStats works on a view and in view pipelines as expected.
(function() {
    "use strict";

    let viewsDB = db.getSiblingDB("views_stats");
    const matchStage = {$match: {}};
    const collStatsStage = {$collStats: {latencyStats: {}}};

    function clear() {
        assert.commandWorked(viewsDB.dropDatabase());
    }

    function getCollStats(ns) {
        return viewsDB[ns].latencyStats().next();
    }

    function checkCollStatsBelongTo(stats, expectedNs) {
        assert.eq(stats.ns,
                  viewsDB[expectedNs].getFullName(),
                  "Expected coll stats for " + expectedNs + " but got " + stats.ns);
    }

    function makeView(viewNs, viewOnNs, pipeline) {
        if (!pipeline) {
            pipeline = [];
        }
        let res = viewsDB.runCommand({create: viewNs, viewOn: viewOnNs, pipeline: pipeline});
        assert.commandWorked(res);
    }

    clear();

    // Check basic latency stats on a view.
    makeView("a", "b");
    checkCollStatsBelongTo(viewsDB["a"].latencyStats().next(), "a");
    clear();

    // Check that latency stats does not prepend the view pipeline.
    makeView("a", "b", [matchStage]);
    checkCollStatsBelongTo(viewsDB["a"].latencyStats().next(), "a");
    clear();

    // Check that latency stats works inside a pipeline.
    makeView("a", "b", [collStatsStage]);
    checkCollStatsBelongTo(viewsDB["a"].latencyStats().next(), "a");
    checkCollStatsBelongTo(viewsDB["b"].latencyStats().next(), "b");
    // Since the $collStats stage is in the pipeline, it should refer to the viewOn namespace.
    checkCollStatsBelongTo(viewsDB["a"].aggregate().next(), "b");
    clear();

    // Check that the first $collStats pipeline stage found will not resolve further views.
    makeView("a", "b", [collStatsStage, matchStage]);
    makeView("b", "c", [collStatsStage]);
    checkCollStatsBelongTo(viewsDB["a"].latencyStats().next(), "a");
    checkCollStatsBelongTo(viewsDB["b"].latencyStats().next(), "b");
    checkCollStatsBelongTo(viewsDB["c"].latencyStats().next(), "c");
    checkCollStatsBelongTo(viewsDB["a"].aggregate().next(), "b");
    checkCollStatsBelongTo(viewsDB["b"].aggregate().next(), "c");
    clear();
}());