#!/usr/bin/env python3
"""Extract hosts from href attributes in an HTML file and write them as *host* per line.

Usage:
  python main.py INPUT_HTML [OUTPUT_TXT]

If OUTPUT_TXT is not provided, the script writes to <INPUT_BASENAME>_links.txt
alongside the input file.
"""

from __future__ import annotations

import argparse
from html.parser import HTMLParser
import os
from urllib.parse import urlparse


class _HrefParser(HTMLParser):
    def __init__(self) -> None:
        super().__init__()
        self.hrefs: list[str] = []

    def handle_starttag(self, tag: str, attrs):  # type: ignore[override]
        # Collect any href attribute on any tag
        for k, v in attrs:
            if k.lower() == "href" and v is not None:
                self.hrefs.append(v)


def extract_hosts_from_html(html_text: str) -> list[str]:
    """Parse HTML text, extract href values, and return a list of hostnames.

    Rules:
    - Only http/https URLs are considered.
    - Output is the network location (host[:port]) without scheme or path.
    - Duplicates are removed, preserving first-seen order.
    """
    parser = _HrefParser()
    parser.feed(html_text)

    seen: set[str] = set()
    hosts: list[str] = []
    for href in parser.hrefs:
        parsed = urlparse(href)
        if parsed.scheme in {"http", "https"} and parsed.netloc:
            host = parsed.netloc
            if host not in seen:
                seen.add(host)
                hosts.append(host)
    return hosts


def main() -> int:
    ap = argparse.ArgumentParser(
        description="Extract hosts from hrefs in an HTML file."
    )
    ap.add_argument("input_html", help="Path to input HTML file")
    ap.add_argument(
        "output_txt",
        nargs="?",
        help="Path to output text file (defaults to <input_basename>_links.txt in the same directory)",
    )
    args = ap.parse_args()

    input_path = args.input_html
    if not os.path.isfile(input_path):
        raise SystemExit(f"Input file not found: {input_path}")

    out_path = args.output_txt
    if not out_path:
        base = os.path.splitext(os.path.basename(input_path))[0]
        out_path = os.path.join(os.path.dirname(input_path), f"{base}_links.txt")

    with open(input_path, encoding="utf-8", errors="ignore") as f:
        html_text = f.read()

    hosts = extract_hosts_from_html(html_text)

    with open(out_path, "w", encoding="utf-8") as f:
        for host in hosts:
            f.write(f"*{host}*\n")

    print(f"Wrote {len(hosts)} host(s) to {out_path}")
    return 0


if __name__ == "__main__":
    raise SystemExit(main())