/**
 * Copyright (C) 2018 MongoDB Inc.
 *
 * This program is free software: you can redistribute it and/or  modify
 * it under the terms of the GNU Affero General Public License, version 3,
 * as published by the Free Software Foundation.
 *
 * 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
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * 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 GNU Affero General 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 "mongo/stdx/condition_variable.h"
#include "mongo/stdx/mutex.h"
#include "mongo/util/clock_source.h"
#include "mongo/util/time_support.h"

namespace mongo {

/**
 * Waitable is a lightweight type that can be used with stdx::condition_variable and can do other
 * work while the condvar 'waits'.
 *
 * It handles this dance by using a special hook that condvar provides to register itself (as a
 * notifyable, which it inherits from) during calls to wait.  Then, rather than actually waiting on
 * the condvar, it invokes its run/run_until methods.
 *
 * The current implementer of Waitable is the transport layer baton type, which performs delayed IO
 * when it would otherwise block.
 */
class Waitable : public Notifyable {
public:
    static void wait(Waitable* waitable,
                     ClockSource* clkSource,
                     stdx::condition_variable& cv,
                     stdx::unique_lock<stdx::mutex>& lk) {
        if (waitable) {
            cv._runWithNotifyable(*waitable, [&]() noexcept {
                lk.unlock();
                waitable->run(clkSource);
                lk.lock();
            });
        } else {
            cv.wait(lk);
        }
    }

    template <typename Predicate>
    static void wait(Waitable* waitable,
                     ClockSource* clkSource,
                     stdx::condition_variable& cv,
                     stdx::unique_lock<stdx::mutex>& lk,
                     Predicate pred) {
        while (!pred()) {
            wait(waitable, clkSource, cv, lk);
        }
    }

    static stdx::cv_status wait_until(
        Waitable* waitable,
        ClockSource* clkSource,
        stdx::condition_variable& cv,
        stdx::unique_lock<stdx::mutex>& lk,
        const stdx::chrono::time_point<stdx::chrono::system_clock>& timeout_time) {
        if (waitable) {
            auto rval = stdx::cv_status::no_timeout;

            cv._runWithNotifyable(*waitable, [&]() noexcept {
                lk.unlock();
                if (waitable->run_until(clkSource, Date_t(timeout_time)) == TimeoutState::Timeout) {
                    rval = stdx::cv_status::timeout;
                }
                lk.lock();
            });

            return rval;
        } else {
            return cv.wait_until(lk, timeout_time);
        }
    }

    template <typename Predicate>
    static bool wait_until(Waitable* waitable,
                           ClockSource* clkSource,
                           stdx::condition_variable& cv,
                           stdx::unique_lock<stdx::mutex>& lk,
                           const stdx::chrono::time_point<stdx::chrono::system_clock>& timeout_time,
                           Predicate pred) {
        while (!pred()) {
            if (wait_until(waitable, clkSource, cv, lk, timeout_time) == stdx::cv_status::timeout) {
                return pred();
            }
        }

        return true;
    }

protected:
    ~Waitable() noexcept {}

    enum class TimeoutState {
        NoTimeout,
        Timeout,
    };

    /**
     * Run some amount of work.  The intention is that this function perform work until it's
     * possible that the surrounding condvar clause could have finished.
     *
     * Note that like regular condvar.wait, this allows implementers the flexibility to possibly
     * return early.
     *
     * We take a clock source here to allow for synthetic timeouts.
     */
    virtual void run(ClockSource* clkSource) noexcept = 0;

    /**
     * Like run, but only until the passed deadline has passed.
     */
    virtual TimeoutState run_until(ClockSource* clkSource, Date_t deadline) noexcept = 0;
};

}  // namespace mongo