/**
 *    Copyright (C) 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/distinct_scan.h"

#include "mongo/db/exec/filter.h"
#include "mongo/db/exec/working_set_computed_data.h"
#include "mongo/db/index/index_access_method.h"
#include "mongo/db/index/index_cursor.h"
#include "mongo/db/index/index_descriptor.h"

namespace mongo {

    DistinctScan::DistinctScan(const DistinctParams& params, WorkingSet* workingSet)
        : _workingSet(workingSet),
          _descriptor(params.descriptor),
          _iam(params.descriptor->getIndexCatalog()->getIndex(params.descriptor)),
          _btreeCursor(NULL),
          _hitEnd(false),
          _params(params) { }

    void DistinctScan::initIndexCursor() {
        // Create an IndexCursor over the btree we're distinct-ing over.
        CursorOptions cursorOptions;

        if (1 == _params.direction) {
            cursorOptions.direction = CursorOptions::INCREASING;
        }
        else {
            cursorOptions.direction = CursorOptions::DECREASING;
        }

        IndexCursor *cursor;
        Status s = _iam->newCursor(&cursor);
        verify(s.isOK());
        verify(cursor);
        // Is this assumption always valid?  See SERVER-12397
        _btreeCursor.reset(static_cast<BtreeIndexCursor*>(cursor));
        _btreeCursor->setOptions(cursorOptions);

        // Create a new bounds checker.  The bounds checker gets our start key and assists in
        // executing the scan and staying within the required bounds.
        _checker.reset(new IndexBoundsChecker(&_params.bounds,
                                              _descriptor->keyPattern(),
                                              _params.direction));

        int nFields = _descriptor->keyPattern().nFields();
        // The start key is dumped into these two.
        vector<const BSONElement*> key;
        vector<bool> inc;
        key.resize(nFields);
        inc.resize(nFields);
        if (_checker->getStartKey(&key, &inc)) {
            _btreeCursor->seek(key, inc);
            _keyElts.resize(nFields);
            _keyEltsInc.resize(nFields);
        }
        else {
            _hitEnd = true;
        }
    }

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

        if (NULL == _btreeCursor.get()) {
            // First call to work().  Perform cursor init.
            initIndexCursor();
            checkEnd();
        }

        if (isEOF()) { return PlanStage::IS_EOF; }

        // Grab the next (key, value) from the index.
        BSONObj ownedKeyObj = _btreeCursor->getKey().getOwned();
        DiskLoc loc = _btreeCursor->getValue();

        // The underlying IndexCursor points at the *next* thing we want to return.  We do this so
        // that if we're scanning an index looking for docs to delete we don't continually clobber
        // the thing we're pointing at.

        // We skip to the next value of the _params.fieldNo-th field in the index key pattern.
        // This is the field we're distinct-ing over.
        _btreeCursor->skip(_btreeCursor->getKey(),
                           _params.fieldNo + 1,
                           true,
                           _keyElts,
                           _keyEltsInc);

        // And make sure we're within the bounds.
        checkEnd();

        // Package up the result for the caller.
        WorkingSetID id = _workingSet->allocate();
        WorkingSetMember* member = _workingSet->get(id);
        member->loc = loc;
        member->keyData.push_back(IndexKeyDatum(_descriptor->keyPattern(), ownedKeyObj));
        member->state = WorkingSetMember::LOC_AND_IDX;

        *out = id;
        ++_commonStats.advanced;
        return PlanStage::ADVANCED;
    }

    bool DistinctScan::isEOF() {
        if (NULL == _btreeCursor.get()) {
            // Have to call work() at least once.
            return false;
        }

        return _hitEnd || _btreeCursor->isEOF();
    }

    void DistinctScan::prepareToYield() {
        ++_commonStats.yields;

        if (isEOF() || (NULL == _btreeCursor.get())) { return; }
        // We save these so that we know if the cursor moves during the yield.  If it moves, we have
        // to make sure its ending position is valid w.r.t. our bounds.
        _savedKey = _btreeCursor->getKey().getOwned();
        _savedLoc = _btreeCursor->getValue();
        _btreeCursor->savePosition();
    }

    void DistinctScan::recoverFromYield() {
        ++_commonStats.unyields;

        if (isEOF() || (NULL == _btreeCursor.get())) { return; }

        // We can have a valid position before we check isEOF(), restore the position, and then be
        // EOF upon restore.
        if (!_btreeCursor->restorePosition().isOK() || _btreeCursor->isEOF()) {
            _hitEnd = true;
            return;
        }

        if (!_savedKey.binaryEqual(_btreeCursor->getKey()) || _savedLoc != _btreeCursor->getValue()) {
            // Our restored position might be past endKey, see if we've hit the end.
            checkEnd();
        }
    }

    void DistinctScan::invalidate(const DiskLoc& dl, InvalidationType type) {
        ++_commonStats.invalidates;
    }

    void DistinctScan::checkEnd() {
        if (isEOF()) {
            _commonStats.isEOF = true;
            return;
        }

        // Use _checker to see how things are.
        for (;;) {
            IndexBoundsChecker::KeyState keyState;
            keyState = _checker->checkKey(_btreeCursor->getKey(),
                                          &_keyEltsToUse,
                                          &_movePastKeyElts,
                                          &_keyElts,
                                          &_keyEltsInc);

            if (IndexBoundsChecker::DONE == keyState) {
                _hitEnd = true;
                break;
            }

            // This seems weird but it's the old definition of nscanned.
            ++_specificStats.keysExamined;

            if (IndexBoundsChecker::VALID == keyState) {
                break;
            }

            verify(IndexBoundsChecker::MUST_ADVANCE == keyState);
            _btreeCursor->skip(_btreeCursor->getKey(), _keyEltsToUse, _movePastKeyElts,
                               _keyElts, _keyEltsInc);

            // Must check underlying cursor EOF after every cursor movement.
            if (_btreeCursor->isEOF()) {
                _hitEnd = true;
                break;
            }
        }
    }

    PlanStageStats* DistinctScan::getStats() {
        _commonStats.isEOF = isEOF();
        auto_ptr<PlanStageStats> ret(new PlanStageStats(_commonStats, STAGE_DISTINCT));
        ret->specific.reset(new DistinctScanStats(_specificStats));
        return ret.release();
    }

}  // namespace mongo