import qwarc.aiohttp
from qwarc.const import *
import qwarc.utils
import qwarc.warc


import aiohttp as _aiohttp
if _aiohttp.__version__ != '2.3.10':
	raise ImportError('aiohttp must be version 2.3.10')
import asyncio
import collections
import concurrent.futures
import itertools
import logging
import os
import random
import sqlite3
import yarl


class Item:
	itemType = None

	def __init__(self, itemValue, session, headers, warc):
		self.itemValue = itemValue
		self.session = session
		self.headers = headers
		self.warc = warc
		self.stats = {'tx': 0, 'rx': 0, 'requests': 0}

		self.childItems = []

	async def fetch(self, url, responseHandler = qwarc.utils.handle_response_default):
		'''
		HTTP GET a URL

		url: str or yarl.URL
		responseHandler: a callable that determines how the response is handled. See qwarc.utils.handle_response_default for details.

		Returns response (a ClientResponse object or None) and history (a tuple of (response, exception) tuples).
			response can be None and history can be an empty tuple, depending on the circumstances (e.g. timeouts).
		'''

		#TODO: Rewrite using 'async with self.session.get'

		url = yarl.URL(url) # Explicitly convert for normalisation, percent-encoding, etc.
		history = []
		attempt = 0
		#TODO redirectLevel
		while True:
			attempt += 1
			response = None
			exc = None
			action = ACTION_RETRY
			writeToWarc = True
			try:
				try:
					with _aiohttp.Timeout(60):
						logging.info('Fetching {}'.format(url))
						response = await self.session.get(url, headers = self.headers, allow_redirects = False)
						try:
							ret = await response.text(errors = 'surrogateescape')
						except:
							# No calling the handleResponse callback here because this is really bad. The not-so-bad exceptions (e.g. an error during reading the response) will be caught further down.
							response.close()
							raise
						else:
							tx = len(response.rawRequestData)
							rx = len(response.rawResponseData)
							logging.info('Fetched {}: {} (tx {}, rx {})'.format(url, response.status, tx, rx))
							self.stats['tx'] += tx
							self.stats['rx'] += rx
							self.stats['requests'] += 1
				except (asyncio.TimeoutError, _aiohttp.ClientError) as e:
					logging.error('Request for {} failed: {!r}'.format(url, e))
					action, writeToWarc = await responseHandler(url, attempt, response, e)
					exc = e # Pass the exception outward for the history
				else:
					action, writeToWarc = await responseHandler(url, attempt, response, None)
				history.append((response, exc))
				if action in (ACTION_SUCCESS, ACTION_IGNORE):
					return response, tuple(history)
				elif action == ACTION_FOLLOW_OR_SUCCESS:
					redirectUrl = response.headers.get('Location') or response.headers.get('URI')
					if not redirectUrl:
						return response, tuple(history)
					url = url.join(yarl.URL(redirectUrl))
					attempt = 0
				elif action == ACTION_RETRY:
					# Nothing to do, just go to the next cycle
					pass
			finally:
				if response:
					if writeToWarc:
						self.warc.write_client_response(response)
					await response.release()

	async def process(self):
		raise NotImplementedError

	@classmethod
	def generate(cls):
		yield from () # Generate no items by default

	@classmethod
	def _gen(cls):
		for x in cls.generate():
			yield (cls.itemType, x, STATUS_TODO) 

	def add_item(self, itemClassOrType, itemValue):
		if issubclass(itemClassOrType, Item):
			item = (itemClassOrType.itemType, itemValue)
		else:
			item = (itemClassOrType, itemValue)
		if item not in self.childItems:
			self.childItems.append(item)


class QWARC:
	def __init__(self, itemClasses, warcBasePath, dbPath, concurrency = 1, memoryLimit = 0, minFreeDisk = 0, warcSizeLimit = 0):
		'''
		itemClasses: iterable of Item
		warcBasePath: str, base name of the WARC files
		dbPath: str, path to the sqlite3 database file
		concurrency: int, number of concurrently processed items
		memoryLimit: int, gracefully stop when the process uses more than memoryLimit bytes of RSS; 0 disables the memory check
		minFreeDisk: int, pause when there's less than minFreeDisk space on the partition where WARCs are written; 0 disables the disk space check
		warcSizeLimit: int, size of each WARC file; 0 if the WARCs should not be split
		'''

		self._itemClasses = itemClasses
		self._itemTypeMap = {cls.itemType: cls for cls in itemClasses}
		self._warcBasePath = warcBasePath
		self._dbPath = dbPath
		self._concurrency = concurrency
		self._memoryLimit = memoryLimit
		self._minFreeDisk = minFreeDisk
		self._warcSizeLimit = warcSizeLimit

	async def obtain_exclusive_db_lock(self, db):
		c = db.cursor()
		while True:
			try:
				c.execute('BEGIN EXCLUSIVE')
				break
			except sqlite3.OperationalError as e:
				if str(e) != 'database is locked':
					raise
				await asyncio.sleep(1)
		return c

	def _make_item(self, itemType, itemValue, session, headers, warc):
		try:
			itemClass = self._itemTypeMap[itemType]
		except KeyError:
			raise RuntimeError('No such item type: {!r}'.format(itemType))
		return itemClass(itemValue, session, headers, warc)

	async def run(self, loop):
		headers = [('User-Agent', 'Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Firefox/52.0')] #TODO: Move elsewhere

		tasks = set()
		sleepTasks = set()
		sessions = [] # aiohttp.ClientSession instances
		freeSessions = collections.deque() # ClientSession instances that are currently free

		for i in range(self._concurrency):
			session = _aiohttp.ClientSession(
			  connector = qwarc.aiohttp.TCPConnector(loop = loop),
			  request_class = qwarc.aiohttp.ClientRequest,
			  response_class = qwarc.aiohttp.ClientResponse,
			  skip_auto_headers = ['Accept-Encoding'],
			  loop = loop
			)
			sessions.append(session)
			freeSessions.append(session)

		warc = qwarc.warc.WARC(self._warcBasePath, self._warcSizeLimit)

		db = sqlite3.connect(self._dbPath, timeout = 1)
		db.isolation_level = None # Transactions are handled manually below.
		db.execute('PRAGMA synchronous = OFF')

		try:
			async def wait_for_free_task():
				nonlocal tasks, freeSessions, db, emptyTodoSleep
				done, pending = await asyncio.wait(tasks, return_when = concurrent.futures.FIRST_COMPLETED)
				for future in done:
					# TODO Replace all of this with `if future.cancelled():`
					try:
						await future #TODO: Is this actually necessary? asyncio.wait only returns 'done' futures...
					except concurrent.futures.CancelledError as e:
						# Got cancelled, nothing we can do about it, but let's log a warning if it's a process task
						if isinstance(future, asyncio.Task):
							if future.taskType == 'process_item':
								logging.warning('Task for {}:{} cancelled: {!r}'.format(future.itemType, future.itemValue, future))
							elif future.taskType == 'sleep':
								sleepTasks.remove(future)
						continue
					if future.taskType == 'sleep':
						# Dummy task for empty todo list, see below.
						sleepTasks.remove(future)
						continue
					item = future.item
					logging.info('{itemType}:{itemValue} done: {requests} requests, {tx} tx, {rx} rx'.format(itemType = future.itemType, itemValue = future.itemValue, **item.stats))
					cursor = await self.obtain_exclusive_db_lock(db)
					try:
						cursor.execute('UPDATE items SET status = ? WHERE id = ?', (STATUS_DONE, future.id))
						if item.childItems:
							it = iter(item.childItems)
							while True:
								values = [(t, v, STATUS_TODO) for t, v in itertools.islice(it, 100000)]
								if not values:
									break
								cursor.executemany('INSERT INTO items (type, value, status) VALUES (?, ?, ?)', values)
						cursor.execute('COMMIT')
					except:
						cursor.execute('ROLLBACK')
						raise
					freeSessions.append(item.session)
				tasks = pending

			while True:
				while len(tasks) >= self._concurrency:
					emptyTodoFullReached = True
					await wait_for_free_task()

				if self._minFreeDisk and too_little_disk_space(self._minFreeDisk):
					logging.info('Disk space is low, sleeping')
					sleepTask = asyncio.sleep(random.uniform(self._concurrency / 2, self._concurrency * 1.5))
					sleepTask.taskType = 'sleep'
					tasks.add(sleepTask)
					sleepTasks.add(sleepTask)
					continue

				cursor = await self.obtain_exclusive_db_lock(db)
				try:
					cursor.execute('SELECT id, type, value, status FROM items WHERE status = ? LIMIT 1', (STATUS_TODO,))
					result = cursor.fetchone()
					if not result:
						if cursor.execute('SELECT id, status FROM items WHERE status != ? LIMIT 1', (STATUS_DONE,)).fetchone():
							# There is currently no item to do, but there are still some in progress, so more TODOs may appear in the future.
							# It would be nice if we could just await wait_for_free_task() here, but that doesn't work because those TODOs might be in another process.
							# So instead, we insert a dummy task which just sleeps a bit. Average sleep time is equal to concurrency, i.e. one check per second.
							#TODO: The average sleep time is too large if there are only few sleep tasks; scale with len(sleepTasks)/self._concurrency?
							sleepTask = asyncio.ensure_future(asyncio.sleep(random.uniform(self._concurrency / 2, self._concurrency * 1.5)))
							sleepTask.taskType = 'sleep'
							tasks.add(sleepTask)
							sleepTasks.add(sleepTask)
							cursor.execute('COMMIT')
							continue
						else:
							# Really nothing to do anymore
							#TODO: Another process may be running create_db, in which case we'd still want to wait...
							# create_db could insert a dummy item which is marked as done when the DB is ready
							cursor.execute('COMMIT')
							break
					emptyTodoSleep = 0
					id, itemType, itemValue, status = result
					cursor.execute('UPDATE items SET status = ? WHERE id = ?', (STATUS_INPROGRESS, id))
					cursor.execute('COMMIT')
				except:
					cursor.execute('ROLLBACK')
					raise

				session = freeSessions.popleft()
				item = self._make_item(itemType, itemValue, session, headers, warc)
				task = asyncio.ensure_future(item.process())
				#TODO: Is there a better way to add custom information to a task/coroutine object?
				task.taskType = 'process'
				task.id = id
				task.itemType = itemType
				task.itemValue = itemValue
				task.item = item
				tasks.add(task)
				if os.path.exists('STOP'):
					logging.info('Gracefully shutting down due to STOP file')
					break
				if self._memoryLimit and uses_too_much_memory(self._memoryLimit):
					logging.info('Gracefully shutting down due to memory usage (current = {} > limit = {})'.format(get_rss(), self._memoryLimit))
					break

			for sleepTask in sleepTasks:
				sleepTask.cancel()

			while len(tasks):
				await wait_for_free_task()

			logging.info('Done')
		except (Exception, KeyboardInterrupt) as e:
			# Kill all tasks
			for task in tasks:
				task.cancel()
			await asyncio.wait(tasks, return_when = concurrent.futures.ALL_COMPLETED)

			raise
		finally:
			for session in sessions:
				session.close()
			warc.close()
			db.close()

	def create_db(self):
		db = sqlite3.connect(self._dbPath, timeout = 1)
		db.execute('PRAGMA synchronous = OFF')
		with db:
			db.execute('CREATE TABLE items (id INTEGER PRIMARY KEY, type TEXT, value TEXT, status INTEGER)')
			db.execute('CREATE INDEX items_status_idx ON items (status)')

		it = itertools.chain(*(i._gen() for i in self._itemClasses))
		while True:
			values = tuple(itertools.islice(it, 100000))
			if not values:
				break
			with db:
				db.executemany('INSERT INTO items (type, value, status) VALUES (?, ?, ?)', values)