"""Extract off-platform file-host links from a post body.

Pure (no I/O) so it's unit-testable and reusable by EVERY in-house downloader's
import path — every platform stores its body in `Post.description`, so running
this there covers them all. Finds links to the supported external file hosts in
a post's HTML body (both `<a href="...">` anchors and bare URLs in text),
unwraps a Patreon outbound-redirect wrapper, and preserves the FULL url
including the `#fragment` (mega.nz puts the decryption key there) and the query
string — without those a mega download is impossible.
"""
from __future__ import annotations

import re
from dataclasses import dataclass
from html import unescape
from urllib.parse import parse_qs, urlsplit

# Supported file-host enum values (kept in sync with the external_link CHECK).
SUPPORTED_HOSTS = ("mega", "gdrive", "mediafire", "dropbox", "pixeldrain")

# Bare-domain suffix → canonical host label. Matched against the URL netloc
# (exact or as a dotted suffix, so www./dl. subdomains resolve too).
_HOST_MAP = {
    "mega.nz": "mega",
    "mega.co.nz": "mega",
    "drive.google.com": "gdrive",
    "mediafire.com": "mediafire",
    "dropbox.com": "dropbox",
    "pixeldrain.com": "pixeldrain",
}

# `<a href="...">label</a>` — DOTALL so a label spanning tags/newlines is caught.
_HREF_RE = re.compile(
    r"""<a\b[^>]*?\bhref=["']([^"']+)["'][^>]*>(.*?)</a>""",
    re.IGNORECASE | re.DOTALL,
)
_TAG_RE = re.compile(r"<[^>]+>")
# Bare http(s) URL in text. Stops at whitespace, quotes, angle brackets, and
# closing brackets — but KEEPS `#`, `&`, `?`, `=` so fragments/queries survive.
_URL_RE = re.compile(r"""https?://[^\s"'<>)\]}]+""", re.IGNORECASE)


@dataclass(frozen=True)
class ExtractedLink:
    host: str            # one of SUPPORTED_HOSTS
    url: str             # full url incl. query + #fragment
    label: str | None    # visible anchor text, when present


def _netloc(url: str) -> str:
    # Lowercase host without credentials or port.
    return urlsplit(url).netloc.lower().split("@")[-1].split(":")[0]


def host_for(url: str) -> str | None:
    """Canonical host label for a url, or None if it's not a supported host."""
    netloc = _netloc(url)
    for suffix, host in _HOST_MAP.items():
        if netloc == suffix or netloc.endswith("." + suffix):
            return host
    return None


def _unwrap(url: str) -> str:
    """Unwrap a Patreon outbound-redirect wrapper to its inner target, so a
    wrapped mega/gdrive link resolves to the real host. Patreon has used both
    `www.patreon.com/...?url=<encoded>` and the `l.patreon.com` shim; check the
    common target-param names. Non-Patreon urls pass through untouched."""
    netloc = _netloc(url)
    if not (netloc == "patreon.com" or netloc.endswith(".patreon.com")):
        return url
    qs = parse_qs(urlsplit(url).query)
    for key in ("url", "u", "ext_url", "redirect", "target"):
        vals = qs.get(key)
        if vals and vals[0]:
            return unescape(vals[0]).strip()
    return url


def extract_external_links(html: str | None) -> list[ExtractedLink]:
    """All supported-host links in `html`, de-duplicated by url (first wins, so
    an anchor's label is kept over a later bare sighting of the same url)."""
    if not html:
        return []
    found: dict[str, ExtractedLink] = {}

    # 1) Anchors first — they carry a human label ("Mega - Streamable").
    for raw_href, inner in _HREF_RE.findall(html):
        url = _unwrap(unescape(raw_href).strip())
        host = host_for(url)
        if host is None:
            continue
        label = unescape(_TAG_RE.sub("", inner)).strip() or None
        found.setdefault(url, ExtractedLink(host=host, url=url, label=label))

    # 2) Bare URLs pasted in text (no label). Trailing prose punctuation is
    #    trimmed; the href values already captured above de-dup away here.
    for raw in _URL_RE.findall(html):
        url = _unwrap(unescape(raw).strip().rstrip(".,;"))
        host = host_for(url)
        if host is None:
            continue
        found.setdefault(url, ExtractedLink(host=host, url=url, label=None))

    return list(found.values())