/brz/remove-bazaar

# Copyright (C) 2008 Canonical Limited.

#

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

# it under the terms of the GNU General Public License version 2 as published

# by the Free Software Foundation.

#

# 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., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA

#

"""Functions for dealing with a persistent equivalency table."""

SENTINEL = -1

class EquivalenceTable(object):

    """This class tracks equivalencies between lists of hashable objects.

    :ivar _left_lines: The 'static' lines that will be preserved between runs.

    :ivar _right_lines: The current set of lines that we are matching against

    """

    def __init__(self, left_lines):

        self._left_lines = left_lines

        self._right_lines = None

        # For each line in 'left' give the offset to the other lines which

        # match it.

        self._generate_matching_left_lines()

    def _generate_matching_left_lines(self):

        matches = {}

        for idx, line in enumerate(self._left_lines):

            left_matches, right_matches = matches.setdefault(line, ([], []))

            left_matches.append(idx)

        self._matching_lines = matches

    def _update_right_matches(self):

        matches = self._matching_lines

        to_remove = []

        for line, (left_matches, right_matches) in matches.iteritems():

            if not left_matches: # queue for deletion

                to_remove.append(line)

            else:

                del right_matches[:]

        for line in to_remove:

            del matches[line]

        del to_remove

        for idx, line in enumerate(self._right_lines):

            left_matches, right_matches = matches.setdefault(line, ([], []))

            right_matches.append(idx)

    def set_right_lines(self, right_lines):

        """Use new right lines, and update the equivalences."""

        self._right_lines = right_lines

        self._update_right_matches()

    def get_left_matches(self, right_idx):

        """Return the lines which match the line in right."""

        right_line = self._right_lines[right_idx]

        left_matches, right_matches = self._matching_lines[right_line]

        return left_matches