~bzr-pqm/bzr/bzr.dev

# Copyright (C) 2007 Canonical Ltd

#

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; either version 2 of the License, or

# (at your option) any later version.

#

# This program is distributed in the hope that it will be useful,

# but WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

# GNU General Public License for more details.

#

# You should have received a copy of the GNU General Public License

# along with this program; if not, write to the Free Software

# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

"""A collection of file names which is persisted on a transport."""

from bzrlib.lazy_import import lazy_import

lazy_import(globals(), """

from bzrlib import (

        errors,

        )

""")

class FileNames(object):

    """A collection of file names.

    The file names are persisted to a file on a transport, and cand be

    added, removed and initialised.

    The set of names are stored in a flat file, one name per line.

    New names are allocated sequentially.

    Initialisation creates an empty file.

    This is intended to support management of modest numbers of files in 

    write-locked environments which may be read from unlistable transports.

    The save method must be called to cause the state to be saved to the

    transport.

    Finally, load is used to obtain a previously saved set.

    """

    def __init__(self, transport, index_name):

        """Create a collection on transport called index_name."""

        self._transport = transport

        self._index_name = index_name

        self._names = None

        self._cap = 10000

    def allocate(self):

        for number in xrange(self._cap):

            if str(number) not in self._names:

                self._names.add(str(number))

                return str(number)

        raise errors.BzrError('too many files')

    def initialise(self):

        """Initialise the collection."""

        self._names = set()

    def load(self):

        """Load the names from the transport."""

        self._names = set(self._transport.get_bytes(

            self._index_name).split('\n'))

        self._names.discard('')

    def names(self):

        """What are the names in this collection?"""

        return frozenset(self._names)

    def remove(self, name):

        """Remove name from the collection."""

        self._names.remove(name)

    def save(self):

        """Save the set of names."""

        self._transport.put_bytes(self._index_name, '\n'.join(self._names))