# -*- coding: utf-8 -*-
#
# Copyright (C) 2007-2021 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 https://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 https://trac.edgewall.org/log/.
#
# Author: Alec Thomas <alec@swapoff.org>

import configparser
import os
from fnmatch import fnmatchcase
from itertools import groupby

from trac.config import ConfigurationError, PathOption, UnicodeConfigParser
from trac.core import Component, implements
from trac.perm import IPermissionPolicy, PermissionSystem
from trac.util import to_list
from trac.util.text import exception_to_unicode


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 permission policies (like the
    `DefaultPermissionPolicy`), there's no need to redefine all the
    permissions here. Only additional rights or restrictions should be added.

    === Installation ===
    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 = PathOption('authz_policy', 'authz_file', '',
                            "Location of authz policy configuration file. "
                            "Non-absolute paths are relative to the "
                            "Environment `conf` directory.")

    def __init__(self):
        self.authz = None
        self.authz_mtime = None
        self.groups_by_user = {}

    # IPermissionPolicy methods

    def check_permission(self, action, username, resource, perm):
        if not self.authz_mtime or \
                os.path.getmtime(self.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 parse_authz(self):
        self.log.debug("Parsing authz security policy %s",
                       self.authz_file)

        if not self.authz_file:
            self.log.error("The `[authz_policy] authz_file` configuration "
                           "option in trac.ini is empty or not defined.")
            raise ConfigurationError()
        try:
            authz_mtime = os.path.getmtime(self.authz_file)
        except OSError as e:
            self.log.error("Error parsing authz permission policy file: %s",
                           exception_to_unicode(e))
            raise ConfigurationError()

        self.authz = UnicodeConfigParser(ignorecase_option=False)
        try:
            self.authz.read(self.authz_file)
        except configparser.ParsingError as e:
            self.log.error("Error parsing authz permission policy file: %s",
                           exception_to_unicode(e))
            raise ConfigurationError()
        groups = {}
        if self.authz.has_section('groups'):
            for group, users in self.authz.items('groups'):
                groups[group] = to_list(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.items():
            add_items('@' + group, users)

        all_actions = set(PermissionSystem(self.env).get_actions())
        authz_basename = os.path.basename(self.authz_file)
        for section in self.authz.sections():
            if section == 'groups':
                continue
            for user, actions in self.authz.items(section):
                for action in to_list(actions):
                    if action.startswith('!'):
                        action = action[1:]
                    if action not in all_actions:
                        self.log.warning("The action %s in the [%s] section "
                                         "of %s is not a valid action.",
                                         action, section, authz_basename)
        self.authz_mtime = authz_mtime

    def normalise_resource(self, resource):
        def to_descriptor(resource):
            id = resource.id
            return '%s:%s@%s' % (resource.realm or '*',
                                 id if id is not None else '*',
                                 resource.version or '*')

        def flatten(resource):
            if not resource:
                return ['*:*@*']
            descriptor = to_descriptor(resource)
            if not resource.realm and resource.id is None:
                return [descriptor]
            # 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:
                parent = parent.parent
            if parent:
                return flatten(parent) + [descriptor]
            else:
                return [descriptor]

        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', 'anonymous', 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 fnmatchcase(resource_key, resource_glob):
                for who, permissions in self.authz.items(resource_section):
                    permissions = to_list(permissions)
                    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, str):
                            return [permissions]
                        else:
                            return permissions
        return None