import os
import re
from dataclasses import dataclass
from pathlib import PurePath
from typing import Awaitable, List, Optional, Pattern, Set, Tuple, Union
from urllib.parse import urljoin

from bs4 import BeautifulSoup, Tag

from ..config import Config
from ..logging import ProgressBar, log
from ..output_dir import FileSink
from ..utils import soupify
from .crawler import CrawlError
from .http_crawler import HttpCrawler, HttpCrawlerSection


class KitIpdCrawlerSection(HttpCrawlerSection):
    def target(self) -> str:
        target = self.s.get("target")
        if not target:
            self.missing_value("target")

        if not target.startswith("https://"):
            self.invalid_value("target", target, "Should be a URL")

        return target

    def link_regex(self) -> Pattern[str]:
        regex = self.s.get("link_regex", r"^.*?[^/]+\.(pdf|zip|c|cpp|java)$")
        return re.compile(regex)


@dataclass(unsafe_hash=True)
class KitIpdFile:
    name: str
    url: str


@dataclass
class KitIpdFolder:
    name: str
    files: List[KitIpdFile]

    def explain(self) -> None:
        log.explain_topic(f"Folder {self.name!r}")
        for file in self.files:
            log.explain(f"File {file.name!r} (href={file.url!r})")

    def __hash__(self) -> int:
        return self.name.__hash__()


class KitIpdCrawler(HttpCrawler):

    def __init__(
            self,
            name: str,
            section: KitIpdCrawlerSection,
            config: Config,
    ):
        super().__init__(name, section, config)
        self._url = section.target()
        self._file_regex = section.link_regex()

    async def _run(self) -> None:
        maybe_cl = await self.crawl(PurePath("."))
        if not maybe_cl:
            return

        tasks: List[Awaitable[None]] = []

        async with maybe_cl:
            for item in await self._fetch_items():
                if isinstance(item, KitIpdFolder):
                    tasks.append(self._crawl_folder(item))
                else:
                    # Orphan files are placed in the root folder
                    tasks.append(self._download_file(PurePath("."), item))

        await self.gather(tasks)

    async def _crawl_folder(self, folder: KitIpdFolder) -> None:
        path = PurePath(folder.name)
        if not await self.crawl(path):
            return

        tasks = [self._download_file(path, file) for file in folder.files]

        await self.gather(tasks)

    async def _download_file(self, parent: PurePath, file: KitIpdFile) -> None:
        element_path = parent / file.name
        maybe_dl = await self.download(element_path)
        if not maybe_dl:
            return

        async with maybe_dl as (bar, sink):
            await self._stream_from_url(file.url, sink, bar)

    async def _fetch_items(self) -> Set[Union[KitIpdFile, KitIpdFolder]]:
        page, url = await self.get_page()
        elements: List[Tag] = self._find_file_links(page)
        items: Set[Union[KitIpdFile, KitIpdFolder]] = set()

        for element in elements:
            folder_label = self._find_folder_label(element)
            if folder_label:
                folder = self._extract_folder(folder_label, url)
                if folder not in items:
                    items.add(folder)
                    folder.explain()
            else:
                file = self._extract_file(element, url)
                items.add(file)
                log.explain_topic(f"Orphan file {file.name!r} (href={file.url!r})")
                log.explain("Attributing it to root folder")

        return items

    def _extract_folder(self, folder_tag: Tag, url: str) -> KitIpdFolder:
        files: List[KitIpdFile] = []
        name = folder_tag.getText().strip()

        container: Tag = folder_tag.findNextSibling(name="table")
        for link in self._find_file_links(container):
            files.append(self._extract_file(link, url))

        return KitIpdFolder(name, files)

    @staticmethod
    def _find_folder_label(file_link: Tag) -> Optional[Tag]:
        enclosing_table: Tag = file_link.findParent(name="table")
        if enclosing_table is None:
            return None
        return enclosing_table.findPreviousSibling(name=re.compile("^h[1-6]$"))

    def _extract_file(self, link: Tag, url: str) -> KitIpdFile:
        url = self._abs_url_from_link(url, link)
        name = os.path.basename(url)
        return KitIpdFile(name, url)

    def _find_file_links(self, tag: Union[Tag, BeautifulSoup]) -> List[Tag]:
        return tag.findAll(name="a", attrs={"href": self._file_regex})

    def _abs_url_from_link(self, url: str, link_tag: Tag) -> str:
        return urljoin(url, link_tag.get("href"))

    async def _stream_from_url(self, url: str, sink: FileSink, bar: ProgressBar) -> None:
        async with self.session.get(url, allow_redirects=False) as resp:
            if resp.status == 403:
                raise CrawlError("Received a 403. Are you within the KIT network/VPN?")
            if resp.content_length:
                bar.set_total(resp.content_length)

            async for data in resp.content.iter_chunked(1024):
                sink.file.write(data)
                bar.advance(len(data))

            sink.done()

    async def get_page(self) -> Tuple[BeautifulSoup, str]:
        async with self.session.get(self._url) as request:
            # The web page for Algorithmen für Routenplanung contains some
            # weird comments that beautifulsoup doesn't parse correctly. This
            # hack enables those pages to be crawled, and should hopefully not
            # cause issues on other pages.
            content = (await request.read()).decode("utf-8")
            content = re.sub(r"<!--.*?-->", "", content)
            return soupify(content.encode("utf-8")), str(request.url)