/**
 * Copyright (C) 2017 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.
 */

#pragma once

#include <boost/optional.hpp>

#include "mongo/base/string_data.h"
#include "mongo/bson/bsonobj.h"
#include "mongo/bson/timestamp.h"
#include "mongo/db/pipeline/document.h"
#include "mongo/db/pipeline/value.h"
#include "mongo/util/uuid.h"

namespace mongo {

struct ResumeTokenData {
    /**
     * Flag to indicate if the resume token is from an invalidate notification.
     */
    enum FromInvalidate : bool {
        kFromInvalidate = true,
        kNotFromInvalidate = false,
    };

    ResumeTokenData(){};
    ResumeTokenData(Timestamp clusterTimeIn,
                    int versionIn,
                    size_t applyOpsIndexIn,
                    Value documentKeyIn,
                    const boost::optional<UUID>& uuidIn)
        : clusterTime(clusterTimeIn),
          version(versionIn),
          applyOpsIndex(applyOpsIndexIn),
          documentKey(std::move(documentKeyIn)),
          uuid(uuidIn){};

    bool operator==(const ResumeTokenData& other) const;
    bool operator!=(const ResumeTokenData& other) const {
        return !(*this == other);
    };

    Timestamp clusterTime;
    int version = 1;
    size_t applyOpsIndex = 0;
    Value documentKey;
    boost::optional<UUID> uuid;
    // Flag to indicate that this resume token is from an "invalidate" entry. This will not be set
    // on a token from a command that *would* invalidate a change stream, but rather the invalidate
    // notification itself.
    FromInvalidate fromInvalidate = FromInvalidate::kNotFromInvalidate;
};

std::ostream& operator<<(std::ostream& out, const ResumeTokenData& tokenData);

/**
 * A token passed in by the user to indicate where in the oplog we should start for $changeStream.
 * This token has the following format:
 *   {
 *     _data: String, A hex encoding of the binary generated by keystring encoding the clusterTime,
 *            version, applyOpsIndex, UUID, then documentKey in that order.
 *     _typeBits: BinData - The keystring type bits used for deserialization.
 *   }
 *   The _data field data is encoded such that string comparisons provide the correct ordering of
 *   tokens. Unlike the BinData, this can be sorted correctly using a MongoDB sort. BinData
 *   unfortunately orders by the length of the data first, then by the contents.
 *
 *   As an optimization, the _typeBits field may be missing and should not affect token comparison.
 */
class ResumeToken {
public:
    constexpr static StringData kDataFieldName = "_data"_sd;
    constexpr static StringData kTypeBitsFieldName = "_typeBits"_sd;

    /**
     * Parse a resume token from a BSON object; used as an interface to the IDL parser.
     */
    static ResumeToken parse(const BSONObj& resumeBson) {
        return ResumeToken::parse(Document(resumeBson));
    }

    static ResumeToken parse(const Document& document);

    /**
     * The default no-argument constructor is required by the IDL for types used as non-optional
     * fields.
     */
    ResumeToken() = default;

    /**
     * Parses 'resumeValue' into a ResumeToken using the hex-encoded string format.
     */
    explicit ResumeToken(const ResumeTokenData& resumeValue);

    Document toDocument() const;

    /**
     * Because we use the IDL we require a serializer. However, the serialization format depends on
     * the feature compatibility version, so a serializer without an argument doesn't make sense.
     * This should never be used.
     */
    BSONObj toBSON_do_not_use() const {
        MONGO_UNREACHABLE;
    }

    ResumeTokenData getData() const;

    Timestamp getClusterTime() const {
        return getData().clusterTime;
    }

    bool operator==(const ResumeToken&) const;
    bool operator!=(const ResumeToken& other) const {
        return !(*this == other);
    }

    friend std::ostream& operator<<(std::ostream& out, const ResumeToken& token) {
        return out << token.getData();
    }

private:
    explicit ResumeToken(const Document& resumeData);

    // This is the hex-encoded string encoding all the pieces of the resume token.
    std::string _hexKeyString;

    // Since we are using a KeyString encoding, we might lose some information about what the
    // original types of the serialized values were. For example, the integer 2 and the double 2.0
    // will generate the same KeyString. We keep the type bits around so we can deserialize without
    // losing information.
    Value _typeBits;
};
}  // namespace mongo