/**
 *    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.
 */

#include "mongo/platform/basic.h"

#include <boost/optional.hpp>
#include <memory>

#include "mongo/db/exec/mock_stage.h"
#include "mongo/db/exec/trial_stage.h"
#include "mongo/db/exec/working_set.h"
#include "mongo/db/operation_context.h"
#include "mongo/db/query/mock_yield_policies.h"
#include "mongo/db/service_context_d_test_fixture.h"
#include "mongo/unittest/unittest.h"

namespace mongo {

namespace {

const NamespaceString kTestNss = NamespaceString("db.dummy");

class TrialStageTest : public unittest::Test {
public:
    TrialStageTest()
        : _opCtx(cc().makeOperationContext()),
          _expCtx(make_intrusive<ExpressionContext>(_opCtx.get(), nullptr, kTestNss)) {}

protected:
    // Pushes BSONObjs from the given vector into the given MockStage. Each empty BSONObj in
    // the vector causes a NEED_TIME to be queued up at that point instead of a result.
    void queueData(const std::vector<BSONObj>& results, MockStage* mockStage) {
        for (auto result : results) {
            if (result.isEmpty()) {
                mockStage->enqueueStateCode(PlanStage::NEED_TIME);
                continue;
            }
            const auto id = _ws.allocate();
            auto* member = _ws.get(id);
            member->doc.setValue(Document{result});
            _ws.transitionToOwnedObj(id);
            mockStage->enqueueAdvanced(id);
        }
    }

    // Returns the next result from the TrialStage, or boost::none if there are no more results.
    boost::optional<BSONObj> nextResult(TrialStage* trialStage) {
        PlanStage::StageState state;
        WorkingSetID id;
        do {
            state = trialStage->work(&id);
            if (state == PlanStage::ADVANCED) {
                auto* member = _ws.get(id);
                return member->doc.value().toBson();
            }
        } while (state == PlanStage::NEED_TIME);

        // There are not more results to return.
        ASSERT_TRUE(trialStage->isEOF());
        return boost::none;
    }

    std::unique_ptr<PlanYieldPolicy> yieldPolicy() {
        return std::make_unique<NoopYieldPolicy>(
            opCtx()->getServiceContext()->getFastClockSource());
    }

    OperationContext* opCtx() {
        return _opCtx.get();
    }

    WorkingSet* ws() {
        return &_ws;
    }

private:
    ServiceContext::UniqueOperationContext _opCtx;
    WorkingSet _ws;

protected:
    boost::intrusive_ptr<ExpressionContext> _expCtx;
};

TEST_F(TrialStageTest, AdoptsTrialPlanIfTrialSucceeds) {
    auto trialPlan = std::make_unique<MockStage>(_expCtx.get(), ws());
    auto backupPlan = std::make_unique<MockStage>(_expCtx.get(), ws());

    // Seed the trial plan with 20 results and no NEED_TIMEs.
    std::vector<BSONObj> trialResults;
    for (auto i = 0; i < 20; ++i) {
        trialResults.push_back(BSON("_id" << i));
    }
    queueData(trialResults, trialPlan.get());

    // Set the minimum advanced-to-works ratio to 0.75. Because every work() will result in an
    // ADVANCE, the trial plan will succeed.
    auto trialStage = std::make_unique<TrialStage>(
        _expCtx.get(), ws(), std::move(trialPlan), std::move(backupPlan), 10, 0.75);

    ASSERT_OK(trialStage->pickBestPlan(yieldPolicy().get()));

    // The trial phase completed and we picked the trial plan, not the backup plan.
    ASSERT_TRUE(trialStage->isTrialPhaseComplete());
    ASSERT_FALSE(trialStage->pickedBackupPlan());

    // Confirm that we see the full trialPlan results when we iterate the trialStage.
    for (auto result : trialResults) {
        ASSERT_BSONOBJ_EQ(result, *nextResult(trialStage.get()));
    }
    ASSERT_FALSE(nextResult(trialStage.get()));
    ASSERT_TRUE(trialStage->isEOF());
}

TEST_F(TrialStageTest, AdoptsTrialPlanIfTrialPlanHitsEOF) {
    auto trialPlan = std::make_unique<MockStage>(_expCtx.get(), ws());
    auto backupPlan = std::make_unique<MockStage>(_expCtx.get(), ws());

    // Seed the trial plan with 5 results and no NEED_TIMEs.
    std::vector<BSONObj> trialResults;
    for (auto i = 0; i < 5; ++i) {
        trialResults.push_back(BSON("_id" << i));
    }
    queueData(trialResults, trialPlan.get());

    // We schedule the trial to run for 10 works. Because we hit EOF after 5 results, we will end
    // the trial phase early and adopt the successful trial plan.
    auto trialStage = std::make_unique<TrialStage>(
        _expCtx.get(), ws(), std::move(trialPlan), std::move(backupPlan), 10, 0.75);

    ASSERT_OK(trialStage->pickBestPlan(yieldPolicy().get()));

    // The trial phase completed and we picked the trial plan, not the backup plan.
    ASSERT_TRUE(trialStage->isTrialPhaseComplete());
    ASSERT_FALSE(trialStage->pickedBackupPlan());

    // Get the specific stats for the stage and confirm that the trial completed early.
    auto* stats = static_cast<const TrialStats*>(trialStage->getSpecificStats());
    ASSERT_EQ(stats->trialPeriodMaxWorks, 10U);
    ASSERT_EQ(stats->trialWorks, 5U);

    // Confirm that we see the full trialPlan results when we iterate the trialStage.
    for (auto result : trialResults) {
        ASSERT_BSONOBJ_EQ(result, *nextResult(trialStage.get()));
    }
    ASSERT_FALSE(nextResult(trialStage.get()));
    ASSERT_TRUE(trialStage->isEOF());
}

TEST_F(TrialStageTest, AdoptsBackupPlanIfTrialDoesNotSucceed) {
    auto trialPlan = std::make_unique<MockStage>(_expCtx.get(), ws());
    auto backupPlan = std::make_unique<MockStage>(_expCtx.get(), ws());

    // Seed the trial plan with 20 results. Every second result will produce a NEED_TIME.
    std::vector<BSONObj> trialResults;
    for (auto i = 0; i < 20; ++i) {
        trialResults.push_back((i % 2) ? BSON("_id" << i) : BSONObj());
    }
    queueData(std::move(trialResults), trialPlan.get());

    // Seed the backup plan with 20 different results, so that we can validate that we see the
    // correct dataset once the trial phase is complete.
    std::vector<BSONObj> backupResults;
    for (auto i = 0; i < 20; ++i) {
        backupResults.push_back(BSON("_id" << (-i)));
    }
    queueData(backupResults, backupPlan.get());

    // Set the minimum advanced-to-works ratio to 0.75. Because every second work() will result in a
    // NEED_TIME and the actual ratio is thus 0.5, the trial plan will fail.
    auto trialStage = std::make_unique<TrialStage>(
        _expCtx.get(), ws(), std::move(trialPlan), std::move(backupPlan), 10, 0.75);

    ASSERT_OK(trialStage->pickBestPlan(yieldPolicy().get()));

    // The trial phase completed and we picked the backup plan.
    ASSERT_TRUE(trialStage->isTrialPhaseComplete());
    ASSERT_TRUE(trialStage->pickedBackupPlan());

    // Confirm that we see the full backupPlan results when we iterate the trialStage.
    for (auto result : backupResults) {
        ASSERT_BSONOBJ_EQ(result, *nextResult(trialStage.get()));
    }
    ASSERT_FALSE(nextResult(trialStage.get()));
    ASSERT_TRUE(trialStage->isEOF());
}

}  // namespace
}  // namespace mongo