import os
import logging
from datetime import datetime
from jinja2 import Environment, FileSystemLoader, select_autoescape

logger = logging.getLogger(__name__)

RESEND_API_KEY = os.getenv('RESEND_API_KEY')
TEMPLATES_DIR = os.path.join(os.path.dirname(__file__), '..', 'templates', 'emails')

# Same reasoning as brief_service.py: plain Jinja2, not flask.render_template,
# so this module has no dependency on an active Flask app context.
_jinja_env = Environment(
    loader=FileSystemLoader(TEMPLATES_DIR),
    autoescape=select_autoescape(['html'])
)


def _send(template_name, to_email, subject, context, from_address='alerts@bettersight.io'):
    """
    Renders a Jinja2 template and sends it via Resend. A failed send is
    a side-effect failure — logged only, never raised into the
    caller's primary operation (signup completing, an alert being
    created, etc.) per CLAUDE.md §18 resilience rules.

    Data flow:
      template_name + context → Jinja2 render → Resend Emails.send() →
      True on success / False on failure (logged)
    """
    try:
        import resend
        resend.api_key = RESEND_API_KEY
        template = _jinja_env.get_template(template_name)
        html = template.render(**context)
        resend.Emails.send({
            'from': f'Bettersight <{from_address}>',
            'to': to_email,
            'subject': subject,
            'html': html,
        })
        return True
    except Exception as e:
        logger.error(f'Failed to send {template_name} to {to_email}: {str(e)}')
        return False


def send_welcome_email(to_email, tenant_name, template_url=None):
    """
    Sends the branded welcome email on signup with a Sheet template
    download link. Data flow: tenant email + name + template URL →
    welcome.html rendered → Resend API → inbox (CLAUDE.md §21).
    """
    return _send('welcome.html', to_email, 'Welcome to Bettersight — you\'re all set', {
        'name': tenant_name,
        'template_url': template_url,
    })


def send_trial_reminder_email(to_email, tenant_name, days_left, trial_end_date):
    """
    Sends the "trial ends in N days" reminder — fired 2 days before
    expiry per CLAUDE.md §21 Trial Periods ("n8n fires trial_reminder
    email (2 days before expiry)").
    """
    return _send('trial_reminder.html', to_email, f'Your Bettersight trial ends in {days_left} days', {
        'name': tenant_name,
        'days_left': days_left,
        'trial_end_date': trial_end_date,
    })


def send_price_alert_email(to_email, alert):
    """
    Sends an individual price-change alert email. `alert` is an
    alerts-collection record (competitor name resolved by the caller
    since alerts only store competitor_id).

    Data flow:
      alert dict → price_alert.html rendered → Resend API → inbox
    """
    previous_price = None
    if alert.get('change_amount') is not None and alert.get('majority_price_usd') is not None:
        previous_price = alert['majority_price_usd'] - alert['change_amount']

    return _send('price_alert.html', to_email, f'Price alert — {alert.get("competitor_name", "a competitor")}', {
        'competitor_name': alert.get('competitor_name'),
        'trip_name': alert.get('trip_name'),
        'previous_price': previous_price,
        'current_price': alert.get('majority_price_usd'),
        'change_percent': alert.get('change_percent'),
    })


def send_new_product_email(to_email, alert):
    """
    Sends an individual new-product alert email. Data flow: alert dict
    → new_product.html rendered → Resend API → inbox.
    """
    return _send('new_product.html', to_email, f'New product — {alert.get("competitor_name", "a competitor")}', {
        'competitor_name': alert.get('competitor_name'),
        'trip_name': alert.get('trip_name'),
        'destination': alert.get('destination'),
        'duration_days': alert.get('duration_days'),
        'price_usd': alert.get('majority_price_usd'),
    })


def send_daily_digest_email(to_email, tenant_name, alerts):
    """
    Sends the 6pm daily digest — one email summarising every alert
    from the day, rather than a separate email per alert (CLAUDE.md
    §15 "n8n reads new alert records → sends Resend email notification
    (daily digest)").
    """
    return _send('daily_digest.html', to_email, f'Bettersight daily digest — {len(alerts)} update{"" if len(alerts) == 1 else "s"}', {
        'tenant_name': tenant_name,
        'alerts': alerts,
    })