"""Best-effort SMTP email sending (#18).

A single background worker thread drains a queue, and a send failure is
logged, never raised back to the caller -- booking creation must succeed even
if the mail relay is down.
"""
import os
import queue
import smtplib
import threading
import traceback
from email.message import EmailMessage

SMTP_HOST = os.environ.get("SMTP_HOST", "")
SMTP_PORT = int(os.environ.get("SMTP_PORT", "587"))
SMTP_USERNAME = os.environ.get("SMTP_USERNAME", "")
SMTP_PASSWORD = os.environ.get("SMTP_PASSWORD", "")
# Used when a client has no domain configured -- see booking_mail.py.
MAIL_FALLBACK_FROM = os.environ.get("MAIL_FALLBACK_FROM", "noreply@mivanchenko.de")

_queue = queue.Queue()


def _send_now(msg):
    if not SMTP_HOST:
        print(f"[mailer] SMTP_HOST not configured, skipping send to {msg['To']}", flush=True)
        return
    with smtplib.SMTP(SMTP_HOST, SMTP_PORT, timeout=10) as smtp:
        smtp.starttls()
        if SMTP_USERNAME:
            smtp.login(SMTP_USERNAME, SMTP_PASSWORD)
        smtp.send_message(msg)


def _worker():
    while True:
        msg = _queue.get()
        try:
            _send_now(msg)
        except Exception:  # noqa: BLE001
            print(f"[mailer] send to {msg['To']} failed:", flush=True)
            traceback.print_exc()
        finally:
            _queue.task_done()


threading.Thread(target=_worker, daemon=True).start()


def send_email(to_addr, subject, html_body, from_addr=None):
    """Queue an HTML email for best-effort async delivery. Never raises and
    never blocks the caller on the network -- the actual SMTP conversation
    happens on the background worker thread."""
    msg = EmailMessage()
    msg["Subject"] = subject
    msg["From"] = from_addr or MAIL_FALLBACK_FROM
    msg["To"] = to_addr
    msg.set_content(html_body, subtype="html")
    _queue.put(msg)