/**
 *    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_pull.h"

#include "mongo/base/error_codes.h"
#include "mongo/bson/mutable/algorithm.h"
#include "mongo/db/matcher/expression_parser.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 mb = mutablebson;
namespace str = mongoutils::str;

struct ModifierPull::PreparedState {
    PreparedState(mb::Document& doc)
        : doc(doc), idxFound(0), elemFound(doc.end()), elementsToRemove(), noOp(false) {}

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

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

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

    // Values to be removed.
    std::vector<mb::Element> elementsToRemove;

    // True if this update is a no-op
    bool noOp;
};

ModifierPull::ModifierPull()
    : ModifierInterface(),
      _fieldRef(),
      _posDollar(0),
      _exprElt(),
      _exprObj(),
      _matchExpr(),
      _matcherOnPrimitive(false),
      _preparedState() {}

ModifierPull::~ModifierPull() {}

Status ModifierPull::init(const BSONElement& modExpr, const Options& opts, bool* positional) {
    // 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() << "'");
    }

    _exprElt = modExpr;

    // If the element in the mod is actually an object or a regular expression, we need to
    // build a matcher, instead of just doing an equality comparision.
    if ((_exprElt.type() == mongo::Object) || (_exprElt.type() == mongo::RegEx)) {
        if (_exprElt.type() == Object) {
            _exprObj = _exprElt.embeddedObject();

            // If not is not a query operator, then it is a primitive.
            _matcherOnPrimitive = (_exprObj.firstElement().getGtLtOp() != 0);

            // If the object is primitive then wrap it up into an object.
            if (_matcherOnPrimitive)
                _exprObj = BSON("" << _exprObj);
        } else {
            // For a regex, we also need to wrap and treat like a primitive.
            _matcherOnPrimitive = true;
            _exprObj = _exprElt.wrap("");
        }

        // Build the matcher around the object we built above. Currently, we do not allow
        // $pull operations to contain $where clauses, so preserving this behaviour.
        StatusWithMatchExpression parseResult =
            MatchExpressionParser::parse(_exprObj, MatchExpressionParser::WhereCallback());
        if (!parseResult.isOK())
            return parseResult.getStatus();

        _matchExpr.reset(parseResult.getValue());
    }

    return Status::OK();
}

Status ModifierPull::prepare(mb::Element root, 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'.
    Status status = pathsupport::findLongestPrefix(
        _fieldRef, root, &_preparedState->idxFound, &_preparedState->elemFound);

    // FindLongestPrefix may say the path does not exist at all, which is fine here, or
    // that the path was not viable or otherwise wrong, in which case, the mod cannot
    // proceed.
    if (status.code() == ErrorCodes::NonExistentPath) {
        _preparedState->elemFound = root.getDocument().end();
    } else if (!status.isOK()) {
        return status;
    }

    // We register interest in the field name. The driver needs this info to sort out if
    // there is any conflict among mods.
    execInfo->fieldRef[0] = &_fieldRef;

    if (!_preparedState->elemFound.ok() || _preparedState->idxFound < (_fieldRef.numParts() - 1)) {
        // If no target element exists, then there is nothing to do here.
        _preparedState->noOp = execInfo->noOp = true;
        return Status::OK();
    }

    // This operation only applies to arrays
    if (_preparedState->elemFound.getType() != mongo::Array)
        return Status(ErrorCodes::BadValue, "Cannot apply $pull to a non-array value");

    // If the array is empty, there is nothing to pull, so this is a noop.
    if (!_preparedState->elemFound.hasChildren()) {
        _preparedState->noOp = execInfo->noOp = true;
        return Status::OK();
    }

    // Walk the values in the array
    mb::Element cursor = _preparedState->elemFound.leftChild();
    while (cursor.ok()) {
        if (isMatch(cursor))
            _preparedState->elementsToRemove.push_back(cursor);
        cursor = cursor.rightSibling();
    }

    // If we didn't find any elements to add, then this is a no-op, and therefore in place.
    if (_preparedState->elementsToRemove.empty()) {
        _preparedState->noOp = execInfo->noOp = true;
    }

    return Status::OK();
}

Status ModifierPull::apply() const {
    dassert(_preparedState->noOp == false);

    dassert(_preparedState->elemFound.ok() &&
            _preparedState->idxFound == (_fieldRef.numParts() - 1));

    std::vector<mb::Element>::const_iterator where = _preparedState->elementsToRemove.begin();
    const std::vector<mb::Element>::const_iterator end = _preparedState->elementsToRemove.end();
    for (; where != end; ++where)
        const_cast<mb::Element&>(*where).remove();

    return Status::OK();
}

Status ModifierPull::log(LogBuilder* logBuilder) const {
    mb::Document& doc = logBuilder->getDocument();

    if (!_preparedState->elemFound.ok() || _preparedState->idxFound < (_fieldRef.numParts() - 1)) {
        // If we didn't find the element that we wanted to pull from, we log an unset for
        // that element.
        return logBuilder->addToUnsets(_fieldRef.dottedField());

    } else {
        // TODO: This is copied more or less identically from $push. As a result, it copies the
        // behavior in $push that relies on 'apply' having been called unless this is a no-op.

        // TODO We can log just a positional unset in several cases. For now, let's just log
        // the full resulting array.

        // We'd like to create an entry such as {$set: {<fieldname>: [<resulting aray>]}} under
        // 'logRoot'.  We start by creating the {$set: ...} Element.

        // Then we create the {<fieldname>:[]} Element, that is, an empty array.
        mb::Element logElement = doc.makeElementArray(_fieldRef.dottedField());
        if (!logElement.ok()) {
            return Status(ErrorCodes::InternalError, "cannot create details for $pull mod");
        }

        mb::Element curr = _preparedState->elemFound.leftChild();
        while (curr.ok()) {
            dassert(curr.hasValue());

            // We need to copy each array entry from the resulting document to the log
            // document.
            mb::Element currCopy = doc.makeElementWithNewFieldName(StringData(), curr.getValue());
            if (!currCopy.ok()) {
                return Status(ErrorCodes::InternalError, "could create copy element");
            }
            Status status = logElement.pushBack(currCopy);
            if (!status.isOK()) {
                return Status(ErrorCodes::BadValue, "could not append entry for $pull log");
            }
            curr = curr.rightSibling();
        }

        return logBuilder->addToSets(logElement);
    }
}

bool ModifierPull::isMatch(mutablebson::ConstElement element) {
    // TODO: We are assuming that 'element' hasValue is true. That might be OK if the
    // conflict detection logic will prevent us from ever seeing a deserialized element,
    // but are we sure about that?

    dassert(element.hasValue());

    if (!_matchExpr)
        return (element.compareWithBSONElement(_exprElt, false) == 0);

    if (_matcherOnPrimitive) {
        // TODO: This is kinda slow.
        BSONObj candidate = element.getValue().wrap("");
        return _matchExpr->matchesBSON(candidate);
    }

    if (element.getType() != Object)
        return false;

    return _matchExpr->matchesBSON(element.getValueObject());
}

}  // namespace mongo