#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
Developed by niphlod@gmail.com
License MIT/BSD/GPL

Redis-backed sessions
"""

import logging
from threading import Lock
from gluon import current
from gluon.storage import Storage
from gluon.contrib.redis_utils import acquire_lock, release_lock
from gluon.contrib.redis_utils import register_release_lock
from gluon._compat import to_bytes

logger = logging.getLogger("web2py.session.redis")

locker = Lock()


def RedisSession(redis_conn, session_expiry=False, with_lock=False, db=None):
    """
    Usage example: put in models::

        from gluon.contrib.redis_utils import RConn
        rconn = RConn()
        from gluon.contrib.redis_session import RedisSession
        sessiondb = RedisSession(redis_conn=rconn, with_lock=True, session_expiry=False)
        session.connect(request, response, db = sessiondb)

    Args:
        redis_conn: a redis-like connection object
        with_lock: prevent concurrent modifications to the same session
        session_expiry: delete automatically sessions after n seconds
                        (still need to run sessions2trash.py every 1M sessions
                        or so)

    Simple slip-in storage for session
    """

    locker.acquire()
    try:
        instance_name = 'redis_instance_' + current.request.application
        if not hasattr(RedisSession, instance_name):
            setattr(RedisSession, instance_name,
                    RedisClient(redis_conn, session_expiry=session_expiry, with_lock=with_lock))
        return getattr(RedisSession, instance_name)
    finally:
        locker.release()


class RedisClient(object):

    def __init__(self, redis_conn, session_expiry=False, with_lock=False):
        self.r_server = redis_conn
        self._release_script = register_release_lock(self.r_server)
        self.tablename = None
        self.session_expiry = session_expiry
        self.with_lock = with_lock

    def get(self, what, default):
        return self.tablename

    def Field(self, fieldname, type='string', length=None, default=None,
              required=False, requires=None):
        return None

    def define_table(self, tablename, *fields, **args):
        if not self.tablename:
            self.tablename = MockTable(
                self, self.r_server, tablename, self.session_expiry,
                self.with_lock)
        return self.tablename

    def __getitem__(self, key):
        return self.tablename

    def __call__(self, where=''):
        q = self.tablename.query
        return q

    def commit(self):
        # this is only called by session2trash.py
        pass


class MockTable(object):

    def __init__(self, db, r_server, tablename, session_expiry, with_lock=False):
        # here self.db is the RedisClient instance
        self.db = db
        self.tablename = tablename
        # set the namespace for sessions of this app
        self.keyprefix = 'w2p:sess:%s' % tablename.replace('web2py_session_', '')
        # fast auto-increment id (needed for session handling)
        self.serial = "%s:serial" % self.keyprefix
        # index of all the session keys of this app
        self.id_idx = "%s:id_idx" % self.keyprefix
        # remember the session_expiry setting
        self.session_expiry = session_expiry
        self.with_lock = with_lock

    def __call__(self, record_id, unique_key=None):
        # Support DAL shortcut query: table(record_id)

        # This will call the __getattr__ below
        # returning a MockQuery
        q = self.id

        # Instructs MockQuery, to behave as db(table.id == record_id)
        q.op = 'eq'
        q.value = record_id
        q.unique_key = unique_key

        row = q.select()
        return row[0] if row else Storage()

    def __getattr__(self, key):
        if key == 'id':
            # return a fake query. We need to query it just by id for normal operations
            self.query = MockQuery(
                field='id', db=self.db,
                prefix=self.keyprefix, session_expiry=self.session_expiry,
                with_lock=self.with_lock, unique_key=self.unique_key
            )
            return self.query
        elif key == '_db':
            # needed because of the calls in sessions2trash.py and globals.py
            return self.db

    def insert(self, **kwargs):
        # usually kwargs would be a Storage with several keys:
        # 'locked', 'client_ip','created_datetime','modified_datetime'
        # 'unique_key', 'session_data'
        # retrieve a new key
        newid = str(self.db.r_server.incr(self.serial))
        key = self.keyprefix + ':' + newid
        if self.with_lock:
            key_lock = key + ':lock'
            acquire_lock(self.db.r_server, key_lock, newid)
        with self.db.r_server.pipeline() as pipe:
            # add it to the index
            pipe.sadd(self.id_idx, key)
            # set a hash key with the Storage
            pipe.hmset(key, kwargs)
            if self.session_expiry:
                pipe.expire(key, self.session_expiry)
            pipe.execute()
        if self.with_lock:
            release_lock(self.db, key_lock, newid)
        return newid


class MockQuery(object):
    """a fake Query object that supports querying by id
       and listing all keys. No other operation is supported
    """
    def __init__(self, field=None, db=None, prefix=None, session_expiry=False,
                 with_lock=False, unique_key=None):
        self.field = field
        self.value = None
        self.db = db
        self.keyprefix = prefix
        self.op = None
        self.session_expiry = session_expiry
        self.with_lock = with_lock
        self.unique_key = unique_key

    def __eq__(self, value, op='eq'):
        self.value = value
        self.op = op

    def __gt__(self, value, op='ge'):
        self.value = value
        self.op = op

    def select(self):
        if self.op == 'eq' and self.field == 'id' and self.value:
            # means that someone wants to retrieve the key self.value
            key = self.keyprefix + ':' + str(self.value)
            if self.with_lock:
                acquire_lock(self.db.r_server, key + ':lock', self.value, 2)
            rtn = self.db.r_server.hgetall(key)
            if rtn:
                if self.unique_key:
                    # make sure the id and unique_key are correct
                    if rtn[b'unique_key'] == to_bytes(self.unique_key):
                        rtn[b'update_record'] = self.update  # update record support
                    else:
                        rtn = None
            return [Storage(rtn)] if rtn else []
        elif self.op == 'ge' and self.field == 'id' and self.value == 0:
            # means that someone wants the complete list
            rtn = []
            id_idx = "%s:id_idx" % self.keyprefix
            # find all session keys of this app
            allkeys = self.db.r_server.smembers(id_idx)
            for sess in allkeys:
                val = self.db.r_server.hgetall(sess)
                if not val:
                    if self.session_expiry:
                        # clean up the idx, because the key expired
                        self.db.r_server.srem(id_idx, sess)
                    continue
                val = Storage(val)
                # add a delete_record method (necessary for sessions2trash.py)
                val.delete_record = RecordDeleter(
                    self.db, sess, self.keyprefix)
                rtn.append(val)
            return rtn
        else:
            raise Exception("Operation not supported")

    def update(self, **kwargs):
        # means that the session has been found and needs an update
        if self.op == 'eq' and self.field == 'id' and self.value:
            key = self.keyprefix + ':' + str(self.value)
            if not self.db.r_server.exists(key):
                return None
            with self.db.r_server.pipeline() as pipe:
                pipe.hmset(key, kwargs)
                if self.session_expiry:
                    pipe.expire(key, self.session_expiry)
                rtn = pipe.execute()[0]
            if self.with_lock:
                release_lock(self.db, key + ':lock', self.value)
            return rtn

    def delete(self, **kwargs):
        # means that we want this session to be deleted
        if self.op == 'eq' and self.field == 'id' and self.value:
            id_idx = "%s:id_idx" % self.keyprefix
            key = self.keyprefix + ':' + str(self.value)
            with self.db.r_server.pipeline() as pipe:
                pipe.delete(key)
                pipe.srem(id_idx, key)
                rtn = pipe.execute()
            return rtn[1]


class RecordDeleter(object):
    """Dumb record deleter to support sessions2trash.py"""

    def __init__(self, db, key, keyprefix):
        self.db, self.key, self.keyprefix = db, key, keyprefix

    def __call__(self):
        id_idx = "%s:id_idx" % self.keyprefix
        # remove from the index
        self.db.r_server.srem(id_idx, self.key)
        # remove the key itself
        self.db.r_server.delete(self.key)