# docket - code related to revlog "docket"

#

# Copyright 2021 Pierre-Yves David <pierre-yves.david@octobus.net>

#

# This software may be used and distributed according to the terms of the

# GNU General Public License version 2 or any later version.

### Revlog docket file

#

# The revlog is stored on disk using multiple files:

#

# * a small docket file, containing metadata and a pointer,

#

# * an index file, containing fixed width information about revisions,

#

# * a data file, containing variable width data for these revisions,

from __future__ import absolute_import

import struct

from . import (

    constants,

)

# Docket format

#

# * 4 bytes: revlog version

#          |   This is mandatory as docket must be compatible with the previous

#          |   revlog index header.

S_HEADER = struct.Struct(constants.INDEX_HEADER.format)

class RevlogDocket(object):

    """metadata associated with revlog"""

    def __init__(self, revlog, version_header=None):

        self._version_header = version_header

        self._dirty = False

        self._radix = revlog.radix

        self._path = revlog._docket_file

        self._opener = revlog.opener

    def index_filepath(self):

        """file path to the current index file associated to this docket"""

        # very simplistic version at first

        return b"%s.idx" % self._radix

    def write(self, transaction):

        """write the modification of disk if any

        This make the new content visible to all process"""

        if self._dirty:

            transaction.addbackup(self._path, location=b'store')

            with self._opener(self._path, mode=b'w', atomictemp=True) as f:

                f.write(self._serialize())

            self._dirty = False

    def _serialize(self):

        return S_HEADER.pack(self._version_header)

def default_docket(revlog, version_header):

    """given a revlog version a new docket object for the given revlog"""

    if (version_header & 0xFFFF) != constants.REVLOGV2:

        return None

    docket = RevlogDocket(revlog, version_header=version_header)

    docket._dirty = True

    return docket

def parse_docket(revlog, data):

    """given some docket data return a docket object for the given revlog"""

    header = S_HEADER.unpack(data[: S_HEADER.size])

    (version_header,) = header

    docket = RevlogDocket(

        revlog,

        version_header=version_header,

    )

    return docket