[stgit] / stgit / stack.py

"""Basic quilt-like functionality
"""

__copyright__ = """
Copyright (C) 2005, Catalin Marinas <catalin.marinas@gmail.com>

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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
"""

import sys, os, re

from stgit.utils import *
from stgit import git, basedir, templates
from stgit.config import config


# stack exception class
class StackException(Exception):
    pass

class FilterUntil:
    def __init__(self):
        self.should_print = True
    def __call__(self, x, until_test, prefix):
        if until_test(x):
            self.should_print = False
        if self.should_print:
            return x[0:len(prefix)] != prefix
        return False

#
# Functions
#
__comment_prefix = 'STG:'
__patch_prefix = 'STG_PATCH:'

def __clean_comments(f):
    """Removes lines marked for status in a commit file
    """
    f.seek(0)

    # remove status-prefixed lines
    lines = f.readlines()

    patch_filter = FilterUntil()
    until_test = lambda t: t == (__patch_prefix + '\n')
    lines = [l for l in lines if patch_filter(l, until_test, __comment_prefix)]

    # remove empty lines at the end
    while len(lines) != 0 and lines[-1] == '\n':
        del lines[-1]

    f.seek(0); f.truncate()
    f.writelines(lines)

def edit_file(series, line, comment, show_patch = True):
    fname = '.stgitmsg.txt'
    tmpl = templates.get_template('patchdescr.tmpl')

    f = file(fname, 'w+')
    if line:
        print >> f, line
    elif tmpl:
        print >> f, tmpl,
    else:
        print >> f
    print >> f, __comment_prefix, comment
    print >> f, __comment_prefix, \
          'Lines prefixed with "%s" will be automatically removed.' \
          % __comment_prefix
    print >> f, __comment_prefix, \
          'Trailing empty lines will be automatically removed.'

    if show_patch:
       print >> f, __patch_prefix
       # series.get_patch(series.get_current()).get_top()
       git.diff([], series.get_patch(series.get_current()).get_bottom(), None, f)

    #Vim modeline must be near the end.
    print >> f, __comment_prefix, 'vi: set textwidth=75 filetype=diff nobackup:'
    f.close()

    # the editor
    editor = config.get('stgit.editor')
    if editor:
        pass
    elif 'EDITOR' in os.environ:
        editor = os.environ['EDITOR']
    else:
        editor = 'vi'
    editor += ' %s' % fname

    print 'Invoking the editor: "%s"...' % editor,
    sys.stdout.flush()
    print 'done (exit code: %d)' % os.system(editor)

    f = file(fname, 'r+')

    __clean_comments(f)
    f.seek(0)
    result = f.read()

    f.close()
    os.remove(fname)

    return result

#
# Classes
#

class StgitObject:
    """An object with stgit-like properties stored as files in a directory
    """
    def _set_dir(self, dir):
        self.__dir = dir
    def _dir(self):
        return self.__dir

    def create_empty_field(self, name):
        create_empty_file(os.path.join(self.__dir, name))

    def _get_field(self, name, multiline = False):
        id_file = os.path.join(self.__dir, name)
        if os.path.isfile(id_file):
            line = read_string(id_file, multiline)
            if line == '':
                return None
            else:
                return line
        else:
            return None

    def _set_field(self, name, value, multiline = False):
        fname = os.path.join(self.__dir, name)
        if value and value != '':
            write_string(fname, value, multiline)
        elif os.path.isfile(fname):
            os.remove(fname)

    
class Patch(StgitObject):
    """Basic patch implementation
    """
    def __init__(self, name, series_dir, refs_dir):
        self.__series_dir = series_dir
        self.__name = name
        self._set_dir(os.path.join(self.__series_dir, self.__name))
        self.__refs_dir = refs_dir
        self.__top_ref_file = os.path.join(self.__refs_dir, self.__name)
        self.__log_ref_file = os.path.join(self.__refs_dir,
                                           self.__name + '.log')

    def create(self):
        os.mkdir(self._dir())
        self.create_empty_field('bottom')
        self.create_empty_field('top')

    def delete(self):
        for f in os.listdir(self._dir()):
            os.remove(os.path.join(self._dir(), f))
        os.rmdir(self._dir())
        os.remove(self.__top_ref_file)
        if os.path.exists(self.__log_ref_file):
            os.remove(self.__log_ref_file)

    def get_name(self):
        return self.__name

    def rename(self, newname):
        olddir = self._dir()
        old_top_ref_file = self.__top_ref_file
        old_log_ref_file = self.__log_ref_file
        self.__name = newname
        self._set_dir(os.path.join(self.__series_dir, self.__name))
        self.__top_ref_file = os.path.join(self.__refs_dir, self.__name)
        self.__log_ref_file = os.path.join(self.__refs_dir,
                                           self.__name + '.log')

        os.rename(olddir, self._dir())
        os.rename(old_top_ref_file, self.__top_ref_file)
        if os.path.exists(old_log_ref_file):
            os.rename(old_log_ref_file, self.__log_ref_file)

    def __update_top_ref(self, ref):
        write_string(self.__top_ref_file, ref)

    def __update_log_ref(self, ref):
        write_string(self.__log_ref_file, ref)

    def update_top_ref(self):
        top = self.get_top()
        if top:
            self.__update_top_ref(top)

    def get_old_bottom(self):
        return self._get_field('bottom.old')

    def get_bottom(self):
        return self._get_field('bottom')

    def set_bottom(self, value, backup = False):
        if backup:
            curr = self._get_field('bottom')
            self._set_field('bottom.old', curr)
        self._set_field('bottom', value)

    def get_old_top(self):
        return self._get_field('top.old')

    def get_top(self):
        return self._get_field('top')

    def set_top(self, value, backup = False):
        if backup:
            curr = self._get_field('top')
            self._set_field('top.old', curr)
        self._set_field('top', value)
        self.__update_top_ref(value)

    def restore_old_boundaries(self):
        bottom = self._get_field('bottom.old')
        top = self._get_field('top.old')

        if top and bottom:
            self._set_field('bottom', bottom)
            self._set_field('top', top)
            self.__update_top_ref(top)
            return True
        else:
            return False

    def get_description(self):
        return self._get_field('description', True)

    def set_description(self, line):
        self._set_field('description', line, True)

    def get_authname(self):
        return self._get_field('authname')

    def set_authname(self, name):
        self._set_field('authname', name or git.author().name)

    def get_authemail(self):
        return self._get_field('authemail')

    def set_authemail(self, email):
        self._set_field('authemail', email or git.author().email)

    def get_authdate(self):
        return self._get_field('authdate')

    def set_authdate(self, date):
        self._set_field('authdate', date or git.author().date)

    def get_commname(self):
        return self._get_field('commname')

    def set_commname(self, name):
        self._set_field('commname', name or git.committer().name)

    def get_commemail(self):
        return self._get_field('commemail')

    def set_commemail(self, email):
        self._set_field('commemail', email or git.committer().email)

    def get_log(self):
        return self._get_field('log')

    def set_log(self, value, backup = False):
        self._set_field('log', value)
        self.__update_log_ref(value)


class Series(StgitObject):
    """Class including the operations on series
    """
    def __init__(self, name = None):
        """Takes a series name as the parameter.
        """
        try:
            if name:
                self.__name = name
            else:
                self.__name = git.get_head_file()
            self.__base_dir = basedir.get()
        except git.GitException, ex:
            raise StackException, 'GIT tree not initialised: %s' % ex

        self._set_dir(os.path.join(self.__base_dir, 'patches', self.__name))
        self.__refs_dir = os.path.join(self.__base_dir, 'refs', 'patches',
                                       self.__name)
        self.__base_file = os.path.join(self.__base_dir, 'refs', 'bases',
                                        self.__name)

        self.__applied_file = os.path.join(self._dir(), 'applied')
        self.__unapplied_file = os.path.join(self._dir(), 'unapplied')
        self.__hidden_file = os.path.join(self._dir(), 'hidden')
        self.__current_file = os.path.join(self._dir(), 'current')
        self.__descr_file = os.path.join(self._dir(), 'description')

        # where this series keeps its patches
        self.__patch_dir = os.path.join(self._dir(), 'patches')
        if not os.path.isdir(self.__patch_dir):
            self.__patch_dir = self._dir()

        # if no __refs_dir, create and populate it (upgrade old repositories)
        if self.is_initialised() and not os.path.isdir(self.__refs_dir):
            os.makedirs(self.__refs_dir)
            for patch in self.get_applied() + self.get_unapplied():
                self.get_patch(patch).update_top_ref()

        # trash directory
        self.__trash_dir = os.path.join(self._dir(), 'trash')
        if self.is_initialised() and not os.path.isdir(self.__trash_dir):
            os.makedirs(self.__trash_dir)

    def __patch_name_valid(self, name):
        """Raise an exception if the patch name is not valid.
        """
        if not name or re.search('[^\w.-]', name):
            raise StackException, 'Invalid patch name: "%s"' % name

    def get_branch(self):
        """Return the branch name for the Series object
        """
        return self.__name

    def __set_current(self, name):
        """Sets the topmost patch
        """
        self._set_field('current', name)

    def get_patch(self, name):
        """Return a Patch object for the given name
        """
        return Patch(name, self.__patch_dir, self.__refs_dir)

    def get_current_patch(self):
        """Return a Patch object representing the topmost patch, or
        None if there is no such patch."""
        crt = self.get_current()
        if not crt:
            return None
        return Patch(crt, self.__patch_dir, self.__refs_dir)

    def get_current(self):
        """Return the name of the topmost patch, or None if there is
        no such patch."""
        name = self._get_field('current')
        if name == '':
            return None
        else:
            return name

    def get_applied(self):
        if not os.path.isfile(self.__applied_file):
            raise StackException, 'Branch "%s" not initialised' % self.__name
        f = file(self.__applied_file)
        names = [line.strip() for line in f.readlines()]
        f.close()
        return names

    def get_unapplied(self):
        if not os.path.isfile(self.__unapplied_file):
            raise StackException, 'Branch "%s" not initialised' % self.__name
        f = file(self.__unapplied_file)
        names = [line.strip() for line in f.readlines()]
        f.close()
        return names

    def get_hidden(self):
        if not os.path.isfile(self.__hidden_file):
            return []
        f = file(self.__hidden_file)
        names = [line.strip() for line in f.readlines()]
        f.close()
        return names

    def get_base_file(self):
        self.__begin_stack_check()
        return self.__base_file

    def get_protected(self):
        return os.path.isfile(os.path.join(self._dir(), 'protected'))

    def protect(self):
        protect_file = os.path.join(self._dir(), 'protected')
        if not os.path.isfile(protect_file):
            create_empty_file(protect_file)

    def unprotect(self):
        protect_file = os.path.join(self._dir(), 'protected')
        if os.path.isfile(protect_file):
            os.remove(protect_file)

    def get_description(self):
        return self._get_field('description') or ''

    def set_description(self, line):
        self._set_field('description', line)

    def get_parent_remote(self):
        value = config.get('branch.%s.remote' % self.__name)
        if value:
            return value
        elif 'origin' in git.remotes_list():
            # FIXME: this is for compatibility only.  Should be
            # dropped when all relevant commands record this info.
            return 'origin'
        else:
            raise StackException, 'Cannot find a parent remote for "%s"' % self.__name

    def __set_parent_remote(self, remote):
        value = config.set('branch.%s.remote' % self.__name, remote)

    def get_parent_branch(self):
        value = config.get('branch.%s.merge' % self.__name)
        if value:
            return value
        elif git.rev_parse('heads/origin'):
            # FIXME: this is for compatibility only.  Should be
            # dropped when all relevant commands record this info.
            return 'heads/origin'
        else:
            raise StackException, 'Cannot find a parent branch for "%s"' % self.__name

    def __set_parent_branch(self, name):
        config.set('branch.%s.merge' % self.__name, name)

    def set_parent(self, remote, localbranch):
        if localbranch:
            self.__set_parent_branch(localbranch)
            if remote:
                self.__set_parent_remote(remote)
        elif remote:
            raise StackException, 'Remote "%s" without a branch cannot be used as parent' % remote

    def __patch_is_current(self, patch):
        return patch.get_name() == self.get_current()

    def patch_applied(self, name):
        """Return true if the patch exists in the applied list
        """
        return name in self.get_applied()

    def patch_unapplied(self, name):
        """Return true if the patch exists in the unapplied list
        """
        return name in self.get_unapplied()

    def patch_hidden(self, name):
        """Return true if the patch is hidden.
        """
        return name in self.get_hidden()

    def patch_exists(self, name):
        """Return true if there is a patch with the given name, false
        otherwise."""
        return self.patch_applied(name) or self.patch_unapplied(name)

    def __begin_stack_check(self):
        """Save the current HEAD into .git/refs/heads/base if the stack
        is empty
        """
        if len(self.get_applied()) == 0:
            head = git.get_head()
            write_string(self.__base_file, head)

    def __end_stack_check(self):
        """Remove .git/refs/heads/base if the stack is empty.
        This warning should never happen
        """
        if len(self.get_applied()) == 0 \
           and read_string(self.__base_file) != git.get_head():
            print 'Warning: stack empty but the HEAD and base are different'

    def head_top_equal(self):
        """Return true if the head and the top are the same
        """
        crt = self.get_current_patch()
        if not crt:
            # we don't care, no patches applied
            return True
        return git.get_head() == crt.get_top()

    def is_initialised(self):
        """Checks if series is already initialised
        """
        return os.path.isdir(self.__patch_dir)

    def init(self, create_at=False, parent_remote=None, parent_branch=None):
        """Initialises the stgit series
        """
        bases_dir = os.path.join(self.__base_dir, 'refs', 'bases')

        if os.path.exists(self.__patch_dir):
            raise StackException, self.__patch_dir + ' already exists'
        if os.path.exists(self.__refs_dir):
            raise StackException, self.__refs_dir + ' already exists'
        if os.path.exists(self.__base_file):
            raise StackException, self.__base_file + ' already exists'

        if (create_at!=False):
            git.create_branch(self.__name, create_at)

        os.makedirs(self.__patch_dir)

        self.set_parent(parent_remote, parent_branch)
        
        create_dirs(bases_dir)

        self.create_empty_field('applied')
        self.create_empty_field('unapplied')
        self.create_empty_field('description')
        os.makedirs(os.path.join(self._dir(), 'patches'))
        os.makedirs(self.__refs_dir)
        self.__begin_stack_check()

    def convert(self):
        """Either convert to use a separate patch directory, or
        unconvert to place the patches in the same directory with
        series control files
        """
        if self.__patch_dir == self._dir():
            print 'Converting old-style to new-style...',
            sys.stdout.flush()

            self.__patch_dir = os.path.join(self._dir(), 'patches')
            os.makedirs(self.__patch_dir)

            for p in self.get_applied() + self.get_unapplied():
                src = os.path.join(self._dir(), p)
                dest = os.path.join(self.__patch_dir, p)
                os.rename(src, dest)

            print 'done'

        else:
            print 'Converting new-style to old-style...',
            sys.stdout.flush()

            for p in self.get_applied() + self.get_unapplied():
                src = os.path.join(self.__patch_dir, p)
                dest = os.path.join(self._dir(), p)
                os.rename(src, dest)

            if not os.listdir(self.__patch_dir):
                os.rmdir(self.__patch_dir)
                print 'done'
            else:
                print 'Patch directory %s is not empty.' % self.__name

            self.__patch_dir = self._dir()

    def rename(self, to_name):
        """Renames a series
        """
        to_stack = Series(to_name)

        if to_stack.is_initialised():
            raise StackException, '"%s" already exists' % to_stack.get_branch()
        if os.path.exists(to_stack.__base_file):
            os.remove(to_stack.__base_file)

        git.rename_branch(self.__name, to_name)

        if os.path.isdir(self._dir()):
            rename(os.path.join(self.__base_dir, 'patches'),
                   self.__name, to_stack.__name)
        if os.path.exists(self.__base_file):
            rename(os.path.join(self.__base_dir, 'refs', 'bases'),
                   self.__name, to_stack.__name)
        if os.path.exists(self.__refs_dir):
            rename(os.path.join(self.__base_dir, 'refs', 'patches'),
                   self.__name, to_stack.__name)

        self.__init__(to_name)

    def clone(self, target_series):
        """Clones a series
        """
        try:
            # allow cloning of branches not under StGIT control
            base = read_string(self.get_base_file())
        except:
            base = git.get_head()
        Series(target_series).init(create_at = base)
        new_series = Series(target_series)

        # generate an artificial description file
        new_series.set_description('clone of "%s"' % self.__name)

        # clone self's entire series as unapplied patches
        try:
            # allow cloning of branches not under StGIT control
            applied = self.get_applied()
            unapplied = self.get_unapplied()
            patches = applied + unapplied
            patches.reverse()
        except:
            patches = applied = unapplied = []
        for p in patches:
            patch = self.get_patch(p)
            new_series.new_patch(p, message = patch.get_description(),
                                 can_edit = False, unapplied = True,
                                 bottom = patch.get_bottom(),
                                 top = patch.get_top(),
                                 author_name = patch.get_authname(),
                                 author_email = patch.get_authemail(),
                                 author_date = patch.get_authdate())

        # fast forward the cloned series to self's top
        new_series.forward_patches(applied)

    def delete(self, force = False):
        """Deletes an stgit series
        """
        if self.is_initialised():
            patches = self.get_unapplied() + self.get_applied()
            if not force and patches:
                raise StackException, \
                      'Cannot delete: the series still contains patches'
            for p in patches:
                Patch(p, self.__patch_dir, self.__refs_dir).delete()

            # remove the trash directory
            for fname in os.listdir(self.__trash_dir):
                os.remove(fname)
            os.rmdir(self.__trash_dir)

            # FIXME: find a way to get rid of those manual removals
            # (move functionnality to StgitObject ?)
            if os.path.exists(self.__applied_file):
                os.remove(self.__applied_file)
            if os.path.exists(self.__unapplied_file):
                os.remove(self.__unapplied_file)
            if os.path.exists(self.__hidden_file):
                os.remove(self.__hidden_file)
            if os.path.exists(self.__current_file):
                os.remove(self.__current_file)
            if os.path.exists(self.__descr_file):
                os.remove(self.__descr_file)
            if not os.listdir(self.__patch_dir):
                os.rmdir(self.__patch_dir)
            else:
                print 'Patch directory %s is not empty.' % self.__name
            if not os.listdir(self._dir()):
                remove_dirs(os.path.join(self.__base_dir, 'patches'),
                            self.__name)
            else:
                print 'Series directory %s is not empty.' % self.__name
            if not os.listdir(self.__refs_dir):
                remove_dirs(os.path.join(self.__base_dir, 'refs', 'patches'),
                            self.__name)
            else:
                print 'Refs directory %s is not empty.' % self.__refs_dir

        if os.path.exists(self.__base_file):
            remove_file_and_dirs(
                os.path.join(self.__base_dir, 'refs', 'bases'), self.__name)

    def refresh_patch(self, files = None, message = None, edit = False,
                      show_patch = False,
                      cache_update = True,
                      author_name = None, author_email = None,
                      author_date = None,
                      committer_name = None, committer_email = None,
                      backup = False, sign_str = None, log = 'refresh'):
        """Generates a new commit for the given patch
        """
        name = self.get_current()
        if not name:
            raise StackException, 'No patches applied'

        patch = Patch(name, self.__patch_dir, self.__refs_dir)

        descr = patch.get_description()
        if not (message or descr):
            edit = True
            descr = ''
        elif message:
            descr = message

        if not message and edit:
            descr = edit_file(self, descr.rstrip(), \
                              'Please edit the description for patch "%s" ' \
                              'above.' % name, show_patch)

        if not author_name:
            author_name = patch.get_authname()
        if not author_email:
            author_email = patch.get_authemail()
        if not author_date:
            author_date = patch.get_authdate()
        if not committer_name:
            committer_name = patch.get_commname()
        if not committer_email:
            committer_email = patch.get_commemail()

        if sign_str:
            descr = '%s\n%s: %s <%s>\n' % (descr.rstrip(), sign_str,
                                           committer_name, committer_email)

        bottom = patch.get_bottom()

        commit_id = git.commit(files = files,
                               message = descr, parents = [bottom],
                               cache_update = cache_update,
                               allowempty = True,
                               author_name = author_name,
                               author_email = author_email,
                               author_date = author_date,
                               committer_name = committer_name,
                               committer_email = committer_email)

        patch.set_bottom(bottom, backup = backup)
        patch.set_top(commit_id, backup = backup)
        patch.set_description(descr)
        patch.set_authname(author_name)
        patch.set_authemail(author_email)
        patch.set_authdate(author_date)
        patch.set_commname(committer_name)
        patch.set_commemail(committer_email)

        if log:
            self.log_patch(patch, log)

        return commit_id

    def undo_refresh(self):
        """Undo the patch boundaries changes caused by 'refresh'
        """
        name = self.get_current()
        assert(name)

        patch = Patch(name, self.__patch_dir, self.__refs_dir)
        old_bottom = patch.get_old_bottom()
        old_top = patch.get_old_top()

        # the bottom of the patch is not changed by refresh. If the
        # old_bottom is different, there wasn't any previous 'refresh'
        # command (probably only a 'push')
        if old_bottom != patch.get_bottom() or old_top == patch.get_top():
            raise StackException, 'No undo information available'

        git.reset(tree_id = old_top, check_out = False)
        if patch.restore_old_boundaries():
            self.log_patch(patch, 'undo')

    def new_patch(self, name, message = None, can_edit = True,
                  unapplied = False, show_patch = False,
                  top = None, bottom = None,
                  author_name = None, author_email = None, author_date = None,
                  committer_name = None, committer_email = None,
                  before_existing = False, refresh = True):
        """Creates a new patch
        """
        self.__patch_name_valid(name)

        if self.patch_applied(name) or self.patch_unapplied(name):
            raise StackException, 'Patch "%s" already exists' % name

        if not message and can_edit:
            descr = edit_file(self, None, \
                              'Please enter the description for patch "%s" ' \
                              'above.' % name, show_patch)
        else:
            descr = message

        head = git.get_head()

        self.__begin_stack_check()

        patch = Patch(name, self.__patch_dir, self.__refs_dir)
        patch.create()

        if bottom:
            patch.set_bottom(bottom)
        else:
            patch.set_bottom(head)
        if top:
            patch.set_top(top)
        else:
            patch.set_top(head)

        patch.set_description(descr)
        patch.set_authname(author_name)
        patch.set_authemail(author_email)
        patch.set_authdate(author_date)
        patch.set_commname(committer_name)
        patch.set_commemail(committer_email)

        if unapplied:
            self.log_patch(patch, 'new')

            patches = [patch.get_name()] + self.get_unapplied()

            f = file(self.__unapplied_file, 'w+')
            f.writelines([line + '\n' for line in patches])
            f.close()
        elif before_existing:
            self.log_patch(patch, 'new')

            insert_string(self.__applied_file, patch.get_name())
            if not self.get_current():
                self.__set_current(name)
        else:
            append_string(self.__applied_file, patch.get_name())
            self.__set_current(name)
            if refresh:
                self.refresh_patch(cache_update = False, log = 'new')

    def delete_patch(self, name):
        """Deletes a patch
        """
        self.__patch_name_valid(name)
        patch = Patch(name, self.__patch_dir, self.__refs_dir)

        if self.__patch_is_current(patch):
            self.pop_patch(name)
        elif self.patch_applied(name):
            raise StackException, 'Cannot remove an applied patch, "%s", ' \
                  'which is not current' % name
        elif not name in self.get_unapplied():
            raise StackException, 'Unknown patch "%s"' % name

        # save the commit id to a trash file
        write_string(os.path.join(self.__trash_dir, name), patch.get_top())

        patch.delete()

        unapplied = self.get_unapplied()
        unapplied.remove(name)
        f = file(self.__unapplied_file, 'w+')
        f.writelines([line + '\n' for line in unapplied])
        f.close()

        if self.patch_hidden(name):
            self.unhide_patch(name)

        self.__begin_stack_check()

    def forward_patches(self, names):
        """Try to fast-forward an array of patches.

        On return, patches in names[0:returned_value] have been pushed on the
        stack. Apply the rest with push_patch
        """
        unapplied = self.get_unapplied()
        self.__begin_stack_check()

        forwarded = 0
        top = git.get_head()

        for name in names:
            assert(name in unapplied)

            patch = Patch(name, self.__patch_dir, self.__refs_dir)

            head = top
            bottom = patch.get_bottom()
            top = patch.get_top()

            # top != bottom always since we have a commit for each patch
            if head == bottom:
                # reset the backup information. No logging since the
                # patch hasn't changed
                patch.set_bottom(head, backup = True)
                patch.set_top(top, backup = True)

            else:
                head_tree = git.get_commit(head).get_tree()
                bottom_tree = git.get_commit(bottom).get_tree()
                if head_tree == bottom_tree:
                    # We must just reparent this patch and create a new commit
                    # for it
                    descr = patch.get_description()
                    author_name = patch.get_authname()
                    author_email = patch.get_authemail()
                    author_date = patch.get_authdate()
                    committer_name = patch.get_commname()
                    committer_email = patch.get_commemail()

                    top_tree = git.get_commit(top).get_tree()

                    top = git.commit(message = descr, parents = [head],
                                     cache_update = False,
                                     tree_id = top_tree,
                                     allowempty = True,
                                     author_name = author_name,
                                     author_email = author_email,
                                     author_date = author_date,
                                     committer_name = committer_name,
                                     committer_email = committer_email)

                    patch.set_bottom(head, backup = True)
                    patch.set_top(top, backup = True)

                    self.log_patch(patch, 'push(f)')
                else:
                    top = head
                    # stop the fast-forwarding, must do a real merge
                    break

            forwarded+=1
            unapplied.remove(name)

        if forwarded == 0:
            return 0

        git.switch(top)

        append_strings(self.__applied_file, names[0:forwarded])

        f = file(self.__unapplied_file, 'w+')
        f.writelines([line + '\n' for line in unapplied])
        f.close()

        self.__set_current(name)

        return forwarded

    def merged_patches(self, names):
        """Test which patches were merged upstream by reverse-applying
        them in reverse order. The function returns the list of
        patches detected to have been applied. The state of the tree
        is restored to the original one
        """
        patches = [Patch(name, self.__patch_dir, self.__refs_dir)
                   for name in names]
        patches.reverse()

        merged = []
        for p in patches:
            if git.apply_diff(p.get_top(), p.get_bottom()):
                merged.append(p.get_name())
        merged.reverse()

        git.reset()

        return merged

    def push_patch(self, name, empty = False):
        """Pushes a patch on the stack
        """
        unapplied = self.get_unapplied()
        assert(name in unapplied)

        self.__begin_stack_check()

        patch = Patch(name, self.__patch_dir, self.__refs_dir)

        head = git.get_head()
        bottom = patch.get_bottom()
        top = patch.get_top()

        ex = None
        modified = False

        # top != bottom always since we have a commit for each patch
        if empty:
            # just make an empty patch (top = bottom = HEAD). This
            # option is useful to allow undoing already merged
            # patches. The top is updated by refresh_patch since we
            # need an empty commit
            patch.set_bottom(head, backup = True)
            patch.set_top(head, backup = True)
            modified = True
        elif head == bottom:
            # reset the backup information. No need for logging
            patch.set_bottom(bottom, backup = True)
            patch.set_top(top, backup = True)

            git.switch(top)
        else:
            # new patch needs to be refreshed.
            # The current patch is empty after merge.
            patch.set_bottom(head, backup = True)
            patch.set_top(head, backup = True)

            # Try the fast applying first. If this fails, fall back to the
            # three-way merge
            if not git.apply_diff(bottom, top):
                # if git.apply_diff() fails, the patch requires a diff3
                # merge and can be reported as modified
                modified = True

                # merge can fail but the patch needs to be pushed
                try:
                    git.merge(bottom, head, top, recursive = True)
                except git.GitException, ex:
                    print >> sys.stderr, \
                          'The merge failed during "push". ' \
                          'Use "refresh" after fixing the conflicts'

        append_string(self.__applied_file, name)

        unapplied.remove(name)
        f = file(self.__unapplied_file, 'w+')
        f.writelines([line + '\n' for line in unapplied])
        f.close()

        self.__set_current(name)

        # head == bottom case doesn't need to refresh the patch
        if empty or head != bottom:
            if not ex:
                # if the merge was OK and no conflicts, just refresh the patch
                # The GIT cache was already updated by the merge operation
                if modified:
                    log = 'push(m)'
                else:
                    log = 'push'
                self.refresh_patch(cache_update = False, log = log)
            else:
                # we store the correctly merged files only for
                # tracking the conflict history. Note that the
                # git.merge() operations shouls always leave the index
                # in a valid state (i.e. only stage 0 files)
                self.refresh_patch(cache_update = False, log = 'push(c)')
                raise StackException, str(ex)

        return modified

    def undo_push(self):
        name = self.get_current()
        assert(name)

        patch = Patch(name, self.__patch_dir, self.__refs_dir)
        old_bottom = patch.get_old_bottom()
        old_top = patch.get_old_top()

        # the top of the patch is changed by a push operation only
        # together with the bottom (otherwise the top was probably
        # modified by 'refresh'). If they are both unchanged, there
        # was a fast forward
        if old_bottom == patch.get_bottom() and old_top != patch.get_top():
            raise StackException, 'No undo information available'

        git.reset()
        self.pop_patch(name)
        ret = patch.restore_old_boundaries()
        if ret:
            self.log_patch(patch, 'undo')

        return ret

    def pop_patch(self, name, keep = False):
        """Pops the top patch from the stack
        """
        applied = self.get_applied()
        applied.reverse()
        assert(name in applied)

        patch = Patch(name, self.__patch_dir, self.__refs_dir)

        # only keep the local changes
        if keep and not git.apply_diff(git.get_head(), patch.get_bottom()):
            raise StackException, \
                  'Failed to pop patches while preserving the local changes'

        git.switch(patch.get_bottom(), keep)

        # save the new applied list
        idx = applied.index(name) + 1

        popped = applied[:idx]
        popped.reverse()
        unapplied = popped + self.get_unapplied()

        f = file(self.__unapplied_file, 'w+')
        f.writelines([line + '\n' for line in unapplied])
        f.close()

        del applied[:idx]
        applied.reverse()

        f = file(self.__applied_file, 'w+')
        f.writelines([line + '\n' for line in applied])
        f.close()

        if applied == []:
            self.__set_current(None)
        else:
            self.__set_current(applied[-1])

        self.__end_stack_check()

    def empty_patch(self, name):
        """Returns True if the patch is empty
        """
        self.__patch_name_valid(name)
        patch = Patch(name, self.__patch_dir, self.__refs_dir)
        bottom = patch.get_bottom()
        top = patch.get_top()

        if bottom == top:
            return True
        elif git.get_commit(top).get_tree() \
                 == git.get_commit(bottom).get_tree():
            return True

        return False

    def rename_patch(self, oldname, newname):
        self.__patch_name_valid(newname)

        applied = self.get_applied()
        unapplied = self.get_unapplied()

        if oldname == newname:
            raise StackException, '"To" name and "from" name are the same'

        if newname in applied or newname in unapplied:
            raise StackException, 'Patch "%s" already exists' % newname

        if self.patch_hidden(oldname):
            self.unhide_patch(oldname)
            self.hide_patch(newname)

        if oldname in unapplied:
            Patch(oldname, self.__patch_dir, self.__refs_dir).rename(newname)
            unapplied[unapplied.index(oldname)] = newname

            f = file(self.__unapplied_file, 'w+')
            f.writelines([line + '\n' for line in unapplied])
            f.close()
        elif oldname in applied:
            Patch(oldname, self.__patch_dir, self.__refs_dir).rename(newname)
            if oldname == self.get_current():
                self.__set_current(newname)

            applied[applied.index(oldname)] = newname

            f = file(self.__applied_file, 'w+')
            f.writelines([line + '\n' for line in applied])
            f.close()
        else:
            raise StackException, 'Unknown patch "%s"' % oldname

    def log_patch(self, patch, message):
        """Generate a log commit for a patch
        """
        top = git.get_commit(patch.get_top())
        msg = '%s\t%s' % (message, top.get_id_hash())

        old_log = patch.get_log()
        if old_log:
            parents = [old_log]
        else:
            parents = []

        log = git.commit(message = msg, parents = parents,
                         cache_update = False, tree_id = top.get_tree(),
                         allowempty = True)
        patch.set_log(log)

    def hide_patch(self, name):
        """Add the patch to the hidden list.
        """
        if not self.patch_exists(name):
            raise StackException, 'Unknown patch "%s"' % name
        elif self.patch_hidden(name):
            raise StackException, 'Patch "%s" already hidden' % name

        append_string(self.__hidden_file, name)

    def unhide_patch(self, name):
        """Add the patch to the hidden list.
        """
        if not self.patch_exists(name):
            raise StackException, 'Unknown patch "%s"' % name
        hidden = self.get_hidden()
        if not name in hidden:
            raise StackException, 'Patch "%s" not hidden' % name

        hidden.remove(name)

        f = file(self.__hidden_file, 'w+')
        f.writelines([line + '\n' for line in hidden])
        f.close()