# obsolete.py - obsolete markers handling

#

# Copyright 2012 Pierre-Yves David <pierre-yves.david@ens-lyon.org>

#                Logilab SA        <contact@logilab.fr>

#

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

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

"""Obsolete markers handling

An obsolete marker maps an old changeset to a list of new

changesets. If the list of new changesets is empty, the old changeset

is said to be "killed". Otherwise, the old changeset is being

"replaced" by the new changesets.

Obsolete markers can be used to record and distribute changeset graph

transformations performed by history rewriting operations, and help

building new tools to reconciliate conflicting rewriting actions. To

facilitate conflicts resolution, markers include various annotations

besides old and news changeset identifiers, such as creation date or

author name.

The old obsoleted changeset is called "precursor" and possible replacements are

called "successors".  Markers that used changeset X as a precursors are called

"successor markers of X" because they hold information about the successors of

X. Markers that use changeset Y as a successors are call "precursor markers of

Y" because they hold information about the precursors of Y.

Examples:

- When changeset A is replacement by a changeset A', one marker is stored:

    (A, (A'))

- When changesets A and B are folded into a new changeset C two markers are

  stored:

    (A, (C,)) and (B, (C,))

- When changeset A is simply "pruned" from the graph, a marker in create:

    (A, ())

- When changeset A is split into B and C, a single marker are used:

    (A, (C, C))

  We use a single marker to distinct the "split" case from the "divergence"

  case. If two independents operation rewrite the same changeset A in to A' and

  A'' when have an error case: divergent rewriting. We can detect it because

  two markers will be created independently:

  (A, (B,)) and (A, (C,))

Format

------

Markers are stored in an append-only file stored in

'.hg/store/obsstore'.

The file starts with a version header:

- 1 unsigned byte: version number, starting at zero.

The header is followed by the markers. Each marker is made of:

- 1 unsigned byte: number of new changesets "R", could be zero.

- 1 unsigned 32-bits integer: metadata size "M" in bytes.

- 1 byte: a bit field. It is reserved for flags used in obsolete

  markers common operations, to avoid repeated decoding of metadata

  entries.

- 20 bytes: obsoleted changeset identifier.

- N*20 bytes: new changesets identifiers.

- M bytes: metadata as a sequence of nul-terminated strings. Each

  string contains a key and a value, separated by a color ':', without

  additional encoding. Keys cannot contain '\0' or ':' and values

  cannot contain '\0'.

"""

import struct

import util, base85, node

from i18n import _

_pack = struct.pack

_unpack = struct.unpack

_SEEK_END = 2 # os.SEEK_END was introduced in Python 2.5

# the obsolete feature is not mature enough to be enabled by default.

# you have to rely on third party extension extension to enable this.

_enabled = False

# data used for parsing and writing

_fmversion = 0

_fmfixed   = '>BIB20s'

_fmnode = '20s'

_fmfsize = struct.calcsize(_fmfixed)

_fnodesize = struct.calcsize(_fmnode)

### obsolescence marker flag

## bumpedfix flag

#

# When a changeset A' succeed to a changeset A which became public, we call A'

# "bumped" because it's a successors of a public changesets

#

# o    A' (bumped)

# |`:

# | o  A

# |/

# o    Z

#

# The way to solve this situation is to create a new changeset Ad as children

# of A. This changeset have the same content than A'. So the diff from A to A'

# is the same than the diff from A to Ad. Ad is marked as a successors of A'

#

# o   Ad

# |`:

# | x A'

# |'|

# o | A

# |/

# o Z

#

# But by transitivity Ad is also a successors of A. To avoid having Ad marked

# as bumped too, we add the `bumpedfix` flag to the marker. <A', (Ad,)>.

# This flag mean that the successors express the changes between the public and

# bumped version and fix the situation, breaking the transitivity of

# "bumped" here.

bumpedfix = 1

def _readmarkers(data):

    """Read and enumerate markers from raw data"""

    off = 0

    diskversion = _unpack('>B', data[off:off + 1])[0]

    off += 1

    if diskversion != _fmversion:

        raise util.Abort(_('parsing obsolete marker: unknown version %r')

                         % diskversion)

    # Loop on markers

    l = len(data)

    while off + _fmfsize <= l:

        # read fixed part

        cur = data[off:off + _fmfsize]

        off += _fmfsize

        nbsuc, mdsize, flags, pre = _unpack(_fmfixed, cur)

        # read replacement

        sucs = ()

        if nbsuc:

            s = (_fnodesize * nbsuc)

            cur = data[off:off + s]

            sucs = _unpack(_fmnode * nbsuc, cur)

            off += s

        # read metadata

        # (metadata will be decoded on demand)

        metadata = data[off:off + mdsize]

        if len(metadata) != mdsize:

            raise util.Abort(_('parsing obsolete marker: metadata is too '

                               'short, %d bytes expected, got %d')

                             % (mdsize, len(metadata)))

        off += mdsize

        yield (pre, sucs, flags, metadata)

def encodemeta(meta):

    """Return encoded metadata string to string mapping.

    Assume no ':' in key and no '\0' in both key and value."""

    for key, value in meta.iteritems():

        if ':' in key or '\0' in key:

            raise ValueError("':' and '\0' are forbidden in metadata key'")

        if '\0' in value:

            raise ValueError("':' are forbidden in metadata value'")

    return '\0'.join(['%s:%s' % (k, meta[k]) for k in sorted(meta)])

def decodemeta(data):

    """Return string to string dictionary from encoded version."""

    d = {}

    for l in data.split('\0'):

        if l:

            key, value = l.split(':')

            d[key] = value

    return d

class marker(object):

    """Wrap obsolete marker raw data"""

    def __init__(self, repo, data):

        # the repo argument will be used to create changectx in later version

        self._repo = repo

        self._data = data

        self._decodedmeta = None

    def precnode(self):

        """Precursor changeset node identifier"""

        return self._data[0]

    def succnodes(self):

        """List of successor changesets node identifiers"""

        return self._data[1]

    def metadata(self):

        """Decoded metadata dictionary"""

        if self._decodedmeta is None:

            self._decodedmeta = decodemeta(self._data[3])

        return self._decodedmeta

    def date(self):

        """Creation date as (unixtime, offset)"""

        parts = self.metadata()['date'].split(' ')

        return (float(parts[0]), int(parts[1]))

class obsstore(object):

    """Store obsolete markers

    Markers can be accessed with two mappings:

    - precursors[x] -> set(markers on precursors edges of x)

    - successors[x] -> set(markers on successors edges of x)

    """

    def __init__(self, sopener):

        # caches for various obsolescence related cache

        self.caches = {}

        self._all = []

        # new markers to serialize

        self.precursors = {}

        self.successors = {}

        self.sopener = sopener

        data = sopener.tryread('obsstore')

        if data:

            self._load(_readmarkers(data))

    def __iter__(self):

        return iter(self._all)

    def __nonzero__(self):

        return bool(self._all)

    def create(self, transaction, prec, succs=(), flag=0, metadata=None):

        """obsolete: add a new obsolete marker

        * ensuring it is hashable

        * check mandatory metadata

        * encode metadata

        """

        if metadata is None:

            metadata = {}

        if 'date' not in metadata:

            metadata['date'] = "%d %d" % util.makedate()

        if len(prec) != 20:

            raise ValueError(prec)

        for succ in succs:

            if len(succ) != 20:

                raise ValueError(succ)

        marker = (str(prec), tuple(succs), int(flag), encodemeta(metadata))

        self.add(transaction, [marker])

    def add(self, transaction, markers):

        """Add new markers to the store

        Take care of filtering duplicate.

        Return the number of new marker."""

        if not _enabled:

            raise util.Abort('obsolete feature is not enabled on this repo')

        new = [m for m in markers if m not in self._all]

        if new:

            f = self.sopener('obsstore', 'ab')

            try:

                # Whether the file's current position is at the begin or at

                # the end after opening a file for appending is implementation

                # defined. So we must seek to the end before calling tell(),

                # or we may get a zero offset for non-zero sized files on

                # some platforms (issue3543).

                f.seek(0, _SEEK_END)

                offset = f.tell()

                transaction.add('obsstore', offset)

                # offset == 0: new file - add the version header

                for bytes in _encodemarkers(new, offset == 0):

                    f.write(bytes)

            finally:

                # XXX: f.close() == filecache invalidation == obsstore rebuilt.

                # call 'filecacheentry.refresh()'  here

                f.close()

            self._load(new)

            # new marker *may* have changed several set. invalidate the cache.

            self.caches.clear()

        return len(new)

    def mergemarkers(self, transaction, data):

        markers = _readmarkers(data)

        self.add(transaction, markers)

    def _load(self, markers):

        for mark in markers:

            self._all.append(mark)

            pre, sucs = mark[:2]

            self.successors.setdefault(pre, set()).add(mark)

            for suc in sucs:

                self.precursors.setdefault(suc, set()).add(mark)

        if node.nullid in self.precursors:

            raise util.Abort(_('bad obsolescence marker detected: '

                               'invalid successors nullid'))

def _encodemarkers(markers, addheader=False):

    # Kept separate from flushmarkers(), it will be reused for

    # markers exchange.

    if addheader:

        yield _pack('>B', _fmversion)

    for marker in markers:

        yield _encodeonemarker(marker)

def _encodeonemarker(marker):

    pre, sucs, flags, metadata = marker

    nbsuc = len(sucs)

    format = _fmfixed + (_fmnode * nbsuc)

    data = [nbsuc, len(metadata), flags, pre]

    data.extend(sucs)

    return _pack(format, *data) + metadata

# arbitrary picked to fit into 8K limit from HTTP server

# you have to take in account:

# - the version header

# - the base85 encoding

_maxpayload = 5300

def listmarkers(repo):

    """List markers over pushkey"""

    if not repo.obsstore:

        return {}

    keys = {}

    parts = []

    currentlen = _maxpayload * 2  # ensure we create a new part

    for marker in  repo.obsstore:

        nextdata = _encodeonemarker(marker)

        if (len(nextdata) + currentlen > _maxpayload):

            currentpart = []

            currentlen = 0

            parts.append(currentpart)

        currentpart.append(nextdata)

        currentlen += len(nextdata)

    for idx, part in enumerate(reversed(parts)):

        data = ''.join([_pack('>B', _fmversion)] + part)

        keys['dump%i' % idx] = base85.b85encode(data)

    return keys

def pushmarker(repo, key, old, new):

    """Push markers over pushkey"""

    if not key.startswith('dump'):

        repo.ui.warn(_('unknown key: %r') % key)

        return 0

    if old:

        repo.ui.warn(_('unexpected old value') % key)

        return 0

    data = base85.b85decode(new)

    lock = repo.lock()

    try:

        tr = repo.transaction('pushkey: obsolete markers')

        try:

            repo.obsstore.mergemarkers(tr, data)

            tr.close()

            return 1

        finally:

            tr.release()

    finally:

        lock.release()

def allmarkers(repo):

    """all obsolete markers known in a repository"""

    for markerdata in repo.obsstore:

        yield marker(repo, markerdata)

def precursormarkers(ctx):

    """obsolete marker marking this changeset as a successors"""

    for data in ctx._repo.obsstore.precursors.get(ctx.node(), ()):

        yield marker(ctx._repo, data)

def successormarkers(ctx):

    """obsolete marker making this changeset obsolete"""

    for data in ctx._repo.obsstore.successors.get(ctx.node(), ()):

        yield marker(ctx._repo, data)

def allsuccessors(obsstore, nodes, ignoreflags=0):

    """Yield node for every successor of <nodes>.

    Some successors may be unknown locally.

    This is a linear yield unsuited to detecting split changesets."""

    remaining = set(nodes)

    seen = set(remaining)

    while remaining:

        current = remaining.pop()

        yield current

        for mark in obsstore.successors.get(current, ()):

            # ignore marker flagged with with specified flag

            if mark[2] & ignoreflags:

                continue

            for suc in mark[1]:

                if suc not in seen:

                    seen.add(suc)