#!/usr/bin/env python3
"""
notify_mattermost.py — post a message to a Mattermost channel via Incoming Webhook.

Dependency-free (stdlib urllib). The webhook URL is a secret and is read from the
environment — NEVER hardcode it (Helgen ethos: no secrets in the repo).

Setup (one-time):
  1. In Mattermost: Main Menu → Integrations → Incoming Webhooks → Add. Pick the
     channel, copy the URL (looks like https://<host>/hooks/xxxxxxxxxxxxxxxxx).
  2. export MATTERMOST_WEBHOOK_URL="https://<host>/hooks/xxxxxxxxxxxxxxxxx"

Usage:
  python3 notify_mattermost.py "Backend hotfix deployed ✅"
  echo "multi-line\nstatus" | python3 notify_mattermost.py -
  python3 notify_mattermost.py --channel ops --username "Drogheda Bot" "RTK fix restored"
  python3 notify_mattermost.py --dry-run "test"        # print payload, don't send

Exit codes: 0 ok · 2 usage/config error · 1 send failure.
"""
import argparse
import json
import os
import sys
import urllib.request
import urllib.error

DEFAULT_USERNAME = "Drogheda Bot"
DEFAULT_ICON = ":satellite:"


def build_payload(text, channel=None, username=DEFAULT_USERNAME, icon=DEFAULT_ICON):
    payload = {"text": text, "username": username}
    if icon:
        payload["icon_emoji"] = icon
    if channel:
        payload["channel"] = channel  # override the webhook's default channel
    return payload


def send(url, payload, timeout=10):
    data = json.dumps(payload).encode("utf-8")
    req = urllib.request.Request(
        url, data=data, headers={"Content-Type": "application/json"}, method="POST"
    )
    with urllib.request.urlopen(req, timeout=timeout) as resp:
        return resp.status, resp.read().decode("utf-8", "ignore")


def main(argv=None):
    p = argparse.ArgumentParser(description="Post a message to Mattermost via webhook.")
    p.add_argument("text", help="Message text (Markdown ok). Use '-' to read from stdin.")
    p.add_argument("--channel", help="Override channel (name without #).")
    p.add_argument("--username", default=DEFAULT_USERNAME)
    p.add_argument("--icon", default=DEFAULT_ICON, help="Emoji, e.g. :satellite:")
    p.add_argument("--url", default=os.environ.get("MATTERMOST_WEBHOOK_URL"),
                   help="Webhook URL (defaults to $MATTERMOST_WEBHOOK_URL).")
    p.add_argument("--dry-run", action="store_true", help="Print payload; do not send.")
    args = p.parse_args(argv)

    text = sys.stdin.read().rstrip("\n") if args.text == "-" else args.text
    if not text.strip():
        print("error: empty message", file=sys.stderr)
        return 2

    payload = build_payload(text, args.channel, args.username, args.icon)

    if args.dry_run:
        print(json.dumps(payload, indent=2, ensure_ascii=False))
        return 0

    if not args.url:
        print("error: no webhook URL. Set MATTERMOST_WEBHOOK_URL or pass --url.",
              file=sys.stderr)
        return 2

    try:
        status, body = send(args.url, payload)
        if status == 200:
            print("ok")
            return 0
        print(f"send failed: HTTP {status}: {body}", file=sys.stderr)
        return 1
    except urllib.error.URLError as e:
        print(f"send failed: {e}", file=sys.stderr)
        return 1


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