"""Reads F95zone metadata with an optional personal session cookie."""
import re
import urllib.error
import urllib.request
from html import unescape
from html.parser import HTMLParser
from urllib.parse import urljoin, urlparse

THREAD_RE = re.compile(r"^/threads/[^/]+\.\d+/?|^/threads/\d+/?")
UA = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124 Safari/537.36"
MAX_BYTES = 3 * 1024 * 1024
MAX_IMAGE_BYTES = 20 * 1024 * 1024
# first-post fields that are not part of the description itself
STOP_LABELS = ("thread updated", "release date", "developer", "censored", "version", "os",
               "language", "store", "genre", "installation", "changelog", "developer notes",
               "download", "animations")


def _request(url: str, referer: str | None = None, cookie: str = "", user_agent: str = "") -> urllib.request.Request:
    headers = {"User-Agent": user_agent or UA, "Accept-Language": "en-US,en;q=0.8"}
    if referer:
        headers["Referer"] = referer
    request = urllib.request.Request(url, headers=headers)
    cookie = cookie.strip()
    if "\r" in cookie or "\n" in cookie:
        raise F95Error("Некорректные cookie F95zone")
    if cookie:
        # Redirect handlers explicitly reapply the cookie after validating the next host.
        request.add_unredirected_header("Cookie", cookie)
    return request


def image_url(value: str) -> str | None:
    """Only download images hosted by F95; never follow arbitrary post links."""
    try:
        url = urljoin("https://f95zone.to/", value.strip())
        p = urlparse(url)
        port = p.port
    except ValueError:
        return None
    host = (p.hostname or "").lower()
    if (value.strip() and p.scheme in ("http", "https")
            and (host == "f95zone.to" or host.endswith(".f95zone.to"))
            and not p.username and not p.password and port in (None, 80, 443)
            and not p.path.startswith("/styles/") and "logo" not in p.path.lower()):
        return p._replace(scheme="https", fragment="").geturl()
    return None


class _F95Redirect(urllib.request.HTTPRedirectHandler):
    images = False

    def redirect_request(self, req, fp, code, msg, headers, newurl):
        target = image_url(newurl)
        if not target or (not self.images and urlparse(target).hostname not in ("f95zone.to", "www.f95zone.to")):
            raise F95Error("Неожиданный редирект F95zone")
        redirected = super().redirect_request(req, fp, code, msg, headers, target)
        if redirected is not None:
            cookie = req.get_header("Cookie", "")
            if cookie:
                redirected.add_unredirected_header("Cookie", cookie)
        return redirected


class _ImageRedirect(_F95Redirect):
    images = True


def fetch_image(url: str, thread_url: str, cookie: str = "", user_agent: str = "") -> bytes:
    target = image_url(url)
    if not target:
        raise F95Error("Недопустимая ссылка на превью F95zone")
    request = _request(target, thread_url, cookie, user_agent)
    try:
        with urllib.request.build_opener(_ImageRedirect()).open(request, timeout=15) as response:
            if response.headers.get_content_type() == "text/html":
                raise F95AuthError("F95zone запрашивает авторизацию для превью")
            data = response.read(MAX_IMAGE_BYTES + 1)
        if len(data) > MAX_IMAGE_BYTES:
            raise F95Error("Превью F95zone слишком большое")
        return data
    except urllib.error.HTTPError as e:
        if e.code in (401, 403):
            raise F95AuthError("F95zone не принял cookie или ограничил доступ к превью") from e
        raise F95Error("Не удалось скачать превью F95zone") from e
    except OSError as e:
        raise F95Error("Не удалось скачать превью F95zone") from e


class F95Error(Exception):
    pass


class F95AuthError(F95Error):
    pass


def validate_url(url: str) -> str:
    p = urlparse(url.strip())
    if p.scheme not in ("http", "https") or (p.hostname or "").lower() not in ("f95zone.to", "www.f95zone.to"):
        raise F95Error("Ссылка должна вести на тему f95zone.to")
    if not THREAD_RE.match(p.path):
        raise F95Error("Это не ссылка на тему (нужен вид f95zone.to/threads/…)")
    return f"https://f95zone.to{p.path}"


def fetch(url: str, cookie: str = "", user_agent: str = "") -> str:
    req = _request(url, cookie=cookie, user_agent=user_agent)
    try:
        with urllib.request.build_opener(_F95Redirect()).open(req, timeout=15) as r:
            final = urlparse(r.geturl())
            if (final.hostname or "") not in ("f95zone.to", "www.f95zone.to"):
                raise F95Error("Неожиданный редирект")
            return r.read(MAX_BYTES).decode("utf-8", "replace")
    except F95Error:
        raise
    except urllib.error.HTTPError as e:
        if e.code in (401, 403):
            raise F95AuthError("F95zone не принял cookie или ограничил доступ к теме") from e
        if e.code >= 500:
            raise F95Error(f"F95zone сейчас недоступен (ответил {e.code}), попробуйте позже")
        raise F95Error(f"F95zone ответил {e.code} (тема недоступна или сайт блокирует запрос)")
    except OSError:
        raise F95Error("Не удалось связаться с F95zone")


class _Parser(HTMLParser):
    """Collects <title>-less data: og:title, tag items and the text of the first .bbWrapper."""

    def __init__(self) -> None:
        super().__init__(convert_charrefs=True)
        self.og_title = ""
        self.og_image = None
        self.post_image = None
        self.tags: list[str] = []
        self.post: list[str] = []
        self.template = ""
        self.logged_in = None
        self._in_tag = False
        self._tag_buf = ""
        self._depth = 0      # div depth inside the first bbWrapper; 0 = outside
        self._done = False
        self._skip = 0       # inside hidden/spoiler blocks

    def handle_starttag(self, tag, attrs):
        a = dict(attrs)
        cls = (a.get("class") or "").split()
        if tag == "html":
            self.template = a.get("data-template") or ""
            self.logged_in = a.get("data-logged-in")
        elif tag == "meta" and a.get("property") == "og:title":
            self.og_title = a.get("content") or ""
        elif tag == "meta" and a.get("property") == "og:image":
            self.og_image = image_url(a.get("content") or "")
        elif tag == "a" and "tagItem" in cls:
            self._in_tag, self._tag_buf = True, ""
        if self._done:
            return
        if self._depth == 0:
            if tag == "div" and "bbWrapper" in cls and not self.post:
                self._depth = 1
            return
        if tag == "div":
            self._depth += 1
            if self._skip or {"bbCodeSpoiler", "messageHide"} & set(cls):
                self._skip += 1
        elif tag == "img" and "bbImage" in cls and not self._skip and not self.post_image:
            for key in ("data-src", "src"):
                if candidate := image_url(a.get(key) or ""):
                    self.post_image = candidate
                    break
        elif tag == "br" and not self._skip:
            self.post.append("\n")
        elif tag in ("script", "style"):
            self._skip += 1

    def handle_endtag(self, tag):
        if tag == "a" and self._in_tag:
            self._in_tag = False
            if t := self._tag_buf.strip().lower():
                self.tags.append(t)
        if self._depth and tag == "div":
            if self._skip:
                self._skip -= 1
            self._depth -= 1
            if self._depth == 0:
                self._done = True
        elif self._depth and tag in ("script", "style") and self._skip:
            self._skip -= 1

    def handle_data(self, data):
        if self._in_tag:
            self._tag_buf += data
        if self._depth and not self._skip and not self._done:
            self.post.append(data)


def parse(html: str) -> dict:
    p = _Parser()
    p.feed(html)
    if p.template == "login":
        raise F95AuthError("F95zone запрашивает авторизацию")
    if not p.post:
        raise F95Error("Тема не найдена или недоступна")
    title = unescape(p.og_title)
    # "VN - Ren'Py - Hooked! [v0.6.0] [BlenderKnight]" -> "Hooked!"
    title = re.sub(r"\s*\[[^\]]*\]", "", title)
    title = re.sub(r"^(?:[A-Za-z0-9'’ ]{1,20} - )+", "", title).strip()
    return {"title": title, "description": _description("".join(p.post)),
            "tags": sorted(set(p.tags)), "image_url": p.og_image or p.post_image,
            "logged_in": p.logged_in}


def _description(text: str) -> str:
    text = text.replace("​", "").replace("\xa0", " ")
    lines = [ln.strip() for ln in text.splitlines()]
    out: list[str] = []
    started = False
    for ln in lines:
        label = ln.split(":", 1)[0].strip().lower() if ":" in ln else ""
        if label in STOP_LABELS and started:
            break
        if label == "overview":
            started = True
            ln = ln.split(":", 1)[1].strip()
            if not ln:
                continue
        elif not started and label in STOP_LABELS:
            continue
        started = started or bool(ln)
        out.append(ln)
    return re.sub(r"\n{3,}", "\n\n", "\n".join(out)).strip()


def load(url: str, cookie: str = "", user_agent: str = "") -> dict:
    url = validate_url(url)
    return {**parse(fetch(url, cookie, user_agent)), "url": url}