/**
 *    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 <vector>

#include "mongo/executor/async_timer_interface.h"
#include "mongo/platform/mutex.h"
#include "mongo/stdx/unordered_set.h"

namespace mongo {
namespace executor {

/**
 * Underlying mock timer implementation.
 *
 * If asyncWait() is called after the timer has expired, the provided callback will
 * fire immediately.
 */
class AsyncTimerMockImpl {
public:
    explicit AsyncTimerMockImpl(Milliseconds expiration);

    /**
     * Cancel operations waiting on this timer, invoking their handlers with an
     * 'operation aborted' error code.
     */
    void cancel();

    /**
     * Perform an asynchronous wait on this timer. If timer has expired, callback
     * runs immediately, synchronously.
     */
    void asyncWait(AsyncTimerInterface::Handler handler);

    /**
     * Advance current time. If the given interval is greater than or equal to the
     * time left on the timer, expire and call callbacks now.
     */
    void fastForward(Milliseconds time);

    /**
     * Return the amount of time left on this timer.
     */
    Milliseconds timeLeft();

    /**
     * Reset the timer.
     */
    void expireAfter(Milliseconds expiration);

    /**
     * Returns the number of handlers on this timer.
     */
    int jobs();

private:
    void _callAllHandlers(std::error_code ec);

    Mutex _mutex = MONGO_MAKE_LATCH("AsyncTimerMockImpl::_mutex");
    Milliseconds _timeLeft;
    std::vector<AsyncTimerInterface::Handler> _handlers;
};

/**
 * A wrapper around a shared AsyncTimerMockImpl that AsyncTimerMockFactory holds.
 *
 * This abstraction is necessary to fulfill ownership requirements on both
 * sides of the factory: AsyncOp owns its AsyncTimerMock objects, and it can safely
 * destroy these without destroying the underlying AsyncTimerMockImpl objects
 * accessed by tests and introducing races.
 */
class AsyncTimerMock : public AsyncTimerInterface {
public:
    AsyncTimerMock(std::shared_ptr<AsyncTimerMockImpl> timer);

    void cancel() override;

    void asyncWait(AsyncTimerInterface::Handler handler) override;

    void expireAfter(Milliseconds expiration) override;

private:
    // Unfortunate, but it makes the ownership model sane.
    std::shared_ptr<AsyncTimerMockImpl> _timer;
};

/**
 * A factory that returns mock timers to be used by tests.
 *
 * Shared pointers to timer impls are kept in a set here for access by tests,
 * and these are also passed into the returned AsyncTimerMock objects.
 */
class AsyncTimerFactoryMock : public AsyncTimerFactoryInterface {
public:
    AsyncTimerFactoryMock() = default;

    /**
     * Create and return a new AsyncTimerMock object.
     */
    std::unique_ptr<AsyncTimerInterface> make(Milliseconds expiration) override;

    /**
     * Advance the current "time" and make stale timers expire.
     */
    void fastForward(Milliseconds time);

    /**
     * This will start at 0ms since the epoch and increment when fastForward is called.
     */
    Date_t now() override;

    /**
     * Returns the number of pending jobs across all timers.
     */
    int jobs();

private:
    stdx::recursive_mutex _timersMutex;
    stdx::unordered_set<std::shared_ptr<AsyncTimerMockImpl>> _timers;
    Milliseconds _curTime;
};

}  // namespace executor
}  // namespace mongo