/**
 * Test that index keys with empty string values are allowed on 4.0 and that upgrading with
 * such indexes will succeed.
 */

(function() {
    'use strict';

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

    const dbpath = MongoRunner.dataPath + 'empty_string_index_value';
    resetDbpath(dbpath);

    const oldVersion = '4.0';
    const newVersion = 'latest';

    // We set noCleanData to true in order to preserve the data files across mongod restart.
    const mongodOptions = {dbpath: dbpath, noCleanData: true, binVersion: oldVersion};

    // Start up an old binary version mongod.
    let conn = MongoRunner.runMongod(mongodOptions);

    assert.neq(null, conn, `mongod was unable able to start with version ${oldVersion}`);

    // Set up a collection on a 4.0 binary version node with one document and an index with
    // an empty string as index value, and then shut it down.
    let testDB = conn.getDB('test');
    assert.commandWorked(testDB.createCollection('testColl'));
    assert.commandWorked(testDB.testColl.insert({a: 1}));
    assert.commandWorked(testDB.testColl.createIndex({a: ""}));
    MongoRunner.stopMongod(conn);

    // Restart the mongod with the latest binary version and the 4.0 version data files.
    mongodOptions.binVersion = newVersion;
    conn = MongoRunner.runMongod(mongodOptions);
    assert.neq(null, conn);

    // Confirm that mongod startup does not fail due to the index specification
    // containing an empty string.
    testDB = conn.getDB('test');
    testDB.testColl.find();
    assert.eq(1,
              testDB.testColl.count({}, {hint: {a: ""}}),
              `data from ${oldVersion} should be available; options: ` + tojson(mongodOptions));

    assert.neq(null,
               GetIndexHelpers.findByKeyPattern(testDB.testColl.getIndexes(), {a: ""}),
               `index from ${oldVersion} should be available; options: ` + tojson(mongodOptions));

    // Verify that indexes with empty string values cannot be created
    assert.commandFailedWithCode(testDB.testColl.createIndex({x: ""}),
                                 ErrorCodes.CannotCreateIndex);

    MongoRunner.stopMongod(conn);

})();