# 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.

"""

import collections

import struct

from .. import error, requirements as requirementsmod

from ..revlogutils import constants, flagutil

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

def get_sidedata_helpers(repo, remote_sd_categories, pull=False):

    """

    Returns a dictionary mapping revlog types to tuples of

    `(repo, computers, removers)`:

        * `repo` is used as an argument for computers

        * `computers` is a list of `(category, (keys, computer, flags)` that

           compute the missing sidedata categories that were asked:

           * `category` is the sidedata category

           * `keys` are the sidedata keys to be affected

           * `flags` is a bitmask (an integer) of flags to remove when

              removing the category.

           * `computer` is the function `(repo, store, rev, sidedata)` that

             returns a tuple of

             `(new sidedata dict, (flags to add, flags to remove))`.

             For example, it will return `({}, (0, 1 << 15))` to return no

             sidedata, with no flags to add and one flag to remove.

        * `removers` will remove the keys corresponding to the categories

          that are present, but not needed.

        If both `computers` and `removers` are empty, sidedata will simply not

        be transformed.

    """

    # Computers for computing sidedata on-the-fly

    sd_computers = collections.defaultdict(list)

    # Computers for categories to remove from sidedata

    sd_removers = collections.defaultdict(list)

    to_generate = remote_sd_categories - repo._wanted_sidedata

    to_remove = repo._wanted_sidedata - remote_sd_categories

    if pull:

        to_generate, to_remove = to_remove, to_generate

    for revlog_kind, computers in repo._sidedata_computers.items():

        for category, computer in computers.items():

            if category in to_generate:

                sd_computers[revlog_kind].append(computer)

            if category in to_remove:

                sd_removers[revlog_kind].append(computer)

    sidedata_helpers = (repo, sd_computers, sd_removers)

    return sidedata_helpers

def run_sidedata_helpers(store, sidedata_helpers, sidedata, rev):

    """Returns the sidedata for the given revision after running through

    the given helpers.

    - `store`: the revlog this applies to (changelog, manifest, or filelog

      instance)

    - `sidedata_helpers`: see `get_sidedata_helpers`

    - `sidedata`: previous sidedata at the given rev, if any

    - `rev`: affected rev of `store`

    """

    repo, sd_computers, sd_removers = sidedata_helpers

    kind = store.revlog_kind

    flags_to_add = 0

    flags_to_remove = 0

    for _keys, sd_computer, _flags in sd_computers.get(kind, []):

        sidedata, flags = sd_computer(repo, store, rev, sidedata)

        flags_to_add |= flags[0]

        flags_to_remove |= flags[1]

    for keys, _computer, flags in sd_removers.get(kind, []):

        for key in keys:

            sidedata.pop(key, None)

        flags_to_remove |= flags

    return sidedata, (flags_to_add, flags_to_remove)

def set_sidedata_spec_for_repo(repo):

    # prevent cycle metadata -> revlogutils.sidedata -> metadata

    from .. import metadata

    if requirementsmod.COPIESSDC_REQUIREMENT in repo.requirements:

        repo.register_wanted_sidedata(SD_FILES)

    repo.register_sidedata_computer(

        constants.KIND_CHANGELOG,

        SD_FILES,

        (SD_FILES,),

        metadata.copies_sidedata_computer,

        flagutil.REVIDX_HASCOPIESINFO,

    )