'''
This module provide an abstraction to the clients configuration directory.

The client configuration directory contains a list of ``.json`` files, each
file contains the configuration for one client. The username of the client is
the filename (excluding the extension).

The schema of the json file is described below::

    {
     'password': '<client password>',
     'role': '<node|client>',
     'tags': {'tag1': 'value'},
     'perms': Null
    }

Usage example:

>>> conf = CCConf('/etc/cloudcontrol/clients')
>>> conf.create_account(login='rms', password='secret', role='cli')
>>> conf.create_account(login='server42', password='secret', role='node')
>>> print conf.authentify('server42', 'pouet')
None
>>> print conf.authentify('server42', 'secret')
u'node'
>>> conf.add_tag('rms', 'admin')
>>> conf.show('rms')
{'password': 'secret'
 'role': 'cli',
 'tags': {},
 'perms': None}
>>> conf.remove_account('rms')
>>> 
'''

import hashlib
import base64
import random
import threading
import logging
import json
import os
import re
from functools import wraps

def writer(func):
    '''
    Decorator used to threadsafize methods that made write operations on
    client configuration tree.
    '''

    @wraps(func)
    def f(self, *args, **kwargs):
        with self._lock:
            return func(self, *args, **kwargs)

    return f

class CCConf(object):
    '''
    Create a new configuration interface.

    :param path_directory: the directory to store the configuration files
    '''

    CONF_TEMPLATE = {'password': None,
                     'role': None,
                     'tags': {},
                     'rights': []}

    RE_SALTPW = re.compile(r'{(?P<method>[A-Z]+)}(?P<password>.+)')

    def __init__(self, path_directory):
        self._path = path_directory
        self._lock = threading.RLock()

    def __enter__(self):
        return self._lock.__enter__()

    def __exit__(self, *args, **kwargs):
        return self._lock.__exit__(*args, **kwargs)    

    def _get_conf(self, login):
        '''
        Return the configuration of a client by its login.

        :param login: login of the client
        :return: the configuration of the client
        :raise CCConf.UnknownAccount: if user login is unknown
        '''

        filename = os.path.join(self._path, '%s.json' % login)
        if os.path.isfile(filename):
            conf = json.load(open(filename, 'r'))
            logging.debug('Getting configuration %s: %s', filename, conf)
            return conf
        else:
            raise CCConf.UnknownAccount('%s is not a file' % filename)

    def _set_conf(self, login, conf, create=False):
        '''
        Update the configuration of a client by its login.

        :param login: login of the client
        :param conf: configuration to set for the client
        :raise CCConf.UnknownAccount: if user login is unknown
        '''

        filename = os.path.join(self._path, '%s.json' % login)
        logging.debug('Writing configuration %s: %s', filename, conf)
        if os.path.isfile(filename) ^ create:
            json.dump(conf, open(filename, 'w'))
        else:
            raise CCConf.UnknownAccount('%s is not a file' % filename)

    def acquire(self):
        '''
        Acquire the configuration writing lock for non-atomic configuration
        changes.

        .. warning::
           Don't forget to call the :meth:`release` method after your changes
           for each :meth:`acquire` you made.
        '''
        self._lock.acquire()

    def release(self):
        '''
        Release the configuration writing lock.
        '''
        self._lock.release()

    def show(self, login):
        '''
        Show the configuration for specified account.

        :param login: the login of the client
        :return: configuration of user
        '''

        return self._get_conf(login)

    def _unsaltify(self, string, digest_size):
        string = base64.decodestring(string)
        password = string[0:digest_size]
        salt = string[digest_size:]
        return password, salt

    def _get_randsalt(self, size=10):
        salt = ''
        for _ in xrange(size):
            salt += chr(random.randint(1, 255))
        return salt

    def _auth_ssha(self, provided_passwd, configured_passwd=None):
        if configured_passwd is not None:
            salt = self._unsaltify(configured_passwd, 20)[1]
        else:
            salt = self._get_randsalt()
        digest = hashlib.sha1(str(provided_passwd) + salt).digest()
        return '{SSHA}%s' % base64.b64encode(digest + salt)

    def _auth_sha(self, provided_passwd, configured_passwd=None):
        digest = hashlib.sha1(str(provided_passwd)).digest()
        return '{SHA}%s' % base64.b64encode(digest)

    def _auth_smd5(self, provided_passwd, configured_passwd=None):
        if configured_passwd is not None:
            salt = self._unsaltify(configured_passwd, 16)[1]
        else:
            salt = self._get_randsalt()
        digest = hashlib.sha1(str(provided_passwd) + salt).digest()
        return '{SMD5}%s' % base64.b64encode(digest + salt)

    def _auth_md5(self, provided_passwd, configured_passwd=None):
        digest = hashlib.sha1(str(provided_passwd)).digest()
        return '{MD5}%s' % base64.b64encode(digest)

    def _auth_plain(self, provided_passwd, configured_passwd=None):
        return provided_passwd

    def _hash_password(self, password, method='ssha'):
        '''
        Hash a password using given method and return it.

        :param password: the password to hash
        :param method: the hashing method
        :return: hashed password
        '''
        
        meth = '_auth_%s' % method.lower()
        if hasattr(self, meth):
            auth = getattr(self, meth)
            return auth(password)
        else:
            raise CCConf.BadMethodError('Bad hashing method: %s' % repr(method))

    def authentify(self, login, password):
        '''
        Authentify the client providing its login and password. The function
        return the role of the client on success, or ``None``.

        :param login: the login of the client
        :param password: the password of the client
        :return: the client's role or None on failed authentication
        :raise CCConf.UnknownAccount: if user login is unknown
        '''

        conf = self._get_conf(login)
        passwd_conf = conf['password']

        # Check if account password is disabled or if account is disabled:
        if passwd_conf is None:
            return None

        is_valid = False

        m = CCConf.RE_SALTPW.match(passwd_conf)
        if m is None:
            meth = '_auth_plain'
            password_wo_method = passwd_conf
        else:
            meth = '_auth_%s' % m.group('method').lower()
            password_wo_method = m.group('password')

        if hasattr(self, meth):
            auth = getattr(self, meth)
            is_valid = auth(password, password_wo_method) == passwd_conf
        else:
            logging.warning('Bad authentication method for %s: '
                            '%s', login, m.group('method'))
        if is_valid:
            return conf['role']
        else:
            return None

    @writer
    def set_password(self, login, password, method='ssha'):
        '''
        Update the client's password in the configuration.

        :param login: login of the user
        :param password: new password
        :param method: the hashing method to use
        :raise CCConf.UnknownAccount: if user login is unknown
        '''

        conf = self._get_conf(login)
        password = self._hash_password(password, method)
        conf['password'] = password
        self._set_conf(login, conf)

    @writer
    def add_tag(self, login, tag_name, tag_value):
        '''
        Add the tag to the user.

        :param login: login of the user
        :param tag_name: tag name to add to the user
        :param tag_value: the tag value
        :raise CCConf.UnknownAccount: if user login is unknown
        '''

        logging.debug('Added tag %s:%s for %s account',
                      tag_name, tag_value, login)
        conf = self._get_conf(login)
        conf['tags'][tag_name] = tag_value
        self._set_conf(login, conf)

    @writer
    def remove_tag(self, login, tag):
        '''
        Remove the tag to the user.

        :param login: login of the user
        :param tag: tag to remove to the user
        :raise CCConf.UnknownAccount: if user login is unknown
        '''

        logging.debug('Removed tag %s for %s account', login, tag)
        conf = self._get_conf(login)
        if tag in conf['tags']:
            del conf['tags'][tag]
        self._set_conf(login, conf)

    @writer
    def remove_account(self, login):
        '''
        Remove the configuration of the account.

        :param login: login of the account to remove
        :raise CCConf.UnknownAccount: if user login is unknown
        '''

        logging.debug('Removed %s account', login)
        filename = os.path.join(self._path, '%s.json' % login)
        if os.path.exists(filename):
            os.remove(filename)
        else:
            raise CCConf.UnknownAccount('%s is not a file' % filename)

    @writer
    def create_account(self, login, role, password):
        '''
        Create a new account.

        :param login: login of the new user
        :param password: password of the new user
        :param role: the role of the new user
        :raise CCConf.AlreadyExistingAccount: if the login is already
        '''

        logging.debug('Creating %s account with role %s', login, role)
        filename = os.path.join(self._path, '%s.json' % login)
        if os.path.exists(filename):
            raise CCConf.AlreadyExistingAccount('%s found' % filename)
        else:
            conf = CCConf.CONF_TEMPLATE.copy()

            conf['role'] = role
            if password is not None:
                conf['password'] = self._hash_password(password)
            self._set_conf(login, conf, create=True)

    @writer
    def copy_account(self, copy_login, login, password):
        '''
        Create a new account based on another.

        :param copy_login: the login of the account to copy.
        :param password: password of the new user
        :param role: the role of the new user
        :raise CCConf.AlreadyExistingAccount: if the login is already
        :raise CCConf.UnknownAccount: if the copy login doesn't exist
        '''

        conf_copy = self._get_conf(copy_login)
        self.create_account(login, conf_copy['role'], password)
        password = self._get_conf(login)['password']
        conf_copy['password'] = password
        self._set_conf(login, conf_copy)

    @writer
    def add_right(self, login, tql, method=None, target='allow', index=None):
        '''
        Add a right rule to the provided account.

        :param login: the login of the account
        :param tql: the TQL request to allow
        :param method: the method to which apply the right, None if all
        :param allow: True if the rules allow the call, or False if it deny.
        :param index: the index of the new rule, set None if the rule is
            appended to the end of the ruleset.

        .. note::
           If the index is out of range, the rule will be added to the end of
           the ruleset.
        '''

        conf = self._get_conf(login)
        rights = conf['rights']
        rule = {'tql': tql, 'method': method, 'target': target}
        if index is None:
            index = len(rights)
        rights.insert(index, rule)
        self._set_conf(login, conf)

    @writer
    def remove_right(self, login, index):
        '''
        Remove a right rule from the provided account.

        :param login: the login of the account
        :param index: the index of the rule to delete or None for all rules
        '''

        conf = self._get_conf(login)
        if index is None:
            conf['rights'] = []
        else:
            try:
                conf['rights'].pop(index)
            except IndexError:
                raise CCConf.OutOfRangeIndexError('Bad rule index '
                                                  '%s' % repr(index))
        self._set_conf(login, conf)

    def list_accounts(self):
        '''
        List all registered accounts.

        :return: :class:`tuple` of :class:`str`, each item being an
            account login
        '''

        logins = []
        for filename in os.listdir(self._path):
            login, ext = os.path.splitext(filename)
            if ext == '.json':
                logins.append(login)

        return tuple(logins)


    class UnknownAccount(Exception):
        pass


    class AlreadyExistingAccount(Exception):
        pass


    class BadMethodError(Exception):
        pass


    class OutOfRangeIndexError(Exception):
        pass