from threading import Thread
from urllib.robotparser import RobotFileParser
from urllib.error import URLError
from urllib.parse import urlparse

from ssl import CertificateError
from random import sample, randrange, randint
import re
from datetime import datetime, timedelta

import asyncio
import aiohttp
import async_timeout

from bs4 import BeautifulSoup, Comment

from profiles.models import BrowserFingerprint, SearchEngine

# Ugly hack to use this module alone instead of integrating it with Django
# from django.conf import settings

# Gets all the direct bookmarks in the html.
# We want this to avoid following this kind of bookmark

HARD_LIMIT = 20
MAX_PER_PAGE = 10

FOOTER_URL = re.compile(".*footer.*")


class Settings:
    USER_AGENT = 'Default User'

settings = Settings()


def url_getter(html, current_page, root_url):
    links_list = [] # The final resutl
    soup = BeautifulSoup(html, "html.parser")
    # Get only the body
    body = soup.find('body')
    if not body:
        return links_list
    # remove the body
    if body.footer:
        body.footer.decompose()
    # remove all comments
    comments = soup.findAll(text=lambda text: isinstance(text, Comment))
    for comment in comments:
        comment.extract()

    footers = soup.findAll(id=FOOTER_URL)
    for footer in footers:
        footer.extract()

    # Remove all bookmark links pointing to the current html page.
    links = map(lambda link: link.get("href", ""), body.find_all("a"))
    for link in links:
        if link: #Edge case, if no href found.
            if link.startswith("http"):
                links_list.append(link)
            elif link.startswith('/'): #Internal link, linking to page root url
                links_list.append(root_url + link)
            elif link.startswith("#"):
                continue
            else:
                links_list.append(current_page + "/" + link)

    ## uniqifier works with python <= 3.6
    #seen = set()
    #links_list = [x for x in links_list if x not in seen and not seen.add(x)]
    # uniqifier
    # Works only with python >= 3.6
    links_list = list(dict.fromkeys(links_list))

    forbidden_words = ['login', 'agreement', 'mailto', 'settings']
    links_list = [link for link in links_list if not any(word in link.lower()
                                                         for word in
                                                         forbidden_words)]

    return links_list


class WebsiteSchedulerMeta(type):
    """ Meta-class for WebsiteScheduler, allowing a singleton class-like
    interface, but spawning one instance per canonical website URL """

    _instances = {}
    _canonicalize = re.compile(r'(https?://)?([^/]+)(/?|$)')

    def canonical_url(cls, url):
        """ Canonicalize a url """
        return cls._canonicalize.search(url).groups()[1]

    def __call__(cls, url, *args, **kwargs):
        canonical = cls.canonical_url(url)
        if canonical not in cls._instances:
            cls._instances[canonical] = \
                super(WebsiteSchedulerMeta, cls) \
                .__call__(canonical, *args, **kwargs)
        return cls._instances[canonical]


class WebsiteScheduler(metaclass=WebsiteSchedulerMeta):
    """ Schedule the accesses to a website as of robots.txt """

    search_engines = []  # Must be set by CrawlingThread.__init__

    def __init__(self, name, user_agent):
        self.name = name
        self.last_crawled = datetime.fromtimestamp(0)
        self.dead = False
        self.can_fetch_b = False
        self.user_agent = (user_agent if user_agent is not None
                           else settings.USER_AGENT)
        if any(self.urlroot() in item for item in self.search_engines):
            print("found a search engine for %s" % self.urlroot())
            self.crawl_delay = timedelta(seconds=5)
            self.can_fetch_b = True
        else:
            try:
                robots_url = self.urlroot() + 'robots.txt'
                self.robot_parser = RobotFileParser(robots_url)
                self.robot_parser.read()  # TODO async?
            except (URLError, CertificateError):
                try:
                    robots_url = self.unsafe_urlroot() + 'robots.txt'
                    self.robot_parser = RobotFileParser(robots_url)
                    self.robot_parser.read()
                except URLError:  # Almost surely an offline website.
                    self.dead = True
                    self.crawl_delay = 0
            except Exception as e:
                print(e)
                raise e
            if not self.robot_parser.default_entry:
                self.dead = True
            if not self.dead:
                delay = self.robot_parser.crawl_delay(self.user_agent)
                if delay is None:
                    req_rate = self.robot_parser.request_rate(self.user_agent)
                    if req_rate is None:
                        delay = 5
                    else:
                        delay = req_rate.requests, req_rate.seconds
                self.crawl_delay = timedelta(seconds=delay)

    def urlroot(self):
        ''' Get the root url for this website '''
        return 'https://{}/'.format(self.name)

    def unsafe_urlroot(self):
        return 'http://{}/'.format(self.name)

    def fetch_delay(self):
        ''' Get the delay needed before fetching a page is possible '''
        can_fetch_time = self.last_crawled + self.crawl_delay
        if can_fetch_time < datetime.now():
            return timedelta(0)
        return can_fetch_time - datetime.now()

    def can_fetch(self, url):
        ''' Check whether this program can fetch a given page '''
        return ((self.can_fetch_b)
                or ((not self.dead) and
                    self.robot_parser.can_fetch(self.user_agent, url)))

    def fetching(self):
        ''' Tell the scheduler that a page is being fetched now '''
        self.last_crawled = datetime.now()


class CrawlingThread(Thread):
    """ A separate thread for the crawling task. This is needed to use asyncio,
    since the thread will need its own event loop. """

    def __init__(self, url):
        engine_list = [engine.url for engine in SearchEngine.objects.all()]
        WebsiteScheduler.search_engines = engine_list

        nb_fingerprint = len(BrowserFingerprint.objects.all())
        fingerprint = BrowserFingerprint.objects.all()[
            randint(0, nb_fingerprint - 1)]
        self.headers = fingerprint.serialize_headers()

        self.output_tree = []
        super(CrawlingThread, self).__init__()
        self.url = url

    def run(self):
        tasks = []

        #tasks.append(async_crawler("http://plus.google.com/+Python"))
        #tasks.append(async_crawler('https://python.org/'))
        tasks.append(run_crawl(self.url, self.output_tree, self.headers))

        try:
            loop = asyncio.new_event_loop()
            asyncio.set_event_loop(loop)
            loop.run_until_complete(asyncio.wait(tasks))
        finally:
            loop.close()


class PageGetter:
    """ Asynchronously get a webpage, abiding by robots.txt """

    headers = None

    def __init__(self, session, url, user_agent):
        self.url = url
        self.session = session
        self.user_agent = user_agent

    async def get(self, ssl=True):
        """ Actually retrieve the webpage """
        scheduler = WebsiteScheduler(self.url, self.user_agent)
        if not scheduler.can_fetch(self.url):
            return None

        delay = scheduler.fetch_delay()
        while delay > timedelta(0):
            await asyncio.sleep(delay.total_seconds())
            delay = scheduler.fetch_delay()
        scheduler.fetching()
        async with async_timeout.timeout(10):
            async with self.session.get(self.url, verify_ssl=ssl) as resp:
                try:
                    return await resp.text()
                except UnicodeDecodeError:
                    return None


async def async_print(url):
    """ Debug function to follow what's actually happening """
    async with aiohttp.ClientSession() as session:
        html = await PageGetter(session, url,
                                settings.USER_AGENT).get(ssl=False)

        print('GOT {}HTML for {}'.format(
            'None ' if html is None else '',
            url,
        ))


class CrawlElem:
    ''' Describes a crawled element, to be assembled into a tree '''

    def __init__(self, url, parent):
        self.url = url
        self.parent = parent


async def run_crawl(url, output_tree, headers=None):
    ''' Starts a crawling session '''

    if headers is None:
        headers = {}
    if 'User-Agent' not in headers:
        headers['User-Agent'] = settings.USER_AGENT

    user_agent = headers['User-Agent']
    crawled = set()

    async with aiohttp.ClientSession(headers=headers) as session:
        await async_crawler(
            url, output_tree, crawled, user_agent, session, None)


def simplify_url(url):
    anchor = url.find('#')
    if anchor >= 0:
        url = url[:anchor]

    prot = url.find('://')
    if prot >= 0:
        url = url[prot+3:]

    if url.startswith('www.'):
        url = url[4:]

    return url


async def async_crawler(url, out_tree, crawled, user_agent, session, parent):
    if len(crawled) >= HARD_LIMIT:
        return
    crawled.add(simplify_url(url))
    parsed_url = urlparse(url)
    print("Crawling {}".format(url))
    try:
        with async_timeout.timeout(3):
            html = await PageGetter(session, url, user_agent).get(ssl=False)
    except asyncio.TimeoutError:
        return

    new_tasks = []

    if html:
        this_elem = CrawlElem(url, parent)
        out_tree.append(this_elem)
        new_urls = url_getter(
            html,
            url,
            parsed_url.scheme + "://" + parsed_url.netloc
        )
        if new_urls:
            sampled = sample(
                new_urls,
                randrange(min(MAX_PER_PAGE, len(new_urls)))
            )
            for sample_url in sampled:
                if simplify_url(sample_url) not in crawled:
                    new_tasks.append(async_crawler(
                        sample_url, out_tree, crawled, user_agent, session,
                        this_elem))
    else:
        print("No html received")
    if len(crawled) >= HARD_LIMIT:
        return
    if new_tasks:
        await asyncio.wait(new_tasks)