# -*- coding: utf-8 -*-

# 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 3 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, see <http://www.gnu.org/licenses/>.

"""

kallithea.lib.utils

~~~~~~~~~~~~~~~~~~~

Utilities library for Kallithea

This file was forked by the Kallithea project in July 2014.

Original author and date, and relevant copyright and licensing information is below:

:created_on: Apr 18, 2010

:author: marcink

:copyright: (c) 2013 RhodeCode GmbH, and others.

:license: GPLv3, see LICENSE.md for more details.

"""

import datetime

import logging

import os

import re

import sys

import traceback

import urllib.error

from distutils.version import StrictVersion

import beaker.cache

import mercurial.config

import mercurial.ui

import kallithea.config.conf

from kallithea.lib.exceptions import InvalidCloneUriException

from kallithea.lib.utils2 import ascii_bytes, aslist, get_current_authuser, safe_bytes, safe_str

from kallithea.lib.vcs.backends.git.repository import GitRepository

from kallithea.lib.vcs.backends.hg.repository import MercurialRepository

from kallithea.lib.vcs.conf import settings

from kallithea.lib.vcs.exceptions import RepositoryError, VCSError

from kallithea.lib.vcs.utils.fakemod import create_module

from kallithea.lib.vcs.utils.helpers import get_scm

from kallithea.model import meta

from kallithea.model.db import RepoGroup, Repository, Setting, Ui, User, UserGroup, UserLog

log = logging.getLogger(__name__)

REMOVED_REPO_PAT = re.compile(r'rm__\d{8}_\d{6}_\d{6}_.*')

#==============================================================================

# PERM DECORATOR HELPERS FOR EXTRACTING NAMES FOR PERM CHECKS

#==============================================================================

def get_repo_slug(request):

    _repo = request.environ['pylons.routes_dict'].get('repo_name')

    if _repo:

        _repo = _repo.rstrip('/')

    return _repo

def get_repo_group_slug(request):

    _group = request.environ['pylons.routes_dict'].get('group_name')

    if _group:

        _group = _group.rstrip('/')

    return _group

def get_user_group_slug(request):

    _group = request.environ['pylons.routes_dict'].get('id')

    _group = UserGroup.get(_group)

    if _group:

        return _group.users_group_name

    return None

def _get_permanent_id(s):

    """Helper for decoding stable URLs with repo ID. For a string like '_123'

    return 123.

    """

    by_id_match = re.match(r'^_(\d+)$', s)

    if by_id_match is None:

        return None

    return int(by_id_match.group(1))

def fix_repo_id_name(path):

    """

    Rewrite repo_name for _<ID> permanent URLs.

    Given a path, if the first path element is like _<ID>, return the path with

    this part expanded to the corresponding full repo name, else return the

    provided path.

    """

    first, rest = path, ''

    if '/' in path:

        first, rest_ = path.split('/', 1)

        rest = '/' + rest_

    repo_id = _get_permanent_id(first)

    if repo_id is not None:

        repo = Repository.get(repo_id)

        if repo is not None:

            return repo.repo_name + rest

    return path

def action_logger(user, action, repo, ipaddr='', commit=False):

    """

    Action logger for various actions made by users

    :param user: user that made this action, can be a unique username string or

        object containing user_id attribute

    :param action: action to log, should be on of predefined unique actions for

        easy translations

    :param repo: string name of repository or object containing repo_id,

        that action was made on

    :param ipaddr: optional IP address from what the action was made

    """

    # if we don't get explicit IP address try to get one from registered user

    # in tmpl context var

    if not ipaddr:

        ipaddr = getattr(get_current_authuser(), 'ip_addr', '')

    if getattr(user, 'user_id', None):

        user_obj = User.get(user.user_id)

    elif isinstance(user, str):

        user_obj = User.get_by_username(user)

    else:

        raise Exception('You have to provide a user object or a username')

    if getattr(repo, 'repo_id', None):

        repo_obj = Repository.get(repo.repo_id)

        repo_name = repo_obj.repo_name

    elif isinstance(repo, str):

        repo_name = repo.lstrip('/')

        repo_obj = Repository.get_by_repo_name(repo_name)

    else:

        repo_obj = None

        repo_name = ''

    user_log = UserLog()

    user_log.user_id = user_obj.user_id

    user_log.username = user_obj.username

    user_log.action = action

    user_log.repository = repo_obj

    user_log.repository_name = repo_name

    user_log.action_date = datetime.datetime.now()

    user_log.user_ip = ipaddr

    meta.Session().add(user_log)

    log.info('Logging action:%s on %s by user:%s ip:%s',

             action, repo, user_obj, ipaddr)

    if commit:

        meta.Session().commit()

def get_filesystem_repos(path):

    """

    Scans given path for repos and return (name,(type,path)) tuple

    :param path: path to scan for repositories

    :param recursive: recursive search and return names with subdirs in front

    """

    # remove ending slash for better results

    path = path.rstrip(os.sep)

    log.debug('now scanning in %s', path)

    def isdir(*n):

        return os.path.isdir(os.path.join(*n))

    for root, dirs, _files in os.walk(path):

        recurse_dirs = []

        for subdir in dirs:

            # skip removed repos

            if REMOVED_REPO_PAT.match(subdir):

                continue

            # skip .<something> dirs TODO: rly? then we should prevent creating them ...

            if subdir.startswith('.'):

                continue

            cur_path = os.path.join(root, subdir)

            if isdir(cur_path, '.git'):

                log.warning('ignoring non-bare Git repo: %s', cur_path)

                continue

            if (isdir(cur_path, '.hg') or

                isdir(cur_path, '.svn') or

                isdir(cur_path, 'objects') and (isdir(cur_path, 'refs') or

                                                os.path.isfile(os.path.join(cur_path, 'packed-refs')))):

                if not os.access(cur_path, os.R_OK) or not os.access(cur_path, os.X_OK):

                    log.warning('ignoring repo path without access: %s', cur_path)

                    continue

                if not os.access(cur_path, os.W_OK):

                    log.warning('repo path without write access: %s', cur_path)

                try:

                    scm_info = get_scm(cur_path)

                    assert cur_path.startswith(path)

                    repo_path = cur_path[len(path) + 1:]

                    yield repo_path, scm_info

                    continue # no recursion

                except VCSError:

                    # We should perhaps ignore such broken repos, but especially

                    # the bare git detection is unreliable so we dive into it

                    pass

            recurse_dirs.append(subdir)

        dirs[:] = recurse_dirs

def is_valid_repo_uri(repo_type, url, ui):

    """Check if the url seems like a valid remote repo location

    Raise InvalidCloneUriException if any problems"""

    if repo_type == 'hg':

        if url.startswith('http') or url.startswith('ssh'):

            # initially check if it's at least the proper URL

            # or does it pass basic auth

            try:

                MercurialRepository._check_url(url, ui)

            except urllib.error.URLError as e:

                raise InvalidCloneUriException('URI %s URLError: %s' % (url, e))

        elif url.startswith('svn+http'):

            try:

                from hgsubversion.svnrepo import svnremoterepo

            except ImportError:

                raise InvalidCloneUriException('URI type %s not supported - hgsubversion is not available' % (url,))

            svnremoterepo(ui, url).svn.uuid

        elif url.startswith('git+http'):

            raise InvalidCloneUriException('URI type %s not implemented' % (url,))

        else:

            raise InvalidCloneUriException('URI %s not allowed' % (url,))

    elif repo_type == 'git':

        if url.startswith('http') or url.startswith('git'):

            # initially check if it's at least the proper URL

            # or does it pass basic auth

            try:

                GitRepository._check_url(url)

            except urllib.error.URLError as e:

                raise InvalidCloneUriException('URI %s URLError: %s' % (url, e))

        elif url.startswith('svn+http'):

            raise InvalidCloneUriException('URI type %s not implemented' % (url,))

        elif url.startswith('hg+http'):

            raise InvalidCloneUriException('URI type %s not implemented' % (url,))

        else:

            raise InvalidCloneUriException('URI %s not allowed' % (url))

def is_valid_repo(repo_name, base_path, scm=None):

    """

    Returns True if given path is a valid repository False otherwise.

    If scm param is given also compare if given scm is the same as expected

    from scm parameter

    :param repo_name:

    :param base_path:

    :param scm:

    :return True: if given path is a valid repository

    """

    # TODO: paranoid security checks?

    full_path = os.path.join(base_path, repo_name)

    try:

        scm_ = get_scm(full_path)

        if scm:

            return scm_[0] == scm

        return True

    except VCSError:

        return False

def is_valid_repo_group(repo_group_name, base_path, skip_path_check=False):

    """

    Returns True if given path is a repository group False otherwise

    :param repo_name:

    :param base_path:

    """

    full_path = os.path.join(base_path, repo_group_name)

    # check if it's not a repo

    if is_valid_repo(repo_group_name, base_path):

        return False

    try:

        # we need to check bare git repos at higher level

        # since we might match branches/hooks/info/objects or possible

        # other things inside bare git repo

        get_scm(os.path.dirname(full_path))

        return False

    except VCSError:

        pass

    # check if it's a valid path

    if skip_path_check or os.path.isdir(full_path):

        return True

    return False

# propagated from mercurial documentation

ui_sections = ['alias', 'auth',

                'decode/encode', 'defaults',

                'diff', 'email',

                'extensions', 'format',

                'merge-patterns', 'merge-tools',

                'hooks', 'http_proxy',

                'smtp', 'patch',

                'paths', 'profiling',

                'server', 'trusted',

                'ui', 'web', ]

def make_ui(repo_path=None):

    """

    Create an Mercurial 'ui' object based on database Ui settings, possibly

    augmenting with content from a hgrc file.

    """

    baseui = mercurial.ui.ui()

    # clean the baseui object

    baseui._ocfg = mercurial.config.config()

    baseui._ucfg = mercurial.config.config()

    baseui._tcfg = mercurial.config.config()

    sa = meta.Session()

        if ui_.ui_active:

            log.debug('config from db: [%s] %s=%r', ui_.ui_section,

                      ui_.ui_key, ui_.ui_value)

            baseui.setconfig(ascii_bytes(ui_.ui_section), ascii_bytes(ui_.ui_key),

                             b'' if ui_.ui_value is None else safe_bytes(ui_.ui_value))

    # force set push_ssl requirement to False, Kallithea handles that

    baseui.setconfig(b'web', b'push_ssl', False)

    baseui.setconfig(b'web', b'allow_push', b'*')

    # prevent interactive questions for ssh password / passphrase

    ssh = baseui.config(b'ui', b'ssh', default=b'ssh')

    baseui.setconfig(b'ui', b'ssh', b'%s -oBatchMode=yes -oIdentitiesOnly=yes' % ssh)

    # push / pull hooks

    baseui.setconfig(b'hooks', b'changegroup.kallithea_log_push_action', b'python:kallithea.lib.hooks.log_push_action')

    baseui.setconfig(b'hooks', b'outgoing.kallithea_log_pull_action', b'python:kallithea.lib.hooks.log_pull_action')

    if repo_path is not None:

        hgrc_path = os.path.join(repo_path, '.hg', 'hgrc')

        if os.path.isfile(hgrc_path):

            log.debug('reading hgrc from %s', hgrc_path)

            cfg = mercurial.config.config()

            cfg.read(safe_bytes(hgrc_path))

            for section in ui_sections:

                for k, v in cfg.items(section):

                    log.debug('config from file: [%s] %s=%s', section, k, v)

                    baseui.setconfig(ascii_bytes(section), ascii_bytes(k), safe_bytes(v))

        else:

            log.debug('hgrc file is not present at %s, skipping...', hgrc_path)

    assert baseui.plain()  # set by hgcompat.monkey_do (invoked from import of vcs.backends.hg) to minimize potential impact of loading config files

    return baseui

def set_app_settings(config):

    """

    Updates app config with new settings from database

    :param config:

    """

    hgsettings = Setting.get_app_settings()

    for k, v in hgsettings.items():

        config[k] = v

def set_vcs_config(config):

    """

    Patch VCS config with some Kallithea specific stuff

    :param config: kallithea.CONFIG

    """

    settings.BACKENDS = {

        'hg': 'kallithea.lib.vcs.backends.hg.MercurialRepository',

        'git': 'kallithea.lib.vcs.backends.git.GitRepository',

    }

    settings.GIT_EXECUTABLE_PATH = config.get('git_path', 'git')

    settings.GIT_REV_FILTER = config.get('git_rev_filter', '--all').strip()

    settings.DEFAULT_ENCODINGS = aslist(config.get('default_encoding',

                                                        'utf-8'), sep=',')

def set_indexer_config(config):

    """

    Update Whoosh index mapping

    :param config: kallithea.CONFIG

    """

    log.debug('adding extra into INDEX_EXTENSIONS')

    kallithea.config.conf.INDEX_EXTENSIONS.extend(re.split(r'\s+', config.get('index.extensions', '')))

    log.debug('adding extra into INDEX_FILENAMES')

    kallithea.config.conf.INDEX_FILENAMES.extend(re.split(r'\s+', config.get('index.filenames', '')))

def map_groups(path):

    """

    Given a full path to a repository, create all nested groups that this

    repo is inside. This function creates parent-child relationships between

    groups and creates default perms for all new groups.

    :param paths: full path to repository

    """

    from kallithea.model.repo_group import RepoGroupModel

    sa = meta.Session()

    groups = path.split(Repository.url_sep())

    parent = None

    group = None

    # last element is repo in nested groups structure

    groups = groups[:-1]

    rgm = RepoGroupModel()

    owner = User.get_first_admin()

    for lvl, group_name in enumerate(groups):

        group_name = '/'.join(groups[:lvl] + [group_name])

        group = RepoGroup.get_by_group_name(group_name)

        desc = '%s group' % group_name

        # skip folders that are now removed repos

        if REMOVED_REPO_PAT.match(group_name):

            break

        if group is None:

            log.debug('creating group level: %s group_name: %s',

                      lvl, group_name)

            group = RepoGroup(group_name, parent)

            group.group_description = desc

            group.owner = owner

            sa.add(group)

            rgm._create_default_perms(group)

            sa.flush()

        parent = group

    return group

def repo2db_mapper(initial_repo_dict, remove_obsolete=False,

                   install_git_hooks=False, user=None, overwrite_git_hooks=False):

    """

    maps all repos given in initial_repo_dict, non existing repositories

    are created, if remove_obsolete is True it also check for db entries

    that are not in initial_repo_dict and removes them.

    :param initial_repo_dict: mapping with repositories found by scanning methods

    :param remove_obsolete: check for obsolete entries in database

    :param install_git_hooks: if this is True, also check and install git hook

        for a repo if missing

    :param overwrite_git_hooks: if this is True, overwrite any existing git hooks

        that may be encountered (even if user-deployed)

    """

    from kallithea.model.repo import RepoModel

    from kallithea.model.scm import ScmModel

    sa = meta.Session()

    repo_model = RepoModel()

    if user is None:

        user = User.get_first_admin()

    added = []

    # creation defaults

    defs = Setting.get_default_repo_settings(strip_prefix=True)

    enable_statistics = defs.get('repo_enable_statistics')

    enable_downloads = defs.get('repo_enable_downloads')

    private = defs.get('repo_private')

    for name, repo in initial_repo_dict.items():

        group = map_groups(name)

        db_repo = repo_model.get_by_repo_name(name)

        # found repo that is on filesystem not in Kallithea database

        if not db_repo:

            log.info('repository %s not found, creating now', name)

            added.append(name)

            desc = (repo.description

                    if repo.description != 'unknown'

                    else '%s repository' % name)

            new_repo = repo_model._create_repo(

                repo_name=name,

                repo_type=repo.alias,

                description=desc,

                repo_group=getattr(group, 'group_id', None),

                owner=user,

                enable_downloads=enable_downloads,

                enable_statistics=enable_statistics,

                private=private,

                state=Repository.STATE_CREATED

            )

            sa.commit()

            # we added that repo just now, and make sure it has githook

            # installed, and updated server info

            if new_repo.repo_type == 'git':

                git_repo = new_repo.scm_instance

                ScmModel().install_git_hooks(git_repo)

                # update repository server-info

                log.debug('Running update server info')

                git_repo._update_server_info()

            new_repo.update_changeset_cache()

        elif install_git_hooks:

            if db_repo.repo_type == 'git':

                ScmModel().install_git_hooks(db_repo.scm_instance, force_create=overwrite_git_hooks)

    removed = []

    # remove from database those repositories that are not in the filesystem

    for repo in sa.query(Repository).all():

        if repo.repo_name not in initial_repo_dict:

            if remove_obsolete:

                log.debug("Removing non-existing repository found in db `%s`",

                          repo.repo_name)

                try:

                    RepoModel().delete(repo, forks='detach', fs_remove=False)

                    sa.commit()

                except Exception:

                    #don't hold further removals on error

                    log.error(traceback.format_exc())

                    sa.rollback()

            removed.append(repo.repo_name)

    return added, removed

def load_rcextensions(root_path):

    path = os.path.join(root_path, 'rcextensions', '__init__.py')

    if os.path.isfile(path):

        rcext = create_module('rc', path)

        EXT = kallithea.EXTENSIONS = rcext

        log.debug('Found rcextensions now loading %s...', rcext)

        # Additional mappings that are not present in the pygments lexers

        kallithea.config.conf.LANGUAGES_EXTENSIONS_MAP.update(getattr(EXT, 'EXTRA_MAPPINGS', {}))

        # OVERRIDE OUR EXTENSIONS FROM RC-EXTENSIONS (if present)

        if getattr(EXT, 'INDEX_EXTENSIONS', []):

            log.debug('settings custom INDEX_EXTENSIONS')

            kallithea.config.conf.INDEX_EXTENSIONS = getattr(EXT, 'INDEX_EXTENSIONS', [])

        # ADDITIONAL MAPPINGS

        log.debug('adding extra into INDEX_EXTENSIONS')

        kallithea.config.conf.INDEX_EXTENSIONS.extend(getattr(EXT, 'EXTRA_INDEX_EXTENSIONS', []))

        # auto check if the module is not missing any data, set to default if is

        # this will help autoupdate new feature of rcext module

        #from kallithea.config import rcextensions

        #for k in dir(rcextensions):

        #    if not k.startswith('_') and not hasattr(EXT, k):

        #        setattr(EXT, k, getattr(rcextensions, k))

#==============================================================================

# MISC

#==============================================================================

git_req_ver = StrictVersion('1.7.4')

def check_git_version():

    """

    Checks what version of git is installed on the system, and raise a system exit

    if it's too old for Kallithea to work properly.

    """

    if 'git' not in kallithea.BACKENDS:

        return None

    if not settings.GIT_EXECUTABLE_PATH:

        log.warning('No git executable configured - check "git_path" in the ini file.')

        return None

    try:

        stdout, stderr = GitRepository._run_git_command(['--version'])

    except RepositoryError as e:

        # message will already have been logged as error

        log.warning('No working git executable found - check "git_path" in the ini file.')

        return None

    if stderr:

        log.warning('Error/stderr from "%s --version":\n%s', settings.GIT_EXECUTABLE_PATH, safe_str(stderr))

    if not stdout:

        log.warning('No working git executable found - check "git_path" in the ini file.')

        return None

    output = safe_str(stdout).strip()

    m = re.search(r"\d+.\d+.\d+", output)

    if m:

        ver = StrictVersion(m.group(0))

        log.debug('Git executable: "%s", version %s (parsed from: "%s")',

                  settings.GIT_EXECUTABLE_PATH, ver, output)

        if ver < git_req_ver:

            log.error('Kallithea detected %s version %s, which is too old '

                      'for the system to function properly. '

                      'Please upgrade to version %s or later. '

                      'If you strictly need Mercurial repositories, you can '

                      'clear the "git_path" setting in the ini file.',

                      settings.GIT_EXECUTABLE_PATH, ver, git_req_ver)

            log.error("Terminating ...")

            sys.exit(1)

    else:

        ver = StrictVersion('0.0.0')

        log.warning('Error finding version number in "%s --version" stdout:\n%s',

                    settings.GIT_EXECUTABLE_PATH, output)

    return ver

#===============================================================================

# CACHE RELATED METHODS

#===============================================================================

def conditional_cache(region, prefix, condition, func):

    """

    Conditional caching function use like::

        def _c(arg):

            #heavy computation function

            return data

        # depending from condition the compute is wrapped in cache or not

        compute = conditional_cache('short_term', 'cache_desc', condition=True, func=func)

        return compute(arg)

    :param region: name of cache region

    :param prefix: cache region prefix

    :param condition: condition for cache to be triggered, and return data cached

    :param func: wrapped heavy function to compute

    """

    wrapped = func

    if condition:

        log.debug('conditional_cache: True, wrapping call of '

                  'func: %s into %s region cache' % (region, func))

        wrapped = beaker.cache._cache_decorate((prefix,), None, None, region)(func)

    return wrapped

# -*- coding: utf-8 -*-

# 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 3 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, see <http://www.gnu.org/licenses/>.

"""

kallithea.model.db

~~~~~~~~~~~~~~~~~~

Database Models for Kallithea

This file was forked by the Kallithea project in July 2014.

Original author and date, and relevant copyright and licensing information is below:

:created_on: Apr 08, 2010

:author: marcink

:copyright: (c) 2013 RhodeCode GmbH, and others.

:license: GPLv3, see LICENSE.md for more details.

"""

import base64

import collections

import datetime

import functools

import hashlib

import logging

import os

import time

import traceback

import ipaddr

import sqlalchemy

from beaker.cache import cache_region, region_invalidate

from sqlalchemy import Boolean, Column, DateTime, Float, ForeignKey, Index, Integer, LargeBinary, String, Unicode, UnicodeText, UniqueConstraint

from sqlalchemy.ext.hybrid import hybrid_property

from sqlalchemy.orm import class_mapper, joinedload, relationship, validates

from tg.i18n import lazy_ugettext as _

from webob.exc import HTTPNotFound

import kallithea

from kallithea.lib import ext_json

from kallithea.lib.caching_query import FromCache

from kallithea.lib.exceptions import DefaultUserException

from kallithea.lib.utils2 import (Optional, ascii_bytes, aslist, get_changeset_safe, get_clone_url, remove_prefix, safe_bytes, safe_int, safe_str, str2bool,

                                  urlreadable)

from kallithea.lib.vcs import get_backend

from kallithea.lib.vcs.backends.base import EmptyChangeset

from kallithea.lib.vcs.utils.helpers import get_scm

from kallithea.lib.vcs.utils.lazy import LazyProperty

from kallithea.model.meta import Base, Session

URL_SEP = '/'

log = logging.getLogger(__name__)

#==============================================================================

# BASE CLASSES

#==============================================================================

def _hash_key(k):

    return hashlib.md5(safe_bytes(k)).hexdigest()

class BaseDbModel(object):

    """

    Base Model for all classes

    """

    @classmethod

    def _get_keys(cls):

        """return column names for this model """

        # Note: not a normal dict - iterator gives "users.firstname", but keys gives "firstname"

        return class_mapper(cls).c.keys()

    def get_dict(self):

        """

        return dict with keys and values corresponding

        to this model data """

        d = {}

        for k in self._get_keys():

            d[k] = getattr(self, k)

        # also use __json__() if present to get additional fields

        _json_attr = getattr(self, '__json__', None)

        if _json_attr:

            # update with attributes from __json__

            if callable(_json_attr):

                _json_attr = _json_attr()

            for k, val in _json_attr.items():

                d[k] = val

        return d

    def get_appstruct(self):

        """return list with keys and values tuples corresponding

        to this model data """

        return [

            (k, getattr(self, k))

            for k in self._get_keys()

        ]

    def populate_obj(self, populate_dict):

        """populate model with data from given populate_dict"""

        for k in self._get_keys():

            if k in populate_dict:

                setattr(self, k, populate_dict[k])

    @classmethod

    def query(cls):

        return Session().query(cls)

    @classmethod

    def get(cls, id_):

        if id_:

            return cls.query().get(id_)

    @classmethod

    def guess_instance(cls, value, callback=None):

        """Haphazardly attempt to convert `value` to a `cls` instance.

        If `value` is None or already a `cls` instance, return it. If `value`

        is a number (or looks like one if you squint just right), assume it's

        a database primary key and let SQLAlchemy sort things out. Otherwise,

        fall back to resolving it using `callback` (if specified); this could

        e.g. be a function that looks up instances by name (though that won't

        work if the name begins with a digit). Otherwise, raise Exception.

        """

        if value is None:

            return None

        if isinstance(value, cls):

            return value

        if isinstance(value, int):

            return cls.get(value)

        if isinstance(value, str) and value.isdigit():

            return cls.get(int(value))

        if callback is not None:

            return callback(value)

        raise Exception(

            'given object must be int, long or Instance of %s '

            'got %s, no callback provided' % (cls, type(value))

        )

    @classmethod

    def get_or_404(cls, id_):

        try:

            id_ = int(id_)

        except (TypeError, ValueError):

            raise HTTPNotFound

        res = cls.query().get(id_)

        if res is None:

            raise HTTPNotFound

        return res

    @classmethod

    def delete(cls, id_):

        obj = cls.query().get(id_)

        Session().delete(obj)

    def __repr__(self):

        return '<DB:%s>' % (self.__class__.__name__)