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

Checks all budgeted categories for the current month and returns alert dicts
for any that just crossed 80% or 100%. Also sends an email if SMTP is configured.

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

log = logging.getLogger(__name__)


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


def get_budget_alerts(month_str=None):
    """
    Return list of alert dicts for budget categories at or over threshold.

    Each dict: {category, spent, limit, pct, level}
    level: 'over' (≥100%) | 'warning' (≥80%)

    Only returns categories that have a budget set.
    """
    from app.services.budget_service import get_budget_summary

    if month_str is None:
        today = date.today()
        month_str = 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 and flash any threshold alerts.
    Optionally sends an email summary if SMTP is configured.

    Call this after committing an expense transaction.

    flash_fn: Flask's flash() function (passed in to avoid circular imports)
    """
    try:
        alerts = get_budget_alerts()
    except Exception as exc:
        log.error('[alert] check failed: %s', exc, exc_info=True)
        return

    if not alerts:
        return

    email_lines = []
    for a in alerts:
        cat_name = a['category'].name if a['category'] else 'Unknown'
        pct      = a['pct']
        spent    = a['spent']
        limit    = a['limit']
        symbol   = current_app.config.get('APP_CURRENCY_SYMBOL', '$')

        if a['level'] == 'over':
            msg = (f'Budget exceeded: <strong>{cat_name}</strong> — '
                   f'{symbol}{spent:,.2f} spent of {symbol}{limit:,.2f} limit ({pct:.0f}%)')
            flash_fn(msg, 'danger')
        else:
            msg = (f'Budget warning: <strong>{cat_name}</strong> — '
                   f'{symbol}{spent:,.2f} of {symbol}{limit:,.2f} ({pct:.0f}% used)')
            flash_fn(msg, 'warning')

        email_lines.append(
            f'<li><b>{cat_name}</b>: {symbol}{spent:,.2f} / {symbol}{limit:,.2f} '
            f'({pct:.0f}%) — <b>{"EXCEEDED" if a["level"]=="over" else "Warning"}</b></li>'
        )

    if _smtp_configured() and email_lines:
        today = date.today().strftime('%B %Y')
        body = (
            f'<h3>PFM Budget Alert — {today}</h3>'
            f'<p>The following budget categories need your attention:</p>'
            f'<ul>{"".join(email_lines)}</ul>'
            f'<p><a href="{current_app.config.get("APP_URL","")}/budgets">View Budgets →</a></p>'
        )
        _send_email(f'PFM Budget Alert — {today}', body)