# transaction.py - simple journaling scheme for mercurial

#

# This transaction scheme is intended to gracefully handle program

# errors and interruptions. More serious failures like system crashes

# can be recovered with an fsck-like tool. As the whole repository is

# effectively log-structured, this should amount to simply truncating

# anything that isn't referenced in the changelog.

#

# Copyright 2005, 2006 Matt Mackall <mpm@selenic.com>

#

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

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

from i18n import _

import errno

import error

def active(func):

    def _active(self, *args, **kwds):

        if self.count == 0:

            raise error.Abort(_(

                'cannot use transaction when it is already committed/aborted'))

        return func(self, *args, **kwds)

    return _active

def _playback(journal, report, opener, entries, unlink=True):

    for f, o, ignore in entries:

        if o or not unlink:

            try:

                fp = opener(f, 'a')

                fp.truncate(o)

                fp.close()

            except IOError:

                report(_("failed to truncate %s\n") % f)

                raise

        else:

            try:

                opener.unlink(f)

            except (IOError, OSError), inst:

                if inst.errno != errno.ENOENT:

                    raise

    opener.unlink(journal)

class transaction(object):

    def __init__(self, report, opener, journal, after=None, createmode=None):

        self.count = 1

        self.usages = 1

        self.report = report

        self.opener = opener

        self.after = after

        self.entries = []

        self.map = {}

        self.journal = journal

        self._queue = []

        self.file = opener.open(self.journal, "w")

        if createmode is not None:

            opener.chmod(self.journal, createmode & 0666)

    def __del__(self):

        if self.journal:

            self._abort()

    @active

    def startgroup(self):

        self._queue.append([])

    @active

    def endgroup(self):

        q = self._queue.pop()

        d = ''.join(['%s\0%d\n' % (x[0], x[1]) for x in q])

        self.entries.extend(q)

        self.file.write(d)

        self.file.flush()

    @active

    def add(self, file, offset, data=None):

        if file in self.map:

            return

        if self._queue:

            self._queue[-1].append((file, offset, data))

            return

        self.entries.append((file, offset, data))

        self.map[file] = len(self.entries) - 1

        # add enough data to the journal to do the truncate

        self.file.write("%s\0%d\n" % (file, offset))

        self.file.flush()

    @active

    def find(self, file):

        if file in self.map:

            return self.entries[self.map[file]]

        return None

    @active

    def replace(self, file, offset, data=None):

        '''

        replace can only replace already committed entries

        that are not pending in the queue

        '''

        if file not in self.map:

            raise KeyError(file)

        index = self.map[file]

        self.entries[index] = (file, offset, data)

        self.file.write("%s\0%d\n" % (file, offset))

        self.file.flush()

    @active

    def nest(self):

        self.count += 1

        self.usages += 1

        return self

    def release(self):

        if self.count > 0:

            self.usages -= 1

        # if the transaction scopes are left without being closed, fail

        if self.count > 0 and self.usages == 0:

            self._abort()

    def running(self):

        return self.count > 0

    @active

    def close(self):

        '''commit the transaction'''

        self.count -= 1

        if self.count != 0:

            return

        self.file.close()

        self.entries = []

        if self.after:

            self.after()

        if self.opener.isfile(self.journal):

            self.opener.unlink(self.journal)

        self.journal = None

    @active

    def abort(self):

        '''abort the transaction (generally called on error, or when the

        transaction is not explicitly committed before going out of

        scope)'''

        self._abort()

    def _abort(self):

        self.count = 0

        self.usages = 0

        self.file.close()

        try:

            if not self.entries:

                if self.journal:

                    self.opener.unlink(self.journal)

                return

            self.report(_("transaction abort!\n"))

            try:

                _playback(self.journal, self.report, self.opener,

                          self.entries, False)

                self.report(_("rollback completed\n"))

            except Exception:

                self.report(_("rollback failed - please run hg recover\n"))

        finally:

            self.journal = None

def rollback(opener, file, report):

    entries = []

    fp = opener.open(file)

    lines = fp.readlines()

    fp.close()

    for l in lines:

        f, o = l.split('\0')

        entries.append((f, int(o), None))

    _playback(file, report, opener, entries)