"""
Alert Service — budget threshold alerts triggered after expense transactions.

Checks budgeted categories and flashes/emails when spending crosses 80% or 100%.
Dedup: alert_sent_80 / alert_sent_100 flags on each Budget row prevent repeat
emails within the same month.  Flags default to False on new Budget rows.

Usage (in routes after db.session.commit()):
    from app.services.alert_service import check_and_flash_budget_alerts
    check_and_flash_budget_alerts(flash_fn)
"""

import logging
import smtplib
import ssl
from datetime import date
from email.mime.text import MIMEText
from email.mime.multipart import MIMEMultipart
from flask import current_app

from app.extensions import db

log = logging.getLogger('app.alert_service')


def _smtp_configured():
    cfg = current_app.config
    return all([
        cfg.get('SMTP_HOST'),
        cfg.get('SMTP_USER'),
        cfg.get('SMTP_PASSWORD'),
        cfg.get('ALERT_EMAIL'),
    ])


def _send_email(subject, body_html):
    cfg    = current_app.config
    host   = cfg['SMTP_HOST']
    port   = int(cfg.get('SMTP_PORT', 587))
    user   = cfg['SMTP_USER']
    pw     = cfg['SMTP_PASSWORD']
    to_addr = cfg['ALERT_EMAIL']

    msg = MIMEMultipart('alternative')
    msg['Subject'] = subject
    msg['From']    = user
    msg['To']      = to_addr
    msg.attach(MIMEText(body_html, 'html'))

    try:
        ctx = ssl.create_default_context()
        with smtplib.SMTP(host, port) as srv:
            srv.ehlo()
            srv.starttls(context=ctx)
            srv.login(user, pw)
            srv.sendmail(user, to_addr, msg.as_string())
        log.info('[alert] email sent: %s → %s', subject, to_addr)
        return True
    except Exception as exc:
        log.error('[alert] email failed: %s', exc, exc_info=True)
        return False


def send_test_email():
    """Send a test email to verify SMTP config.  Returns (ok: bool, message: str)."""
    if not _smtp_configured():
        return False, ('SMTP not configured. '
                       'Set SMTP_HOST, SMTP_USER, SMTP_PASSWORD, and ALERT_EMAIL in .env.')
    to_addr = current_app.config['ALERT_EMAIL']
    body = (
        '<p>This is a test email from your <strong>Personal Finance Management</strong> app.</p>'
        '<p>Budget alerts are configured correctly.</p>'
    )
    ok = _send_email('PFM — Test Email', body)
    if ok:
        return True, f'Test email sent to {to_addr}.'
    return False, 'SMTP error — check server logs for details.'


def get_budget_alerts(month_str=None):
    """
    Return list of alert dicts for budget categories at or over threshold.
    Does NOT check dedup flags — use for display purposes only.

    Each dict: {category, spent, limit, pct, level}
    level: 'over' (≥100%) | 'warning' (≥80%)
    """
    from app.services.budget_service import get_budget_summary

    if month_str is None:
        month_str = date.today().strftime('%Y-%m')

    summary = get_budget_summary(month_str)
    alerts = []
    for item in summary:
        if not item['has_budget'] or item['pct'] is None:
            continue
        pct = item['pct']
        if pct >= 100:
            alerts.append({**item, 'level': 'over'})
        elif pct >= 80:
            alerts.append({**item, 'level': 'warning'})
    return alerts


def check_and_flash_budget_alerts(flash_fn):
    """
    Check current month's budgets.  For each category that newly crossed 80% or
    100%, flash a message and (if SMTP configured and user has alerts enabled)
    send one email.  Dedup flags on the Budget row prevent repeat sends.

    Call this after committing an expense transaction.
    flash_fn: Flask's flash() (passed in to avoid circular imports at module level)
    """
    from app.models.budget import Budget
    from app.models.user import User
    from app.services.budget_service import get_month_spending

    user = User.query.first()
    alerts_enabled = user.budget_alerts_enabled if user else False
    symbol = (user.currency_symbol or '$') if user else '$'

    month_str = date.today().strftime('%Y-%m')

    try:
        budgets = Budget.query.filter_by(month=month_str).all()
    except Exception as exc:
        log.error('[alert] failed to query budgets: %s', exc)
        return

    dirty_budgets = []

    for b in budgets:
        try:
            limit = float(b.limit_amount) + float(b.rollover_amount or 0)
            if limit <= 0:
                continue
            spent = get_month_spending(b.category_id, month_str)
            pct   = spent / limit * 100
            cat   = b.category
            cat_name = cat.name if cat else 'Unknown'

            # 100% threshold — only fire if not already sent this month
            if pct >= 100 and not b.alert_sent_100:
                msg = (f'Budget exceeded: <strong>{cat_name}</strong> — '
                       f'{symbol}{spent:,.2f} of {symbol}{limit:,.2f} ({pct:.0f}%)')
                flash_fn(msg, 'danger')
                if alerts_enabled and _smtp_configured():
                    _send_single_alert_email(cat_name, spent, limit, pct, symbol, threshold=100)
                b.alert_sent_100 = True
                dirty_budgets.append(b)

            # 80% threshold — only fire if not already sent (and 100% not yet hit)
            elif pct >= 80 and not b.alert_sent_80:
                msg = (f'Budget warning: <strong>{cat_name}</strong> — '
                       f'{symbol}{spent:,.2f} of {symbol}{limit:,.2f} ({pct:.0f}% used)')
                flash_fn(msg, 'warning')
                if alerts_enabled and _smtp_configured():
                    _send_single_alert_email(cat_name, spent, limit, pct, symbol, threshold=80)
                b.alert_sent_80 = True
                dirty_budgets.append(b)

        except Exception as exc:
            log.error('[alert] error checking budget %s: %s', b.id, exc)

    if dirty_budgets:
        try:
            db.session.commit()
        except Exception as exc:
            log.error('[alert] failed to save alert flags: %s', exc)
            db.session.rollback()


def _send_single_alert_email(cat_name, spent, limit, pct, symbol, threshold):
    label     = '100%+' if threshold >= 100 else '80%'
    remaining = max(limit - spent, 0)
    color     = '#ef4444' if threshold >= 100 else '#f59e0b'
    emoji     = '🚨' if threshold >= 100 else '⚠️'
    app_url   = current_app.config.get('APP_URL', '')

    body = f"""
<html><body style="font-family:sans-serif;color:#0f172a;max-width:520px;margin:0 auto;">
  <div style="background:#0f172a;padding:20px 24px;border-radius:8px 8px 0 0;">
    <h2 style="color:#f1f5f9;margin:0;font-size:18px;">{emoji} Budget Alert — {label}</h2>
  </div>
  <div style="border:1px solid #e2e8f0;border-top:none;padding:24px;border-radius:0 0 8px 8px;">
    <p style="font-size:15px;margin-top:0;">
      Your <strong>{cat_name}</strong> budget has reached
      <strong style="color:{color};">{pct:.0f}%</strong>.
    </p>
    <table style="width:100%;border-collapse:collapse;font-size:13px;margin-bottom:16px;">
      <tr style="background:#f8fafc;">
        <td style="padding:8px 12px;border:1px solid #e2e8f0;">Spent</td>
        <td style="padding:8px 12px;border:1px solid #e2e8f0;font-weight:bold;color:#ef4444;">{symbol}{spent:,.2f}</td>
      </tr>
      <tr>
        <td style="padding:8px 12px;border:1px solid #e2e8f0;">Budget limit</td>
        <td style="padding:8px 12px;border:1px solid #e2e8f0;">{symbol}{limit:,.2f}</td>
      </tr>
      <tr style="background:#f8fafc;">
        <td style="padding:8px 12px;border:1px solid #e2e8f0;">Remaining</td>
        <td style="padding:8px 12px;border:1px solid #e2e8f0;color:{'#ef4444' if remaining==0 else '#10b981'};">{symbol}{remaining:,.2f}</td>
      </tr>
    </table>
    <a href="{app_url}/budgets"
       style="display:inline-block;background:#3b82f6;color:#fff;padding:10px 20px;border-radius:6px;text-decoration:none;font-size:13px;">
      View Budgets →
    </a>
    <p style="font-size:11px;color:#94a3b8;margin-top:20px;margin-bottom:0;">
      Disable alerts in Settings → Profile.
    </p>
  </div>
</body></html>"""

    subject = f'Budget Alert: {cat_name} at {label} ({pct:.0f}% used)'
    _send_email(subject, body)