/*
 * A class with helper functions which operate on change streams. The class maintains a list of
 * opened cursors and kills them on cleanup.
 */
import {FixtureHelpers} from "jstests/libs/fixture_helpers.js";
import {getCollectionNameFromFullNamespace} from "jstests/libs/namespace_utils.js";

/**
 * Enumeration of the possible types of change streams.
 */
export const ChangeStreamWatchMode = Object.freeze({
    kCollection: 1,
    kDb: 2,
    kCluster: 3,
});

/**
 * Returns a truncated json object if the size of 'jsonObj' is greater than 'maxErrorSizeBytes'.
 */
export function tojsonMaybeTruncate(jsonObj) {
    // Maximum size for the json object.
    const maxErrorSizeBytes = 1024 * 1024;

    return tojson(jsonObj).substring(0, maxErrorSizeBytes);
}

/**
 * Helper function used internally by ChangeStreamTest. If no passthrough is active, it is exactly
 * the same as calling db.runCommand. If a passthrough is active and has defined a function
 * 'changeStreamPassthroughAwareRunCommand', then this method will be overridden to allow individual
 * streams to explicitly exempt themselves from being modified by the passthrough.
 */
export function isChangeStreamPassthrough() {
    return typeof changeStreamPassthroughAwareRunCommand != "undefined";
}

/**
 * Helper function to retrieve the type of change stream based on the passthrough suite in which the
 * test is being run. If no passthrough is active, this method returns the kCollection watch mode.
 */
export function changeStreamPassthroughType() {
    return typeof globalThis.ChangeStreamPassthroughHelpers === "undefined"
        ? ChangeStreamWatchMode.kCollection
        : globalThis.ChangeStreamPassthroughHelpers.passthroughType();
}

export function runCommandChangeStreamPassthroughAware(db, cmdObj, noPassthrough) {
    if (!isChangeStreamPassthrough()) {
        return db.runCommand(cmdObj);
    }

    return globalThis.changeStreamPassthroughAwareRunCommand(db, cmdObj, noPassthrough);
}

/**
 * Asserts that the given opType triggers an invalidate entry depending on the type of change
 * stream.
 *     - single collection streams: drop, rename, and dropDatabase.
 *     - whole DB streams: dropDatabase.
 *     - whole cluster streams: none.
 * Returns the invalidate document if there was one, or null otherwise.
 */
export function assertInvalidateOp({cursor, opType}) {
    if (
        !isChangeStreamPassthrough() ||
        (changeStreamPassthroughType() == ChangeStreamWatchMode.kDb && opType == "dropDatabase")
    ) {
        assert.soon(() => cursor.hasNext());
        const invalidate = cursor.next();
        assert.eq(invalidate.operationType, "invalidate");
        assert(!cursor.hasNext());
        assert(cursor.isExhausted());
        assert(cursor.isClosed());
        return invalidate;
    }
    return null;
}

export function canonicalizeEventForTesting(event, expected) {
    for (let fieldName of [
        "_id",
        "clusterTime",
        "txnNumber",
        "lsid",
        "collectionUUID",
        "wallTime",
        "operationDescription",
        "updateDescription",
        "commitTimestamp",
        "nsType",
    ]) {
        if (!expected.hasOwnProperty(fieldName)) {
            delete event[fieldName];
        }
    }

    // Exclude "updateDescription.disambiguatedPaths" if not explicitly specified in the expected
    // event. This is necessary because in v8.2.0, we expose this field unconditionally, but in
    // versions before or after v8.2.0 the field is only exposed if the change stream is opened with
    // '{showExpandedEvents: true}'.
    if (
        expected.hasOwnProperty("updateDescription") &&
        !expected.updateDescription.hasOwnProperty("disambiguatedPaths") &&
        event.hasOwnProperty("updateDescription")
    ) {
        delete event.updateDescription.disambiguatedPaths;
    }

    return event;
}

/**
 * Helper function that sets a global variable to `true`, runs the callback and then sets back the
 * global variable to `false`. The global variable can be checked by command overrides to check if
 * the command was executed from inside the ChangeStreamTest fixture or not.
 */
function runInFixture(callback) {
    globalThis.isInsideChangeStreamTestFixture = true;
    try {
        return callback();
    } finally {
        globalThis.isInsideChangeStreamTestFixture = false;
    }
}

/**
 * Returns true if a change stream event matches the given expected event, false otherwise. Ignores
 * the resume token, clusterTime, and other unknowable fields unless they are explicitly listed in
 * the expected event.
 */
function isChangeStreamEventEq(actualEvent, expectedEvent, eventModifier = canonicalizeEventForTesting) {
    const testEvent = eventModifier(Object.assign({}, actualEvent), expectedEvent);
    return friendlyEqual(sortDoc(testEvent), sortDoc(expectedEvent));
}

/**
 * Helper to check whether a change event matches the given expected event. Throws assertion failure
 * if change events do not match.
 */
export function assertChangeStreamEventEq(actualEvent, expectedEvent, eventModifier) {
    assert(
        isChangeStreamEventEq(actualEvent, expectedEvent, eventModifier),
        () =>
            "Change events did not match. Expected: " +
            tojsonMaybeTruncate(expectedEvent) +
            ", Actual: " +
            tojsonMaybeTruncate(actualEvent),
    );
}

/**
 * Asserts that there are no changes waiting on the change stream cursor.
 */
export function assertNoChanges(cursor) {
    assert(!cursor.hasNext(), () => {
        return "Unexpected change set: " + tojson(cursor.toArray());
    });
}

/**
 * Helper to check that there are no transaction operations past end of transaction event.
 */
export function assertEndOfTransaction(changes) {
    const finishedTransactions = new Set();
    for (const change of changes) {
        assert.eq(
            change.hasOwnProperty("lsid"),
            change.hasOwnProperty("txnNumber"),
            "Found change eventy with inconsistent lsid and txnNumber: " + tojson(change),
        );
        if (change.hasOwnProperty("lsid")) {
            const txnId = tojsononeline({lsid: change.lsid, txnNumber: change.txnNumber});
            if (change.operationType == "endOfTransaction") {
                finishedTransactions.add(txnId);
            } else {
                assert.eq(
                    finishedTransactions.has(txnId),
                    false,
                    "Found change event past endOfTransaction: " + tojson(change),
                );
            }
        }
    }
}

export function isResumableChangeStreamError(error) {
    return "errorLabels" in error && error.errorLabels.includes("ResumableChangeStreamError");
}

export function ChangeStreamTest(_db, options) {
    // Keeps track of cursors opened during the test so that we can be sure to
    // clean them up before the test completes.
    let _allCursors = [];
    // Map to store cursor-specific data
    let _cursorData = new Map();
    let self = this;
    options = options || {};
    const eventModifier = options.eventModifier || canonicalizeEventForTesting;

    function updateResumeToken(cursor, changeEvents) {
        // This isn't fool proof since anyone can just a getMore command on the raw cursor.
        const cursorId = String(cursor.id);
        if (!_cursorData.has(cursorId)) {
            _cursorData.set(cursorId, {});
        }
        const cursorInfo = _cursorData.get(cursorId);

        if (changeEvents && changeEvents.length > 0) {
            cursorInfo.resumeToken = changeEvents[changeEvents.length - 1]._id || cursor.postBatchResumeToken;
        } else if (cursor.postBatchResumeToken) {
            cursorInfo.resumeToken = cursor.postBatchResumeToken;
        }
    }

    function addResumeToken(pipeline, resumeToken) {
        let csStage = pipeline[0]["$changeStream"];
        csStage["resumeAfter"] = resumeToken;
        pipeline[0] = {$changeStream: csStage};
        return pipeline;
    }

    /**
     * Starts a change stream cursor with the given pipeline on the given collection. It uses
     * the 'aggregateOptions' if provided and saves the cursor so that it can be cleaned up later.
     * If 'doNotModifyInPassthroughs' is 'true' and the test is running in a $changeStream
     * upconversion passthrough, then this stream will not be modified and will run as though no
     * passthrough were active.
     *
     * Returns the cursor returned by the 'aggregate' command.
     */
    self.startWatchingChanges = function ({pipeline, collection, aggregateOptions, doNotModifyInPassthroughs}) {
        aggregateOptions = aggregateOptions || {};
        aggregateOptions.cursor = aggregateOptions.cursor || {batchSize: 1};

        // The 'collection' argument may be a collection name, DBCollection object, or '1' which
        // indicates all collections in _db.
        assert(collection instanceof DBCollection || typeof collection === "string" || collection === 1);
        const collName = collection instanceof DBCollection ? collection.getName() : collection;

        return runInFixture(() => {
            let maxRetries = 3;
            let res;
            for (let attemptNumber = 1; attemptNumber <= maxRetries; attemptNumber++) {
                try {
                    res = assert.commandWorked(
                        runCommandChangeStreamPassthroughAware(
                            _db,
                            Object.merge({aggregate: collName, pipeline: pipeline}, aggregateOptions),
                            doNotModifyInPassthroughs,
                        ),
                    );
                    break;
                } catch (e) {
                    if (attemptNumber === maxRetries || !isResumableChangeStreamError(e)) {
                        throw e;
                    }
                }
            }
            assert.neq(res.cursor.id, 0);
            _cursorData.set(String(res.cursor.id), {
                pipeline: pipeline,
                collName: collName,
                doNotModifyInPassthroughs: doNotModifyInPassthroughs,
            });
            updateResumeToken(res.cursor, res.cursor.firstBatch);
            _allCursors.push({db: _db.getName(), coll: collName, cursorId: res.cursor.id});
            return {...res.cursor, _changeStreamVersion: res._changeStreamVersion};
        });
    };

    /**
     * Returns a change stream cursor that listens for every change in the cluster. Assumes that the
     * ChangeStreamTest has been created on the 'admin' db, and will assert if not. It uses the
     * 'aggregateOptions' if provided and saves the cursor so that it can be cleaned up later.
     */
    self.startWatchingAllChangesForCluster = function (aggregateOptions, changeStreamOptions = {}) {
        assert.eq(_db.getName(), "admin");
        return self.startWatchingChanges({
            pipeline: [{$changeStream: Object.assign({allChangesForCluster: true}, changeStreamOptions)}],
            collection: 1,
            aggregateOptions: aggregateOptions,
        });
    };

    /**
     * Restarts the change stream and modify 'cursor' by replacing it's contents thus updating it's
     * cursor ID.
     */
    self.restartChangeStream = function (cursor) {
        const cursorId = String(cursor.id);
        const cursorInfo = _cursorData.get(cursorId);
        if (!cursorInfo || !cursorInfo.resumeToken) {
            throw new Error("Cannot resume change stream - no resume token available for cursor");
        }
        const pipeline = addResumeToken(cursorInfo.pipeline, cursorInfo.resumeToken);
        const newCursor = self.startWatchingChanges({
            pipeline: pipeline,
            collection: cursorInfo.collName,
            aggregateOptions: {cursor: {batchSize: 0}},
            doNotModifyInPassthroughs: cursorInfo.doNotModifyInPassthroughs,
        });
        Object.assign(cursor, newCursor);
    };

    /**
     * Issues a 'getMore' on the provided cursor and returns the cursor returned. The getMore can be
     * interrupted with a ResumableChangeStreamError. We restart the changeStream pipeline and retry
     * getMore 3 times.
     */
    self.getNextBatch = function (cursor) {
        const maxRetries = 3;
        for (let attemptNumber = 1; attemptNumber <= maxRetries; attemptNumber++) {
            try {
                let collName = getCollectionNameFromFullNamespace(cursor.ns);
                const res = assert.commandWorked(
                    _db.runCommand({getMore: cursor.id, collection: collName, batchSize: 1}),
                );
                cursor = res.cursor;
                updateResumeToken(cursor, getBatchFromCursorDocument(cursor));
                return cursor;
            } catch (e) {
                if (attemptNumber === maxRetries || !isResumableChangeStreamError(e)) {
                    throw e;
                }
                self.restartChangeStream(cursor);
            }
        }
        throw new Error("Failed to get next batch after retries");
    };

    /**
     * Returns the next batch of documents from the cursor. This encapsulates logic for checking
     * if it's the first batch or another batch afterwards.
     */
    function getBatchFromCursorDocument(cursor) {
        return cursor.nextBatch === undefined ? cursor.firstBatch : cursor.nextBatch;
    }

    /**
     * Returns the next consumed document from a cursor or returns null if there wasn't one.
     * This does not issue any getMores, instead relying off the batch inside 'cursor'.
     */
    function getNextDocFromCursor(cursor) {
        let nextBatch = getBatchFromCursorDocument(cursor);
        if (nextBatch.length === 0) {
            return null;
        }
        assert.eq(nextBatch.length, 1, "Batch length wasn't 0 or 1: " + tojsonMaybeTruncate(cursor));

        // Reset the nextBatch, as the document is consumed.
        delete cursor.firstBatch;
        cursor.nextBatch = [];

        return nextBatch[0];
    }

    self.getNextChanges = function (cursor, numChanges, skipFirst) {
        let changes = [];

        for (let i = 0; i < numChanges; i++) {
            // Since the first change may be on the original cursor, we need to check for that
            // change on the cursor before we move the cursor forward.
            if (i === 0 && !skipFirst) {
                changes[0] = getNextDocFromCursor(cursor);
                if (changes[0]) {
                    continue;
                }
            }

            assert.soon(
                () => {
                    assert.neq(
                        cursor.id,
                        NumberLong(0),
                        () =>
                            "Cursor has been closed unexpectedly. Observed change stream events: " +
                            tojsonMaybeTruncate(changes),
                    );
                    cursor = self.getNextBatch(cursor);
                    changes[i] = getNextDocFromCursor(cursor);
                    return changes[i] !== null;
                },
                () => {
                    return (
                        "timed out waiting for another result from the change stream, observed changes: " +
                        tojsonMaybeTruncate(changes) +
                        ", expected changes: " +
                        numChanges
                    );
                },
            );
        }
        return changes;
    };

    /**
     * Checks if the change has been invalidated.
     */
    function isInvalidated(change) {
        return change.operationType === "invalidate";
    }

    /**
     * Asserts that the last observed change was the change we expect to see. This also asserts
     * that if we do not expect the cursor to be invalidated, that we do not see the cursor
     * invalidated. Omits the observed change's resume token and cluster time from the comparison,
     * unless the expected change explicitly lists an '_id' or 'clusterTime' field to compare
     * against.
     */
    function assertChangeIsExpected(expectedChanges, numChangesSeen, observedChanges, expectInvalidate) {
        if (expectedChanges) {
            assertChangeStreamEventEq(observedChanges[numChangesSeen], expectedChanges[numChangesSeen], eventModifier);
        } else if (!expectInvalidate) {
            assert(
                !isInvalidated(observedChanges[numChangesSeen]),
                "Change was invalidated when it should not have been. Number of changes seen: " +
                    numChangesSeen +
                    ", observed changes: " +
                    tojsonMaybeTruncate(observedChanges) +
                    ", expected changes: " +
                    tojsonMaybeTruncate(expectedChanges),
            );
        }
    }

    /**
     * Iterates through the change stream and asserts that the next changes are the expected ones.
     * This can be provided with either an expected size or a list of expected changes.
     * If 'expectInvalidate' is provided, then it will expect the change stream to be invalidated
     * at the end. The caller is still expected to provide an invalidate entry in 'expectedChanges'.
     *
     * Returns a list of the changes seen.
     */
    self.assertNextChangesEqual = function ({
        cursor,
        expectedChanges,
        expectedNumChanges,
        expectInvalidate,
        skipFirstBatch,
        ignoreOrder,
    }) {
        expectInvalidate = expectInvalidate || false;
        skipFirstBatch = skipFirstBatch || false;

        // Assert that the expected length matches the length of the expected batch.
        if (expectedChanges !== undefined && expectedNumChanges !== undefined) {
            assert.eq(
                expectedChanges.length,
                expectedNumChanges,
                "Expected change's size must match expected number of changes",
            );
        }

        // Convert 'expectedChanges' to an array, even if it contains just a single element.
        if (expectedChanges !== undefined && !(expectedChanges instanceof Array)) {
            let arrayVersion = new Array();
            arrayVersion.push(expectedChanges);
            expectedChanges = arrayVersion;
        }

        // Set the expected number of changes based on the size of the expected change list.
        if (expectedNumChanges === undefined) {
            assert.neq(expectedChanges, undefined);
            expectedNumChanges = expectedChanges.length;
        }

        let changes = self.getNextChanges(cursor, expectedNumChanges, skipFirstBatch);
        if (ignoreOrder) {
            const errMsgFunc = () => `${tojsonMaybeTruncate(changes)} != ${tojsonMaybeTruncate(expectedChanges)}`;
            assert.eq(changes.length, expectedNumChanges, errMsgFunc);
            for (let i = 0; i < changes.length; i++) {
                assert(
                    expectedChanges.some((expectedChange) => {
                        return isChangeStreamEventEq(changes[i], expectedChange, eventModifier);
                    }),
                    errMsgFunc,
                );
            }
        } else {
            for (let i = 0; i < changes.length; i++) {
                assertChangeIsExpected(expectedChanges, i, changes, expectInvalidate);
            }
        }

        // If we expect invalidation, the final change should have operation type "invalidate".
        if (expectInvalidate) {
            assert(
                isInvalidated(changes[changes.length - 1]),
                "Last change was not invalidated when it was expected: " + tojsonMaybeTruncate(changes),
            );

            // We make sure that the next batch kills the cursor after an invalidation entry.
            let finalCursor = self.getNextBatch(cursor);
            assert.eq(finalCursor.id, 0, "Final cursor was not killed: " + tojsonMaybeTruncate(finalCursor));
        }

        return changes;
    };

    /**
     * Iterates through the change stream and asserts that the next changes are the expected ones.
     * The order of the change events from the cursor relative to their order in the list of
     * expected changes is ignored, however.
     *
     * Returns a list of the changes seen.
     */
    self.assertNextChangesEqualUnordered = function ({
        cursor,
        expectedChanges,
        expectedNumChanges,
        expectInvalidate,
        skipFirstBatch,
    }) {
        return self.assertNextChangesEqual({
            cursor: cursor,
            expectedChanges: expectedChanges,
            expectedNumChanges: expectedNumChanges,
            expectInvalidate: expectInvalidate,
            skipFirstBatch: skipFirstBatch,
            ignoreOrder: true,
        });
    };

    /**
     * Iterates through the change stream and asserts that the next changes are the expected ones.
     *
     * The method enforces a strict order of events for replica set deployments. In sharded
     * clusters, due to the possibility of interleaved events across shards, the order is not
     * strictly enforced, allowing for flexibility in the sequence of events.
     */
    self.assertNextChangesEqualWithDeploymentAwareness = function (...args) {
        const assertEqualFunc = FixtureHelpers.isMongos(db)
            ? self.assertNextChangesEqualUnordered
            : self.assertNextChangesEqual;
        return assertEqualFunc(...args);
    };

    /**
     * Retrieves the next batch in the change stream and confirms that it is empty.
     */
    self.assertNoChange = function (cursor) {
        cursor = self.getNextBatch(cursor);
        assert.eq(0, cursor.nextBatch.length, () => "Cursor had changes: " + tojsonMaybeTruncate(cursor));
        return cursor;
    };

    /**
     * Gets the next document in the change stream. This always executes a 'getMore' first.
     * If the current batch has a document in it, that one will be ignored.
     */
    self.getOneChange = function (cursor, expectInvalidate = false) {
        const changes = self.getNextChanges(cursor, 1, true);

        if (expectInvalidate) {
            assert(
                isInvalidated(changes[changes.length - 1]),
                "Last change was not invalidated when it was expected: " + tojsonMaybeTruncate(changes),
            );

            // We make sure that the next batch kills the cursor after an invalidation entry.
            let finalCursor = self.getNextBatch(cursor);
            assert.eq(finalCursor.id, 0, "Final cursor was not killed: " + tojsonMaybeTruncate(finalCursor));
        }

        return changes[0];
    };

    /**
     * Kills all outstanding cursors.
     */
    self.cleanUp = function () {
        for (let testCursor of _allCursors) {
            if (typeof testCursor.coll === "string") {
                assert.commandWorked(
                    _db.getSiblingDB(testCursor.db).runCommand({
                        killCursors: testCursor.coll,
                        cursors: [testCursor.cursorId],
                    }),
                );
            } else if (testCursor.coll == 1) {
                // Collection '1' indicates that the change stream was opened against an entire
                // database and is considered 'collectionless'.
                assert.commandWorked(
                    _db.getSiblingDB(testCursor.db).runCommand({
                        killCursors: "$cmd.aggregate",
                        cursors: [testCursor.cursorId],
                    }),
                );
            }
        }
    };

    /**
     * Returns the document to be used for the value of a $changeStream stage, given a watchMode
     * of type ChangeStreamWatchMode and optional resumeAfter value.
     */
    self.getChangeStreamStage = function (watchMode, resumeAfter) {
        const changeStreamDoc = {};
        if (resumeAfter) {
            changeStreamDoc.resumeAfter = resumeAfter;
        }

        if (watchMode == ChangeStreamWatchMode.kCluster) {
            changeStreamDoc.allChangesForCluster = true;
        }
        return changeStreamDoc;
    };

    /**
     * Create a change stream of the given watch mode (see ChangeStreamWatchMode) on the given
     * collection. Will resume from a given point if resumeAfter is specified.
     */
    self.getChangeStream = function ({watchMode, coll, resumeAfter}) {
        return self.startWatchingChanges({
            pipeline: [{$changeStream: self.getChangeStreamStage(watchMode, resumeAfter)}],
            collection: watchMode == ChangeStreamWatchMode.kCollection ? coll : 1,
            // Use a batch size of 0 to prevent any notifications from being returned in the first
            // batch. These would be ignored by ChangeStreamTest.getOneChange().
            aggregateOptions: {cursor: {batchSize: 0}},
        });
    };

    /**
     * Asserts that the change stream cursor given by 'cursor' returns at least one 'dropType'
     * notification before returning the next notification given by 'expectedNext'. If running in a
     * sharded passthrough suite, the expectation is to receive a 'dropType' notification from each
     * shard that has at least one chunk. If the change stream is watching the single collection,
     * then the first drop will invalidate the stream.
     *
     * Returns an array of documents which includes all drop events consumed and the expected change
     * itself.
     */
    self.consumeDropUpTo = function ({cursor, dropType, expectedNext, expectInvalidate}) {
        expectInvalidate = expectInvalidate || false;

        let results = [];
        let change = self.getOneChange(cursor, expectInvalidate);
        while (change.operationType == dropType) {
            results.push(change);
            change = self.getOneChange(cursor, expectInvalidate);
        }
        results.push(change);
        assertChangeIsExpected([expectedNext], 0, [change], expectInvalidate);

        return results;
    };

    /**
     * Asserts that the notifications from the change stream cursor include 0 or more 'drop'
     * notifications followed by a 'dropDatabase' notification.
     *
     * Returns the list of notifications.
     */
    self.assertDatabaseDrop = function ({cursor, db}) {
        return self.consumeDropUpTo({
            cursor: cursor,
            dropType: "drop",
            expectedNext: {operationType: "dropDatabase", ns: {db: db.getName()}},
        });
    };
}

/**
 * Asserts that the given pipeline will eventually return an error with the provided code, either in
 * the initial aggregate, or a subsequent getMore. Throws an exception if there are any results from
 * running the pipeline, or if it doesn't throw an error within the window of assert.soon(). If
 * 'doNotModifyInPassthroughs' is 'true' and the test is running in a $changeStream upconversion
 * passthrough, then this stream will not be modified and will run as though no passthrough were
 * active.
 */
ChangeStreamTest.assertChangeStreamThrowsCode = function assertChangeStreamThrowsCode({
    db,
    collName,
    pipeline,
    expectedCode,
    doNotModifyInPassthroughs,
}) {
    try {
        runInFixture(() => {
            // Run a passthrough-aware initial 'aggregate' command to open the change stream.
            const res = assert.commandWorked(
                runCommandChangeStreamPassthroughAware(
                    db,
                    {aggregate: collName, pipeline: pipeline, cursor: {batchSize: 1}},
                    doNotModifyInPassthroughs,
                ),
            );

            // Create a cursor using the command response, and begin issuing getMores. We expect
            // csCursor.hasNext() to throw the expected code before assert.soon() times out.
            const csCursor = new DBCommandCursor(db, res, 1);
            assert.soon(() => csCursor.hasNext());
            assert(false, `Unexpected result from cursor: ${tojsonMaybeTruncate(csCursor.next())}`);
        });
    } catch (error) {
        assert.eq(error.code, expectedCode, `Caught unexpected error: ${tojsonMaybeTruncate(error)}`);
        return true;
    }
    assert(false, "expected this to be unreachable");
};

/**
 * Static method for determining which database to run the change stream aggregation on based on
 * the watchMode.
 */
ChangeStreamTest.getDBForChangeStream = function (watchMode, dbObj) {
    if (watchMode == ChangeStreamWatchMode.kCluster) {
        return dbObj.getSiblingDB("admin");
    }
    return dbObj;
};

/**
 * A set of functions to help validate the behaviour of $changeStreams for a given namespace.
 */
export function assertChangeStreamNssBehaviour(dbName, collName = "test", options, assertFunc) {
    const testDb = db.getSiblingDB(dbName);
    options = options || {};
    return runInFixture(() => {
        const res = testDb.runCommand(
            Object.assign({aggregate: collName, pipeline: [{$changeStream: options}], cursor: {}}),
        );
        return assertFunc(res);
    });
}

export function assertValidChangeStreamNss(dbName, collName = "test", options) {
    const res = assertChangeStreamNssBehaviour(dbName, collName, options, assert.commandWorked);
    assert.commandWorked(
        db
            .getSiblingDB(dbName)
            .runCommand({killCursors: collName == 1 ? "$cmd.aggregate" : collName, cursors: [res.cursor.id]}),
    );
}

export function assertInvalidChangeStreamNss(dbName, collName = "test", options) {
    assertChangeStreamNssBehaviour(dbName, collName, options, (res) =>
        assert.commandFailedWithCode(res, [ErrorCodes.InvalidNamespace, ErrorCodes.InvalidOptions]),
    );
}

export const kPreImagesCollectionDatabase = "config";
export const kPreImagesCollectionName = "system.preimages";

/**
 * Asserts that 'changeStreamPreAndPostImages' collection option is present and is enabled for
 * collection.
 */
export function assertChangeStreamPreAndPostImagesCollectionOptionIsEnabled(db, collName) {
    const collectionInfos = db.getCollectionInfos({name: collName});
    assert(
        collectionInfos.length === 1 &&
            collectionInfos[0].hasOwnProperty("options") &&
            collectionInfos[0].options.hasOwnProperty("changeStreamPreAndPostImages") &&
            collectionInfos[0].options["changeStreamPreAndPostImages"]["enabled"] === true,
        collectionInfos,
    );
}

/**
 * Asserts that 'changeStreamPreAndPostImages' collection option is absent in the collection.
 */
export function assertChangeStreamPreAndPostImagesCollectionOptionIsAbsent(db, collName) {
    const collectionInfos = db.getCollectionInfos({name: collName});
    assert(!collectionInfos[0].options.hasOwnProperty("changeStreamPreAndPostImages"));
}

export function getPreImagesCollection(connection) {
    return connection.getDB(kPreImagesCollectionDatabase).getCollection(kPreImagesCollectionName);
}

// Returns the pre-images written while performing the write operations.
export function preImagesForOps(db, writeOps) {
    const preImagesColl = getPreImagesCollection(db.getMongo());
    const preImagesCollSortSpec = {"_id.ts": 1, "_id.applyOpsIndex": 1};

    // Determine the id of the last pre-image document written to be able to determine the pre-image
    // documents written by 'writeOps()'. The pre-image purging job may concurrently remove some
    // pre-image documents while this function is executing.
    const preImageIdsBefore = preImagesColl.find({}, {}).sort(preImagesCollSortSpec).allowDiskUse().toArray();
    const lastPreImageId =
        preImageIdsBefore.length > 0 ? preImageIdsBefore[preImageIdsBefore.length - 1]._id : undefined;

    // Perform the write operations.
    writeOps();

    // Return only newly written pre-images.
    const preImageFilter = lastPreImageId ? {"_id.ts": {$gt: lastPreImageId.ts}} : {};
    const result = preImagesColl.find(preImageFilter).sort(preImagesCollSortSpec).allowDiskUse().toArray();

    // Verify that the result is correct by checking if the last pre-image still exists. However, if
    // no pre-image document existed before 'writeOps()' invocation, the result may be incorrect.
    assert(
        lastPreImageId === undefined || preImagesColl.find({_id: lastPreImageId}).itcount() == 1,
        "Last pre-image document has been removed by the pre-image purging job.",
    );
    return result;
}

/**
 * Returns documents from the pre-images collection from 'connection' ordered by _id.ts,
 * _id.applyOpsIndex ascending.
 */
export function getPreImages(connection) {
    return getPreImagesCollection(connection)
        .find()
        .sort({"_id.ts": 1, "_id.applyOpsIndex": 1})
        .allowDiskUse()
        .toArray();
}

export function findPreImagesCollectionDescriptions(db) {
    return db.getSiblingDB(kPreImagesCollectionDatabase).runCommand("listCollections", {
        filter: {name: kPreImagesCollectionName},
    });
}

/**
 * Asserts that pre-images collection is absent in configDB.
 */
export function assertPreImagesCollectionIsAbsent(db) {
    const result = findPreImagesCollectionDescriptions(db);
    assert.eq(result.cursor.firstBatch.length, 0);
}

/**
 * Asserts that pre-images collection is created in the configDB and has clustered index on _id.
 */
export function assertPreImagesCollectionExists(db) {
    const collectionInfos = findPreImagesCollectionDescriptions(db);
    assert.eq(collectionInfos.cursor.firstBatch.length, 1, collectionInfos);
    const preImagesCollectionDescription = collectionInfos.cursor.firstBatch[0];
    assert.eq(preImagesCollectionDescription.name, "system.preimages");

    // Verifies that the pre-images collection is clustered by _id.
    assert(preImagesCollectionDescription.hasOwnProperty("options"), preImagesCollectionDescription);
    assert(preImagesCollectionDescription.options.hasOwnProperty("clusteredIndex"), preImagesCollectionDescription);
    const clusteredIndexDescription = preImagesCollectionDescription.options.clusteredIndex;
    assert(clusteredIndexDescription, preImagesCollectionDescription);
}