/**
 *    Copyright (C) 2013 10gen 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.
 */

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

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

#include "mongo/db/exec/plan_stage.h"
#include "mongo/db/exec/scoped_timer.h"
#include "mongo/db/exec/working_set_common.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/matcher/expression.h"
#include "mongo/db/record_id.h"
#include "mongo/stdx/memory.h"
#include "mongo/util/log.h"
#include "mongo/util/mongoutils/str.h"

namespace mongo {

using std::endl;
using std::unique_ptr;
using std::vector;
using stdx::make_unique;

static const char* kIdField = "_id";

// static
const char* ProjectionStage::kStageType = "PROJECTION";

ProjectionStage::ProjectionStage(OperationContext* opCtx,
                                 const ProjectionStageParams& params,
                                 WorkingSet* ws,
                                 PlanStage* child)
    : PlanStage(kStageType, opCtx), _ws(ws), _projImpl(params.projImpl) {
    _children.emplace_back(child);
    _projObj = params.projObj;

    if (ProjectionStageParams::NO_FAST_PATH == _projImpl) {
        _exec.reset(
            new ProjectionExec(params.projObj, params.fullExpression, *params.whereCallback));
    } else {
        // We shouldn't need the full expression if we're fast-pathing.
        invariant(NULL == params.fullExpression);

        // Sanity-check the input.
        invariant(_projObj.isOwned());
        invariant(!_projObj.isEmpty());

        // Figure out what fields are in the projection.
        getSimpleInclusionFields(_projObj, &_includedFields);

        // If we're pulling data out of one index we can pre-compute the indices of the fields
        // in the key that we pull data from and avoid looking up the field name each time.
        if (ProjectionStageParams::COVERED_ONE_INDEX == params.projImpl) {
            // Sanity-check.
            _coveredKeyObj = params.coveredKeyObj;
            invariant(_coveredKeyObj.isOwned());

            BSONObjIterator kpIt(_coveredKeyObj);
            while (kpIt.more()) {
                BSONElement elt = kpIt.next();
                auto fieldIt = _includedFields.find(elt.fieldNameStringData());
                if (_includedFields.end() == fieldIt) {
                    // Push an unused value on the back to keep _includeKey and _keyFieldNames
                    // in sync.
                    _keyFieldNames.push_back(StringData());
                    _includeKey.push_back(false);
                } else {
                    // If we are including this key field store its field name.
                    _keyFieldNames.push_back(fieldIt->first);
                    _includeKey.push_back(true);
                }
            }
        } else {
            invariant(ProjectionStageParams::SIMPLE_DOC == params.projImpl);
        }
    }
}

// static
void ProjectionStage::getSimpleInclusionFields(const BSONObj& projObj, FieldSet* includedFields) {
    // The _id is included by default.
    bool includeId = true;

    // Figure out what fields are in the projection.  TODO: we can get this from the
    // ParsedProjection...modify that to have this type instead of a vector.
    BSONObjIterator projObjIt(projObj);
    while (projObjIt.more()) {
        BSONElement elt = projObjIt.next();
        // Must deal with the _id case separately as there is an implicit _id: 1 in the
        // projection.
        if (mongoutils::str::equals(elt.fieldName(), kIdField) && !elt.trueValue()) {
            includeId = false;
            continue;
        }
        (*includedFields)[elt.fieldNameStringData()] = true;
    }

    if (includeId) {
        (*includedFields)[kIdField] = true;
    }
}

// static
void ProjectionStage::transformSimpleInclusion(const BSONObj& in,
                                               const FieldSet& includedFields,
                                               BSONObjBuilder& bob) {
    // Look at every field in the source document and see if we're including it.
    BSONObjIterator inputIt(in);
    while (inputIt.more()) {
        BSONElement elt = inputIt.next();
        auto fieldIt = includedFields.find(elt.fieldNameStringData());
        if (includedFields.end() != fieldIt) {
            // If so, add it to the builder.
            bob.append(elt);
        }
    }
}

Status ProjectionStage::transform(WorkingSetMember* member) {
    // The default no-fast-path case.
    if (ProjectionStageParams::NO_FAST_PATH == _projImpl) {
        return _exec->transform(member);
    }

    BSONObjBuilder bob;

    // Note that even if our fast path analysis is bug-free something that is
    // covered might be invalidated and just be an obj.  In this case we just go
    // through the SIMPLE_DOC path which is still correct if the covered data
    // is not available.
    //
    // SIMPLE_DOC implies that we expect an object so it's kind of redundant.
    if ((ProjectionStageParams::SIMPLE_DOC == _projImpl) || member->hasObj()) {
        // If we got here because of SIMPLE_DOC the planner shouldn't have messed up.
        invariant(member->hasObj());

        // Apply the SIMPLE_DOC projection.
        transformSimpleInclusion(member->obj.value(), _includedFields, bob);
    } else {
        invariant(ProjectionStageParams::COVERED_ONE_INDEX == _projImpl);
        // We're pulling data out of the key.
        invariant(1 == member->keyData.size());
        size_t keyIndex = 0;

        // Look at every key element...
        BSONObjIterator keyIterator(member->keyData[0].keyData);
        while (keyIterator.more()) {
            BSONElement elt = keyIterator.next();
            // If we're supposed to include it...
            if (_includeKey[keyIndex]) {
                // Do so.
                bob.appendAs(elt, _keyFieldNames[keyIndex]);
            }
            ++keyIndex;
        }
    }

    member->keyData.clear();
    member->loc = RecordId();
    member->obj = Snapshotted<BSONObj>(SnapshotId(), bob.obj());
    member->transitionToOwnedObj();
    return Status::OK();
}

bool ProjectionStage::isEOF() {
    return child()->isEOF();
}

PlanStage::StageState ProjectionStage::work(WorkingSetID* out) {
    ++_commonStats.works;

    // Adds the amount of time taken by work() to executionTimeMillis.
    ScopedTimer timer(&_commonStats.executionTimeMillis);

    WorkingSetID id = WorkingSet::INVALID_ID;
    StageState status = child()->work(&id);

    // Note that we don't do the normal if isEOF() return EOF thing here.  Our child might be a
    // tailable cursor and isEOF() would be true even if it had more data...
    if (PlanStage::ADVANCED == status) {
        WorkingSetMember* member = _ws->get(id);
        // Punt to our specific projection impl.
        Status projStatus = transform(member);
        if (!projStatus.isOK()) {
            warning() << "Couldn't execute projection, status = " << projStatus.toString() << endl;
            *out = WorkingSetCommon::allocateStatusMember(_ws, projStatus);
            return PlanStage::FAILURE;
        }

        *out = id;
        ++_commonStats.advanced;
    } else if (PlanStage::FAILURE == status || PlanStage::DEAD == status) {
        *out = id;
        // If a stage fails, it may create a status WSM to indicate why it
        // failed, in which case 'id' is valid.  If ID is invalid, we
        // create our own error message.
        if (WorkingSet::INVALID_ID == id) {
            mongoutils::str::stream ss;
            ss << "projection stage failed to read in results from child";
            Status status(ErrorCodes::InternalError, ss);
            *out = WorkingSetCommon::allocateStatusMember(_ws, status);
        }
    } else if (PlanStage::NEED_TIME == status) {
        _commonStats.needTime++;
    } else if (PlanStage::NEED_YIELD == status) {
        _commonStats.needYield++;
        *out = id;
    }

    return status;
}

unique_ptr<PlanStageStats> ProjectionStage::getStats() {
    _commonStats.isEOF = isEOF();
    unique_ptr<PlanStageStats> ret = make_unique<PlanStageStats>(_commonStats, STAGE_PROJECTION);

    unique_ptr<ProjectionStats> projStats = make_unique<ProjectionStats>(_specificStats);
    projStats->projObj = _projObj;
    ret->specific = std::move(projStats);

    ret->children.push_back(child()->getStats().release());
    return ret;
}

const SpecificStats* ProjectionStage::getSpecificStats() const {
    return &_specificStats;
}

}  // namespace mongo