whipper-gui/morituri/common/common.py

# -*- Mode: Python; test-case-name: morituri.test.test_common_common -*-
# vi:si:et:sw=4:sts=4:ts=4

# Morituri - for those about to RIP

# Copyright (C) 2009 Thomas Vander Stichele

# This file is part of morituri.
# 
# morituri 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 3 of the License, or
# (at your option) any later version.
# 
# morituri 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 morituri.  If not, see <http://www.gnu.org/licenses/>.

import os
import tempfile
import shutil

SAMPLES_PER_FRAME = 588
WORDS_PER_FRAME = SAMPLES_PER_FRAME * 2
BYTES_PER_FRAME = SAMPLES_PER_FRAME * 4
FRAMES_PER_SECOND = 75

def msfToFrames(msf):
    """
    Converts a string value in MM:SS:FF to frames.

    @param msf: the MM:SS:FF value to convert
    @type  msf: str

    @rtype:   int
    @returns: number of frames
    """
    if not ':' in msf:
        return int(msf)

    m, s, f = msf.split(':')

    return 60 * FRAMES_PER_SECOND * int(m) + FRAMES_PER_SECOND * int(s) + int(f)

def framesToMSF(frames, frameDelimiter=':'):
    f = frames % FRAMES_PER_SECOND
    frames -= f
    s = (frames / FRAMES_PER_SECOND) % 60
    frames -= s * 60
    m = frames / FRAMES_PER_SECOND / 60

    return "%02d:%02d%s%02d" % (m, s, frameDelimiter, f)

def framesToHMSF(frames):
    # cdparanoia style
    f = frames % FRAMES_PER_SECOND
    frames -= f
    s = (frames / FRAMES_PER_SECOND) % 60
    frames -= s * FRAMES_PER_SECOND
    m = (frames / FRAMES_PER_SECOND / 60) % 60
    frames -= m * FRAMES_PER_SECOND * 60
    h = frames / FRAMES_PER_SECOND / 60 / 60

    return "%02d:%02d:%02d.%02d" % (h, m, s, f)

class Persister(object):
    """
    I wrap an optional pickle to persist an object to disk.

    Instantiate me with a path to automatically unpickle the object.
    Call persist to store the object to disk; it will get stored if it
    changed from the on-disk object.

    @ivar object: the persistent object
    """

    def __init__(self, path=None, default=None):
        """
        If path is not given, the object will not be persisted.
        This allows code to transparently deal with both persisted and
        non-persisted objects, since the persist method will just end up
        doing nothing.
        """
        self._path = path
        self.object = None

        self._unpickle(default)

    def persist(self, obj=None):
        """
        Persist the given object, if we have a persistence path and the
        object changed.

        If object is not given, re-persist our object, always.
        If object is given, only persist if it was changed.
        """
        # don't pickle if it's already ok
        if obj and obj == self.object:
            return

        # store the object on ourselves if not None
        if obj is not None:
            self.object = obj

        # don't pickle if there is no path
        if not self._path:
            return

        # default to pickling our object again
        if obj is None:
            obj = self.object

        # pickle
        self.object = obj
        (fd, path) = tempfile.mkstemp(suffix='.morituri.pickle')
        handle = os.fdopen(fd, 'wb')
        import pickle
        pickle.dump(obj, handle, 2)
        handle.close()
        # do an atomic move
        shutil.move(path, self._path)

    def _unpickle(self, default=None):
        self.object = default

        if not self._path:
            return None

        if not os.path.exists(self._path):
            return None

        handle = open(self._path)
        import pickle
        self.object = pickle.load(handle)

    def delete(self):
        self.object = None
        os.unlink(self._path)


class PersistedCache(object):
    """
    I wrap a directory of persisted objects.
    """

    path = None

    def __init__(self, path):
        self.path = path
        try:
            os.makedirs(self.path)
        except OSError, e:
            if e.errno != 17: # FIXME
                raise


    def _getPath(self, key):
        return os.path.join(self.path, '%s.pickle' % key)

    def get(self, key):
        """
        Returns the persister for the given key.
        """
        persister = Persister(self._getPath(key))
        if persister.object:
            if hasattr(persister.object, 'instanceVersion'):
                o = persister.object
                if o.instanceVersion < o.__class__.classVersion:
                    persister.delete()

        return persister