/**
 *    Copyright (C) 2013-2014 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.
 */

#include "mongo/db/exec/oplogstart.h"

#include "mongo/db/catalog/collection.h"
#include "mongo/db/catalog/database.h"
#include "mongo/db/client.h"
#include "mongo/db/concurrency/write_conflict_exception.h"

namespace mongo {

    using std::vector;

    const char* OplogStart::kStageType = "OPLOG_START";

    // Does not take ownership.
    OplogStart::OplogStart(OperationContext* txn,
                           const Collection* collection,
                           MatchExpression* filter,
                           WorkingSet* ws)
        : _txn(txn),
          _needInit(true),
          _backwardsScanning(false),
          _extentHopping(false),
          _done(false),
          _collection(collection),
          _workingSet(ws),
          _filter(filter) { }

    OplogStart::~OplogStart() { }

    PlanStage::StageState OplogStart::work(WorkingSetID* out) {
        // We do our (heavy) init in a work(), where work is expected.
        if (_needInit) {
            CollectionScanParams params;
            params.collection = _collection;
            params.direction = CollectionScanParams::BACKWARD;
            _cs.reset(new CollectionScan(_txn, params, _workingSet, NULL));

            _needInit = false;
            _backwardsScanning = true;
            _timer.reset();
        }

        // If we're still reading backwards, keep trying until timing out.
        if (_backwardsScanning) {
            verify(!_extentHopping);
            // Still have time to succeed with reading backwards.
            if (_timer.seconds() < _backwardsScanTime) {
                return workBackwardsScan(out);
            }

            try {
                // If this throws WCE, it leave us in a state were the next call to work will retry.
                switchToExtentHopping();
            }
            catch (const WriteConflictException& wce) {
                _subIterators.clear();
                *out = WorkingSet::INVALID_ID;
                return NEED_YIELD;
            }
        }

        // Don't find it in time?  Swing from extent to extent like tarzan.com.
        verify(_extentHopping);
        return workExtentHopping(out);
    }

    PlanStage::StageState OplogStart::workExtentHopping(WorkingSetID* out) {
        if (_done || _subIterators.empty()) {
            return PlanStage::IS_EOF;
        }

        // we work from the back to the front since the back has the newest data.
        try {
            // TODO: should we ever check fetcherForNext()?
            if (auto record = _subIterators.back()->next()) {
                BSONObj obj = record->data.releaseToBson();
                if (!_filter->matchesBSON(obj)) {
                    _done = true;
                    WorkingSetID id = _workingSet->allocate();
                    WorkingSetMember* member = _workingSet->get(id);
                    member->loc = record->id;
                    member->obj = {_txn->recoveryUnit()->getSnapshotId(), std::move(obj)};
                    member->state = WorkingSetMember::LOC_AND_UNOWNED_OBJ;
                    *out = id;
                    return PlanStage::ADVANCED;
                }
            }
        }
        catch (const WriteConflictException& wce) {
            *out = WorkingSet::INVALID_ID;
            return PlanStage::NEED_YIELD;
        }

        _subIterators.pop_back();
        return PlanStage::NEED_TIME;
    }

    void OplogStart::switchToExtentHopping() {
        // Set up our extent hopping state.
        _subIterators = _collection->getManyCursors(_txn);

        // Transition from backwards scanning to extent hopping.
        _backwardsScanning = false;
        _extentHopping = true;

        // Toss the collection scan we were using.
        _cs.reset();
    }

    PlanStage::StageState OplogStart::workBackwardsScan(WorkingSetID* out) {
        PlanStage::StageState state = _cs->work(out);

        // EOF.  Just start from the beginning, which is where we've hit.
        if (PlanStage::IS_EOF == state) {
            _done = true;
            return state;
        }

        if (PlanStage::ADVANCED != state) { return state; }

        WorkingSetMember* member = _workingSet->get(*out);
        verify(member->hasObj());
        verify(member->hasLoc());

        if (!_filter->matchesBSON(member->obj.value())) {
            _done = true;
            // RecordId is returned in *out.
            return PlanStage::ADVANCED;
        }
        else {
            _workingSet->free(*out);
            return PlanStage::NEED_TIME;
        }
    }

    bool OplogStart::isEOF() { return _done; }

    void OplogStart::invalidate(OperationContext* txn, const RecordId& dl, InvalidationType type) {
        if (_needInit) { return; }

        if (INVALIDATION_DELETION != type) { return; }

        if (_cs) {
            _cs->invalidate(txn, dl, type);
        }

        for (size_t i = 0; i < _subIterators.size(); i++) {
            _subIterators[i]->invalidate(dl);
        }
    }

    void OplogStart::saveState() {
        _txn = NULL;
        if (_cs) {
            _cs->saveState();
        }

        for (size_t i = 0; i < _subIterators.size(); i++) {
            _subIterators[i]->savePositioned();
        }
    }

    void OplogStart::restoreState(OperationContext* opCtx) {
        invariant(_txn == NULL);
        _txn = opCtx;
        if (_cs) {
            _cs->restoreState(opCtx);
        }

        for (size_t i = 0; i < _subIterators.size(); i++) {
            if (!_subIterators[i]->restore(opCtx)) {
                _subIterators.erase(_subIterators.begin() + i);
                // need to hit same i on next pass through loop
                i--;
            }
        }
    }

    PlanStageStats* OplogStart::getStats() {
        std::unique_ptr<PlanStageStats> ret(new PlanStageStats(CommonStats(kStageType),
                                                               STAGE_OPLOG_START));
        ret->specific.reset(new CollectionScanStats());
        return ret.release();
    }

    vector<PlanStage*> OplogStart::getChildren() const {
        vector<PlanStage*> empty;
        return empty;
    }

    int OplogStart::_backwardsScanTime = 5;

}  // namespace mongo