const express = require('express');
const router = express.Router();
const { getDb, ensureUserDefaultCategories } = require('../db/database');
const {
  auditBillsForUser,
  categoryBelongsToUser,
  insertBill,
  serializeBill,
  parseTemplateData,
  sanitizeTemplateData,
  validateBillData,
  computeBalanceDelta,
  applyBalanceDelta,
} = require('../services/billsService');
const { amortizationSchedule, debtAprSnapshot } = require('../services/aprService');
const { standardizeError } = require('../middleware/errorFormatter');
const { validatePaymentInput, serializePayment } = require('../services/paymentValidation');
const { addMerchantRule, syncBillPaymentsFromSimplefin, merchantMatches } = require('../services/billMerchantRuleService');
const { normalizeMerchant } = require('../services/subscriptionService');
const { decorateTransaction } = require('../services/transactionService');
const {
  accountingActiveSql,
  applyBankPaymentAsSourceOfTruth,
} = require('../services/paymentAccountingService');
const { localDateString, todayLocal } = require('../utils/dates');
const { roundMoney, sumMoney, toCents, fromCents } = require('../utils/money');

// ── GET /api/bills ────────────────────────────────────────────────────────────
router.get('/', (req, res) => {
  const db = getDb();
  ensureUserDefaultCategories(req.user.id);
  const includeInactive = req.query.inactive === 'true';
  // LEFT JOIN on pre-grouped subqueries — one query instead of N+1 correlated EXISTS lookups.
  const bills = db.prepare(`
    SELECT b.*, c.name AS category_name,
      CASE WHEN hr.bill_id IS NOT NULL THEN 1 ELSE 0 END AS has_history_ranges,
      CASE WHEN mr.bill_id IS NOT NULL THEN 1 ELSE 0 END AS has_merchant_rule,
      CASE WHEN lt.matched_bill_id IS NOT NULL THEN 1 ELSE 0 END AS has_linked_transactions
    FROM bills b
    LEFT JOIN categories c ON b.category_id = c.id AND c.deleted_at IS NULL
    LEFT JOIN (SELECT DISTINCT bill_id FROM bill_history_ranges) hr ON hr.bill_id = b.id
    LEFT JOIN (SELECT DISTINCT bill_id FROM bill_merchant_rules) mr ON mr.bill_id = b.id
    LEFT JOIN (SELECT DISTINCT matched_bill_id FROM transactions WHERE match_status = 'matched') lt ON lt.matched_bill_id = b.id
    WHERE b.user_id = ?
      AND b.deleted_at IS NULL
      ${includeInactive ? '' : 'AND b.active = 1'}
    ORDER BY CASE WHEN b.sort_order IS NULL THEN 1 ELSE 0 END, b.sort_order ASC, b.due_day ASC, b.name ASC
  `).all(req.user.id);
  res.json(bills.map(serializeBill));
});

// ── PUT /api/bills/reorder ───────────────────────────────────────────────────
router.put('/reorder', (req, res) => {
  const db = getDb();
  const entries = Object.entries(req.body || {}).map(([billId, sortOrder]) => ({
    billId: Number(billId),
    sortOrder: Number(sortOrder),
  }));

  if (entries.length === 0) {
    return res.status(400).json(standardizeError('At least one bill order is required', 'VALIDATION_ERROR', 'reorder'));
  }

  const invalid = entries.find(({ billId, sortOrder }) => (
    !Number.isInteger(billId) || billId <= 0 || !Number.isInteger(sortOrder) || sortOrder < 0
  ));
  if (invalid) {
    return res.status(400).json(standardizeError('Reorder payload must map bill ids to non-negative integer positions', 'VALIDATION_ERROR', 'reorder'));
  }

  const ids = entries.map(item => item.billId);
  const placeholders = ids.map(() => '?').join(',');
  const owned = db.prepare(`
    SELECT id
    FROM bills
    WHERE user_id = ? AND deleted_at IS NULL AND id IN (${placeholders})
  `).all(req.user.id, ...ids);
  if (owned.length !== ids.length) {
    return res.status(404).json(standardizeError('One or more bills were not found', 'NOT_FOUND', 'bill_id'));
  }

  const update = db.prepare("UPDATE bills SET sort_order = ?, updated_at = datetime('now') WHERE id = ? AND user_id = ?");
  const applyOrder = db.transaction((items) => {
    for (const item of items) update.run(item.sortOrder, item.billId, req.user.id);
  });
  applyOrder(entries);

  const bills = db.prepare(`
    SELECT b.*, c.name AS category_name
    FROM bills b
    LEFT JOIN categories c ON b.category_id = c.id AND c.deleted_at IS NULL
    WHERE b.user_id = ? AND b.deleted_at IS NULL AND b.active = 1
    ORDER BY CASE WHEN b.sort_order IS NULL THEN 1 ELSE 0 END, b.sort_order ASC, b.due_day ASC, b.name ASC
  `).all(req.user.id);

  res.json({ success: true, bills: bills.map(serializeBill) });
});

// ── GET /api/bills/audit?inactive=true ───────────────────────────────────────
router.get('/audit', (req, res) => {
  const db = getDb();
  ensureUserDefaultCategories(req.user.id);
  const includeInactive = req.query.inactive === 'true';
  res.json(auditBillsForUser(db, req.user.id, includeInactive));
});

// ── GET /api/bills/drift-report ──────────────────────────────────────────────
router.get('/drift-report', (req, res) => {
  const { getDriftReport } = require('../services/driftService');
  try {
    res.json(getDriftReport(req.user.id));
  } catch (err) {
    res.status(500).json({ error: 'Failed to compute drift report' });
  }
});

// GET /api/bills/merchant-rules — all rules for this user across all bills
router.get('/merchant-rules', (req, res) => {
  try {
    const rules = getDb().prepare(`
      SELECT bmr.id, bmr.merchant, bmr.auto_attribute_late, bmr.created_at,
             b.id AS bill_id, b.name AS bill_name
      FROM bill_merchant_rules bmr
      JOIN bills b ON b.id = bmr.bill_id AND b.deleted_at IS NULL
      WHERE bmr.user_id = ?
      ORDER BY b.name COLLATE NOCASE ASC, LENGTH(bmr.merchant) DESC, bmr.merchant ASC
    `).all(req.user.id);
    res.json({ rules });
  } catch (err) {
    console.error('[bills/merchant-rules GET]', err.message);
    res.status(500).json({ error: 'Failed to load merchant rules' });
  }
});

// ── POST /api/bills/:id/snooze-drift ─────────────────────────────────────────
// Registered early (before /:id) but path has suffix so no conflict
router.post('/:id/snooze-drift', (req, res) => {
  const db = getDb();
  const id = parseInt(req.params.id, 10);
  if (!Number.isInteger(id) || id <= 0) return res.status(400).json({ error: 'Invalid id' });
  const bill = db.prepare('SELECT id, user_id FROM bills WHERE id = ? AND deleted_at IS NULL').get(id);
  if (!bill || bill.user_id !== req.user.id) return res.status(404).json({ error: 'Not found' });
  const until = new Date();
  until.setDate(until.getDate() + 30);
  const untilStr = localDateString(until);
  db.prepare('UPDATE bills SET drift_snoozed_until = ? WHERE id = ?').run(untilStr, id);
  res.json({ ok: true, drift_snoozed_until: untilStr });
});

// Bill templates store money fields (expected_amount, current_balance, minimum_payment)
// in integer cents, matching validateBillData's normalized output. Convert back to
// dollars for API responses, mirroring serializeBill.
function serializeTemplateData(data) {
  if (!data) return data;
  const out = { ...data };
  if (out.expected_amount != null) out.expected_amount = fromCents(out.expected_amount);
  if (out.current_balance != null) out.current_balance = fromCents(out.current_balance);
  if (out.minimum_payment != null) out.minimum_payment = fromCents(out.minimum_payment);
  return out;
}

// ── GET /api/bills/templates ─────────────────────────────────────────────────
router.get('/templates', (req, res) => {
  const db = getDb();
  const rows = db.prepare(`
    SELECT id, name, data, created_at, updated_at
    FROM bill_templates
    WHERE user_id = ?
    ORDER BY name COLLATE NOCASE ASC
  `).all(req.user.id);

  res.json(rows.map(row => ({
    ...row,
    data: serializeTemplateData(parseTemplateData(row.data)),
  })));
});

// ── POST /api/bills/templates ────────────────────────────────────────────────
router.post('/templates', (req, res) => {
  const db = getDb();
  const name = String(req.body.name || '').trim();
  if (name.length < 2) {
    return res.status(400).json(standardizeError('Template name must be at least 2 characters', 'VALIDATION_ERROR', 'name'));
  }

  const data = sanitizeTemplateData(req.body.data || {});
  if (Object.keys(data).length === 0) {
    return res.status(400).json(standardizeError('Template data is required', 'VALIDATION_ERROR', 'data'));
  }
  const validation = validateBillData(data);
  if (validation.errors.length > 0) {
    const firstError = validation.errors[0];
    return res.status(400).json(standardizeError(firstError.message, 'VALIDATION_ERROR', `data.${firstError.field}`));
  }
  if (!categoryBelongsToUser(db, validation.normalized.category_id, req.user.id)) {
    return res.status(400).json(standardizeError('category_id is invalid for this user', 'VALIDATION_ERROR', 'data.category_id'));
  }
  const normalizedData = sanitizeTemplateData(validation.normalized);

  const result = db.prepare(`
    INSERT INTO bill_templates (user_id, name, data, updated_at)
    VALUES (?, ?, ?, datetime('now'))
    ON CONFLICT(user_id, name) DO UPDATE SET
      data = excluded.data,
      updated_at = datetime('now')
  `).run(req.user.id, name, JSON.stringify(normalizedData));

  const template = db.prepare(`
    SELECT id, name, data, created_at, updated_at
    FROM bill_templates
    WHERE user_id = ? AND name = ?
  `).get(req.user.id, name);

  res.status(result.changes > 0 ? 201 : 200).json({
    ...template,
    data: serializeTemplateData(parseTemplateData(template.data)),
  });
});

// ── DELETE /api/bills/templates/:templateId ──────────────────────────────────
router.delete('/templates/:templateId', (req, res) => {
  const db = getDb();
  const templateId = parseInt(req.params.templateId, 10);
  if (!Number.isInteger(templateId)) {
    return res.status(400).json(standardizeError('template_id must be an integer', 'VALIDATION_ERROR', 'template_id'));
  }
  const result = db.prepare('DELETE FROM bill_templates WHERE id = ? AND user_id = ?').run(templateId, req.user.id);
  if (result.changes === 0) return res.status(404).json(standardizeError('Template not found', 'NOT_FOUND', 'template_id'));
  res.json({ success: true });
});

// ── POST /api/bills/:id/duplicate ────────────────────────────────────────────
router.post('/:id/duplicate', (req, res) => {
  const db = getDb();
  const body = req.body || {};
  const billId = parseInt(req.params.id, 10);
  if (!Number.isInteger(billId)) {
    return res.status(400).json(standardizeError('bill_id must be an integer', 'VALIDATION_ERROR', 'bill_id'));
  }
  const source = db.prepare('SELECT * FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(billId, req.user.id);
  if (!source) return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND', 'bill_id'));

  const draft = {
    ...sanitizeTemplateData(serializeBill(source)),
    ...sanitizeTemplateData(body),
    name: String(body.name || `${source.name} (Copy)`).trim(),
  };
  const validation = validateBillData(draft);
  if (validation.errors.length > 0) {
    const firstError = validation.errors[0];
    return res.status(400).json(standardizeError(firstError.message, 'VALIDATION_ERROR', firstError.field));
  }
  const { normalized } = validation;
  if (!categoryBelongsToUser(db, normalized.category_id, req.user.id)) {
    return res.status(400).json(standardizeError('category_id is invalid for this user', 'VALIDATION_ERROR', 'category_id'));
  }

  res.status(201).json(serializeBill(insertBill(db, req.user.id, normalized)));
});

// ── GET /api/bills/:id/monthly-state?year=&month= ─────────────────────────────
router.get('/:id/monthly-state', (req, res) => {
  const db = getDb();
  const billId = parseInt(req.params.id, 10);
  if (!db.prepare('SELECT id FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(billId, req.user.id))
    return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND', 'bill_id'));

  const year  = parseInt(req.query.year,  10);
  const month = parseInt(req.query.month, 10);
  if (isNaN(year)  || year  < 2000 || year  > 2100)
    return res.status(400).json(standardizeError('year must be a 4-digit integer between 2000 and 2100', 'VALIDATION_ERROR', 'year'));
  if (isNaN(month) || month < 1    || month > 12)
    return res.status(400).json(standardizeError('month must be an integer between 1 and 12', 'VALIDATION_ERROR', 'month'));

  const mbs = db.prepare(
    'SELECT actual_amount, notes, is_skipped FROM monthly_bill_state WHERE bill_id=? AND year=? AND month=?'
  ).get(billId, year, month);

  res.json({
    bill_id:       billId,
    year,
    month,
    actual_amount: fromCents(mbs?.actual_amount),
    notes:         mbs?.notes         ?? null,
    is_skipped:    !!(mbs?.is_skipped),
  });
});

// ── PUT /api/bills/:id/monthly-state ──────────────────────────────────────────
router.put('/:id/monthly-state', (req, res) => {
  const db = getDb();
  const billId = parseInt(req.params.id, 10);
  if (!db.prepare('SELECT id FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(billId, req.user.id))
    return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND', 'bill_id'));

  const { year, month, actual_amount, notes, is_skipped, snoozed_until } = req.body;

  const y = parseInt(year,  10);
  const m = parseInt(month, 10);
  if (isNaN(y) || y < 2000 || y > 2100)
    return res.status(400).json(standardizeError('year must be a 4-digit integer between 2000 and 2100', 'VALIDATION_ERROR', 'year'));
  if (isNaN(m) || m < 1 || m > 12)
    return res.status(400).json(standardizeError('month must be an integer between 1 and 12', 'VALIDATION_ERROR', 'month'));

  if (actual_amount !== undefined && actual_amount !== null) {
    const amt = parseFloat(actual_amount);
    if (isNaN(amt) || amt < 0)
      return res.status(400).json(standardizeError('actual_amount must be a non-negative number or null', 'VALIDATION_ERROR', 'actual_amount'));
  }

  if (snoozed_until !== undefined && snoozed_until !== null) {
    if (!/^\d{4}-\d{2}-\d{2}$/.test(snoozed_until))
      return res.status(400).json(standardizeError('snoozed_until must be an ISO date string (YYYY-MM-DD) or null', 'VALIDATION_ERROR', 'snoozed_until'));
  }

  // Partial-update semantics: fields omitted from the request keep their
  // existing values instead of being wiped by the upsert.
  const existing = db.prepare(
    'SELECT actual_amount, notes, is_skipped, snoozed_until FROM monthly_bill_state WHERE bill_id=? AND year=? AND month=?'
  ).get(billId, y, m);

  const amt        = actual_amount  !== undefined ? (actual_amount  === null ? null : toCents(actual_amount)) : (existing?.actual_amount ?? null);
  const noteVal    = notes          !== undefined ? (notes          || null) : (existing?.notes ?? null);
  const skipVal    = is_skipped     !== undefined ? (is_skipped     ? 1 : 0) : (existing?.is_skipped ?? 0);
  const snoozeVal  = snoozed_until  !== undefined ? (snoozed_until  || null) : (existing?.snoozed_until ?? null);

  db.prepare(`
    INSERT INTO monthly_bill_state (bill_id, year, month, actual_amount, notes, is_skipped, snoozed_until, updated_at)
    VALUES (?, ?, ?, ?, ?, ?, ?, datetime('now'))
    ON CONFLICT(bill_id, year, month) DO UPDATE SET
      actual_amount = excluded.actual_amount,
      notes         = excluded.notes,
      is_skipped    = excluded.is_skipped,
      snoozed_until = excluded.snoozed_until,
      updated_at    = datetime('now')
  `).run(billId, y, m, amt, noteVal, skipVal, snoozeVal);

  const saved = db.prepare(
    'SELECT * FROM monthly_bill_state WHERE bill_id=? AND year=? AND month=?'
  ).get(billId, y, m);

  res.json({
    bill_id:       saved.bill_id,
    year:          saved.year,
    month:         saved.month,
    actual_amount: fromCents(saved.actual_amount),
    notes:         saved.notes,
    is_skipped:    !!saved.is_skipped,
    snoozed_until: saved.snoozed_until ?? null,
    created_at:    saved.created_at,
    updated_at:    saved.updated_at,
  });
});

// ── GET /api/bills/:id ────────────────────────────────────────────────────────
router.get('/:id', (req, res) => {
  const db = getDb();
  const bill = db.prepare(`
    SELECT b.*, c.name AS category_name,
      CASE WHEN EXISTS(
        SELECT 1 FROM bill_history_ranges WHERE bill_id = b.id
      ) THEN 1 ELSE 0 END AS has_history_ranges,
      CASE WHEN EXISTS(
        SELECT 1 FROM bill_merchant_rules WHERE bill_id = b.id AND user_id = b.user_id
      ) THEN 1 ELSE 0 END AS has_merchant_rule,
      CASE WHEN EXISTS(
        SELECT 1 FROM transactions WHERE matched_bill_id = b.id AND match_status = 'matched' AND user_id = b.user_id
      ) THEN 1 ELSE 0 END AS has_linked_transactions
    FROM bills b
    LEFT JOIN categories c ON b.category_id = c.id AND c.deleted_at IS NULL
    WHERE b.id = ? AND b.user_id = ? AND b.deleted_at IS NULL
  `).get(req.params.id, req.user.id);
  if (!bill) return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND', 'bill_id'));

  let autopay_stats = null;
  if (bill.autopay_enabled) {
    autopay_stats = db.prepare(`
      SELECT COUNT(*) AS total,
             SUM(autopay_failure) AS failures,
             MAX(CASE WHEN autopay_failure = 1 THEN paid_date END) AS last_failure_date,
             MAX(CASE WHEN autopay_failure = 1 THEN notes END) AS last_failure_notes
      FROM payments
      WHERE bill_id = ? AND deleted_at IS NULL AND paid_date >= date('now', '-12 months')
    `).get(bill.id);
    autopay_stats = {
      total: autopay_stats.total || 0,
      failures: autopay_stats.failures || 0,
      last_failure_date: autopay_stats.last_failure_date || null,
      last_failure_notes: autopay_stats.last_failure_notes || null,
    };
  }

  res.json({ ...serializeBill(bill), autopay_stats });
});

// ── POST /api/bills/:id/verify-autopay ───────────────────────────────────────
router.post('/:id/verify-autopay', (req, res) => {
  const db = getDb();
  const id = parseInt(req.params.id, 10);
  if (!Number.isInteger(id) || id <= 0) {
    return res.status(400).json(standardizeError('Invalid id', 'VALIDATION_ERROR', 'bill_id'));
  }
  const bill = db.prepare('SELECT id, autopay_enabled FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(id, req.user.id);
  if (!bill) return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND', 'bill_id'));
  if (!bill.autopay_enabled) {
    return res.status(400).json(standardizeError('Bill does not have autopay enabled', 'VALIDATION_ERROR', 'autopay_enabled'));
  }
  const now = new Date().toISOString();
  db.prepare("UPDATE bills SET autopay_verified_at = ?, updated_at = ? WHERE id = ? AND user_id = ?").run(now, now, id, req.user.id);
  res.json({ ok: true, autopay_verified_at: now });
});

// ── POST /api/bills ───────────────────────────────────────────────────────────
router.post('/', (req, res) => {
  const db = getDb();
  const body = req.body || {};
  let payload = body;

  if (body.source_bill_id !== undefined && body.source_bill_id !== null && body.source_bill_id !== '') {
    const sourceBillId = parseInt(body.source_bill_id, 10);
    if (!Number.isInteger(sourceBillId)) {
      return res.status(400).json(standardizeError('source_bill_id must be an integer', 'VALIDATION_ERROR', 'source_bill_id'));
    }
    const source = db.prepare('SELECT * FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(sourceBillId, req.user.id);
    if (!source) return res.status(404).json(standardizeError('Source bill not found', 'NOT_FOUND', 'source_bill_id'));
    payload = {
      ...sanitizeTemplateData(serializeBill(source)),
      ...sanitizeTemplateData(body),
      name: String(body.name || `${source.name} (Copy)`).trim(),
    };
  }

  // Validate and normalize bill data
  const validation = validateBillData(payload);
  if (validation.errors.length > 0) {
    const firstError = validation.errors[0];
    return res.status(400).json(standardizeError(firstError.message, 'VALIDATION_ERROR', firstError.field));
  }

  const { normalized } = validation;

  // Validate category_id exists for this user
  if (!categoryBelongsToUser(db, normalized.category_id, req.user.id)) {
    return res.status(400).json(standardizeError('category_id is invalid for this user', 'VALIDATION_ERROR', 'category_id'));
  }

  res.status(201).json(serializeBill(insertBill(db, req.user.id, normalized)));
});

// ── PUT /api/bills/:id ────────────────────────────────────────────────────────
router.put('/:id', (req, res) => {
  const db = getDb();
  const existing = db.prepare('SELECT * FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(req.params.id, req.user.id);
  if (!existing) return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND', 'bill_id'));

  // Validate and normalize bill data
  const validation = validateBillData(req.body, existing);
  if (validation.errors.length > 0) {
    const firstError = validation.errors[0];
    return res.status(400).json(standardizeError(firstError.message, 'VALIDATION_ERROR', firstError.field));
  }

  const { normalized } = validation;

  // Validate category_id exists for this user if changed
  if (!categoryBelongsToUser(db, normalized.category_id, req.user.id)) {
    return res.status(400).json(standardizeError('category_id is invalid for this user', 'VALIDATION_ERROR', 'category_id'));
  }

  const inactiveReason = typeof req.body.inactive_reason === 'string' ? req.body.inactive_reason.trim() || null : null;
  const wasActive = existing.active === 1;
  const nowActive = normalized.active === 1;
  const inactivatedAt = (!wasActive || nowActive) ? existing.inactivated_at : (inactiveReason ? todayLocal() : existing.inactivated_at);

  db.prepare(`
    UPDATE bills SET
      name = ?, category_id = ?, due_day = ?, override_due_date = ?, bucket = ?,
      expected_amount = ?, interest_rate = ?, billing_cycle = ?, autopay_enabled = ?, autodraft_status = ?, auto_mark_paid = ?,
      website = ?, username = ?, account_info = ?, has_2fa = ?, notes = ?, active = ?,
      history_visibility = ?, cycle_type = ?, cycle_day = ?,
      current_balance = ?, minimum_payment = ?, snowball_order = ?, snowball_include = ?, snowball_exempt = ?,
      is_subscription = ?, subscription_type = ?, reminder_days_before = ?, subscription_source = ?, subscription_detected_at = ?,
      inactive_reason = ?, inactivated_at = ?,
      updated_at = datetime('now')
    WHERE id = ? AND user_id = ?
  `).run(
    normalized.name,
    normalized.category_id,
    normalized.due_day,
    normalized.override_due_date,
    normalized.bucket,
    normalized.expected_amount,
    normalized.interest_rate,
    normalized.billing_cycle,
    normalized.autopay_enabled,
    normalized.autodraft_status,
    normalized.auto_mark_paid,
    normalized.website,
    normalized.username,
    normalized.account_info,
    normalized.has_2fa,
    normalized.notes,
    normalized.active,
    normalized.history_visibility,
    normalized.cycle_type,
    normalized.cycle_day,
    normalized.current_balance,
    normalized.minimum_payment,
    normalized.snowball_order,
    normalized.snowball_include,
    normalized.snowball_exempt,
    normalized.is_subscription,
    normalized.subscription_type,
    normalized.reminder_days_before,
    normalized.subscription_source,
    normalized.subscription_detected_at,
    inactiveReason,
    inactivatedAt,
    req.params.id,
    req.user.id,
  );

  const updated = db.prepare('SELECT * FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(req.params.id, req.user.id);
  res.json(serializeBill(updated));
});

// ── PUT /api/bills/:id/archived ──────────────────────────────────────────────
router.put('/:id/archived', (req, res) => {
  const db = getDb();
  const id = parseInt(req.params.id, 10);
  if (!Number.isInteger(id) || id <= 0) {
    return res.status(400).json(standardizeError('Invalid id', 'VALIDATION_ERROR', 'bill_id'));
  }
  const bill = db.prepare('SELECT id FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(id, req.user.id);
  if (!bill) return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND', 'bill_id'));

  const archived = !!req.body?.archived;
  db.prepare("UPDATE bills SET active = ?, updated_at = datetime('now') WHERE id = ? AND user_id = ?")
    .run(archived ? 0 : 1, id, req.user.id);

  const updated = db.prepare('SELECT * FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(id, req.user.id);
  res.json({ ...serializeBill(updated), archived: !updated.active });
});

// ── DELETE /api/bills/:id — soft delete for 30-day recovery ───────────────────
router.delete('/:id', (req, res) => {
  const db = getDb();
  const bill = db.prepare('SELECT id, name FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(req.params.id, req.user.id);
  if (!bill) return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND', 'bill_id'));

  db.prepare("UPDATE bills SET deleted_at = datetime('now'), active = 0, updated_at = datetime('now') WHERE id = ? AND user_id = ?")
    .run(req.params.id, req.user.id);

  res.json({
    success: true,
    deleted_bill_id:   bill.id,
    deleted_bill_name: bill.name,
    recoverable_until_days: 30,
  });
});

// POST /api/bills/:id/restore — undo bill soft delete
router.post('/:id/restore', (req, res) => {
  const db = getDb();
  const bill = db.prepare('SELECT id, name FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NOT NULL').get(req.params.id, req.user.id);
  if (!bill) return res.status(404).json(standardizeError('Deleted bill not found', 'NOT_FOUND', 'bill_id'));

  db.prepare("UPDATE bills SET deleted_at = NULL, active = 1, updated_at = datetime('now') WHERE id = ? AND user_id = ?")
    .run(req.params.id, req.user.id);

  res.json(serializeBill(db.prepare('SELECT * FROM bills WHERE id = ? AND user_id = ?').get(req.params.id, req.user.id)));
});

// POST /api/bills/:id/sync-simplefin-payments
// Scan unmatched SimpleFIN transactions for this bill's merchant rules and
// backfill any missing payments.
router.post('/:id/sync-simplefin-payments', (req, res) => {
  const billId = parseInt(req.params.id, 10);
  if (!Number.isInteger(billId)) return res.status(400).json(standardizeError('Invalid bill id', 'VALIDATION_ERROR'));
  const db = getDb();
  const bill = db.prepare('SELECT id FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(billId, req.user.id);
  if (!bill) return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND'));
  try {
    const result = syncBillPaymentsFromSimplefin(db, req.user.id, billId);
    res.json(result);
  } catch (err) {
    res.status(500).json(standardizeError(err.message || 'Sync failed', 'SYNC_ERROR'));
  }
});

// ── GET /api/bills/:id/payments?page=1&limit=20 ───────────────────────────────
router.get('/:id/payments', (req, res) => {
  const db = getDb();
  const bill = db.prepare('SELECT id, name FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(req.params.id, req.user.id);
  if (!bill) return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND', 'bill_id'));

  const limit  = Math.min(parseInt(req.query.limit || '20', 10), 100);
  const page   = Math.max(parseInt(req.query.page  || '1',  10), 1);
  const offset = (page - 1) * limit;

  const total = db.prepare(
    'SELECT COUNT(*) AS n FROM payments WHERE bill_id = ? AND deleted_at IS NULL'
  ).get(req.params.id).n;

  const items = db.prepare(
    'SELECT * FROM payments WHERE bill_id = ? AND deleted_at IS NULL ORDER BY paid_date DESC LIMIT ? OFFSET ?'
  ).all(req.params.id, limit, offset);

  res.json({
    bill_id:    parseInt(req.params.id, 10),
    bill_name:  bill.name,
    total,
    page,
    limit,
    pages:      Math.ceil(total / limit),
    payments:   items.map(serializePayment),
  });
});

// ── GET /api/bills/:id/transactions ──────────────────────────────────────────
router.get('/:id/transactions', (req, res) => {
  const db = getDb();
  const billId = parseInt(req.params.id, 10);
  if (!Number.isInteger(billId)) {
    return res.status(400).json(standardizeError('bill_id must be an integer', 'VALIDATION_ERROR', 'bill_id'));
  }

  const bill = db.prepare('SELECT id, name FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(billId, req.user.id);
  if (!bill) return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND', 'bill_id'));

  const rows = db.prepare(`
    SELECT
      t.id, t.user_id, t.data_source_id, t.account_id, t.provider_transaction_id,
      t.source_type, t.transaction_type, t.posted_date, t.transacted_at, t.amount,
      t.currency, t.description, t.payee, t.memo, t.category, t.matched_bill_id,
      t.match_status, t.ignored, t.created_at, t.updated_at,
      ds.type AS data_source_type, ds.provider AS data_source_provider,
      ds.name AS data_source_name, ds.status AS data_source_status,
      fa.name AS account_name, fa.org_name AS account_org_name,
      fa.account_type AS account_type,
      b.name AS matched_bill_name,
      p.id AS linked_payment_id,
      p.amount AS linked_payment_amount,
      p.paid_date AS linked_payment_date,
      p.payment_source AS linked_payment_source,
      p.method AS linked_payment_method
    FROM transactions t
    LEFT JOIN data_sources ds ON ds.id = t.data_source_id AND ds.user_id = t.user_id
    LEFT JOIN financial_accounts fa ON fa.id = t.account_id AND fa.user_id = t.user_id
    LEFT JOIN bills b ON b.id = t.matched_bill_id AND b.user_id = t.user_id AND b.deleted_at IS NULL
    JOIN payments p ON p.transaction_id = t.id AND p.bill_id = ? AND p.deleted_at IS NULL
    WHERE t.user_id = ?
      AND t.matched_bill_id = ?
      AND t.match_status = 'matched'
      AND t.ignored = 0
    ORDER BY COALESCE(t.posted_date, substr(t.transacted_at, 1, 10), t.created_at) DESC, t.id DESC
  `).all(billId, req.user.id, billId);

  const transactions = rows.map(row => decorateTransaction({
    ...row,
    linked_payment: row.linked_payment_id ? {
      id: row.linked_payment_id,
      amount: fromCents(row.linked_payment_amount),
      paid_date: row.linked_payment_date,
      payment_source: row.linked_payment_source,
      method: row.linked_payment_method,
    } : null,
  }));

  res.json({
    bill_id: billId,
    bill_name: bill.name,
    total: transactions.length,
    transactions,
  });
});

// ── POST /api/bills/:id/toggle-paid — toggle Paid/Unpaid status ──────────────
router.post('/:id/toggle-paid', (req, res) => {
  const db = getDb();
  const billId = parseInt(req.params.id, 10);

  // Get bill - always scope to the requesting user
  const bill = db.prepare('SELECT id, expected_amount, user_id, due_day, current_balance, interest_rate, autopay_enabled FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(billId, req.user.id);

  if (!bill) return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND', 'bill_id'));

  // Scope to year/month if provided
  const year  = req.body.year  !== undefined ? parseInt(req.body.year,  10) : null;
  const month = req.body.month !== undefined ? parseInt(req.body.month, 10) : null;
  if ((year === null) !== (month === null)) {
    return res.status(400).json(standardizeError('year and month must both be provided or both omitted', 'VALIDATION_ERROR', 'year'));
  }
  if (year !== null && (Number.isNaN(year) || year < 2000 || year > 2100)) {
    return res.status(400).json(standardizeError('year must be a 4-digit integer between 2000 and 2100', 'VALIDATION_ERROR', 'year'));
  }
  if (month !== null && (Number.isNaN(month) || month < 1 || month > 12)) {
    return res.status(400).json(standardizeError('month must be an integer between 1 and 12', 'VALIDATION_ERROR', 'month'));
  }

  let currentPayment;
  if (year !== null && month !== null) {
    currentPayment = db.prepare(
      `SELECT * FROM payments WHERE bill_id = ? AND deleted_at IS NULL AND ${accountingActiveSql()} AND strftime('%Y', paid_date) = ? AND strftime('%m', paid_date) = ? ORDER BY paid_date DESC LIMIT 1`
    ).get(billId, String(year), String(month).padStart(2, '0'));
  } else {
    currentPayment = db.prepare(
      `SELECT * FROM payments WHERE bill_id = ? AND deleted_at IS NULL AND ${accountingActiveSql()} ORDER BY paid_date DESC LIMIT 1`
    ).get(billId);
  }

  // If paid (has payment), remove it → Unpaid
  if (currentPayment) {
    // Reverse any balance delta that was applied when this payment was created
    if (currentPayment.balance_delta != null) {
      const freshBill = db.prepare('SELECT current_balance FROM bills WHERE id = ?').get(billId);
      if (freshBill?.current_balance != null) {
        const restored = Math.max(0, freshBill.current_balance - currentPayment.balance_delta);
        db.prepare("UPDATE bills SET current_balance = ?, updated_at = datetime('now') WHERE id = ?").run(restored, billId);
      }
    }
    db.prepare("UPDATE payments SET deleted_at = datetime('now') WHERE id = ?").run(currentPayment.id);
    res.json({
      success: true,
      isPaid: false,
      action: 'removed_payment',
      paymentId: currentPayment.id,
    });
    return;
  }

  // If unpaid, create payment → Paid
  // Use expected_amount if no amount provided
  const amount = req.body.amount !== undefined ? req.body.amount : fromCents(bill.expected_amount);
  
  // Determine paid_date
  let paidDate = req.body.paid_date;
  if (!paidDate && year !== null && month !== null) {
    // Calculate paid_date from bill's due_day clamped to the month's days
    const daysInMonth = new Date(year, month, 0).getDate();
    const day = Math.min(Math.max(Number(bill.due_day), 1), daysInMonth);
    paidDate = `${year}-${String(month).padStart(2, '0')}-${String(day).padStart(2, '0')}`;
  } else if (!paidDate) {
    paidDate = todayLocal();
  }
  
  const method = req.body.method || null;
  const notes = req.body.notes || null;

  const paymentValidation = validatePaymentInput(
    { amount, paid_date: paidDate, payment_source: req.body.payment_source ?? 'manual' },
    { requireBillId: false },
  );
  if (paymentValidation.error) {
    return res.status(400).json(standardizeError(paymentValidation.error, 'VALIDATION_ERROR', paymentValidation.field));
  }
  const payment = paymentValidation.normalized;

  // Compute balance delta for debt bills before inserting
  const balCalc = computeBalanceDelta(bill, payment.amount);

  const result = db.prepare(
    'INSERT INTO payments (bill_id, amount, paid_date, method, notes, balance_delta, interest_delta, payment_source) VALUES (?, ?, ?, ?, ?, ?, ?, ?)'
  ).run(billId, payment.amount, payment.paid_date, method, notes, balCalc?.balance_delta ?? null, balCalc?.interest_delta ?? null, payment.payment_source);

  applyBalanceDelta(db, billId, balCalc);
  res.status(201).json({
    success: true,
    isPaid: true,
    action: 'created_payment',
    payment: serializePayment(db.prepare('SELECT * FROM payments WHERE id = ?').get(result.lastInsertRowid)),
  });
});

// ── GET /api/bills/:id/history-ranges ────────────────────────────────────────
router.get('/:id/history-ranges', (req, res) => {
  const db = getDb();
  if (!db.prepare('SELECT id FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(req.params.id, req.user.id))
    return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND', 'bill_id'));

  const ranges = db.prepare(
    'SELECT * FROM bill_history_ranges WHERE bill_id = ? ORDER BY start_year ASC, start_month ASC'
  ).all(req.params.id);

  const bill = db.prepare('SELECT history_visibility FROM bills WHERE id = ? AND deleted_at IS NULL').get(req.params.id);

  res.json({ bill_id: parseInt(req.params.id, 10), history_visibility: bill.history_visibility, ranges });
});

// ── POST /api/bills/:id/history-ranges ───────────────────────────────────────
router.post('/:id/history-ranges', (req, res) => {
  const db = getDb();
  if (!db.prepare('SELECT id FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(req.params.id, req.user.id))
    return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND', 'bill_id'));

  const { start_year, start_month, end_year, end_month, label } = req.body;

  const sy = parseInt(start_year, 10);
  const sm = parseInt(start_month, 10);
  if (isNaN(sy) || sy < 2000 || sy > 2100)
    return res.status(400).json(standardizeError('start_year must be between 2000 and 2100', 'VALIDATION_ERROR', 'start_year'));
  if (isNaN(sm) || sm < 1 || sm > 12)
    return res.status(400).json(standardizeError('start_month must be between 1 and 12', 'VALIDATION_ERROR', 'start_month'));

  let ey = null, em = null;
  if (end_year != null) {
    ey = parseInt(end_year, 10);
    if (isNaN(ey) || ey < 2000 || ey > 2100)
      return res.status(400).json(standardizeError('end_year must be between 2000 and 2100', 'VALIDATION_ERROR', 'end_year'));
  }
  if (end_month != null) {
    em = parseInt(end_month, 10);
    if (isNaN(em) || em < 1 || em > 12)
      return res.status(400).json(standardizeError('end_month must be between 1 and 12', 'VALIDATION_ERROR', 'end_month'));
  }
  if ((ey == null) !== (em == null)) {
    return res.status(400).json(standardizeError('end_year and end_month must both be provided or both omitted', 'VALIDATION_ERROR', 'end_year'));
  }
  if (ey != null) {
    const startVal = sy * 12 + sm;
    const endVal   = ey * 12 + em;
    if (endVal < startVal)
      return res.status(400).json(standardizeError('end date must be on or after start date', 'VALIDATION_ERROR', 'end_year'));
  }

  const result = db.prepare(`
    INSERT INTO bill_history_ranges (bill_id, start_year, start_month, end_year, end_month, label)
    VALUES (?, ?, ?, ?, ?, ?)
  `).run(req.params.id, sy, sm, ey, em, label || null);

  const created = db.prepare('SELECT * FROM bill_history_ranges WHERE id = ?').get(result.lastInsertRowid);
  res.status(201).json(created);
});

// ── PUT /api/bills/:id/history-ranges/:rangeId ───────────────────────────────
router.put('/:id/history-ranges/:rangeId', (req, res) => {
  const db = getDb();
  if (!db.prepare('SELECT id FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(req.params.id, req.user.id))
    return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND', 'bill_id'));

  const range = db.prepare('SELECT * FROM bill_history_ranges WHERE id = ? AND bill_id = ?')
    .get(req.params.rangeId, req.params.id);
  if (!range) return res.status(404).json(standardizeError('History range not found', 'NOT_FOUND', 'rangeId'));

  const { start_year, start_month, end_year, end_month, label } = req.body;

  const sy = start_year != null ? parseInt(start_year, 10) : range.start_year;
  const sm = start_month != null ? parseInt(start_month, 10) : range.start_month;
  if (isNaN(sy) || sy < 2000 || sy > 2100)
    return res.status(400).json(standardizeError('start_year must be between 2000 and 2100', 'VALIDATION_ERROR', 'start_year'));
  if (isNaN(sm) || sm < 1 || sm > 12)
    return res.status(400).json(standardizeError('start_month must be between 1 and 12', 'VALIDATION_ERROR', 'start_month'));

  let ey = range.end_year;
  let em = range.end_month;
  if (end_year !== undefined) ey = end_year != null ? parseInt(end_year, 10) : null;
  if (end_month !== undefined) em = end_month != null ? parseInt(end_month, 10) : null;

  if (ey != null && (isNaN(ey) || ey < 2000 || ey > 2100))
    return res.status(400).json(standardizeError('end_year must be between 2000 and 2100', 'VALIDATION_ERROR', 'end_year'));
  if (em != null && (isNaN(em) || em < 1 || em > 12))
    return res.status(400).json(standardizeError('end_month must be between 1 and 12', 'VALIDATION_ERROR', 'end_month'));
  if ((ey == null) !== (em == null))
    return res.status(400).json(standardizeError('end_year and end_month must both be provided or both omitted', 'VALIDATION_ERROR', 'end_year'));
  if (ey != null && (ey * 12 + em) < (sy * 12 + sm))
    return res.status(400).json(standardizeError('end date must be on or after start date', 'VALIDATION_ERROR', 'end_year'));

  db.prepare(`
    UPDATE bill_history_ranges
    SET start_year = ?, start_month = ?, end_year = ?, end_month = ?, label = ?,
        updated_at = datetime('now')
    WHERE id = ? AND bill_id = ?
  `).run(sy, sm, ey, em, label !== undefined ? (label || null) : range.label, req.params.rangeId, req.params.id);

  const updated = db.prepare('SELECT * FROM bill_history_ranges WHERE id = ?').get(req.params.rangeId);
  res.json(updated);
});

// ── DELETE /api/bills/:id/history-ranges/:rangeId ────────────────────────────
router.delete('/:id/history-ranges/:rangeId', (req, res) => {
  const db = getDb();
  if (!db.prepare('SELECT id FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(req.params.id, req.user.id))
    return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND', 'bill_id'));

  const range = db.prepare('SELECT id FROM bill_history_ranges WHERE id = ? AND bill_id = ?')
    .get(req.params.rangeId, req.params.id);
  if (!range) return res.status(404).json(standardizeError('History range not found', 'NOT_FOUND', 'rangeId'));

  db.prepare('DELETE FROM bill_history_ranges WHERE id = ? AND bill_id = ?')
    .run(req.params.rangeId, req.params.id);

  res.json({ success: true });
});

// ── GET /api/bills/:id/amortization — full month-by-month schedule for a debt bill ──
router.get('/:id/amortization', (req, res) => {
  const db     = getDb();
  const billId = parseInt(req.params.id, 10);
  const bill   = db.prepare('SELECT * FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(billId, req.user.id);
  if (!bill) return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND', 'bill_id'));

  const balance  = fromCents(Number(bill.current_balance));
  const apr      = Number(bill.interest_rate) || 0;
  const minPmt   = fromCents(Number(bill.minimum_payment) || 0);

  // Optional override: ?payment=X lets callers model "what if I pay more?"
  let payment = minPmt;
  if (req.query.payment !== undefined) {
    const qp = parseFloat(req.query.payment);
    if (!Number.isFinite(qp) || qp <= 0) {
      return res.status(400).json(standardizeError('payment must be a positive number', 'VALIDATION_ERROR', 'payment'));
    }
    payment = qp;
  }

  // Optional ?max_months=N (default 360, hard cap 600)
  let maxMonths = 360;
  if (req.query.max_months !== undefined) {
    const qm = parseInt(req.query.max_months, 10);
    if (Number.isInteger(qm) && qm > 0) maxMonths = Math.min(qm, 600);
  }

  if (!Number.isFinite(balance) || balance <= 0) {
    return res.json({ bill_id: billId, schedule: [], apr_snapshot: null, error: 'No current balance set' });
  }

  const schedule    = amortizationSchedule(balance, apr, payment, maxMonths);
  const apr_snapshot = debtAprSnapshot({ ...bill, current_balance: balance, minimum_payment: minPmt });
  const total_interest = schedule.reduce((s, r) => s + r.interest, 0);

  res.json({
    bill_id:       billId,
    balance,
    apr,
    payment,
    schedule,
    summary: {
      months:          schedule.length,
      total_interest:  roundMoney(total_interest),
      total_paid:      sumMoney(schedule, r => r.payment),
      capped:          schedule.length >= maxMonths && schedule[schedule.length - 1]?.balance > 0,
    },
    apr_snapshot,
  });
});

// ── PATCH /api/bills/:id/snowball — update only snowball_include / snowball_exempt ──
router.patch('/:id/snowball', (req, res) => {
  const db = getDb();
  const billId = parseInt(req.params.id, 10);
  if (!db.prepare('SELECT id FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(billId, req.user.id)) {
    return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND', 'bill_id'));
  }
  const include = req.body.snowball_include !== undefined ? (req.body.snowball_include ? 1 : 0) : undefined;
  const exempt  = req.body.snowball_exempt  !== undefined ? (req.body.snowball_exempt  ? 1 : 0) : undefined;
  const parts = [];
  const vals  = [];
  if (include !== undefined) { parts.push('snowball_include = ?'); vals.push(include); }
  if (exempt  !== undefined) { parts.push('snowball_exempt = ?');  vals.push(exempt);  }
  if (parts.length === 0) return res.status(400).json(standardizeError('Nothing to update', 'VALIDATION_ERROR'));
  parts.push("updated_at = datetime('now')");
  db.prepare(`UPDATE bills SET ${parts.join(', ')} WHERE id = ? AND user_id = ?`).run(...vals, billId, req.user.id);
  res.json({ id: billId, snowball_include: include, snowball_exempt: exempt });
});

// ── PATCH /api/bills/:id/balance — lightweight balance-only update ────────────
router.patch('/:id/balance', (req, res) => {
  const db = getDb();
  const billId = parseInt(req.params.id, 10);
  if (!db.prepare('SELECT id FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(billId, req.user.id)) {
    return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND', 'bill_id'));
  }

  const raw = req.body.current_balance;
  let val = null;
  if (raw !== null && raw !== '' && raw !== undefined) {
    val = parseFloat(raw);
    if (!Number.isFinite(val) || val < 0) {
      return res.status(400).json(standardizeError('current_balance must be a non-negative number', 'VALIDATION_ERROR', 'current_balance'));
    }
    val = roundMoney(val);
  }

  db.prepare("UPDATE bills SET current_balance = ?, updated_at = datetime('now') WHERE id = ?").run(toCents(val), billId);
  res.json({ id: billId, current_balance: val });
});

// ── Merchant rule helpers ─────────────────────────────────────────────────────

function requireBill(db, billId, userId) {
  return db.prepare('SELECT id, name FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(billId, userId);
}

// Count unmatched transactions that would match a normalized merchant string.
function previewMatchCount(db, userId, normalized) {
  if (!normalized || normalized.length < 2) return 0;
  const txRows = db.prepare(`
    SELECT t.payee, t.description, t.memo
    FROM transactions t
    LEFT JOIN financial_accounts fa ON fa.id = t.account_id AND fa.user_id = t.user_id
    WHERE t.user_id = ?
      AND t.match_status = 'unmatched'
      AND t.ignored = 0
      AND t.amount < 0
      AND (t.account_id IS NULL OR fa.id IS NULL OR fa.monitored = 1)
  `).all(userId);
  return txRows.filter(tx => {
    const txMerchant = normalizeMerchant(tx.payee || tx.description || tx.memo || '');
    return txMerchant && merchantMatches(txMerchant, normalized);
  }).length;
}

// Find bills (other than this one) that already claim this merchant.
function findConflicts(db, userId, billId, normalized) {
  return db.prepare(`
    SELECT b.id, b.name
    FROM bill_merchant_rules bmr
    JOIN bills b ON b.id = bmr.bill_id AND b.user_id = bmr.user_id AND b.deleted_at IS NULL
    WHERE bmr.user_id = ? AND bmr.merchant = ? AND bmr.bill_id != ?
  `).all(userId, normalized, billId);
}

// ── GET /api/bills/:id/merchant-rules ────────────────────────────────────────

router.get('/:id/merchant-rules', (req, res) => {
  const db = getDb();
  const billId = parseInt(req.params.id, 10);
  if (!Number.isInteger(billId) || billId < 1)
    return res.status(400).json(standardizeError('Invalid bill id', 'VALIDATION_ERROR'));
  if (!requireBill(db, billId, req.user.id))
    return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND'));

  const rules = db.prepare(`
    SELECT id, merchant, auto_attribute_late, created_at FROM bill_merchant_rules
    WHERE user_id = ? AND bill_id = ?
    ORDER BY created_at ASC
  `).all(req.user.id, billId);

  // Suggest recent unmatched transactions as quick-pick options
  const suggestions = db.prepare(`
    SELECT t.id, t.payee, t.description, t.memo, t.amount, t.posted_date, t.transacted_at
    FROM transactions t
    LEFT JOIN financial_accounts fa ON fa.id = t.account_id AND fa.user_id = t.user_id
    WHERE t.user_id = ?
      AND t.match_status = 'unmatched'
      AND t.ignored = 0
      AND t.amount < 0
      AND (t.account_id IS NULL OR fa.id IS NULL OR fa.monitored = 1)
    ORDER BY COALESCE(t.posted_date, substr(t.transacted_at, 1, 10)) DESC
    LIMIT 30
  `).all(req.user.id).map(tx => {
    const raw = tx.payee || tx.description || tx.memo || '';
    const normalized = normalizeMerchant(raw);
    return { id: tx.id, label: raw.trim(), normalized, amount: tx.amount,
      date: tx.posted_date || String(tx.transacted_at || '').slice(0, 10) };
  }).filter(s => s.normalized.length >= 2);

  res.json({ rules, suggestions });
});

// ── GET /api/bills/:id/merchant-rules/preview ─────────────────────────────────

router.get('/:id/merchant-rules/preview', (req, res) => {
  const db = getDb();
  const billId = parseInt(req.params.id, 10);
  if (!Number.isInteger(billId) || billId < 1)
    return res.status(400).json(standardizeError('Invalid bill id', 'VALIDATION_ERROR'));
  if (!requireBill(db, billId, req.user.id))
    return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND'));

  const raw = String(req.query.merchant || '').trim();
  const normalized = normalizeMerchant(raw);
  if (!normalized || normalized.length < 2)
    return res.json({ match_count: 0, conflicts: [], normalized: '' });

  const match_count = previewMatchCount(db, req.user.id, normalized);
  const conflicts   = findConflicts(db, req.user.id, billId, normalized);

  res.json({ match_count, conflicts, normalized });
});

// ── POST /api/bills/:id/merchant-rules ───────────────────────────────────────

router.post('/:id/merchant-rules', (req, res) => {
  const db = getDb();
  const billId = parseInt(req.params.id, 10);
  if (!Number.isInteger(billId) || billId < 1)
    return res.status(400).json(standardizeError('Invalid bill id', 'VALIDATION_ERROR'));
  if (!requireBill(db, billId, req.user.id))
    return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND'));

  const raw = String(req.body?.merchant || '').trim();
  const normalized = normalizeMerchant(raw);
  if (!normalized || normalized.length < 2)
    return res.status(400).json(standardizeError('merchant must be at least 2 characters after normalisation', 'VALIDATION_ERROR', 'merchant'));

  const conflicts = findConflicts(db, req.user.id, billId, normalized);

  try {
    db.prepare(`
      INSERT INTO bill_merchant_rules (user_id, bill_id, merchant)
      VALUES (?, ?, ?)
      ON CONFLICT(user_id, bill_id, merchant) DO NOTHING
    `).run(req.user.id, billId, normalized);
  } catch (err) {
    return res.status(500).json(standardizeError('Failed to save rule', 'DB_ERROR'));
  }

  // Retroactively apply the new rule to existing unmatched transactions
  const { added } = syncBillPaymentsFromSimplefin(db, req.user.id, billId);

  const rule = db.prepare('SELECT id, merchant, created_at FROM bill_merchant_rules WHERE user_id = ? AND bill_id = ? AND merchant = ?')
    .get(req.user.id, billId, normalized);

  res.status(201).json({ rule, retroactive_matches: added, conflicts });
});

// ── DELETE /api/bills/:id/merchant-rules/:ruleId ──────────────────────────────

// ── GET /api/bills/:id/merchant-rules/candidates ─────────────────────────────
// All transactions matching this bill's merchant rules — any match_status.
// Each item includes the current status so the user knows what will happen.

router.get('/:id/merchant-rules/candidates', (req, res) => {
  const db = getDb();
  const billId = parseInt(req.params.id, 10);
  if (!Number.isInteger(billId) || billId < 1)
    return res.status(400).json(standardizeError('Invalid bill id', 'VALIDATION_ERROR'));
  const bill = requireBill(db, billId, req.user.id);
  if (!bill) return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND'));

  const rules = db.prepare(
    'SELECT merchant FROM bill_merchant_rules WHERE user_id = ? AND bill_id = ?'
  ).all(req.user.id, billId).map(r => r.merchant);

  if (rules.length === 0) return res.json({ candidates: [] });

  // Fetch all negative transactions for this user — any match status
  let txRows;
  try {
    txRows = db.prepare(`
      SELECT t.id, t.amount, t.payee, t.description, t.memo,
             t.posted_date, t.transacted_at, t.match_status,
             t.matched_bill_id,
             b.name AS matched_bill_name
      FROM transactions t
      LEFT JOIN bills b ON b.id = t.matched_bill_id AND b.user_id = t.user_id AND b.deleted_at IS NULL
      WHERE t.user_id = ? AND t.amount < 0 AND t.ignored = 0
      ORDER BY COALESCE(t.posted_date, substr(t.transacted_at,1,10)) DESC
      LIMIT 500
    `).all(req.user.id);
  } catch {
    return res.json({ candidates: [] });
  }

  // Existing payments for this bill keyed by transaction_id
  const existingPayments = new Set(
    db.prepare('SELECT transaction_id FROM payments WHERE bill_id = ? AND transaction_id IS NOT NULL AND deleted_at IS NULL')
      .all(billId).map(r => r.transaction_id)
  );

  const candidates = [];
  for (const tx of txRows) {
    const txMerchant = normalizeMerchant(tx.payee || tx.description || tx.memo || '');
    if (!txMerchant) continue;
    const matches = rules.some(r => merchantMatches(txMerchant, r));
    if (!matches) continue;

    const paidDate = tx.posted_date || (tx.transacted_at ? String(tx.transacted_at).slice(0, 10) : null);
    if (!paidDate) continue;

    let status;
    if (existingPayments.has(tx.id)) {
      status = 'payment_exists';
    } else if (tx.match_status === 'matched' && tx.matched_bill_id === billId) {
      status = 'matched_this_bill';
    } else if (tx.match_status === 'matched' && tx.matched_bill_id !== billId) {
      status = 'matched_other_bill';
    } else {
      status = 'unmatched';
    }

    candidates.push({
      id:               tx.id,
      payee:            tx.payee || tx.description || '(no description)',
      amount:           Math.round(Math.abs(tx.amount)) / 100,
      paid_date:        paidDate,
      status,
      matched_bill_name: tx.matched_bill_name || null,
    });
  }

  res.json({ candidates });
});

// ── POST /api/bills/:id/merchant-rules/import-historical ──────────────────────
// Import a specific list of transaction IDs as payments for this bill.

router.post('/:id/merchant-rules/import-historical', (req, res) => {
  const db = getDb();
  const billId = parseInt(req.params.id, 10);
  if (!Number.isInteger(billId) || billId < 1)
    return res.status(400).json(standardizeError('Invalid bill id', 'VALIDATION_ERROR'));
  const bill = requireBill(db, billId, req.user.id);
  if (!bill) return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND'));

  const ids = req.body?.transaction_ids;
  if (!Array.isArray(ids) || ids.length === 0)
    return res.status(400).json(standardizeError('transaction_ids must be a non-empty array', 'VALIDATION_ERROR'));

  const validIds = ids.filter(id => Number.isInteger(id) && id > 0);
  if (validIds.length === 0)
    return res.status(400).json(standardizeError('No valid transaction ids provided', 'VALIDATION_ERROR'));

  const getBill       = db.prepare('SELECT * FROM bills WHERE id = ? AND deleted_at IS NULL');
  const getTx         = db.prepare('SELECT * FROM transactions WHERE id = ? AND user_id = ? AND amount < 0');
  const insertPayment = db.prepare(`
    INSERT OR IGNORE INTO payments (bill_id, amount, paid_date, payment_source, transaction_id)
    VALUES (?, ?, ?, 'provider_sync', ?)
  `);
  const updateTx      = db.prepare(`
    UPDATE transactions SET matched_bill_id = ?, match_status = 'matched', updated_at = datetime('now') WHERE id = ?
  `);

  let imported = 0;
  const lateAttributions = [];

  try {
    db.transaction(() => {
      for (const txId of validIds) {
        const tx = getTx.get(txId, req.user.id);
        if (!tx) continue;

        const paidDate = tx.posted_date || (tx.transacted_at ? String(tx.transacted_at).slice(0, 10) : null);
        if (!paidDate) continue;

        const amountCents = Math.round(Math.abs(tx.amount));
        const amount      = fromCents(amountCents);
        const billRow = getBill.get(billId);

        const result = insertPayment.run(billId, amountCents, paidDate, txId);
        if (result.changes > 0) {
          const insertedPayment = db.prepare('SELECT * FROM payments WHERE transaction_id = ? AND bill_id = ? AND deleted_at IS NULL').get(txId, billId);
          updateTx.run(billId, txId);
          imported++;

          // Check for late attribution
          const { normalizeMerchant: nm, ..._ } = { normalizeMerchant };
          const rules2 = db.prepare('SELECT due_day FROM bills WHERE id = ?').get(billId);
          if (rules2?.due_day) {
            const { lateAttributionCandidate } = require('../services/billMerchantRuleService');
            // inline check
            const paid = new Date(paidDate + 'T00:00:00');
            const dom  = paid.getDate();
            if (dom <= 5) {
              const prevEnd = new Date(paid.getFullYear(), paid.getMonth(), 0);
              if (rules2.due_day <= prevEnd.getDate()) {
                const suggested = localDateString(prevEnd);
                if (insertedPayment) {
                  lateAttributions.push({ payment_id: insertedPayment.id, bill_name: bill.name, original_date: paidDate, suggested_date: suggested, amount });
                }
              }
            }
          }
          if (billRow && insertedPayment) applyBankPaymentAsSourceOfTruth(db, billRow, insertedPayment);
        }
      }
    })();
  } catch (err) {
    console.error('[import-historical] Transaction failed:', err.message);
    return res.status(500).json(standardizeError('Import failed', 'DB_ERROR'));
  }

  res.json({ imported, late_attributions: lateAttributions });
});

// PATCH /api/bills/:id/merchant-rules/:ruleId/auto-attribute
// Toggle the auto_attribute_late flag for a single merchant rule.
router.patch('/:id/merchant-rules/:ruleId/auto-attribute', (req, res) => {
  const db = getDb();
  const billId  = parseInt(req.params.id,     10);
  const ruleId  = parseInt(req.params.ruleId, 10);
  if (!Number.isInteger(billId) || billId < 1 || !Number.isInteger(ruleId) || ruleId < 1)
    return res.status(400).json(standardizeError('Invalid id', 'VALIDATION_ERROR'));
  if (!requireBill(db, billId, req.user.id))
    return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND'));

  const enabled = req.body?.enabled ? 1 : 0;
  const changes = db.prepare(
    "UPDATE bill_merchant_rules SET auto_attribute_late = ? WHERE id = ? AND user_id = ? AND bill_id = ?"
  ).run(enabled, ruleId, req.user.id, billId).changes;

  if (changes === 0) return res.status(404).json(standardizeError('Rule not found', 'NOT_FOUND'));
  res.json({ id: ruleId, auto_attribute_late: enabled === 1 });
});

router.delete('/:id/merchant-rules/:ruleId', (req, res) => {
  const db = getDb();
  const billId  = parseInt(req.params.id, 10);
  const ruleId  = parseInt(req.params.ruleId, 10);
  if (!Number.isInteger(billId) || billId < 1 || !Number.isInteger(ruleId) || ruleId < 1)
    return res.status(400).json(standardizeError('Invalid id', 'VALIDATION_ERROR'));
  if (!requireBill(db, billId, req.user.id))
    return res.status(404).json(standardizeError('Bill not found', 'NOT_FOUND'));

  const changes = db.prepare('DELETE FROM bill_merchant_rules WHERE id = ? AND user_id = ? AND bill_id = ?')
    .run(ruleId, req.user.id, billId).changes;

  if (changes === 0)
    return res.status(404).json(standardizeError('Rule not found', 'NOT_FOUND'));

  res.json({ success: true });
});

module.exports = router;