# sidedata.py - Logic around store extra data alongside revlog revisions

#

# Copyright 2019 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.

"""core code for "sidedata" support

The "sidedata" are stored alongside the revision without actually being part of

its content and not affecting its hash. It's main use cases is to cache

important information related to a changesets.

The current implementation is experimental and subject to changes. Do not rely

on it in production.

Sidedata are stored in the revlog itself, thanks to a new version of the

revlog. The following format is currently used::

    initial header:

        <number of sidedata; 2 bytes>

    sidedata (repeated N times):

        <sidedata-key; 2 bytes>

        <sidedata-entry-length: 4 bytes>

        <sidedata-content-sha1-digest: 20 bytes>

        <sidedata-content; X bytes>

    normal raw text:

        <all bytes remaining in the rawtext>

This is a simple and effective format. It should be enough to experiment with

the concept.

"""

from __future__ import absolute_import

import struct

from .. import error

from ..utils import hashutil

## sidedata type constant

# reserve a block for testing purposes.

SD_TEST1 = 1

SD_TEST2 = 2

SD_TEST3 = 3

SD_TEST4 = 4

SD_TEST5 = 5

SD_TEST6 = 6

SD_TEST7 = 7

# key to store copies related information

SD_P1COPIES = 8

SD_P2COPIES = 9

SD_FILESADDED = 10

SD_FILESREMOVED = 11

SD_FILES = 12

# internal format constant

SIDEDATA_HEADER = struct.Struct('>H')

SIDEDATA_ENTRY = struct.Struct('>HL20s')

def serialize_sidedata(sidedata):

    sidedata = list(sidedata.items())

    sidedata.sort()

    buf = [SIDEDATA_HEADER.pack(len(sidedata))]

    for key, value in sidedata:

        digest = hashutil.sha1(value).digest()

        buf.append(SIDEDATA_ENTRY.pack(key, len(value), digest))

    for key, value in sidedata:

        buf.append(value)

    buf = b''.join(buf)

    return buf

def deserialize_sidedata(blob):

    sidedata = {}

    offset = 0

    (nbentry,) = SIDEDATA_HEADER.unpack(blob[: SIDEDATA_HEADER.size])

    offset += SIDEDATA_HEADER.size

    dataoffset = SIDEDATA_HEADER.size + (SIDEDATA_ENTRY.size * nbentry)

    for i in range(nbentry):

        nextoffset = offset + SIDEDATA_ENTRY.size

        key, size, storeddigest = SIDEDATA_ENTRY.unpack(blob[offset:nextoffset])

        offset = nextoffset

        # read the data associated with that entry

        nextdataoffset = dataoffset + size

        entrytext = bytes(blob[dataoffset:nextdataoffset])

        readdigest = hashutil.sha1(entrytext).digest()

        if storeddigest != readdigest:

            raise error.SidedataHashError(key, storeddigest, readdigest)

        sidedata[key] = entrytext

        dataoffset = nextdataoffset

    return sidedata