#!/usr/bin/env python3
"""Read RSS / Atom / JSON Feed sources and discover feeds behind a page URL.

Standard library only, so it runs in any Hermes environment without an install
step. Output is JSON (``--json``) or a compact text listing.

    python3 feed.py read https://example.com/feed.xml [--limit N] [--since 2026-09-01]
    python3 feed.py discover https://example.com/
    python3 feed.py read https://example.com/  ->  discovers, then reads the first feed
"""

from __future__ import annotations

import argparse
import html
import json
import re
import sys
import urllib.error
import urllib.parse
import urllib.request
import xml.etree.ElementTree as ET
from datetime import datetime, timezone
from email.utils import parsedate_to_datetime

USER_AGENT = "hermes-agent/1.0 (rss-feeds skill; +https://github.com/NousResearch/hermes-agent)"
TIMEOUT = 20
NS = {
    "atom": "http://www.w3.org/2005/Atom",
    "dc": "http://purl.org/dc/elements/1.1/",
    "content": "http://purl.org/rss/1.0/modules/content/",
    "media": "http://search.yahoo.com/mrss/",
}
FEED_TYPES = ("application/rss+xml", "application/atom+xml", "application/feed+json", "application/json")
COMMON_FEED_PATHS = ("/feed", "/feed.xml", "/rss", "/rss.xml", "/atom.xml", "/index.xml", "/feed.json", "/blog/feed", "/blog/rss.xml")
_TAG_RE = re.compile(r"<[^>]+>")
_WS_RE = re.compile(r"\s+")


def fetch(url: str) -> tuple[bytes, str]:
    req = urllib.request.Request(url, headers={"User-Agent": USER_AGENT, "Accept": "*/*"})
    with urllib.request.urlopen(req, timeout=TIMEOUT) as resp:
        return resp.read(), resp.headers.get("Content-Type", "")


def strip_html(text: str | None) -> str:
    if not text:
        return ""
    return _WS_RE.sub(" ", html.unescape(_TAG_RE.sub(" ", text))).strip()


def parse_date(value: str | None) -> str | None:
    """Normalise RFC 822 (RSS) and ISO 8601 (Atom/JSON Feed) dates to UTC ISO."""
    if not value:
        return None
    value = value.strip()
    try:
        dt = parsedate_to_datetime(value)
    except (TypeError, ValueError):
        try:
            dt = datetime.fromisoformat(value.replace("Z", "+00:00"))
        except ValueError:
            return value
    if dt.tzinfo is None:
        dt = dt.replace(tzinfo=timezone.utc)
    return dt.astimezone(timezone.utc).isoformat()


def _text(el, *paths) -> str | None:
    for p in paths:
        found = el.find(p, NS)
        if found is not None and (found.text or "").strip():
            return found.text
    return None


def _atom_link(entry) -> str | None:
    alternate = None
    for link in entry.findall("atom:link", NS) + entry.findall("link"):
        href = link.get("href")
        if not href:
            continue
        rel = link.get("rel", "alternate")
        if rel == "alternate":
            return href
        alternate = alternate or href
    return alternate


def parse_xml(data: bytes) -> dict:
    root = ET.fromstring(data)
    tag = root.tag.rsplit("}", 1)[-1].lower()
    if tag == "feed":  # Atom
        title = strip_html(_text(root, "atom:title"))
        entries = []
        for e in root.findall("atom:entry", NS):
            entries.append({
                "title": strip_html(_text(e, "atom:title")),
                "link": _atom_link(e),
                "published": parse_date(_text(e, "atom:published", "atom:updated")),
                "author": strip_html(_text(e, "atom:author/atom:name", "dc:creator")),
                "summary": strip_html(_text(e, "atom:summary", "atom:content"))[:2000],
            })
        return {"format": "atom", "title": title, "entries": entries}
    channel = root.find("channel") if tag == "rss" else root  # RSS 2.0 vs RDF/RSS 1.0
    if channel is None:
        raise ValueError(f"unrecognised XML root <{tag}>")
    entries = []
    for item in channel.iter("item") if tag == "rss" else root.iter("{http://purl.org/rss/1.0/}item"):
        entries.append({
            "title": strip_html(_text(item, "title", "{http://purl.org/rss/1.0/}title")),
            "link": (_text(item, "link", "{http://purl.org/rss/1.0/}link") or "").strip() or None,
            "published": parse_date(_text(item, "pubDate", "dc:date")),
            "author": strip_html(_text(item, "dc:creator", "author")),
            "summary": strip_html(_text(item, "content:encoded", "description", "{http://purl.org/rss/1.0/}description"))[:2000],
        })
    return {"format": "rss", "title": strip_html(_text(channel, "title", "{http://purl.org/rss/1.0/}title")), "entries": entries}


def parse_json_feed(data: bytes) -> dict:
    doc = json.loads(data)
    entries = []
    for item in doc.get("items", []):
        authors = item.get("authors") or ([item["author"]] if item.get("author") else [])
        entries.append({
            "title": strip_html(item.get("title")),
            "link": item.get("url") or item.get("external_url"),
            "published": parse_date(item.get("date_published") or item.get("date_modified")),
            "author": ", ".join(a.get("name", "") for a in authors if isinstance(a, dict)) or None,
            "summary": strip_html(item.get("summary") or item.get("content_text") or item.get("content_html"))[:2000],
        })
    return {"format": "jsonfeed", "title": strip_html(doc.get("title")), "entries": entries}


def parse_feed(data: bytes, content_type: str = "") -> dict:
    head = data.lstrip()[:1]
    if head == b"{" or "json" in content_type:
        return parse_json_feed(data)
    return parse_xml(data)


def discover(page_url: str, page_html: bytes | None = None) -> list[str]:
    """Return candidate feed URLs for a page: <link rel=alternate> first, then well-known paths."""
    if page_html is None:
        page_html, _ = fetch(page_url)
    text = page_html.decode("utf-8", "replace")
    found: list[str] = []
    for m in re.finditer(r"<link\b[^>]*>", text, re.I):
        tag = m.group(0)
        type_m = re.search(r"""type\s*=\s*["']([^"']+)""", tag, re.I)
        href_m = re.search(r"""href\s*=\s*["']([^"']+)""", tag, re.I)
        rel_m = re.search(r"""rel\s*=\s*["']([^"']+)""", tag, re.I)
        if not href_m or not type_m or type_m.group(1).lower() not in FEED_TYPES:
            continue
        if rel_m and "alternate" not in rel_m.group(1).lower():
            continue
        url = urllib.parse.urljoin(page_url, html.unescape(href_m.group(1)))
        if url not in found:
            found.append(url)
    if found:
        return found
    parsed = urllib.parse.urlsplit(page_url)
    base = f"{parsed.scheme}://{parsed.netloc}"
    return [base + p for p in COMMON_FEED_PATHS]


def looks_like_feed(data: bytes, content_type: str) -> bool:
    head = data.lstrip()[:300].lower()
    return head.startswith(b"{") and b"items" in data[:2000] or b"<rss" in head or b"<feed" in head or b"<rdf" in head


def read(url: str) -> dict:
    data, ctype = fetch(url)
    if looks_like_feed(data, ctype):
        feed = parse_feed(data, ctype)
        feed["url"] = url
        return feed
    candidates = discover(url, data)
    errors = []
    for cand in candidates:
        try:
            cdata, cctype = fetch(cand)
        except (urllib.error.URLError, OSError) as exc:
            errors.append(f"{cand}: {exc}")
            continue
        if looks_like_feed(cdata, cctype):
            feed = parse_feed(cdata, cctype)
            feed["url"] = cand
            feed["discovered_from"] = url
            return feed
    raise SystemExit(f"no feed found at {url}; tried {len(candidates)} candidates\n" + "\n".join(errors))


def filter_entries(entries: list[dict], limit: int, since: str | None) -> list[dict]:
    if since:
        cutoff = datetime.fromisoformat(since).replace(tzinfo=timezone.utc) if "T" not in since else datetime.fromisoformat(since.replace("Z", "+00:00"))
        if cutoff.tzinfo is None:
            cutoff = cutoff.replace(tzinfo=timezone.utc)
        entries = [e for e in entries if e["published"] and datetime.fromisoformat(e["published"]) >= cutoff]
    entries.sort(key=lambda e: e["published"] or "", reverse=True)
    return entries[:limit]


def render_text(feed: dict) -> str:
    lines = [f"{feed.get('title') or '(untitled feed)'}  [{feed['format']}]  {feed['url']}"]
    for e in feed["entries"]:
        when = (e["published"] or "")[:10]
        by = f"  — {e['author']}" if e.get("author") else ""
        lines.append(f"- {when}  {e['title'] or '(no title)'}{by}\n  {e['link'] or ''}")
        if e.get("summary"):
            lines.append(f"  {e['summary'][:300]}")
    return "\n".join(lines)


def main(argv: list[str] | None = None) -> int:
    ap = argparse.ArgumentParser(description=__doc__, formatter_class=argparse.RawDescriptionHelpFormatter)
    sub = ap.add_subparsers(dest="cmd", required=True)
    r = sub.add_parser("read", help="read a feed (or discover one behind a page URL)")
    r.add_argument("url")
    r.add_argument("--limit", type=int, default=20)
    r.add_argument("--since", help="ISO date/datetime; drop older entries")
    r.add_argument("--json", action="store_true")
    d = sub.add_parser("discover", help="list feed URLs advertised by a page")
    d.add_argument("url")
    d.add_argument("--json", action="store_true")
    args = ap.parse_args(argv)

    try:
        if args.cmd == "discover":
            urls = discover(args.url)
            print(json.dumps(urls, indent=2) if args.json else "\n".join(urls))
            return 0
        feed = read(args.url)
        feed["entries"] = filter_entries(feed["entries"], args.limit, args.since)
        print(json.dumps(feed, indent=2, ensure_ascii=False) if args.json else render_text(feed))
        return 0
    except urllib.error.HTTPError as exc:
        print(f"HTTP {exc.code} for {exc.url}", file=sys.stderr)
        return 2
    except (urllib.error.URLError, ET.ParseError, ValueError, json.JSONDecodeError) as exc:
        print(f"error: {exc}", file=sys.stderr)
        return 2


if __name__ == "__main__":
    sys.exit(main())