/**
 *    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.
 */

#include "mongo/db/ops/modifier_unset.h"

#include "mongo/base/error_codes.h"
#include "mongo/bson/mutable/document.h"
#include "mongo/db/ops/field_checker.h"
#include "mongo/db/ops/log_builder.h"
#include "mongo/db/ops/path_support.h"
#include "mongo/util/mongoutils/str.h"

namespace mongo {

    namespace str = mongoutils::str;

    struct ModifierUnset::PreparedState {

        PreparedState(mutablebson::Document* targetDoc)
            : doc(*targetDoc)
            , idxFound(0)
            , elemFound(doc.end())
            , noOp(false) {
        }

        // Document that is going to be changed.
        mutablebson::Document& doc;

        // Index in _fieldRef for which an Element exist in the document.
        size_t idxFound;

        // Element corresponding to _fieldRef[0.._idxFound].
        mutablebson::Element elemFound;

        // This $set is a no-op?
        bool noOp;

    };

    ModifierUnset::ModifierUnset()
        : _fieldRef()
        , _posDollar(0)
        , _val() {
    }

    ModifierUnset::~ModifierUnset() {
    }

    Status ModifierUnset::init(const BSONElement& modExpr, const Options& opts,
                               bool* positional) {

        //
        // field name analysis
        //

        // Perform standard field name and updateable checks.
        _fieldRef.parse(modExpr.fieldName());
        Status status = fieldchecker::isUpdatable(_fieldRef);
        if (! status.isOK()) {
            return status;
        }

        // If a $-positional operator was used, get the index in which it occurred
        // and ensure only one occurrence.
        size_t foundCount;
        bool foundDollar = fieldchecker::isPositional(_fieldRef, &_posDollar, &foundCount);

        if (positional)
            *positional = foundDollar;

        if (foundDollar && foundCount > 1) {
            return Status(ErrorCodes::BadValue,
                          str::stream() << "Too many positional (i.e. '$') elements found in path '"
                                        << _fieldRef.dottedField() << "'");
        }


        //
        // value analysis
        //

        // Unset takes any value, since there is no semantics attached to such value.
        _val = modExpr;

        return Status::OK();
    }

    Status ModifierUnset::prepare(mutablebson::Element root,
                                  const StringData& matchedField,
                                  ExecInfo* execInfo) {

        _preparedState.reset(new PreparedState(&root.getDocument()));

        // If we have a $-positional field, it is time to bind it to an actual field part.
        if (_posDollar) {
            if (matchedField.empty()) {
                return Status(ErrorCodes::BadValue,
                              str::stream() << "The positional operator did not find the match "
                                               "needed from the query. Unexpanded update: "
                                            << _fieldRef.dottedField());
            }
            _fieldRef.setPart(_posDollar, matchedField);
        }


        // Locate the field name in 'root'. Note that if we don't have the full path in the
        // doc, there isn't anything to unset, really.
        Status status = pathsupport::findLongestPrefix(_fieldRef,
                                                       root,
                                                       &_preparedState->idxFound,
                                                       &_preparedState->elemFound);
        if (!status.isOK() ||
            _preparedState->idxFound != (_fieldRef.numParts() -1)) {
            execInfo->noOp = _preparedState->noOp = true;
            execInfo->fieldRef[0] = &_fieldRef;

            return Status::OK();
        }

        // If there is indeed something to unset, we register so, along with the interest in
        // the field name. The driver needs this info to sort out if there is any conflict
        // among mods.
        execInfo->fieldRef[0] = &_fieldRef;

        // The only way for an $unset to be inplace is for its target field to be the last one
        // of the object. That is, it is always the right child on its paths. The current
        // rationale is that there should be no holes in a BSONObj and, to be in place, no
        // field boundaries must change.
        //
        // TODO:
        // mutablebson::Element curr = _preparedState->elemFound;
        // while (curr.ok()) {
        //     if (curr.rightSibling().ok()) {
        //     }
        //     curr = curr.parent();
        // }

        return Status::OK();
    }

    Status ModifierUnset::apply() const {
        dassert(!_preparedState->noOp);

        // Our semantics says that, if we're unseting an element of an array, we swap that
        // value to null. The rationale is that we don't want other array elements to change
        // indices. (That could be achieved with $pull-ing element from it.)
        if (_preparedState->elemFound.parent().ok() &&
            _preparedState->elemFound.parent().getType() == Array) {
            return _preparedState->elemFound.setValueNull();
        }
        else {
            return _preparedState->elemFound.remove();
        }
    }

    Status ModifierUnset::log(LogBuilder* logBuilder) const {
        return logBuilder->addToUnsets(_fieldRef.dottedField());
    }

} // namespace mongo
