/** @file
 * @brief Glass changesets
 */
/* Copyright 2014 Olly Betts
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see
 * <https://www.gnu.org/licenses/>.
 */

#ifndef XAPIAN_INCLUDED_GLASS_CHANGES_H
#define XAPIAN_INCLUDED_GLASS_CHANGES_H

#include "glass_defs.h"
#include <string>

class GlassChanges {
    /// File descriptor to write changeset to (or -1 for none).
    int changes_fd;

    std::string changes_stem;

    /** The maximum number of changesets to keep.
     *
     *  If a replica is more than this number of changesets behind, it will
     *  need to be sent a full copy of the database (which can be more
     *  efficient if a lot has changed).
     */
    glass_revision_number_t max_changesets;

    /** The oldest changeset which might exist on disk.
     *
     *  Used to optimise removal of old changesets by giving us a point to
     *  start looking for ones to delete.
     */
    glass_revision_number_t oldest_changeset;

  public:
    explicit GlassChanges(const std::string & db_dir)
        : changes_fd(-1),
          changes_stem(db_dir + "/changes"),
          oldest_changeset(0) { }

    ~GlassChanges();

    GlassChanges * start(glass_revision_number_t old_rev,
                         glass_revision_number_t rev,
                         int flags);

    void write_block(const char * p, size_t len);

    void write_block(const std::string & s) {
        write_block(s.data(), s.size());
    }

    void set_oldest_changeset(glass_revision_number_t rev) {
        oldest_changeset = rev;
    }

    glass_revision_number_t get_oldest_changeset() const {
        return oldest_changeset;
    }

    void commit(glass_revision_number_t new_rev, int flags);

    static void check(const std::string & changes_file);
};

#endif // XAPIAN_INCLUDED_GLASS_CHANGES_H
