import asyncio

from html.parser import HTMLParser
from random import sample
from sys import stderr
from urllib.parse import urlparse

from httpx import AsyncClient

from .linkmap import LinkMap


class HTMLLinkFinder(HTMLParser):

    links = []

    def handle_starttag(self, tag, attrs):
        if tag != "a":
            return
        for a in attrs:
            attr, val = a
            if attr != "href":
                continue
            if val.startswith("https://") or val.startswith("http://"):
                if not val in self.links:
                    self.links.append(val)

    def get_links(self, input_html:str):
        self.feed(input_html)
        return self.links


class LinkMapFromSitelinksGenerator:

    site_request_max_len = 10000000 # bytes
    site_request_timeout = 10 # seconds
    generated_linkmap = LinkMap()
    max_links_per_site = 3
    max_depth = 3
    enable_log = False

    def log(self, something):
        if self.enable_log:
            print(something, file=stderr)

    async def _get_html(self, url:str, client:AsyncClient) -> str:
        content = bytearray()
        content_size = 0
        # receive up to self.site_request_max_len bytes after
        # a maximum of self.site_request_timeout seconds
        self.log(f"Request: {url}")
        async with client.stream(
            "GET",
            url,
            timeout=self.site_request_timeout,
            follow_redirects=True
        ) as stream:
            async for chunk in stream.aiter_bytes(1024):
                content_size += len(chunk)
                if content_size > self.site_request_max_len:
                    self.log(f"Maximum content length exceeded! received: {content_size} (maximum: {self.site_request_max_len})")
                    break
                else:
                    content.extend(chunk)
        # decode
        try:
            html_content = content.decode()
        except UnicodeDecodeError:
            self.log(f"Couldn't decode {url}")
            html_content = ""
        return html_content

    async def _get_linked_sites_coro(self, url, client:AsyncClient):
        linked_sites = []
        try:
            html = await self._get_html(url, client)
            found_links = HTMLLinkFinder().get_links(html)
            found_links = sample(found_links, min(self.max_links_per_site, len(found_links)))
            for l in found_links:
                self.log(f"Found {l}")
                if l != None:
                    linked_sites.append(l)
        except KeyboardInterrupt:
            exit("KeyboardInterrupt")
        except Exception as e:
            self.log("An exception occcured while trying to get links from '" + url + "': ")
            self.log(e)
        return url, linked_sites

    async def _get_linked_sites(self, urls:list, client:AsyncClient):
        # get results
        results = await asyncio.gather(*[self._get_linked_sites_coro(url, client) for url in urls])
        results_as_dict = {}
        for url, links in results:
            results_as_dict[url] = links
        return results_as_dict

    async def _generate_linkmap(self, start_urls:list, _current_depth:int, client:AsyncClient):
        linkdict = {}
        linked_sites = await self._get_linked_sites(start_urls, client)
        for url in linked_sites:
            linkdict[url] = {}
            self.generated_linkmap.add_link(url)
            for l in linked_sites[url]:
                if l != url:
                    linkdict[url][l] = {}
                    self.generated_linkmap.add_link_connection(url, l)#
        if _current_depth < self.max_depth:
            for url in linkdict:
                linkdict[url] = await self._generate_linkmap(list(linkdict[url]), _current_depth + 1, client)

    async def generate(self, start_url:str, max_depth:int=3, max_links_per_site:int=3):
        self.generated_linkmap = LinkMap()
        self.max_links_per_site = max_links_per_site
        self.max_depth = max_depth
        async with AsyncClient() as client:
            await self._generate_linkmap([start_url], 1, client)

    def get_linkmap(self) -> LinkMap:
        return self.generated_linkmap