# Copyright (C) 2008, One Laptop Per Child
#
# 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; either version 2 of the License, or
# (at your option) any later version.
#
# 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

import os
import logging

MAX_QUERY_LIMIT = 40960
CURRENT_LAYOUT_VERSION = 2

class LayoutManager(object):
    """Provide the logic about how entries are stored inside the datastore
    directory
    """

    def __init__(self):
        profile = os.environ.get('SUGAR_PROFILE', 'default')
        base_dir = os.path.join(os.path.expanduser('~'), '.sugar', profile)

        self._root_path = os.path.join(base_dir, 'datastore')

        if not os.path.exists(self._root_path):
            os.makedirs(self._root_path)

        self._create_if_needed(self.get_checksums_dir())
        self._create_if_needed(self.get_queue_path())

        index_updated_path = os.path.join(self._root_path, 'index_updated')
        if os.path.exists(index_updated_path):
            self._index_updated = True
        elif self._is_empty():
            open(index_updated_path, 'w').close()
            self.set_version(CURRENT_LAYOUT_VERSION)
            self._index_updated = True
        else:
            self._index_updated = False

    def _create_if_needed(self, path):
        if not os.path.exists(path):
            os.makedirs(path)

    def get_version(self):
        version_path = os.path.join(self._root_path, 'version')
        version = 0
        if os.path.exists(version_path):
            try:
                version = int(open(version_path, 'r').read())
            except ValueError:
                logging.exception('Can not read layout version')
                version = 0

        return version

    def set_version(self, version):
        version_path = os.path.join(self._root_path, 'version')
        open(version_path, 'w').write(str(version))

    def get_entry_path(self, uid):
        # os.path.join() is just too slow
        return '%s/%s/%s' % (self._root_path, uid[:2], uid)

    def get_data_path(self, uid):
        return '%s/%s/%s/data' % (self._root_path, uid[:2], uid)

    def get_metadata_path(self, uid):
        return '%s/%s/%s/metadata' % (self._root_path, uid[:2], uid)

    def get_root_path(self):
        return self._root_path

    def get_index_path(self):
        return os.path.join(self._root_path, 'index')

    def get_checksums_dir(self):
        return os.path.join(self._root_path, 'checksums')

    def get_queue_path(self):
        return os.path.join(self.get_checksums_dir(), 'queue')

    def _is_index_updated(self):
        return self._index_updated

    def _set_index_updated(self, index_updated):
        if index_updated != self._index_updated:
            self._index_updated = index_updated

            index_updated_path = os.path.join(self._root_path, 'index_updated')
            if os.path.exists(index_updated_path):
                os.remove(index_updated_path)
            else:
                open(index_updated_path, 'w').close()

    index_updated = property(_is_index_updated, _set_index_updated)

    def find_all(self):
        uids = []
        for f in os.listdir(self._root_path):
            if os.path.isdir(os.path.join(self._root_path, f)) and len(f) == 2:
                for g in os.listdir(os.path.join(self._root_path, f)):
                    if len(g) == 36:
                        uids.append(g)
        return uids

    def _is_empty(self):
        for f in os.listdir(self._root_path):
            if os.path.isdir(os.path.join(self._root_path, f)) and len(f) == 2:
                for g in os.listdir(os.path.join(self._root_path, f)):
                    if len(g) == 36:
                        return False
        return True

_instance = None
def get_instance():
    global _instance
    if _instance is None:
        _instance = LayoutManager()
    return _instance