/**
 * Tests scenario related to SERVER-21697.
 */
(function() {
"use strict";

load("jstests/libs/optimizer_utils.js");  // For checkCascadesOptimizerEnabled.
if (!checkCascadesOptimizerEnabled(db)) {
    jsTestLog("Skipping test because the optimizer is not enabled");
    return;
}

const t = db.cqf_residual_pred_costing;
t.drop();

const bulk = t.initializeUnorderedBulkOp();
const nDocs = 2000;
for (let i = 0; i < nDocs; i++) {
    bulk.insert({a: i % 10, b: i % 10, c: i % 10, d: i % 10});
}
assert.commandWorked(bulk.execute());

assert.commandWorked(t.createIndex({a: 1, b: 1, c: 1, d: 1}));
assert.commandWorked(t.createIndex({a: 1, b: 1, d: 1}));
assert.commandWorked(t.createIndex({a: 1, d: 1}));

try {
    assert.commandWorked(
        db.adminCommand({setParameter: 1, internalCascadesOptimizerFastIndexNullHandling: true}));

    const res = t.explain("executionStats").aggregate([
        {$match: {a: {$eq: 0}, b: {$eq: 0}, c: {$eq: 0}}},
        {$sort: {d: 1}}
    ]);
    assert.eq(nDocs * 0.1, res.executionStats.nReturned);

    // Demonstrate we can pick the indexing covering most fields.
    const indexNode = res.queryPlanner.winningPlan.optimizerPlan.child.leftChild;
    assert.eq("IndexScan", indexNode.nodeType);
    assert.eq("a_1_b_1_c_1_d_1", indexNode.indexDefName);
} finally {
    assert.commandWorked(
        db.adminCommand({setParameter: 1, internalCascadesOptimizerFastIndexNullHandling: false}));
}
}());