#-*- coding: utf-8 -*-

from __future__ import annotations

from datetime import datetime
from sqlite3 import IntegrityError
from threading import Timer
from typing import TYPE_CHECKING, Callable, List, Optional, Tuple, Union

from apprise import Apprise
from dateutil.relativedelta import relativedelta
from dateutil.relativedelta import weekday as du_weekday

from backend.custom_exceptions import (InvalidKeyValue, InvalidTime,
                                       NotificationServiceNotFound,
                                       ReminderNotFound)
from backend.db import get_db
from backend.helpers import (RepeatQuantity, Singleton, SortingMethod,
                             search_filter, when_not_none)
from backend.logging import LOGGER

if TYPE_CHECKING:
	from flask.ctx import AppContext


def __next_selected_day(
	weekdays: List[int],
	weekday: int
) -> int:
	"""Find the next allowed day in the week.

	Args:
		weekdays (List[int]): The days of the week that are allowed.
		Monday is 0, Sunday is 6.
		weekday (int): The current weekday.

	Returns:
		int: The next allowed weekday.
	"""
	return (
		# Get all days later than current, then grab first one.
		[d for d in weekdays if weekday < d]
		or
		# weekday is last allowed day, so it should grab the first
		# allowed day of the week.
		weekdays
	)[0]

def _find_next_time(
	original_time: int,
	repeat_quantity: Union[RepeatQuantity, None],
	repeat_interval: Union[int, None],
	weekdays: Union[List[int], None]
) -> int:
	"""Calculate the next timestep based on original time and repeat/interval
	values.

	Args:
		original_time (int): The original time of the repeating timestamp.

		repeat_quantity (Union[RepeatQuantity, None]): If set, what the quantity
		is of the repetition.

		repeat_interval (Union[int, None]): If set, the value of the repetition.

		weekdays (Union[List[int], None]): If set, on which days the time can
		continue. Monday is 0, Sunday is 6.

	Returns:
		int: The next timestamp in the future.
	"""
	if weekdays is not None:
		weekdays.sort()

	new_time = datetime.fromtimestamp(original_time)
	current_time = datetime.fromtimestamp(datetime.utcnow().timestamp())

	if repeat_quantity is not None:
		td = relativedelta(**{repeat_quantity.value: repeat_interval})
		while new_time <= current_time:
			new_time += td

	elif weekdays is not None:
		# We run the loop contents at least once and then actually use the cond.
		# This is because we need to force the 'free' date to go to one of the
		# selected weekdays.
		# Say it's Monday, we set a reminder for Wednesday and make it repeat
		# on Tuesday and Thursday. Then the first notification needs to go on
		# Thurday, not Wednesday. So run code at least once to force that.
		# Afterwards, it can run normally to push the timestamp into the future.
		one_to_go = True
		while one_to_go or new_time <= current_time:
			next_day = __next_selected_day(weekdays, new_time.weekday())
			proposed_time = new_time + relativedelta(weekday=du_weekday(next_day))
			if proposed_time == new_time:
				proposed_time += relativedelta(weekday=du_weekday(next_day, 2))
			new_time = proposed_time
			one_to_go = False

	result = int(new_time.timestamp())
	LOGGER.debug(
		f'{original_time=}, {current_time=} ' +
		f'and interval of {repeat_interval} {repeat_quantity} ' +
		f'leads to {result}'
	)
	return result


class Reminder:
	"""Represents a reminder
	"""	
	def __init__(self, user_id: int, reminder_id: int) -> None:
		"""Create an instance.

		Args:
			user_id (int): The ID of the user.
			reminder_id (int): The ID of the reminder.

		Raises:
			ReminderNotFound: Reminder with given ID does not exist or is not
			owned by user.
		"""
		self.id = reminder_id

		# Check if reminder exists
		if not get_db().execute(
			"SELECT 1 FROM reminders WHERE id = ? AND user_id = ? LIMIT 1",
			(self.id, user_id)
		).fetchone():
			raise ReminderNotFound

		return

	def _get_notification_services(self) -> List[int]:
		"""Get ID's of notification services linked to the reminder.

		Returns:
			List[int]: The list with ID's.
		"""
		result = [
			r[0]
			for r in get_db().execute("""
				SELECT notification_service_id
				FROM reminder_services
				WHERE reminder_id = ?;
				""",
				(self.id,)
			)
		]
		return result

	def get(self) -> dict:
		"""Get info about the reminder

		Returns:
			dict: The info about the reminder
		"""
		reminder = get_db(dict).execute("""
			SELECT
				id,
				title, text,
				time,
				repeat_quantity,
				repeat_interval,
				weekdays,
				color
			FROM reminders
			WHERE id = ?
			LIMIT 1;
			""",
			(self.id,)
		).fetchone()
		reminder = dict(reminder)

		reminder["weekdays"] = [
			int(n)
			for n in reminder["weekdays"].split(",")
			if n
		] if reminder["weekdays"] else None
		reminder['notification_services'] = self._get_notification_services()

		return reminder

	def update(
		self,
		title: Union[None, str] = None,
		time: Union[None, int] = None,
		notification_services: Union[None, List[int]] = None,
		text: Union[None, str] = None,
		repeat_quantity: Union[None, RepeatQuantity] = None,
		repeat_interval: Union[None, int] = None,
		weekdays: Union[None, List[int]] = None,
		color: Union[None, str] = None
	) -> dict:
		"""Edit the reminder.

		Args:
			title (Union[None, str]): The new title of the entry.
				Defaults to None.

			time (Union[None, int]): The new UTC epoch timestamp when the
			reminder should be send.
				Defaults to None.

			notification_services (Union[None, List[int]]): The new list
			of id's of the notification services to use to send the reminder.
				Defaults to None.

			text (Union[None, str], optional): The new body of the reminder.
				Defaults to None.

			repeat_quantity (Union[None, RepeatQuantity], optional): The new
			quantity of the repeat specified for the reminder.
				Defaults to None.

			repeat_interval (Union[None, int], optional): The new amount of
			repeat_quantity, like "5" (hours).
				Defaults to None.

			weekdays (Union[None, List[int]], optional): The new indexes of
			the days of the week that the reminder should run.
				Defaults to None.

			color (Union[None, str], optional): The new hex code of the color
			of the reminder, which is shown in the web-ui.
				Defaults to None.

		Note about args:
			Either repeat_quantity and repeat_interval are given, weekdays is
			given or neither, but not both.

		Raises:
			NotificationServiceNotFound: One of the notification services was not found.
			InvalidKeyValue: The value of one of the keys is not valid or
			the "Note about args" is violated.

		Returns:
			dict: The new reminder info.
		"""
		LOGGER.info(
			f'Updating notification service {self.id}: '
			+ f'{title=}, {time=}, {notification_services=}, {text=}, '
			+ f'{repeat_quantity=}, {repeat_interval=}, {weekdays=}, {color=}'
		)
		cursor = get_db()

		# Validate data
		if repeat_quantity is None and repeat_interval is not None:
			raise InvalidKeyValue('repeat_quantity', repeat_quantity)
		elif repeat_quantity is not None and repeat_interval is None:
			raise InvalidKeyValue('repeat_interval', repeat_interval)
		elif weekdays is not None and repeat_quantity is not None:
			raise InvalidKeyValue('weekdays', weekdays)

		repeated_reminder = (
			(repeat_quantity is not None and repeat_interval is not None)
			or weekdays is not None
		)

		if time is not None:
			if not repeated_reminder:
				if time < datetime.utcnow().timestamp():
					raise InvalidTime
			time = round(time)

		# Get current data and update it with new values
		data = self.get()
		new_values = {
			'title': title,
			'time': time,
			'text': text,
			'repeat_quantity': repeat_quantity,
			'repeat_interval': repeat_interval,
			'weekdays': when_not_none(
				weekdays,
				lambda w: ",".join(map(str, sorted(w)))
			),
			'color': color
		}
		for k, v in new_values.items():
			if (
				k in ('repeat_quantity', 'repeat_interval', 'weekdays', 'color')
				or v is not None
			):
				data[k] = v

		# Update database
		rq = when_not_none(
			data["repeat_quantity"],
			lambda q: q.value
		)
		if repeated_reminder:
			next_time = _find_next_time(
				data["time"],
				data["repeat_quantity"],
				data["repeat_interval"],
				weekdays
			)
			cursor.execute("""
				UPDATE reminders
				SET
					title=?,
					text=?,
					time=?,
					repeat_quantity=?,
					repeat_interval=?,
					weekdays=?,
					original_time=?,
					color=?
				WHERE id = ?;
				""", (
					data["title"],
					data["text"],
					next_time,
					rq,
					data["repeat_interval"],
					data["weekdays"],
					data["time"],
					data["color"],
					self.id
			))

		else:
			next_time = data["time"]
			cursor.execute("""
				UPDATE reminders
				SET
					title=?,
					text=?,
					time=?,
					repeat_quantity=?,
					repeat_interval=?,
					weekdays=?,
					color=?
				WHERE id = ?;
				""", (
					data["title"],
					data["text"],
					data["time"],
					rq,
					data["repeat_interval"],
					data["weekdays"],
					data["color"],
					self.id
			))

		if notification_services:
			cursor.connection.isolation_level = None
			cursor.execute("BEGIN TRANSACTION;")
			cursor.execute(
				"DELETE FROM reminder_services WHERE reminder_id = ?",
				(self.id,)
			)
			try:
				cursor.executemany("""
					INSERT INTO reminder_services(
						reminder_id,
						notification_service_id
					)
					VALUES (?,?);
					""",
					((self.id, s) for s in notification_services)
				)
				cursor.execute("COMMIT;")

			except IntegrityError:
				raise NotificationServiceNotFound

			finally:
				cursor.connection.isolation_level = ""

		ReminderHandler().find_next_reminder(next_time)
		return self.get()

	def delete(self) -> None:
		"""Delete the reminder
		"""
		LOGGER.info(f'Deleting reminder {self.id}')
		get_db().execute("DELETE FROM reminders WHERE id = ?", (self.id,))
		ReminderHandler().find_next_reminder()
		return

class Reminders:
	"""Represents the reminder library of the user account
	"""

	def __init__(self, user_id: int) -> None:
		"""Create an instance.

		Args:
			user_id (int): The ID of the user.
		"""
		self.user_id = user_id
		return

	def fetchall(
		self,
		sort_by: SortingMethod = SortingMethod.TIME
	) -> List[dict]:
		"""Get all reminders

		Args:
			sort_by (SortingMethod, optional): How to sort the result.
				Defaults to SortingMethod.TIME.

		Returns:
			List[dict]: The id, title, text, time and color of each reminder
		"""
		reminders = [
			dict(r)
			for r in get_db(dict).execute("""
				SELECT
					id,
					title, text,
					time,
					repeat_quantity,
					repeat_interval,
					weekdays,
					color
				FROM reminders
				WHERE user_id = ?;
				""",
				(self.user_id,)
			)
		]
		for r in reminders:
			r["weekdays"] = [
				int(n)
				for n in r["weekdays"].split(",")
				if n
			] if r["weekdays"] else None

		# Sort result
		reminders.sort(key=sort_by.value[0], reverse=sort_by.value[1])

		return reminders

	def search(
		self,
		query: str,
		sort_by: SortingMethod = SortingMethod.TIME) -> List[dict]:
		"""Search for reminders

		Args:
			query (str): The term to search for.
			sort_by (SortingMethod, optional): How to sort the result.
				Defaults to SortingMethod.TIME.

		Returns:
			List[dict]: All reminders that match. Similar output to self.fetchall
		"""
		reminders = [
			r for r in self.fetchall(sort_by)
			if search_filter(query, r)
		]
		return reminders

	def fetchone(self, id: int) -> Reminder:
		"""Get one reminder

		Args:
			id (int): The id of the reminder to fetch

		Returns:
			Reminder: A Reminder instance
		"""		
		return Reminder(self.user_id, id)

	def add(
		self,
		title: str,
		time: int,
		notification_services: List[int],
		text: str = '',
		repeat_quantity: Union[None, RepeatQuantity] = None,
		repeat_interval: Union[None, int] = None,
		weekdays: Union[None, List[int]] = None,
		color: Union[None, str] = None
	) -> Reminder:
		"""Add a reminder

		Args:
			title (str): The title of the entry.

			time (int): The UTC epoch timestamp the the reminder should be send.

			notification_services (List[int]): The id's of the notification services
			to use to send the reminder.

			text (str, optional): The body of the reminder.
				Defaults to ''.

			repeat_quantity (Union[None, RepeatQuantity], optional): The quantity
			of the repeat specified for the reminder.
				Defaults to None.

			repeat_interval (Union[None, int], optional): The amount of repeat_quantity,
			like "5" (hours).
				Defaults to None.

			weekdays (Union[None, List[int]], optional): The indexes of the days
			of the week that the reminder should run.
				Defaults to None.

			color (Union[None, str], optional): The hex code of the color of the
			reminder, which is shown in the web-ui.
				Defaults to None.

		Note about args:
			Either repeat_quantity and repeat_interval are given,
			weekdays is given or neither, but not both.

		Raises:
			NotificationServiceNotFound: One of the notification services was not found.
			InvalidKeyValue: The value of one of the keys is not valid
			or the "Note about args" is violated.

		Returns:
			dict: The info about the reminder.
		"""
		LOGGER.info(
			f'Adding reminder with {title=}, {time=}, {notification_services=}, '
			+ f'{text=}, {repeat_quantity=}, {repeat_interval=}, {weekdays=}, {color=}'
		)
		
		if time < datetime.utcnow().timestamp():
			raise InvalidTime
		time = round(time)

		if repeat_quantity is None and repeat_interval is not None:
			raise InvalidKeyValue('repeat_quantity', repeat_quantity)
		elif repeat_quantity is not None and repeat_interval is None:
			raise InvalidKeyValue('repeat_interval', repeat_interval)
		elif (
			weekdays is not None
			and repeat_quantity is not None
			and repeat_interval is not None
		):
			raise InvalidKeyValue('weekdays', weekdays)

		cursor = get_db()
		for service in notification_services:
			if not cursor.execute("""
				SELECT 1
				FROM notification_services
				WHERE id = ?
					AND user_id = ?
				LIMIT 1;
				""",
				(service, self.user_id)
			).fetchone():
				raise NotificationServiceNotFound

		# Prepare args
		if any((repeat_quantity, weekdays)):
			original_time = time
			time = _find_next_time(
				original_time,
				repeat_quantity,
				repeat_interval,
				weekdays
			)
		else:
			original_time = None

		weekdays_str = when_not_none(
			weekdays,
			lambda w: ",".join(map(str, sorted(w)))
		)
		repeat_quantity_str = when_not_none(
			repeat_quantity,
			lambda q: q.value
		)

		cursor.connection.isolation_level = None
		cursor.execute("BEGIN TRANSACTION;")

		id = cursor.execute("""
			INSERT INTO reminders(
				user_id,
				title, text,
				time,
				repeat_quantity, repeat_interval,
				weekdays,
				original_time,
				color
			)
			VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?);
			""", (
				self.user_id,
				title, text,
				time,
				repeat_quantity_str,
				repeat_interval,
				weekdays_str,
				original_time,
				color
		)).lastrowid

		try:
			cursor.executemany("""
				INSERT INTO reminder_services(
					reminder_id,
					notification_service_id
				)
				VALUES (?, ?);
				""",
				((id, service) for service in notification_services)
			)
			cursor.execute("COMMIT;")

		except IntegrityError:
			raise NotificationServiceNotFound

		finally:
			cursor.connection.isolation_level = ''
		
		ReminderHandler().find_next_reminder(time)

		return self.fetchone(id)

	def test_reminder(
		self,
		title: str,
		notification_services: List[int],
		text: str = ''
	) -> None:
		"""Test send a reminder draft.

		Args:
			title (str): Title title of the entry.

			notification_service (int): The id of the notification service to
			use to send the reminder.

			text (str, optional): The body of the reminder.
				Defaults to ''.
		"""
		LOGGER.info(f'Testing reminder with {title=}, {notification_services=}, {text=}')
		a = Apprise()
		cursor = get_db(dict)

		for service in notification_services:
			url = cursor.execute("""
				SELECT url
				FROM notification_services
				WHERE id = ?
					AND user_id = ?
				LIMIT 1;
				""",
				(service, self.user_id)
			).fetchone()
			if not url:
				raise NotificationServiceNotFound
			a.add(url[0])

		a.notify(title=title, body=text or '\u200B')
		return


class ReminderHandler(metaclass=Singleton):
	"""Handle set reminders.
	
	Note: Singleton.
	"""	
	def __init__(
		self,
		context: Callable[[], AppContext]
	) -> None:
		"""Create instance of handler.

		Args:
			context (Optional[AppContext], optional): `Flask.app_context`.
				Defaults to None.
		"""
		self.context = context
		self.thread: Union[Timer, None] = None
		self.time: Union[int, None] = None
		return

	def __trigger_reminders(self, time: int) -> None:
		"""Trigger all reminders that are set for a certain time

		Args:
			time (int): The time of the reminders to trigger
		"""
		with self.context():
			cursor = get_db(dict)
			reminders = [
				dict(r)
				for r in cursor.execute("""
					SELECT
						id, user_id,
						title, text,
						repeat_quantity, repeat_interval,
						weekdays,
						original_time
					FROM reminders
					WHERE time = ?;
					""",
					(time,)
				)
			]
			
			for reminder in reminders:
				cursor.execute("""
					SELECT url
					FROM reminder_services rs
					INNER JOIN notification_services ns
					ON rs.notification_service_id = ns.id
					WHERE rs.reminder_id = ?;
					""",
					(reminder['id'],)
				)

				# Send reminder
				a = Apprise()
				for url in cursor:
					a.add(url['url'])
				a.notify(title=reminder["title"], body=reminder["text"] or '\u200B')

				self.thread = None
				self.time = None

				if (reminder['repeat_quantity'], reminder['weekdays']) == (None, None):
					# Delete the reminder from the database
					Reminder(reminder["user_id"], reminder["id"]).delete()

				else:
					# Set next time
					new_time = _find_next_time(
						reminder['original_time'],
						when_not_none(
							reminder["repeat_quantity"],
							lambda q: RepeatQuantity(q)
						),
						reminder['repeat_interval'],
						when_not_none(
							reminder["weekdays"],
							lambda w: [int(d) for d in w.split(',')]
						)
					)
					cursor.execute(
						"UPDATE reminders SET time = ? WHERE id = ?;",
						(new_time, reminder['id'])
					)

				self.find_next_reminder()
			return

	def find_next_reminder(self, time: Optional[int] = None) -> None:
		"""Determine when the soonest reminder is and set the timer to that time

		Args:
			time (Optional[int], optional): The timestamp to check for.
			Otherwise check soonest in database.
				Defaults to None.
		"""
		if time is None:
			with self.context():
				soonest_time: Union[Tuple[int], None] = get_db().execute("""
					SELECT DISTINCT r1.time
					FROM reminders r1
					LEFT JOIN reminders r2
					ON r1.time > r2.time
					WHERE r2.id IS NULL;
				""").fetchone()
				if soonest_time is None:
					return
				time = soonest_time[0]

		if (
			self.thread is None
			or time < self.time
		):
			if self.thread is not None:
				self.thread.cancel()

			t = time - datetime.utcnow().timestamp()
			self.thread = Timer(
				t,
				self.__trigger_reminders,
				(time,)
			)
			self.thread.name = "ReminderHandler"
			self.thread.start()
			self.time = time

		return
	
	def stop_handling(self) -> None:
		"""Stop the timer if it's active
		"""
		if self.thread is not None:
			self.thread.cancel()
		return