const express = require('express');
const router = express.Router();
const db = require('../config/database');
const { requireAdmin } = require('../middleware/auth');
const PDFDocument = require('pdfkit');

// ============================================
// Hilfsfunktionen
// ============================================

// Nächsten Rechnungsbetrag für ein Mitglied berechnen
function calcInvoiceAmount(member, period) {
  // Pausiert → 0€
  if (member.status === 'paused') return 0;

  // Erster Monat (anteilig)?
  const firstPeriod = member.first_payment_date
    ? member.first_payment_date.toISOString().substring(0, 7)
    : null;

  if (firstPeriod === period && member.first_payment_amt) {
    return parseFloat(member.first_payment_amt);
  }

  return parseFloat(member.price_monthly);
}

// Periode als lesbarer Text: "2026-04" → "April 2026"
function periodLabel(period) {
  const [year, month] = period.split('-');
  const months = ['Januar','Februar','März','April','Mai','Juni',
                  'Juli','August','September','Oktober','November','Dezember'];
  return `${months[parseInt(month) - 1]} ${year}`;
}

// Aktuelle Periode: "YYYY-MM"
function currentPeriod() {
  const now = new Date();
  return `${now.getFullYear()}-${String(now.getMonth() + 1).padStart(2, '0')}`;
}

// ============================================
// GET /admin/billing – Übersicht
// ============================================
router.get('/', requireAdmin, async (req, res) => {
  try {
    const period = req.query.period || currentPeriod();

    const [runs] = await db.query(
      'SELECT * FROM billing_runs ORDER BY created_at DESC'
    );

    const [invoices] = await db.query(`
      SELECT i.*,
             m.first_name, m.last_name, m.email,
             t.name as tariff_name
      FROM invoices i
      JOIN memberships m ON i.membership_id = m.id
      LEFT JOIN tariffs t ON m.tariff_id = t.id
      WHERE i.period = ?
      ORDER BY m.last_name ASC
    `, [period]);

    const [summary] = await db.query(`
      SELECT 
        COUNT(*) as total,
        SUM(amount) as total_amount,
        SUM(CASE WHEN status='open'      THEN 1 ELSE 0 END) as open_count,
        SUM(CASE WHEN status='paid'      THEN 1 ELSE 0 END) as paid_count,
        SUM(CASE WHEN status='open'      THEN amount ELSE 0 END) as open_amount,
        SUM(CASE WHEN status='paid'      THEN amount ELSE 0 END) as paid_amount
      FROM invoices WHERE period = ?
    `, [period]);

    // Vorschau: Mitglieder die noch keine Rechnung für diese Periode haben
    const [eligible] = await db.query(`
      SELECT m.*, t.price_monthly, t.name as tariff_name
      FROM memberships m
      JOIN tariffs t ON m.tariff_id = t.id
      WHERE m.status IN ('active','paused')
        AND m.contract_start <= LAST_DAY(STR_TO_DATE(CONCAT(?, '-01'), '%Y-%m-%d'))
        AND m.contract_end   >= STR_TO_DATE(CONCAT(?, '-01'), '%Y-%m-%d')
        AND m.id NOT IN (
          SELECT membership_id FROM invoices WHERE period = ?
        )
    `, [period, period, period]);

    const preview_total = eligible.reduce((sum, m) => sum + calcInvoiceAmount(m, period), 0);

    res.render('admin/billing', {
      period, runs, invoices,
      summary: summary[0],
      eligible, preview_total,
      periodLabel: periodLabel(period),
      currentPeriod: currentPeriod(),
      admin: req.session.adminUser,
      success: req.query.success || null,
      error: req.query.error || null
    });
  } catch (err) {
    console.error(err);
    res.redirect('/admin?error=Fehler+in+der+Abrechnung:+' + err.message);
  }
});

// ============================================
// POST /admin/billing/run – Abrechnungslauf
// ============================================
router.post('/run', requireAdmin, async (req, res) => {
  const period = req.body.period || currentPeriod();
  try {
    // Bereits existierende Rechnungen für diesen Monat prüfen
    const [existing] = await db.query(
      'SELECT COUNT(*) as c FROM invoices WHERE period = ?', [period]
    );
    if (existing[0].c > 0) {
      return res.redirect(`/admin/billing?period=${period}&error=Abrechnungslauf+für+${period}+wurde+bereits+durchgeführt`);
    }

    // Alle aktiven/pausierten Mitglieder im Vertragszeitraum
    const [members] = await db.query(`
      SELECT m.*, t.price_monthly, t.name as tariff_name
      FROM memberships m
      JOIN tariffs t ON m.tariff_id = t.id
      WHERE m.status IN ('active','paused')
        AND m.contract_start <= LAST_DAY(STR_TO_DATE(CONCAT(?, '-01'), '%Y-%m-%d'))
        AND (m.contract_end IS NULL OR m.contract_end >= STR_TO_DATE(CONCAT(?, '-01'), '%Y-%m-%d'))
    `, [period, period]);

    if (members.length === 0) {
      return res.redirect(`/admin/billing?period=${period}&error=Keine+aktiven+Mitglieder+für+diesen+Zeitraum`);
    }

    // Billing Run erstellen
    const [runResult] = await db.query(
      'INSERT INTO billing_runs (run_date, period, created_by) VALUES (CURDATE(), ?, ?)',
      [period, req.session.adminUser]
    );
    const runId = runResult.insertId;

    // Rechnungen erstellen
    let totalAmount = 0;
    let invoiceCount = 0;

    for (const member of members) {
      const amount = calcInvoiceAmount(member, period);
      const description = `Mitgliedsbeitrag ${periodLabel(period)} – ${member.tariff_name}`;

      if (amount >= 0) {
        await db.query(`
          INSERT INTO invoices 
            (billing_run_id, membership_id, period, amount, description, iban, account_holder, bank_name)
          VALUES (?, ?, ?, ?, ?, ?, ?, ?)
          ON DUPLICATE KEY UPDATE amount = VALUES(amount)
        `, [runId, member.id, period, amount, description,
            member.iban || '', member.account_holder || '', member.bank_name || '']);
        totalAmount += amount;
        invoiceCount++;
      }
    }

    // Run-Summen aktualisieren
    await db.query(
      'UPDATE billing_runs SET total_amount = ?, invoice_count = ? WHERE id = ?',
      [totalAmount, invoiceCount, runId]
    );

    res.redirect(`/admin/billing?period=${period}&success=${invoiceCount}+Rechnungen+erstellt+(${totalAmount.toFixed(2).replace('.', ',')}+€+gesamt)`);
  } catch (err) {
    console.error(err);
    res.redirect(`/admin/billing?error=Fehler+beim+Abrechnungslauf:+` + encodeURIComponent(err.message));
  }
});

// ============================================
// POST /admin/billing/invoices/:id/paid – Bezahlt markieren
// ============================================
router.post('/invoices/:id/paid', requireAdmin, async (req, res) => {
  const period = req.body.period || currentPeriod();
  try {
    await db.query(
      "UPDATE invoices SET status='paid', paid_at=NOW() WHERE id=?",
      [req.params.id]
    );
    res.redirect(`/admin/billing?period=${period}&success=Rechnung+als+bezahlt+markiert`);
  } catch (err) {
    res.redirect(`/admin/billing?period=${period}&error=Fehler`);
  }
});

// POST – Alle offen als bezahlt markieren
router.post('/mark-all-paid', requireAdmin, async (req, res) => {
  const period = req.body.period || currentPeriod();
  try {
    const [result] = await db.query(
      "UPDATE invoices SET status='paid', paid_at=NOW() WHERE period=? AND status='open'",
      [period]
    );
    res.redirect(`/admin/billing?period=${period}&success=${result.affectedRows}+Rechnungen+als+bezahlt+markiert`);
  } catch (err) {
    res.redirect(`/admin/billing?period=${period}&error=Fehler`);
  }
});

// ============================================
// GET /admin/billing/export/csv – SEPA CSV
// ============================================
router.get('/export/csv', requireAdmin, async (req, res) => {
  const period = req.query.period || currentPeriod();
  try {
    const [invoices] = await db.query(`
      SELECT i.*, m.first_name, m.last_name, m.email
      FROM invoices i
      JOIN memberships m ON i.membership_id = m.id
      WHERE i.period = ? AND i.status = 'open' AND i.amount > 0
      ORDER BY m.last_name ASC
    `, [period]);

    // Alle offenen Rechnungen dieser Periode als bezahlt markieren
    // IDs zuerst laden um Collation-Probleme zu umgehen
    const [openInvoices] = await db.query(
      'SELECT id FROM invoices WHERE CONVERT(period USING utf8mb4) = CONVERT(? USING utf8mb4) AND status = ?',
      [period, 'open']
    );
    if (openInvoices.length > 0) {
      const ids = openInvoices.map(r => r.id);
      await db.query(
        `UPDATE invoices SET status='paid', paid_at=NOW() WHERE id IN (${ids.join(',')})`,
        []
      );
    }

    res.setHeader('Content-Type', 'text/csv; charset=utf-8');
    res.setHeader('Content-Disposition', `attachment; filename="SEPA_${period}.csv"`);

    // BOM für Excel
    res.write('\uFEFF');
    // Header
    res.write('Name;IBAN;BIC;Betrag;Verwendungszweck;Mandatsreferenz;Mandatsdatum\n');

    for (const inv of invoices) {
      const name = `${inv.last_name} ${inv.first_name}`.replace(/;/g, ' ');
      const iban = (inv.iban || '').replace(/\s/g, '');
      const amount = Number(inv.amount).toFixed(2).replace('.', ',');
      const purpose = `Mitgliedsbeitrag ${periodLabel(period)}`.replace(/;/g, ' ');
      const mandateRef = `PF24-${String(inv.membership_id).padStart(5, '0')}`;
      res.write(`${name};${iban};;${amount};${purpose};${mandateRef};${inv.created_at.toISOString().split('T')[0]}\n`);
    }

    res.end();
  } catch (err) {
    console.error(err);
    res.redirect(`/admin/billing?error=CSV+Fehler`);
  }
});

// ============================================
// GET /admin/billing/export/pdf/:invoiceId – Einzelrechnung PDF
// ============================================
router.get('/export/pdf/:invoiceId', requireAdmin, async (req, res) => {
  try {
    const [rows] = await db.query(`
      SELECT i.*, 
             m.first_name, m.last_name, m.email, m.phone,
             m.street, m.zip, m.city,
             t.name as tariff_name, t.duration_months
      FROM invoices i
      JOIN memberships m ON i.membership_id = m.id
      LEFT JOIN tariffs t ON m.tariff_id = t.id
      WHERE i.id = ?
    `, [req.params.invoiceId]);

    if (rows.length === 0) return res.status(404).send('Rechnung nicht gefunden');
    const inv = rows[0];

    res.setHeader('Content-Type', 'application/pdf');
    res.setHeader('Content-Disposition', `attachment; filename="Rechnung_${inv.id}_${inv.period}.pdf"`);

    const doc = new PDFDocument({ margin: 60, size: 'A4' });
    doc.pipe(res);

    // Absender
    doc.fontSize(10).fillColor('#666')
       .text('PlusFit24 UG · Moosleiten 12 · 84089 Aiglsbach', 60, 60);

    // Empfänger
    doc.fontSize(11).fillColor('#000')
       .text(`${inv.first_name} ${inv.last_name}`, 60, 110)
       .text(inv.street || '')
       .text(`${inv.zip} ${inv.city}`);

    // Rechnungstitel
    doc.fontSize(20).fillColor('#2d2dcc')
       .text('RECHNUNG', 60, 220);

    doc.fontSize(10).fillColor('#333')
       .text(`Rechnungsnummer: PF24-${String(inv.id).padStart(6, '0')}`, 60, 255)
       .text(`Datum: ${new Date().toLocaleDateString('de-DE')}`)
       .text(`Zeitraum: ${periodLabel(inv.period)}`);

    // Trennlinie
    doc.moveTo(60, 310).lineTo(535, 310).strokeColor('#ddd').stroke();

    // Tabelle
    doc.fontSize(10).fillColor('#999')
       .text('Beschreibung', 60, 325)
       .text('Betrag', 460, 325, { align: 'right', width: 75 });

    doc.moveTo(60, 340).lineTo(535, 340).strokeColor('#ddd').stroke();

    doc.fontSize(11).fillColor('#000')
       .text(inv.description || `Mitgliedsbeitrag ${periodLabel(inv.period)}`, 60, 350)
       .text(`${Number(inv.amount).toFixed(2).replace('.', ',')} €`, 460, 350, { align: 'right', width: 75 });

    doc.moveTo(60, 375).lineTo(535, 375).strokeColor('#ddd').stroke();

    // Summe
    doc.fontSize(12).fillColor('#2d2dcc')
       .text('Gesamt:', 380, 390)
       .text(`${Number(inv.amount).toFixed(2).replace('.', ',')} €`, 460, 390, { align: 'right', width: 75 });

    doc.fontSize(9).fillColor('#999')
       .text('Alle Beträge inkl. MwSt. gem. § 19 UStG (Kleinunternehmerregelung)', 60, 415);

    // Bankdaten
    doc.moveTo(60, 450).lineTo(535, 450).strokeColor('#eee').stroke();
    doc.fontSize(10).fillColor('#333')
       .text('Bankverbindung des Mitglieds:', 60, 460)
       .text(`IBAN: ${inv.iban || '–'}`, 60, 475)
       .text(`Kontoinhaber: ${inv.account_holder || '–'}`)
       .text(`Geldinstitut: ${inv.bank_name || '–'}`);

    // Footer
    doc.fontSize(9).fillColor('#999')
       .text('PlusFit24 UG · Moosleiten 12 · 84089 Aiglsbach · Gläubiger-ID: DE1200100002549495',
             60, 730, { align: 'center', width: 475 });

    doc.end();
  } catch (err) {
    console.error(err);
    res.status(500).send('PDF Fehler: ' + err.message);
  }
});

module.exports = router;
module.exports.currentPeriod = currentPeriod;