# Mercurial extension to provide 'hg relink' command

#

# Copyright (C) 2007 Brendan Cully <brendan@kublai.com>

#

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

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

"""recreates hardlinks between repository clones"""

from __future__ import absolute_import

import os

import stat

from mercurial.i18n import _

from mercurial import (

    error,

    hg,

    registrar,

    util,

)

from mercurial.utils import (

    stringutil,

)

cmdtable = {}

command = registrar.command(cmdtable)

# Note for extension authors: ONLY specify testedwith = 'ships-with-hg-core' for

# extensions which SHIP WITH MERCURIAL. Non-mainline extensions should

# be specifying the version(s) of Mercurial they are tested with, or

# leave the attribute unspecified.

testedwith = 'ships-with-hg-core'

@command('relink', [], _('[ORIGIN]'))

def relink(ui, repo, origin=None, **opts):

    """recreate hardlinks between two repositories

    When repositories are cloned locally, their data files will be

    hardlinked so that they only use the space of a single repository.

    Unfortunately, subsequent pulls into either repository will break

    hardlinks for any files touched by the new changesets, even if

    both repositories end up pulling the same changes.

    Similarly, passing --rev to "hg clone" will fail to use any

    hardlinks, falling back to a complete copy of the source

    repository.

    This command lets you recreate those hardlinks and reclaim that

    wasted space.

    This repository will be relinked to share space with ORIGIN, which

    must be on the same local disk. If ORIGIN is omitted, looks for

    "default-relink", then "default", in [paths].

    Do not attempt any read operations on this repository while the

    command is running. (Both repositories will be locked against

    writes.)

    """

    if (not util.safehasattr(util, 'samefile') or

        not util.safehasattr(util, 'samedevice')):

        raise error.Abort(_('hardlinks are not supported on this system'))

    src = hg.repository(repo.baseui, ui.expandpath(origin or 'default-relink',

                                          origin or 'default'))

    ui.status(_('relinking %s to %s\n') % (src.store.path, repo.store.path))

    if repo.root == src.root:

        ui.status(_('there is nothing to relink\n'))

        return

    if not util.samedevice(src.store.path, repo.store.path):

        # No point in continuing

        raise error.Abort(_('source and destination are on different devices'))

    locallock = repo.lock()

    try:

        remotelock = src.lock()

        try:

            candidates = sorted(collect(src, ui))

            targets = prune(candidates, src.store.path, repo.store.path, ui)

            do_relink(src.store.path, repo.store.path, targets, ui)

        finally:

            remotelock.release()

    finally:

        locallock.release()

def collect(src, ui):

    seplen = len(os.path.sep)

    candidates = []

    live = len(src['tip'].manifest())

    # Your average repository has some files which were deleted before

    # the tip revision. We account for that by assuming that there are

    # 3 tracked files for every 2 live files as of the tip version of

    # the repository.

    #

    # mozilla-central as of 2010-06-10 had a ratio of just over 7:5.

    total = live * 3 // 2

    src = src.store.path

    pos = 0

    ui.status(_("tip has %d files, estimated total number of files: %d\n")

              % (live, total))

    for dirpath, dirnames, filenames in os.walk(src):

        dirnames.sort()

        relpath = dirpath[len(src) + seplen:]

        for filename in sorted(filenames):

            if filename[-2:] not in ('.d', '.i'):

                continue

            st = os.stat(os.path.join(dirpath, filename))

            if not stat.S_ISREG(st.st_mode):

                continue

            pos += 1

            candidates.append((os.path.join(relpath, filename), st))

    ui.status(_('collected %d candidate storage files\n') % len(candidates))

    return candidates

def prune(candidates, src, dst, ui):

    def linkfilter(src, dst, st):

        try:

            ts = os.stat(dst)

        except OSError:

            # Destination doesn't have this file?

            return False

        if util.samefile(src, dst):

            return False

        if not util.samedevice(src, dst):

            # No point in continuing

            raise error.Abort(

                _('source and destination are on different devices'))

        if st.st_size != ts.st_size:

            return False

        return st

    targets = []

    pos = 0

    for fn, st in candidates:

        pos += 1

        srcpath = os.path.join(src, fn)

        tgt = os.path.join(dst, fn)

        ts = linkfilter(srcpath, tgt, st)

        if not ts:

            ui.debug('not linkable: %s\n' % fn)

            continue

        targets.append((fn, ts.st_size))

    ui.status(_('pruned down to %d probably relinkable files\n') % len(targets))

    return targets

def do_relink(src, dst, files, ui):

    def relinkfile(src, dst):

        bak = dst + '.bak'

        os.rename(dst, bak)

        try:

            util.oslink(src, dst)

        except OSError:

            os.rename(bak, dst)

            raise

        os.remove(bak)

    CHUNKLEN = 65536

    relinked = 0

    savedbytes = 0

    pos = 0

    for f, sz in files:

        pos += 1

        source = os.path.join(src, f)

        tgt = os.path.join(dst, f)

        # Binary mode, so that read() works correctly, especially on Windows

        sfp = open(source, 'rb')

        dfp = open(tgt, 'rb')

        sin = sfp.read(CHUNKLEN)

        while sin:

            din = dfp.read(CHUNKLEN)

            if sin != din:

                break

            sin = sfp.read(CHUNKLEN)

        sfp.close()

        dfp.close()

        if sin:

            ui.debug('not linkable: %s\n' % f)

            continue

        try:

            relinkfile(source, tgt)

            relinked += 1

            savedbytes += sz

        except OSError as inst:

            ui.warn('%s: %s\n' % (tgt, stringutil.forcebytestr(inst)))

    ui.status(_('relinked %d files (%s reclaimed)\n') %

              (relinked, util.bytecount(savedbytes)))