# -*- coding: utf-8 -*-
#
# Copyright (C) 2004-2009 Edgewall Software
# Copyright (C) 2004 Francois Harvey <fharvey@securiweb.net>
# Copyright (C) 2005 Matthew Good <trac@matt-good.net>
# 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: Francois Harvey <fharvey@securiweb.net>
#         Matthew Good <trac@matt-good.net>

import os.path

from trac.config import Option, PathOption
from trac.core import *
from trac.perm import IPermissionPolicy
from trac.util import read_file
from trac.util.text import exception_to_unicode, to_unicode
from trac.util.translation import _
from trac.versioncontrol.api import RepositoryManager


def parent_iter(path):
    while 1:
        yield path
        if path == '/':
            return
        path = path[:-1]
        yield path
        idx = path.rfind('/')
        path = path[:idx + 1]


def join(*args):
    args = (arg.strip('/') for arg in args)
    return '/'.join(arg for arg in args if arg)


class ParseError(Exception):
    """Exception thrown for parse errors in authz files"""


def parse(authz, modules):
    """Parse a Subversion authorization file.
    
    Return a dict of modules, each containing a dict of paths, each containing
    a dict mapping users to permissions. Only modules contained in `modules`
    are retained.
    """
    groups = {}
    aliases = {}
    sections = {}
    section = None
    lineno = 0
    for line in authz.splitlines():
        lineno += 1
        line = to_unicode(line.strip())
        if not line or line.startswith(('#', ';')):
            continue
        if line.startswith('[') and line.endswith(']'):
            section = line[1:-1]
            continue
        if section is None:
            raise ParseError(_('Line %(lineno)d: Entry before first '
                               'section header', lineno=lineno))
        parts = line.split('=', 1)
        if len(parts) != 2:
            raise ParseError(_('Line %(lineno)d: Invalid entry',
                               lineno=lineno))
        name, value = parts
        name = name.strip()
        if section == 'groups':
            group = groups.setdefault(name, set())
            group.update(each.strip() for each in value.split(','))
        elif section == 'aliases':
            aliases[name] = value.strip()
        else:
            parts = section.split(':', 1)
            module, path = parts[0] if len(parts) > 1 else '', parts[-1]
            if module in modules:
                sections.setdefault((module, path), []).append((name, value))

    def resolve(subject, done):
        if subject.startswith('@'):
            done.add(subject)
            for members in groups[subject[1:]] - done:
                for each in resolve(members, done):
                    yield each
        elif subject.startswith('&'):
            yield aliases[subject[1:]]
        else:
            yield subject
    
    authz = {}
    for (module, path), items in sections.iteritems():
        section = authz.setdefault(module, {}).setdefault(path, {})
        for subject, perms in items:
            for user in resolve(subject, set()):
                section.setdefault(user, 'r' in perms)  # The first match wins
    
    return authz


class AuthzSourcePolicy(Component):
    """Permission policy for `source:` and `changeset:` resources using a
    Subversion authz file.
    
    `FILE_VIEW` and `BROWSER_VIEW` permissions are granted as specified in the
    authz file.
    
    `CHANGESET_VIEW` permission is granted for changesets where `FILE_VIEW` is
    granted on at least one modified file, as well as for empty changesets.
    """

    implements(IPermissionPolicy)
    
    authz_file = PathOption('trac', 'authz_file', '',
        """The path to the Subversion
        [http://svnbook.red-bean.com/en/1.5/svn.serverconfig.pathbasedauthz.html authorization (authz) file].
        To enable authz permission checking, the `AuthzSourcePolicy` permission
        policy must be added to `[trac] permission_policies`.
        """)

    authz_module_name = Option('trac', 'authz_module_name', '',
        """The module prefix used in the `authz_file` for the default
        repository. If left empty, the global section is used.
        """)

    _mtime = 0
    _authz = {}
    _users = set()
    
    _handled_perms = frozenset([(None, 'BROWSER_VIEW'),
                                (None, 'CHANGESET_VIEW'),
                                (None, 'FILE_VIEW'),
                                (None, 'LOG_VIEW'),
                                ('source', 'BROWSER_VIEW'),
                                ('source', 'FILE_VIEW'),
                                ('source', 'LOG_VIEW'),
                                ('changeset', 'CHANGESET_VIEW')])

    # IPermissionPolicy methods

    def check_permission(self, action, username, resource, perm):
        realm = resource.realm if resource else None
        if (realm, action) in self._handled_perms:
            authz, users = self._get_authz_info()
            if authz is None:
                return False
            
            if username == 'anonymous':
                usernames = ('$anonymous', '*')
            else:
                usernames = (username, '$authenticated', '*')
            if resource is None:
                return True if users & set(usernames) else None

            rm = RepositoryManager(self.env)
            try:
                repos = rm.get_repository(resource.parent.id)
            except TracError:
                return True # Allow error to be displayed in the repo index
            if repos is None:
                return True
            modules = [resource.parent.id or self.authz_module_name]
            if modules[0]:
                modules.append('')

            def check_path(path):
                path = '/' + join(repos.scope, path)
                if path != '/':
                    path += '/'
                
                # Allow access to parent directories of allowed resources
                if any(section.get(user) is True
                       for module in modules
                       for spath, section in authz.get(module, {}).iteritems()
                       if spath.startswith(path)
                       for user in usernames):
                    return True

                # Walk from resource up parent directories
                for spath in parent_iter(path):
                    for module in modules:
                        section = authz.get(module, {}).get(spath)
                        if section:
                            for user in usernames:
                                result = section.get(user)
                                if result is not None:
                                    return result
            
            if realm == 'source':
                return check_path(resource.id)

            elif realm == 'changeset':
                changes = list(repos.get_changeset(resource.id).get_changes())
                if not changes or any(check_path(change[0])
                                      for change in changes):
                    return True

    def _get_authz_info(self):
        try:
            mtime = os.path.getmtime(self.authz_file)
        except OSError, e:
            if self._authz is not None:
                self.log.error('Error accessing authz file: %s',
                               exception_to_unicode(e))
            self._mtime = mtime = 0
            self._authz = None
            self._users = set()
        if mtime > self._mtime:
            self._mtime = mtime
            rm = RepositoryManager(self.env)
            modules = set(repos.reponame
                          for repos in rm.get_real_repositories())
            if '' in modules and self.authz_module_name:
                modules.add(self.authz_module_name)
            modules.add('')
            self.log.info('Parsing authz file: %s' % self.authz_file)
            try:
                self._authz = parse(read_file(self.authz_file), modules)
                self._users = set(user for paths in self._authz.itervalues()
                                  for path in paths.itervalues()
                                  for user, result in path.iteritems()
                                  if result)
            except Exception, e:
                self._authz = None
                self._users = set()
                self.log.error('Error parsing authz file: %s',
                               exception_to_unicode(e))
        return self._authz, self._users
