# -*- coding: utf-8 -*-
#
# Copyright (C) 2007-2009 Edgewall Software
# Copyright (C) 2007 Alec Thomas <alec@swapoff.org>
# All rights reserved.
#
# This software is licensed as described in the file COPYING, which
# you should have received as part of this distribution. The terms
# are also available at http://trac.edgewall.org/wiki/TracLicense.
#
# This software consists of voluntary contributions made by many
# individuals. For the exact contribution history, see the revision
# history and logs, available at http://trac.edgewall.org/log/.
#
# Author: Alec Thomas <alec@swapoff.org>

from fnmatch import fnmatch
from itertools import groupby
import os

from trac.core import *
from trac.config import Option
from trac.perm import PermissionSystem, IPermissionPolicy

ConfigObj = None
try:
    from configobj import ConfigObj
except ImportError:
    pass


class AuthzPolicy(Component):
    """Permission policy using an authz-like configuration file.
    
    Refer to SVN documentation for syntax of the authz file. Groups are
    supported.
    
    As the fine-grained permissions brought by this permission policy are
    often used in complement of the other pemission policies (like the
    `DefaultPermissionPolicy`), there's no need to redefine all the
    permissions here. Only additional rights or restrictions should be added.
    
    === Installation ===
    Note that this plugin requires the `configobj` package:
    
        http://www.voidspace.org.uk/python/configobj.html
    
    You should be able to install it by doing a simple `easy_install configobj`
    
    Enabling this policy requires listing it in `trac.ini:
    {{{
    [trac]
    permission_policies = AuthzPolicy, DefaultPermissionPolicy
    
    [authz_policy]
    authz_file = conf/authzpolicy.conf
    }}}
    
    This means that the `AuthzPolicy` permissions will be checked first, and
    only if no rule is found will the `DefaultPermissionPolicy` be used.
    
    
    === Configuration ===
    The `authzpolicy.conf` file is a `.ini` style configuration file.
    
     - Each section of the config is a glob pattern used to match against a
       Trac resource descriptor. These descriptors are in the form:
       {{{
       <realm>:<id>@<version>[/<realm>:<id>@<version> ...]
       }}}
       Resources are ordered left to right, from parent to child. If any
       component is inapplicable, `*` is substituted. If the version pattern is
       not specified explicitely, all versions (`@*`) is added implicitly
       
       Example: Match the WikiStart page
       {{{
       [wiki:*]
       [wiki:WikiStart*]
       [wiki:WikiStart@*]
       [wiki:WikiStart]
       }}}
       
       Example: Match the attachment `wiki:WikiStart@117/attachment/FOO.JPG@*`
       on WikiStart
       {{{
       [wiki:*]
       [wiki:WikiStart*]
       [wiki:WikiStart@*]
       [wiki:WikiStart@*/attachment/*]
       [wiki:WikiStart@117/attachment/FOO.JPG]
       }}}
    
     - Sections are checked against the current Trac resource '''IN ORDER''' of
       appearance in the configuration file. '''ORDER IS CRITICAL'''.
    
     - Once a section matches, the current username is matched, '''IN ORDER''',
       against the keys of the section. If a key is prefixed with a `@`, it is
       treated as a group. If a key is prefixed with a `!`, the permission is
       denied rather than granted. The username will match any of 'anonymous',
       'authenticated', <username> or '*', using normal Trac permission rules.
    
    Example configuration:
    {{{
    [groups]
    administrators = athomas
    
    [*/attachment:*]
    * = WIKI_VIEW, TICKET_VIEW
    
    [wiki:WikiStart@*]
    @administrators = WIKI_ADMIN
    anonymous = WIKI_VIEW
    * = WIKI_VIEW
    
    # Deny access to page templates
    [wiki:PageTemplates/*]
    * =
    
    # Match everything else
    [*]
    @administrators = TRAC_ADMIN
    anonymous = BROWSER_VIEW, CHANGESET_VIEW, FILE_VIEW, LOG_VIEW,
        MILESTONE_VIEW, POLL_VIEW, REPORT_SQL_VIEW, REPORT_VIEW, ROADMAP_VIEW,
        SEARCH_VIEW, TICKET_CREATE, TICKET_MODIFY, TICKET_VIEW, TIMELINE_VIEW,
        WIKI_CREATE, WIKI_MODIFY, WIKI_VIEW
    # Give authenticated users some extra permissions
    authenticated = REPO_SEARCH, XML_RPC
    }}}
    """
    implements(IPermissionPolicy)

    authz_file = Option('authz_policy', 'authz_file', '',
                        'Location of authz policy configuration file.')

    authz = None
    authz_mtime = None

    # IPermissionPolicy methods
    
    def check_permission(self, action, username, resource, perm):
        if ConfigObj is None:
            self.log.error('configobj package not found')
            return None
        
        if self.authz_file and not self.authz_mtime or \
                os.path.getmtime(self.get_authz_file()) > self.authz_mtime:
            self.parse_authz()
        resource_key = self.normalise_resource(resource)
        self.log.debug('Checking %s on %s', action, resource_key)
        permissions = self.authz_permissions(resource_key, username)
        if permissions is None:
            return None                 # no match, can't decide
        elif permissions == ['']:
            return False                # all actions are denied

        # FIXME: expand all permissions once for all
        ps = PermissionSystem(self.env)
        for deny, perms in groupby(permissions,
                                   key=lambda p: p.startswith('!')):
            if deny and action in ps.expand_actions([p[1:] for p in perms]):
                return False            # action is explicitly denied
            elif action in ps.expand_actions(perms):
                return True            # action is explicitly granted

        return None                    # no match for action, can't decide

    # Internal methods

    def get_authz_file(self):
        f = self.authz_file
        return f if os.path.isabs(f) else os.path.join(self.env.path, f)

    def parse_authz(self):
        self.log.debug('Parsing authz security policy %s',
                       self.get_authz_file())
        self.authz = ConfigObj(self.get_authz_file(), encoding='utf8')
        groups = {}
        for group, users in self.authz.get('groups', {}).iteritems():
            if isinstance(users, basestring):
                users = [users]
            groups[group] = users
        
        self.groups_by_user = {}
        
        def add_items(group, items):
            for item in items:
                if item.startswith('@'):
                    add_items(group, groups[item[1:]])
                else:
                    self.groups_by_user.setdefault(item, set()).add(group)
                    
        for group, users in groups.iteritems():
            add_items('@' + group, users)

        self.authz_mtime = os.path.getmtime(self.get_authz_file())

    def normalise_resource(self, resource):
        def flatten(resource):
            if not resource:
                return ['*:*@*']
            if not (resource.realm or resource.id):
                return ['%s:%s@%s' % (resource.realm or '*',
                                      resource.id or '*',
                                      resource.version or '*')]
            # XXX Due to the mixed functionality in resource we can end up with
            # ticket, ticket:1, ticket:1@10. This code naively collapses all
            # subsets of the parent resource into one. eg. ticket:1@10
            parent = resource.parent
            while parent and (resource.realm == parent.realm or
                              (resource.realm == parent.realm and
                               resource.id == parent.id)):
                parent = parent.parent
            if parent:
                parent = flatten(parent)
            else:
                parent = []
            return parent + ['%s:%s@%s' % (resource.realm or '*',
                                           resource.id or '*',
                                           resource.version or '*')]
        return '/'.join(flatten(resource))

    def authz_permissions(self, resource_key, username):
        # TODO: Handle permission negation in sections. eg. "if in this
        # ticket, remove TICKET_MODIFY"
        if username and username != 'anonymous':
            valid_users = ['*', 'authenticated', username]
        else:
            valid_users = ['*', 'anonymous']
        for resource_section in [a for a in self.authz.sections
                                 if a != 'groups']:
            resource_glob = resource_section
            if '@' not in resource_glob:
                resource_glob += '@*'

            if fnmatch(resource_key, resource_glob):
                section = self.authz[resource_section]
                for who, permissions in section.iteritems():
                    if who in valid_users or \
                            who in self.groups_by_user.get(username, []):
                        self.log.debug('%s matched section %s for user %s',
                                       resource_key, resource_glob, username)
                        if isinstance(permissions, basestring):
                            return [permissions]
                        else:
                            return permissions
        return None
