"""
app/billing/emails.py
---------------------
Dunning / billing lifecycle emails sent via Flask-Mail in a background thread.

Pattern mirrors app/utils/notifications.py: captures the app object before
spawning the thread so the mail context is valid inside the worker.

Public API:
  send_billing_email(to_addr, event_type, context_dict)
    event_type in ('payment_failed', 'trial_ending', 'subscription_cancelled')
"""

import logging
import threading
from flask import current_app
from flask_mail import Message
from app import mail

logger = logging.getLogger(__name__)

# ── Email templates ────────────────────────────────────────────────────────────

_SUBJECTS = {
    'payment_failed':           'Action Required: Payment failed for your JQC subscription',
    'trial_ending':             'Your JQC free trial ends in 3 days',
    'subscription_cancelled':   'Your JQC subscription has been cancelled',
}

_BODIES = {
    'payment_failed': """\
Hi,

We were unable to process your most recent payment for your JQC subscription.

Please update your payment method to avoid interruption to your service:
  {portal_url}

If you have any questions, please contact support.

— The JQC Team
""",

    'trial_ending': """\
Hi,

Your JQC free trial will end on {trial_ends_at}. After that date, you will
need an active subscription to continue using the service.

Subscribe now to keep your workspace active:
  {subscribe_url}

— The JQC Team
""",

    'subscription_cancelled': """\
Hi,

Your JQC subscription has been cancelled and your workspace access has
been suspended. You can reactivate your subscription at any time:
  {portal_url}

— The JQC Team
""",
}


def send_billing_email(to_addr: str, event_type: str, context_dict: dict):
    """Send a billing lifecycle email in a background thread.

    Args:
        to_addr:      Recipient email address (tenant admin or billing contact).
        event_type:   Key in _SUBJECTS / _BODIES.
        context_dict: Variables substituted into the body template.
    """
    if not to_addr:
        logger.warning('BILLING EMAIL | skipped | event=%s | reason=no_recipient', event_type)
        return

    subject = _SUBJECTS.get(event_type, 'JQC Billing Notification')
    body_template = _BODIES.get(event_type, '')
    try:
        body = body_template.format(**context_dict)
    except KeyError as exc:
        logger.error('BILLING EMAIL | template_error | event=%s | missing_key=%s', event_type, exc)
        body = body_template  # send with unfilled placeholders rather than crashing

    app = current_app._get_current_object()

    def _send():
        try:
            with app.app_context():
                msg = Message(
                    subject=subject,
                    recipients=[to_addr],
                    body=body,
                )
                mail.send(msg)
                logger.info('BILLING EMAIL | sent | event=%s | to=%s', event_type, to_addr)
        except Exception as exc:
            logger.error('BILLING EMAIL | send_failed | event=%s | to=%s | err=%s',
                         event_type, to_addr, exc)

    thread = threading.Thread(target=_send, daemon=True)
    thread.start()