/**
 *    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.
 */

#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kQuery

#include "mongo/platform/basic.h"

#include "mongo/executor/async_multicaster.h"

#include <memory>

#include "mongo/base/status.h"
#include "mongo/db/operation_context.h"
#include "mongo/platform/condition_variable.h"
#include "mongo/platform/mutex.h"
#include "mongo/util/assert_util.h"

namespace mongo {
namespace executor {

AsyncMulticaster::AsyncMulticaster(std::shared_ptr<executor::TaskExecutor> executor,
                                   Options options)
    : _options(options), _executor(std::move(executor)) {}

std::vector<AsyncMulticaster::Reply> AsyncMulticaster::multicast(
    const std::vector<HostAndPort> servers,
    const std::string& theDbName,
    const BSONObj& theCmdObj,
    OperationContext* opCtx,
    Milliseconds timeoutMillis) {

    // Everything goes into a state struct because we can get cancelled, and then our callback would
    // be invoked later.
    struct State {
        State(size_t leftToDo) : leftToDo(leftToDo) {}

        Mutex mutex = MONGO_MAKE_LATCH("State::mutex");
        stdx::condition_variable cv;
        size_t leftToDo;
        size_t running = 0;

        // To indicate which hosts fail.
        std::vector<Reply> out;
    };

    auto state = std::make_shared<State>(servers.size());
    for (const auto& server : servers) {
        stdx::unique_lock<Latch> lk(state->mutex);
        // spin up no more than maxConcurrency tasks at once
        opCtx->waitForConditionOrInterrupt(
            state->cv, lk, [&] { return state->running < _options.maxConcurrency; });
        ++state->running;

        uassertStatusOK(_executor->scheduleRemoteCommand(
            RemoteCommandRequest{server, theDbName, theCmdObj, opCtx, timeoutMillis},
            [state](const TaskExecutor::RemoteCommandCallbackArgs& cbData) {
                stdx::lock_guard<Latch> lk(state->mutex);

                state->out.emplace_back(
                    std::forward_as_tuple(cbData.request.target, cbData.response));

                // If we were the last job, flush the done flag and release via notify.
                if (!--(state->leftToDo)) {
                    state->cv.notify_one();
                }

                if (--(state->running) < kMaxConcurrency) {
                    state->cv.notify_one();
                }
            }));
    }

    stdx::unique_lock<Latch> lk(state->mutex);
    opCtx->waitForConditionOrInterrupt(state->cv, lk, [&] { return state->leftToDo == 0; });

    return std::move(state->out);
}

}  // namespace executor
}  // namespace mongo