'''
rethinkstuff/__init__.py - rethinkdb connection-manager-ish thing and service
registry thing

Copyright (C) 2015-2017 Internet Archive

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
'''

import rethinkdb as r
import logging
import random
import time
import types
import socket
import os
import datetime

try:
    UTC = datetime.timezone.utc
except:
    UTC = r.make_timezone("00:00")

def utcnow():
    """Convenience function to get timezone-aware UTC datetime. RethinkDB
    requires timezone-aware datetime for its native time type, and
    unfortunately datetime.datetime.utcnow() is not timezone-aware. Also python
    2 doesn't come with a timezone implementation."""
    return datetime.datetime.now(UTC)

class RethinkerWrapper(object):
    logger = logging.getLogger('rethinkstuff.RethinkerWrapper')
    def __init__(self, rethinker, wrapped):
        self.rethinker = rethinker
        self.wrapped = wrapped

    def __getattr__(self, name):
        delegate = getattr(self.wrapped, name)
        return self.rethinker.wrap(delegate)

    def __getitem__(self, key):
        return self.rethinker.wrap(self.wrapped.__getitem__)(key)

    def __repr__(self):
        return '<RethinkerWrapper{}>'.format(repr(self.wrapped))

    def run(self, db=None):
        self.wrapped.run  # raise AttributeError early
        while True:
            conn = self.rethinker._random_server_connection()
            is_iter = False
            try:
                result = self.wrapped.run(conn, db=db or self.rethinker.dbname)
                if hasattr(result, '__next__'):
                    is_iter = True
                    def gen():
                        try:
                            yield  # empty yield, see comment below
                            for x in result:
                                yield x
                        finally:
                            result.close()
                            conn.close()
                    g = gen()
                    # Start executing the generator, leaving off after the
                    # empty yield. If we didn't do this, and the caller never
                    # started the generator, the finally block would never run
                    # and the connection would stay open.
                    next(g)
                    return g
                else:
                    return result
            except r.ReqlTimeoutError as e:
                time.sleep(0.5)
            finally:
                if not is_iter:
                    conn.close(noreply_wait=False)

class Rethinker(object):
    '''
    >>> r = Rethinker(db='my_db')
    >>> doc = r.table('my_table').get(1).run()
    '''
    logger = logging.getLogger('rethinkstuff.Rethinker')

    def __init__(self, servers=['localhost'], db=None):
        if isinstance(servers, str):
            self.servers = [servers]
        else:
            self.servers = servers
        self.dbname = db

    # https://github.com/rethinkdb/rethinkdb-example-webpy-blog/blob/master/model.py
    # "Best practices: Managing connections: a connection per request"
    def _random_server_connection(self):
        while True:
            server = random.choice(self.servers)
            try:
                try:
                    host, port = server.split(':')
                    return r.connect(host=host, port=port)
                except ValueError:
                    return r.connect(host=server)
            except Exception as e:
                self.logger.error(
                        'will keep trying after failure connecting to '
                        'rethinkdb server at %s: %s', server, e)
                time.sleep(0.5)

    def wrap(self, delegate):
        if isinstance(delegate, (types.FunctionType, types.MethodType)):
            def wrapper(*args, **kwargs):
                result = delegate(*args, **kwargs)
                if result is not None:
                    return RethinkerWrapper(self, result)
                else:
                    return None
            return wrapper
        else:
            return delegate

    def __getattr__(self, name):
        delegate = getattr(r, name)
        return self.wrap(delegate)

class ServiceRegistry(object):
    '''
    status_info is dict, should have at least these fields
    {
        'id': ...,   # generated by rethinkdb
        'role': 'brozzler-worker',
        'load': 0.5, # load score
        'heartbeat_interval': 20.0,
        'host': 'wbgrp-svc999.us.archive.org',           # set in svcreg.heartbeat() as a fallback
        'pid': 1234,                                     # set in svcreg.heartbeat() as a fallback
        'first_heartbeat': '2015-10-30T03:39:40.080814', # set in svcreg.heartbeat()
        'last_heartbeat': '2015-10-30T05:54:35.422866',  # set in svcreg.heartbeat()
        ... plus anything else you want...
    }
    '''

    logger = logging.getLogger('rethinkstuff.ServiceRegistry')

    def __init__(self, rethinker):
        self.r = rethinker
        self._ensure_table()

    def _ensure_table(self):
        dbs = self.r.db_list().run()
        if not self.r.dbname in dbs:
            self.logger.info('creating rethinkdb database %s', repr(self.r.dbname))
            self.r.db_create(self.r.dbname).run()
        tables = self.r.table_list().run()
        if not 'services' in tables:
            self.logger.info("creating rethinkdb table 'services' in database %s", repr(self.r.dbname))
            self.r.table_create('services', shards=1, replicas=min(3, len(self.r.servers))).run()
            # self.r.table('sites').index_create...?

    def heartbeat(self, status_info):
        '''
        Returns updated status info on success, un-updated status info on
        failure.
        '''
        updated_status_info = dict(status_info)
        updated_status_info['last_heartbeat'] = r.now()
        if not 'first_heartbeat' in updated_status_info:
            updated_status_info['first_heartbeat'] = updated_status_info['last_heartbeat']
        if not 'host' in updated_status_info:
            updated_status_info['host'] = socket.gethostname()
        if not 'pid' in updated_status_info:
            updated_status_info['pid'] = os.getpid()
        try:
            result = self.r.table('services').insert(
                    updated_status_info, conflict='replace',
                    return_changes=True).run()
            return result['changes'][0]['new_val'] # XXX check
        except:
            self.logger.error('error updating service registry', exc_info=True)
            return status_info

    def unregister(self, id):
        result = self.r.table('services').get(id).delete().run()
        if result != {'deleted':1,'errors':0,'inserted':0,'replaced':0,'skipped':0,'unchanged':0}:
            self.logger.warn('unexpected result attempting to delete id=%s from rethinkdb services table: %s', id, result)

    def available_service(self, role):
        try:
            result = self.r.table('services').filter({"role":role}).filter(
                lambda svc: r.now().sub(svc["last_heartbeat"]) < 3 * svc["heartbeat_interval"]   #.default(20.0)
            ).order_by("load")[0].run()
            return result
        except r.ReqlNonExistenceError:
            return None

    def available_services(self, role=None):
        try:
            query = self.r.table('services')
            if role:
                query = query.filter({"role":role})
            query = query.filter(
                lambda svc: r.now().sub(svc["last_heartbeat"]) < 3 * svc["heartbeat_interval"]   #.default(20.0)
            ).order_by("load")
            result = query.run()
            return result
        except r.ReqlNonExistenceError:
            return []

class WatchedDict(dict):
    def __init__(self, d, callback, field):
        self.callback = callback
        self.field = field
        for key in d:
            dict.__setitem__(self, key, watch(
                d[key], callback=self.callback, field=self.field))

    def __setitem__(self, key, value):
        self.callback(self.field)
        return dict.__setitem__(self, key, watch(
            value, callback=self.callback, field=self.field))

    def __delitem__(self, key):
        self.callback(self.field)
        return dict.__delitem__(self, key)

    def clear(self):
        self.callback(self.field)
        return dict.clear(self)

    def pop(self, *args):
        self.callback(self.field)
        return dict.pop(self, *args)

    def popitem(self):
        self.callback(self.field)
        return dict.popitem()

    def setdefault(self, *args):
        self.callback(self.field)
        if len(args) == 2:
            return dict.setdefault(self, args[0], watch(
                args[1], callback=self.callback, field=self.field))
        else:
            return dict.setdefault(self, *args)

    def update(self, *args, **kwargs):
        # looks a little tricky
        raise Exception('not implemented')

class WatchedList(list):
    def __init__(self, l, callback, field):
        self.callback = callback
        self.field = field
        for item in l:
            list.append(self, watch(item, callback=callback, field=self.field))

    def __setitem__(self, index, value):
        self.callback(self.field)
        return list.__setitem__(self, index, watch(
            value, callback=self.callback, field=self.field))

    def __delitem__(self, index):
        self.callback(self.field)
        return list.__delitem__(self, index)

    def append(self, value):
        self.callback(self.field)
        return list.append(self, watch(
            value, callback=self.callback, field=self.field))

    def extend(self, value):
        self.callback(self.field)
        return list.extend(self, watch(
            list(value), callback=self.callback, field=self.field))

    def insert(self, index, value):
        self.callback(self.field)
        return list.insert(self, index, watch(
            value, callback=self.callback, field=self.field))

    def remove(self, value):
        self.callback(self.field)
        return list.remove(self, value)

    def pop(self, index=-1):
        self.callback(self.field)
        return list.pop(self, index)

    def clear(self):
        self.callback(self.field)
        return list.clear(self)

    def sort(self, key=None, reverse=False):
        self.callback(self.field)
        return list.sort(self, key, reverse)

    def reverse(self):
        self.callback(self.field)
        return list.reverse(self)

def watch(obj, callback, field):
    if isinstance(obj, dict):
        return WatchedDict(obj, callback, field)
    elif isinstance(obj, list):
        return WatchedList(obj, callback, field)
    else:
        return obj

class Document(dict, object):
    '''
    Base class for documents in rethinkdb.

    You should subclass this class for each of your rethinkdb tables. You can
    add custom functionality in your subclass if appropriate.

    This class keeps track of changes made to the object and any nested fields.
    After you have made some changes, call update() to persist them to the
    database.

    Changes in nested fields result in updates to their first-level ancestor
    field. For example, if your document starts as {'a': {'b': 'c'}}, then
    you run d['a']['x'] = 'y', then the update will replace the whole 'a'
    field. Nested field updates get too complicated any other way.

    The primary key must be `id`, the rethinkdb default. (XXX we could find out
    what the primary key is from the "table_config" system table.)
    '''
    def __init__(self, rethinker, d={}):
        dict.__setattr__(self, '_r', rethinker)
        for k in d:
            dict.__setitem__(
                    self, k, watch(d[k], callback=self._updated, field=k))
        self._clear_updates()

    def _clear_updates(self):
        dict.__setattr__(self, '_updates', {})
        dict.__setattr__(self, '_deletes', set())

    def __setitem__(self, key, value):
        dict.__setitem__(
                self, key, watch(value, callback=self._updated, field=key))
        self._updated(key)

    __setattr__ = __setitem__
    __getattr__ = dict.__getitem__

    def __delitem__(self, key):
        dict.__delitem__(self, key)
        self._deletes.add(key)
        if key in self._updates:
            del self._updates[key]

    # XXX do we need the other stuff like in WatchedDict?

    def _updated(self, field):
        # callback for all updates
        self._updates[field] = self[field]
        if field in self._deletes:
            self._deletes.remove(field)

    @property
    def table(self):
        '''
        Name of the rethinkdb table.

        Defaults to the name of the class, lowercased. Can be overridden.
        '''
        return self.__class__.__name__.lower()

    def table_create(self):
        '''
        Creates the table.

        Subclasses may want to override to do more things, such as creating
        indexes.
        '''
        self._r.table_create(self.table).run()

    def insert(self):
        result = self._r.table(self.table).insert(self).run()
        if 'generated_keys' in result:
            dict.__setitem__(self, 'id', result['generated_keys'][0])
        self._clear_updates()

    def update(self):
        # hmm, masks dict.update()
        if self._updates:
            # r.literal() to replace, not merge with, nested fields
            updates = {
                    field: r.literal(
                        self._updates[field]) for field in self._updates}
            self._r.table(self.table).get(self.id).update(updates).run()
        if self._deletes:
            self._r.table(self.table).replace(
                    r.row.without(self._deletes)).run()
        self._clear_updates()

    def refresh(self):
        '''
        Refresh from the database.
        '''
        d = self._r.table(self.table).get(self.id).run()
        for k in d:
            dict.__setitem__(
                    self, k, watch(d[k], callback=self._updated, field=k))