/**
 *    Copyright (C) 2018-present MongoDB, Inc.
 *
 *    This program is free software: you can redistribute it and/or modify
 *    it under the terms of the Server Side Public License, version 1,
 *    as published by MongoDB, Inc.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    Server Side Public License for more details.
 *
 *    You should have received a copy of the Server Side Public License
 *    along with this program. If not, see
 *    <http://www.mongodb.com/licensing/server-side-public-license>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the Server Side Public License in all respects for
 *    all of the code used other than as permitted herein. If you modify file(s)
 *    with this exception, you may extend this exception to your version of the
 *    file(s), but you are not obligated to do so. If you do not wish to do so,
 *    delete this exception statement from your version. If you delete this
 *    exception statement from all source files in the program, then also delete
 *    it in the license file.
 */

#pragma once

#include <exception>

#include "mongo/base/string_data.h"
#include "mongo/db/curop.h"
#include "mongo/util/assert_util.h"
#include "mongo/util/fail_point.h"

namespace mongo {

extern FailPoint skipWriteConflictRetries;

/**
 * This is thrown if during a write, two or more operations conflict with each other.
 * For example if two operations get the same version of a document, and then both try to
 * modify that document, this exception will get thrown by one of them.
 */
class WriteConflictException final : public DBException {
public:
    WriteConflictException();
    WriteConflictException(StringData context);

    /**
     * Will log a message if sensible and will do an exponential backoff to make sure
     * we don't hammer the same doc over and over.
     * @param attempt - what attempt is this, 1 based
     * @param operation - e.g. "update"
     */
    static void logAndBackoff(int attempt, StringData operation, StringData ns);

    /**
     * If true, will call printStackTrace on every WriteConflictException created.
     * Can be set via setParameter named traceWriteConflictExceptions.
     */
    static AtomicWord<bool> trace;

private:
    void defineOnlyInFinalSubclassToPreventSlicing() final {}
};

/**
 * Runs the argument function f as many times as needed for f to complete or throw an exception
 * other than WriteConflictException.  For each time f throws a WriteConflictException, logs the
 * error, waits a spell, cleans up, and then tries f again.  Imposes no upper limit on the number
 * of times to re-try f, so any required timeout behavior must be enforced within f.
 *
 * If we are already in a WriteUnitOfWork, we assume that we are being called within a
 * WriteConflictException retry loop up the call stack. Hence, this retry loop is reduced to an
 * invocation of the argument function f without any exception handling and retry logic.
 */
template <typename F>
auto writeConflictRetry(OperationContext* opCtx, StringData opStr, StringData ns, F&& f) {
    invariant(opCtx);
    invariant(opCtx->lockState());
    invariant(opCtx->recoveryUnit());

    // This failpoint disables exception handling for write conflicts. Only allow this exception to
    // escape user operations. Do not allow exceptions to escape internal threads, which may rely on
    // this exception handler to avoid crashing.
    bool userSkipWriteConflictRetry = MONGO_unlikely(skipWriteConflictRetries.shouldFail()) &&
        opCtx->getClient()->isFromUserConnection();
    if (opCtx->lockState()->inAWriteUnitOfWork() || userSkipWriteConflictRetry) {
        return f();
    }

    int attempts = 0;
    while (true) {
        try {
            return f();
        } catch (WriteConflictException const&) {
            CurOp::get(opCtx)->debug().additiveMetrics.incrementWriteConflicts(1);
            WriteConflictException::logAndBackoff(attempts, opStr, ns);
            ++attempts;
            opCtx->recoveryUnit()->abandonSnapshot();
        }
    }
}

}  // namespace mongo