# 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, incorporated herein by reference.

"""recreates hardlinks between repository clones"""

from mercurial import cmdutil, hg, util

from mercurial.i18n import _

import os, stat

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.)

    """

    src = hg.repository(

        cmdutil.remoteui(repo, opts),

        ui.expandpath(origin or 'default-relink', origin or 'default'))

    if not src.local():

        raise util.Abort('must specify local origin repository')

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

    locallock = repo.lock()

    try:

        remotelock = src.lock()

        try:

            candidates = collect(src.store.path, ui)

            targets = prune(candidates, 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 = []

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

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

        for filename in filenames:

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

                continue

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

            if not stat.S_ISREG(st.st_mode):

                continue

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

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

    return candidates

def prune(candidates, dst, ui):

    def linkfilter(dst, st):

        try:

            ts = os.stat(dst)

        except OSError:

            # Destination doesn't have this file?

            return False

        if st.st_ino == ts.st_ino:

            return False

        if st.st_dev != ts.st_dev:

            # No point in continuing

            raise util.Abort(

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

        if st.st_size != ts.st_size:

            return False

        return st

    targets = []

    for fn, st in candidates:

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

        ts = linkfilter(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:

            os.link(src, dst)

        except OSError:

            os.rename(bak, dst)

            raise

        os.remove(bak)

    CHUNKLEN = 65536

    relinked = 0

    savedbytes = 0

    pos = 0

    total = len(files)

    for f, sz in files:

        pos += 1

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

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

        sfp = file(source)

        dfp = file(tgt)

        sin = sfp.read(CHUNKLEN)

        while sin:

            din = dfp.read(CHUNKLEN)

            if sin != din:

                break

            sin = sfp.read(CHUNKLEN)

        if sin:

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

            continue

        try:

            relinkfile(source, tgt)

            ui.progress(_('relink'), pos, f, _(' files'), total)

            relinked += 1

            savedbytes += sz

        except OSError, inst:

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

              (relinked, savedbytes))

cmdtable = {

    'relink': (

        relink,

        [],

        _('[ORIGIN]')

    )

}