# repository.py -- For dealing wih git repositories.
# Copyright (C) 2007 James Westby <jw+debian@jameswestby.net>
# 
# 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; version 2
# of the License.
# 
# 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 Street, Fifth Floor, Boston,
# MA  02110-1301, USA.

import os

from objects import ShaFile

objectdir = 'objects'
symref = 'ref: '

class Repository(object):

  ref_locs = ['', 'refs', 'refs/tags', 'refs/heads', 'refs/remotes']

  def __init__(self, root):
    self._basedir = root

  def basedir(self):
    return self._basedir

  def object_dir(self):
    return os.path.join(self.basedir(), objectdir)

  def _get_ref(self, file):
    f = open(file, 'rb')
    try:
      contents = f.read()
      if contents.startswith(symref):
        ref = contents[len(symref):]
        if ref[-1] == '\n':
          ref = ref[:-1]
        return self.ref(ref)
      assert len(contents) == 41, 'Invalid ref'
      return contents[:-1]
    finally:
      f.close()

  def ref(self, name):
    for dir in self.ref_locs:
      file = os.path.join(self.basedir(), dir, name)
      if os.path.exists(file):
        return self._get_ref(file)

  def head(self):
    return self.ref('HEAD')

  def get_object(self, sha):
    assert len(sha) == 40, "Incorrect sha length"
    dir = sha[:2]
    file = sha[2:]
    path = os.path.join(self.object_dir(), dir, file)
    if not os.path.exists(path):
      return None
    return ShaFile.from_file(path)