# -*- coding: utf-8 -*-
# Copyright 2014, Ian Gulliver
#
# 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 json
import hashlib
import logging
import random
import struct
import uuid

from google.appengine.api import channel
from google.appengine.api import users
from google.appengine.ext import db

import utils


# Profile
#
# Client (⤴︎ Profile)
#
# Instance
#
# Subject
# ↳ Message
# ↳ Pin (⤴︎ Instance)
# ↳ Subscription (⤴︎ Instance)
#   ↳ Event


class DuplicateMessage(Exception):
  def __init__(self, original):
    self.original = original
    super(DuplicateMessage, self).__init__(original)


class AccessDenied(Exception):
  pass


class Profile(db.Model):
  google_user = db.UserProperty()

  _cache = {}

  ADMIN_KEY = db.Key.from_path('Profile', 'admin')

  @classmethod
  @db.transactional()
  def FindOrCreate(cls, google_user):
    key_name = google_user.user_id()
    if key_name in cls._cache:
      return cls._cache[key_name]
    profile = cls.get_by_key_name(key_name)
    if not profile:
      profile = cls(key_name=key_name, google_user=google_user)
      profile.put()
    cls._cache[key_name] = profile
    return profile

  def MergeFrom(self, source_profile):
    # This is non-transactional and racy (new messages can be introduced by the
    # old client after we start). This is hard to solve because we're not in
    # a single hierarchy.
    for message in Message.all().filter('sender =', source_profile):
      message.sender = self;
      message.put()


class Client(db.Model):

  profile = db.ReferenceProperty(reference_class=Profile)
  first_seen = db.DateTimeProperty(required=True, auto_now_add=True)

  @classmethod
  def FromProfile(cls, client_id, profile):
    client = cls(key_name=client_id, profile=profile)
    client.put()
    return client


class Instance(db.Model):
  # key_name=instance_id
  active = db.BooleanProperty(required=True, default=False)
  polling = db.BooleanProperty(required=True, default=False)
  last_poll = db.DateTimeProperty(required=True, auto_now=True)
  generation = db.StringProperty(required=True)

  @classmethod
  def FromID(cls, instance_id):
    logging.info('Instance: %s', instance_id)
    return cls.get_by_key_name(instance_id)

  @classmethod
  def FindOrCreate(cls, instance_id, **kwargs):
    logging.info('Instance: %s', instance_id)
    def _FindOrCreate():
      entity = cls.get_by_key_name(instance_id)
      if entity:
        return entity
      entity = cls(
          key_name=instance_id,
          generation=str(uuid.uuid4()),
          **kwargs)
      entity.put()
      return entity
    return db.run_in_transaction(_FindOrCreate)

  def Delete(self):
    logging.info('Deleting instance %s', self.key().name())

    subscriptions = Subscription.all().filter('instance =', self)
    for subscription in subscriptions:
      subscription.Delete()

    pins = Pin.all().filter('instance =', self)
    for pin in pins:
      pin.Delete()

    self.delete()

  def GetSubscriptions(self):
    return (
        Subscription.all()
        .filter('instance =', self))


class Subject(db.Model):

  name = db.StringProperty(required=True)
  readable_only_by = db.ReferenceProperty(
      reference_class=Profile, collection_name='readable_subject_set')
  writable_only_by = db.ReferenceProperty(
      reference_class=Profile, collection_name='writable_subject_set')

  next_message_id = db.IntegerProperty(required=True, default=1)

  _cache = {}

  @classmethod
  def _UpdateHashWithString(cls, hashobj, string):
    string = string.encode('utf8')
    hashobj.update(struct.pack('!i', len(string)))
    hashobj.update(string)

  @classmethod
  def _KeyName(cls, subject):
    hashobj = hashlib.sha256()
    cls._UpdateHashWithString(hashobj, subject['name'])
    cls._UpdateHashWithString(hashobj, subject.get('readable_only_by', ''))
    cls._UpdateHashWithString(hashobj, subject.get('writable_only_by', ''))
    return hashobj.hexdigest()

  @classmethod
  def FindOrCreate(cls, subject, client):
    if 'readable_only_by' in subject:
      if subject['readable_only_by'] == 'admin':
        readable_only_by = Profile.ADMIN_KEY
      elif subject['readable_only_by'] == 'me':
        readable_only_by = Client.profile.get_value_for_datastore(client)
      else:
        readable_only_by = db.Key.from_path('Profile', int(subject['readable_only_by']))
    else:
      readable_only_by = None

    if 'writable_only_by' in subject:
      if subject['writable_only_by'] == 'admin':
        writable_only_by = Profile.ADMIN_KEY
      elif subject['writable_only_by'] == 'me':
        writable_only_by = Client.profile.get_value_for_datastore(client)
      else:
        writable_only_by = db.Key.from_path('Profile', int(subject['writable_only_by']))
    else:
      writable_only_by = None

    key_name = cls._KeyName(subject)
    obj = cls._cache.get(key_name)
    if obj:
      return obj

    obj = cls.get_or_insert(
        key_name,
        name=subject['name'],
        readable_only_by=readable_only_by,
        writable_only_by=writable_only_by)

    cls._cache[key_name] = obj
    return obj

  @classmethod
  def ReadThrough(cls, key):
    obj = cls._cache.get(key.name())
    if obj:
      return obj

    obj = cls.get(key)
    if obj:
      cls._cache[key.name()] = obj
      return obj

  @db.transactional()
  def GetRecentMessages(self, num_messages):
    query = (
        Message.all()
        .ancestor(self)
        .order('-id_'))
    if num_messages <= 0:
      num_messages = None
    return reversed(query.fetch(limit=num_messages))

  @db.transactional()
  def GetMessagesSince(self, last_id):
    query = (
        Message.all()
        .ancestor(self)
        .filter('id_ >', last_id)
        .order('id_'))
    return list(query)

  @db.transactional()
  def GetPins(self):
    query = (
        Pin.all()
        .ancestor(self))
    return list(query)

  @db.transactional()
  def PutMessage(self, message, sender, sender_message_id, sender_address):
    """Internal helper for SendMessage().

    Unless/until channel.send_message becomes transactional, we have to finish
    the datastore work (and any retries) before we start transmitting to
    channels.
    """
    # We have to reload the Subject inside the transaction to get transactional
    # ID generation
    subject = Subject.get(self.key())

    # sender_message_id should be universal across all subjects, but we check
    # it within just this subject to allow in-transaction verification.
    messages = (
        Message.all()
        .ancestor(subject)
        .filter('sender_message_id =', sender_message_id)
        .fetch(1))
    if messages:
      raise DuplicateMessage(messages[0].ToEvent())

    message_id = subject.next_message_id
    subject.next_message_id += 1
    subject.put()

    obj = Message(
        parent=subject,
        message=message,
        sender=sender,
        sender_message_id=sender_message_id,
        sender_address=sender_address,
        random_value=random.randint(0, 2 ** 32 - 1),
        id_=message_id)
    obj.put()

    return (obj, list(Subscription.all().ancestor(subject)))

  def VerifyWritable(self, sender):
    writable_only_by = Subject.writable_only_by.get_value_for_datastore(self)
    if (not users.is_current_user_admin() and
        writable_only_by and
        writable_only_by != sender):
      raise AccessDenied

  def VerifyReadable(self, reader):
    readable_only_by = Subject.readable_only_by.get_value_for_datastore(self)
    if (not users.is_current_user_admin() and
        readable_only_by and
        readable_only_by != reader):
      raise AccessDenied

  def SendMessage(
      self, message, sender, sender_message_id, sender_address, request):
    self.VerifyWritable(sender)
    readable_only_by_me = (request.get('readable_only_by') == 'me')
    writable_only_by_me = (request.get('writable_only_by') == 'me')
    try:
      obj, subscriptions = self.PutMessage(
          message, sender, sender_message_id, sender_address)
    except DuplicateMessage as e:
      e.original = self.TranslateEvent(
          e.original, readable_only_by_me, writable_only_by_me)
      raise e
    event = obj.ToEvent()
    for subscription in subscriptions:
      subscription.SendMessage(self.TranslateEvent(
          event,
          subscription.readable_only_by_me,
          subscription.writable_only_by_me))
    return self.TranslateEvent(event, readable_only_by_me, writable_only_by_me)

  @db.transactional()
  def PutPin(self, message, sender, sender_message_id,
             instance, sender_address):
    """Internal helper for Pin()."""
    # sender_message_id should be universal across all subjects, but we check
    # it within just this subject to allow in-transaction verification.
    pins = (
        Pin.all()
        .ancestor(self)
        .filter('sender_message_id =', sender_message_id)
        .filter('instance =', instance)
        .fetch(1))
    if pins:
      raise DuplicateMessage(pins[0].ToEvent())

    obj = Pin(
        parent=self,
        message=message,
        sender=sender,
        sender_message_id=sender_message_id,
        sender_address=sender_address,
        instance=instance)
    obj.put()

    return (obj, list(Subscription.all().ancestor(self)))

  def Pin(self, message, sender, sender_message_id, sender_address, instance,
          request):
    self.VerifyWritable(sender)
    readable_only_by_me = (request.get('readable_only_by') == 'me')
    writable_only_by_me = (request.get('writable_only_by') == 'me')
    try:
      obj, subscriptions = self.PutPin(
          message, sender, sender_message_id, instance, sender_address)
    except DuplicateMessage as e:
      e.original = self.TranslateEvent(
          e.original, readable_only_by_me, writable_only_by_me)
      raise e
    event = obj.ToEvent()
    for subscription in subscriptions:
      subscription.SendMessage(self.TranslateEvent(
          event,
          subscription.readable_only_by_me,
          subscription.writable_only_by_me))
    return self.TranslateEvent(event, readable_only_by_me, writable_only_by_me)

  @db.transactional()
  def RemovePin(self, sender, sender_message_id, instance_key):
    pins = (
        Pin.all()
        .ancestor(self)
        .filter('sender =', sender)
        .filter('sender_message_id =', sender_message_id)
        .filter('instance =', instance_key))

    events = []
    # TODO: bulk delete
    for pin in pins:
      events.append(pin.ToEvent(event_type='unpin'))
      pin.delete()

    return (events, list(Subscription.all().ancestor(self)))

  def Unpin(self, sender, sender_message_id, instance_key):
    self.VerifyWritable(sender)
    events, subscriptions = self.RemovePin(sender, sender_message_id, instance_key)
    for event in events:
      for subscription in subscriptions:
        subscription.SendMessage(event)

  def ToDict(self):
    ret = {
      'name': self.name,
    }
    readable_only_by = Subject.readable_only_by.get_value_for_datastore(self)
    if readable_only_by:
      if readable_only_by == Profile.ADMIN_KEY:
        ret['readable_only_by'] = 'admin'
      else:
        ret['readable_only_by'] = str(readable_only_by.id_or_name())
    writable_only_by = Subject.writable_only_by.get_value_for_datastore(self)
    if writable_only_by:
      if writable_only_by == Profile.ADMIN_KEY:
        ret['writable_only_by'] = 'admin'
      else:
        ret['writable_only_by'] = str(writable_only_by.id_or_name())
    return ret

  @classmethod
  def TranslateEvent(cls, event, readable_only_by_me, writable_only_by_me):
    if readable_only_by_me:
      event['subject']['readable_only_by'] = 'me'
    if writable_only_by_me:
      event['subject']['writable_only_by'] = 'me'
    return event

  @classmethod
  def TranslateEvents(cls, events, readable_only_by_me, writable_only_by_me):
    return [cls.TranslateEvent(event, readable_only_by_me, writable_only_by_me)
            for event in events]

  @db.transactional()
  def GetEvents(self, messages, last_id, request, pins=True):
    events = []
    if pins:
      events.extend(m.ToEvent() for m in self.GetPins())
    if messages:
      events.extend(m.ToEvent() for m in self.GetRecentMessages(messages))
    if last_id is not None:
      events.extend(m.ToEvent() for m in self.GetMessagesSince(last_id))

    readable_only_by_me = (request.get('readable_only_by') == 'me')
    writable_only_by_me = (request.get('writable_only_by') == 'me')
    return self.TranslateEvents(
        events, readable_only_by_me, writable_only_by_me)


class Subscription(db.Model):
  # parent=Subject

  instance = db.ReferenceProperty(reference_class=Instance, required=True)
  readable_only_by_me = db.BooleanProperty(required=True, default=False)
  writable_only_by_me = db.BooleanProperty(required=True, default=False)
  polling = db.BooleanProperty(required=True, default=False)

  @classmethod
  @db.transactional()
  def FindOrCreate(cls, subject, client, instance, request,
                   messages=0, last_id=None, polling=False):
    readable_only_by_me = (request.get('readable_only_by') == 'me')
    writable_only_by_me = (request.get('writable_only_by') == 'me')
    subscriptions = (
        cls.all(keys_only=True)
        .ancestor(subject)
        .filter('instance =', instance)
        .filter('readable_only_by_me =', readable_only_by_me)
        .filter('writable_only_by_me =', writable_only_by_me)
        .fetch(1))
    if not subscriptions:
      cls(parent=subject,
          instance=instance,
          readable_only_by_me=readable_only_by_me,
          writable_only_by_me=writable_only_by_me,
          polling=polling).put()
    return subject.GetEvents(messages, last_id, request)

  @classmethod
  @db.transactional()
  def Remove(cls, subject, instance, request):
    readable_only_by_me = (request.get('readable_only_by') == 'me')
    writable_only_by_me = (request.get('writable_only_by') == 'me')
    subscriptions = (
        cls.all()
        .ancestor(subject)
        .filter('instance =', instance)
        .filter('readable_only_by_me =', readable_only_by_me)
        .filter('writable_only_by_me =', writable_only_by_me))
    for subscription in subscriptions:
      subscription.Delete()

  def SendMessage(self, msg):
    encoded = json.dumps(msg, default=utils.EncodeJSON)
    if self.polling:
      Event(parent=self,
            key_name=str(uuid.uuid4()),
            json=encoded).save()
    else:
      instance_key = Subscription.instance.get_value_for_datastore(self)
      channel.send_message(str(instance_key.name()), encoded)

  def GetEvents(self, acks):
    acks = set(acks)
    events = (
        Event.all()
        .ancestor(self))
    ret = []
    to_delete = []
    for e in events:
      if str(e.key().name()) in acks:
        to_delete.append(e)
      else:
        ret.append(e.ToEvent())
    db.delete(to_delete)
    return ret

  def Delete(self):
    events = (
        Event.all()
        .ancestor(self))
    db.delete(events)

    self.delete()


class Event(db.Model):
  # parent=Subscription

  json = db.StringProperty(required=True)

  def ToEvent(self):
    ret = json.loads(self.json)
    ret['event_id'] = str(self.key().name())
    return ret


class Message(db.Model):
  # parent=Subject

  created = db.DateTimeProperty(required=True, auto_now_add=True)
  message = db.TextProperty(required=True)
  sender = db.ReferenceProperty(required=True, reference_class=Profile)
  sender_message_id = db.StringProperty(required=True)
  sender_address = db.StringProperty(required=True)
  # id is reserved
  id_ = db.IntegerProperty(required=True)
  random_value = db.IntegerProperty(required=True)

  def ToEvent(self):
    parent = Subject.ReadThrough(self.parent_key())
    return {
      'event_type':        'message',
      'id':                self.id_,
      'sender':
        str(Message.sender.get_value_for_datastore(self).id_or_name()),
      'subject':           parent.ToDict(),
      'created':           self.created,
      'sender_message_id': self.sender_message_id,
      'random_value':      self.random_value,
      'message':           self.message,
    }


class Pin(db.Model):
  # parent=Subject

  created = db.DateTimeProperty(required=True, auto_now_add=True)
  instance = db.ReferenceProperty(required=True, reference_class=Instance)
  message = db.TextProperty(required=True)
  sender = db.ReferenceProperty(required=True, reference_class=Profile)
  sender_message_id = db.StringProperty(required=True)
  sender_address = db.StringProperty(required=True)

  def ToEvent(self, event_type='pin'):
    parent = Subject.ReadThrough(self.parent_key())
    return {
      'event_type':        event_type,
      'id':                str(self.key().id()),
      'sender':
        str(Pin.sender.get_value_for_datastore(self).id_or_name()),
      'subject':           parent.ToDict(),
      'created':           self.created,
      'sender_message_id': self.sender_message_id,
      'message':           self.message,
    }

  def Delete(self):
    self.parent().Unpin(
        self.sender, self.sender_message_id,
        Pin.instance.get_value_for_datastore(self))