BillTracker/routes/payments.js

const express = require('express');
const { standardizeError } = require('../middleware/errorFormatter');
const router  = require('express').Router();
const { getDb } = require('../db/database');
const { computeBalanceDelta, applyBalanceDelta } = require('../services/billsService');
const { validatePaymentInput, serializePayment } = require('../services/paymentValidation');
const { getCycleRange, resolveDueDate } = require('../services/statusService');
const { markUnmatched } = require('../services/transactionMatchState');
const {
  markProvisionalManualPaymentsOverridden,
  reactivatePaymentsOverriddenBy,
} = require('../services/paymentAccountingService');
const { todayLocal } = require('../utils/dates');
const { fromCents } = require('../utils/money');

// SQL_NOT_DELETED is a compile-time constant SQL fragment, never user-supplied.
// It cannot be a bind parameter (SQL fragments are not parameterisable — only
// values are). Interpolating a hardcoded constant like this is safe by
// construction; do NOT replace this pattern with dynamic/user-controlled input.
const SQL_NOT_DELETED = 'deleted_at IS NULL';
const TRANSACTION_MATCH_SOURCE = 'transaction_match';

function isTransactionLinkedPayment(payment) {
  return payment?.payment_source === TRANSACTION_MATCH_SOURCE || payment?.transaction_id != null;
}

function rejectTransactionLinkedPayment(res) {
  return res.status(409).json(standardizeError(
    'Transaction-linked payments must be changed through transaction match controls',
    'TRANSACTION_PAYMENT_LOCKED',
    'transaction_id',
  ));
}

function parseYearMonth(body) {
  const year = parseInt(body.year, 10);
  const month = parseInt(body.month, 10);
  if (!Number.isInteger(year) || year < 2000 || year > 2100) {
    return { error: standardizeError('year must be a 4-digit integer between 2000 and 2100', 'VALIDATION_ERROR', 'year') };
  }
  if (!Number.isInteger(month) || month < 1 || month > 12) {
    return { error: standardizeError('month must be an integer between 1 and 12', 'VALIDATION_ERROR', 'month') };
  }
  return { year, month };
}

function getAutopaySuggestionContext(db, userId, billId, year, month) {
  const bill = db.prepare(`
    SELECT *
    FROM bills
    WHERE id = ? AND user_id = ? AND deleted_at IS NULL
  `).get(billId, userId);
  if (!bill) return { error: standardizeError('Bill not found', 'NOT_FOUND', 'bill_id'), status: 404 };
  if (!bill.autopay_enabled || bill.autodraft_status !== 'assumed_paid') {
    return { error: standardizeError('Bill is not eligible for autopay suggestions', 'VALIDATION_ERROR', 'bill_id'), status: 400 };
  }

  const state = db.prepare(`
    SELECT actual_amount, is_skipped
    FROM monthly_bill_state
    WHERE bill_id = ? AND year = ? AND month = ?
  `).get(bill.id, year, month);
  if (state?.is_skipped) {
    return { error: standardizeError('Skipped bills cannot be suggested for payment', 'VALIDATION_ERROR', 'bill_id'), status: 400 };
  }

  const dueDate = resolveDueDate(bill, year, month);
  if (!dueDate) {
    return { error: standardizeError('Bill does not occur in the selected month', 'VALIDATION_ERROR', 'month'), status: 400 };
  }
  const amount = fromCents(state?.actual_amount ?? bill.expected_amount);
  return { bill, dueDate, amount };
}

// GET /api/payments?bill_id=&year=&month=
router.get('/', (req, res) => {
  const db = getDb();
  const { bill_id, year, month } = req.query;

  // Validate year/month when provided
  if ((year || month) && !(year && month)) {
    return res.status(400).json(standardizeError('Both year and month are required when filtering by date', 'VALIDATION_ERROR', 'year'));
  }

  let y, m;
  if (year && month) {
    y = parseInt(year, 10);
    m = parseInt(month, 10);
    if (!Number.isInteger(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 (!Number.isInteger(m) || m < 1 || m > 12) {
      return res.status(400).json(standardizeError('month must be an integer between 1 and 12', 'VALIDATION_ERROR', 'month'));
    }
  }

  let query  = `SELECT p.* FROM payments p JOIN bills b ON b.id = p.bill_id WHERE p.${SQL_NOT_DELETED} AND b.user_id = ? AND b.deleted_at IS NULL`;
  const params = [req.user.id];

  if (bill_id) { query += ' AND p.bill_id = ?'; params.push(parseInt(bill_id, 10)); }

  if (y && m) {
    const yStr = String(y);
    const mStr = String(m).padStart(2, '0');
    const daysInMonth = new Date(y, m, 0).getDate();
    const endDay = String(daysInMonth).padStart(2, '0');
    query += ' AND p.paid_date BETWEEN ? AND ?';
    params.push(`${yStr}-${mStr}-01`, `${yStr}-${mStr}-${endDay}`);
  }

  query += ' ORDER BY p.paid_date DESC';
  res.json(db.prepare(query).all(...params).map(serializePayment));
});

// GET /api/payments/recent-auto — provider_sync payments with a linked tx, last 7 days
router.get('/recent-auto', (req, res) => {
  const db = getDb();
  const rows = db.prepare(`
    SELECT p.id, p.bill_id, p.amount, p.paid_date, p.payment_source,
           p.transaction_id, p.balance_delta, p.interest_delta, p.created_at,
           b.name AS bill_name,
           t.payee, t.description, t.amount AS tx_cents, t.posted_date
    FROM payments p
    JOIN bills b ON b.id = p.bill_id
    LEFT JOIN transactions t ON t.id = p.transaction_id
    WHERE b.user_id = ?
      AND p.payment_source = 'provider_sync'
      AND p.transaction_id IS NOT NULL
      AND p.deleted_at IS NULL
      AND b.deleted_at IS NULL
      AND p.created_at >= datetime('now', '-7 days')
    ORDER BY p.created_at DESC
    LIMIT 50
  `).all(req.user.id);
  res.json(rows.map(serializePayment));
});

// GET /api/payments/:id
router.get('/:id', (req, res) => {
  const db = getDb();
  const payment = db.prepare(`SELECT p.* FROM payments p JOIN bills b ON b.id = p.bill_id WHERE p.id = ? AND p.${SQL_NOT_DELETED} AND b.user_id = ? AND b.deleted_at IS NULL`).get(req.params.id, req.user.id);
  if (!payment) return res.status(404).json(standardizeError('Payment not found', 'NOT_FOUND', 'id'));
  res.json(serializePayment(payment));
});

// POST /api/payments/:id/undo-auto — reverse a provider_sync auto-match
router.post('/:id/undo-auto', (req, res) => {
  const db = getDb();
  const payment = db.prepare(`
    SELECT p.* FROM payments p
    JOIN bills b ON b.id = p.bill_id
    WHERE p.id = ? AND p.${SQL_NOT_DELETED} AND b.user_id = ? AND b.deleted_at IS NULL
  `).get(req.params.id, req.user.id);

  if (!payment) return res.status(404).json(standardizeError('Payment not found', 'NOT_FOUND', 'id'));
  if (payment.payment_source !== 'provider_sync') {
    return res.status(409).json(standardizeError('Only provider_sync payments can be undone here', 'NOT_AUTO_MATCH'));
  }
  if (!payment.transaction_id) {
    return res.status(409).json(standardizeError('Payment has no linked transaction', 'NO_TRANSACTION'));
  }

  try {
    db.transaction(() => {
      // Restore balance (same logic as DELETE /:id)
      if (!payment.accounting_excluded && payment.balance_delta != null) {
        const bill = db.prepare('SELECT current_balance FROM bills WHERE id = ?').get(payment.bill_id);
        if (bill?.current_balance != null) {
          const restored = Math.max(0, Number(bill.current_balance) - Number(payment.balance_delta));
          db.prepare(`
            UPDATE bills
            SET current_balance        = ?,
                interest_accrued_month = CASE WHEN ? THEN NULL ELSE interest_accrued_month END,
                updated_at             = datetime('now')
            WHERE id = ?
          `).run(restored, payment.interest_delta != null ? 1 : 0, payment.bill_id);
        }
      }
      reactivatePaymentsOverriddenBy(db, payment.id);
      db.prepare("UPDATE payments SET deleted_at = datetime('now') WHERE id = ?").run(payment.id);
      markUnmatched(db, req.user.id, payment.transaction_id);
    })();
    res.json({ success: true });
  } catch (err) {
    console.error('[payments] undo-auto error:', err.message);
    res.status(500).json(standardizeError('Failed to undo auto-match', 'SERVER_ERROR'));
  }
});

// POST /api/payments — create single payment
router.post('/', (req, res) => {
  const db = getDb();
  const { bill_id, amount, paid_date, method, notes, payment_source, autopay_failure } = req.body;

  const validation = validatePaymentInput({ bill_id, amount, paid_date, payment_source: payment_source ?? 'manual' });
  if (validation.error) {
    return res.status(400).json(standardizeError(validation.error, 'VALIDATION_ERROR', validation.field));
  }
  const payment = validation.normalized;

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

  const balCalc = computeBalanceDelta(bill, payment.amount);
  const failureFlag = autopay_failure ? 1 : 0;
  const result = db.prepare(
    'INSERT INTO payments (bill_id, amount, paid_date, method, notes, balance_delta, interest_delta, payment_source, autopay_failure) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)'
  ).run(payment.bill_id, payment.amount, payment.paid_date, method || null, notes || null, balCalc?.balance_delta ?? null, balCalc?.interest_delta ?? null, payment.payment_source, failureFlag);

  applyBalanceDelta(db, bill.id, balCalc);

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

// POST /api/payments/quick — pay a bill (expected amount, today)
router.post('/quick', (req, res) => {
  const db = getDb();
  const { bill_id, amount, paid_date, method, notes, payment_source } = req.body;

  const billValidation = validatePaymentInput({ bill_id }, { requireAmount: false, requirePaidDate: false });
  if (billValidation.error) {
    return res.status(400).json(standardizeError(billValidation.error, 'VALIDATION_ERROR', billValidation.field));
  }

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

  const paymentValidation = validatePaymentInput(
    {
      amount: amount != null ? amount : fromCents(bill.expected_amount),
      paid_date: paid_date || todayLocal(),
      payment_source: payment_source ?? 'manual',
    },
    { requireBillId: false },
  );
  if (paymentValidation.error) {
    return res.status(400).json(standardizeError(paymentValidation.error, 'VALIDATION_ERROR', paymentValidation.field));
  }
  const payAmount = paymentValidation.normalized.amount;
  const payDate   = paymentValidation.normalized.paid_date;
  const paySource = paymentValidation.normalized.payment_source;

  const balCalc = computeBalanceDelta(bill, payAmount);

  const result = db.prepare(
    'INSERT INTO payments (bill_id, amount, paid_date, method, notes, balance_delta, interest_delta, payment_source) VALUES (?, ?, ?, ?, ?, ?, ?, ?)'
  ).run(bill.id, payAmount, payDate, method || null, notes || null, balCalc?.balance_delta ?? null, balCalc?.interest_delta ?? null, paySource);

  applyBalanceDelta(db, bill.id, balCalc);

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

// POST /api/payments/autopay-suggestions/:billId/confirm
router.post('/autopay-suggestions/:billId/confirm', (req, res) => {
  const db = getDb();
  const ym = parseYearMonth(req.body);
  if (ym.error) return res.status(400).json(ym.error);

  const billId = parseInt(req.params.billId, 10);
  if (!Number.isInteger(billId)) {
    return res.status(400).json(standardizeError('bill_id must be an integer', 'VALIDATION_ERROR', 'bill_id'));
  }

  const context = getAutopaySuggestionContext(db, req.user.id, billId, ym.year, ym.month);
  if (context.error) return res.status(context.status).json(context.error);
  const { bill, dueDate, amount } = context;
  if (dueDate > todayLocal()) {
    return res.status(400).json(standardizeError('Autopay suggestion is not due yet', 'VALIDATION_ERROR', 'paid_date'));
  }
  const paymentValidation = validatePaymentInput(
    { amount, paid_date: dueDate },
    { requireBillId: false },
  );
  if (paymentValidation.error) {
    return res.status(400).json(standardizeError(paymentValidation.error, 'VALIDATION_ERROR', paymentValidation.field));
  }
  const suggestedPayment = paymentValidation.normalized;

  const suggestionRange = getCycleRange(ym.year, ym.month, bill);
  const existing = db.prepare(`
    SELECT p.*
    FROM payments p
    JOIN bills b ON b.id = p.bill_id
    WHERE p.bill_id = ?
      AND b.user_id = ?
      AND p.deleted_at IS NULL
      AND p.paid_date BETWEEN ? AND ?
    ORDER BY p.paid_date DESC
    LIMIT 1
  `).get(bill.id, req.user.id, suggestionRange.start, suggestionRange.end);

  if (existing) {
    db.prepare('DELETE FROM autopay_suggestion_dismissals WHERE user_id = ? AND bill_id = ? AND year = ? AND month = ?')
      .run(req.user.id, bill.id, ym.year, ym.month);
    return res.json({ created: false, payment: serializePayment(existing) });
  }

  const balCalc = computeBalanceDelta(bill, suggestedPayment.amount);
  const result = db.prepare(`
    INSERT INTO payments (bill_id, amount, paid_date, method, notes, balance_delta, interest_delta, payment_source)
    VALUES (?, ?, ?, ?, ?, ?, ?, ?)
  `).run(
    bill.id,
    suggestedPayment.amount,
    suggestedPayment.paid_date,
    'autopay',
    'Confirmed autopay suggestion',
    balCalc?.balance_delta ?? null,
    balCalc?.interest_delta ?? null,
    'manual',
  );

  applyBalanceDelta(db, bill.id, balCalc);
  db.prepare('DELETE FROM autopay_suggestion_dismissals WHERE user_id = ? AND bill_id = ? AND year = ? AND month = ?')
    .run(req.user.id, bill.id, ym.year, ym.month);

  res.status(201).json({ created: true, payment: serializePayment(db.prepare('SELECT * FROM payments WHERE id = ?').get(result.lastInsertRowid)) });
});

// POST /api/payments/autopay-suggestions/:billId/dismiss
router.post('/autopay-suggestions/:billId/dismiss', (req, res) => {
  const db = getDb();
  const ym = parseYearMonth(req.body);
  if (ym.error) return res.status(400).json(ym.error);

  const billId = parseInt(req.params.billId, 10);
  if (!Number.isInteger(billId)) {
    return res.status(400).json(standardizeError('bill_id must be an integer', 'VALIDATION_ERROR', 'bill_id'));
  }
  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'));
  }

  db.prepare(`
    INSERT INTO autopay_suggestion_dismissals (user_id, bill_id, year, month, dismissed_at)
    VALUES (?, ?, ?, ?, datetime('now'))
    ON CONFLICT(user_id, bill_id, year, month)
    DO UPDATE SET dismissed_at = datetime('now')
  `).run(req.user.id, billId, ym.year, ym.month);

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

// POST /api/payments/bulk — record multiple payments in one request
// Bulk payment creation endpoint
// Validation rules:
// - Request body must contain a `payments` array
// - Maximum 50 items per request
// - Each item requires: bill_id (integer), paid_date (valid date), amount (positive number)
// - Duplicate payments (same bill_id + paid_date + amount) are skipped, not created
// - Returns { created: [...], skipped: [...], errors: [...] }
router.post('/bulk', (req, res) => {
  const db = getDb();
  const { payments } = req.body;

  // Validate request body has payments array
  if (!payments || !Array.isArray(payments))
    return res.status(400).json(standardizeError('Request body must contain a `payments` array', 'VALIDATION_ERROR', 'payments'));

  // Validate max items per request (50)
  if (payments.length > 50)
    return res.status(400).json(standardizeError('Maximum 50 items allowed per request', 'VALIDATION_ERROR', 'payments'));

  // Validate each payment item
  for (let i = 0; i < payments.length; i++) {
    const item = payments[i];
    const validation = validatePaymentInput(
      { ...item, payment_source: item.payment_source ?? 'manual' },
      { fieldPrefix: `payments[${i}].` },
    );
    if (validation.error) {
      return res.status(400).json(standardizeError(`Payment at index ${i}: ${validation.error}`, 'VALIDATION_ERROR', validation.field));
    }
  }

  const insert = db.prepare(
    'INSERT INTO payments (bill_id, amount, paid_date, method, notes, balance_delta, interest_delta, payment_source) VALUES (?, ?, ?, ?, ?, ?, ?, ?)'
  );
  const getBillForBalance = db.prepare('SELECT current_balance, interest_rate, interest_accrued_month FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL');

  // Prepare statement for duplicate checking
  const duplicateCheckStmt = db.prepare(
    `SELECT 1 FROM payments p 
     JOIN bills b ON b.id = p.bill_id 
     WHERE b.user_id = ? 
     AND b.deleted_at IS NULL
     AND p.bill_id = ? 
     AND p.paid_date = ? 
     AND p.amount = ? 
     AND p.${SQL_NOT_DELETED}`
  );

  const created = [];
  const skipped = [];
  const errors  = [];

  const runBulk = db.transaction(() => {
    for (const item of payments) {
      const payment = validatePaymentInput({ ...item, payment_source: item.payment_source ?? 'manual' }).normalized;
      const { bill_id, amount: parsedAmt, paid_date, payment_source } = payment;
      const { method, notes } = item;
      
      // Check for duplicates using composite key (bill_id + paid_date + amount)
      const isDuplicate = duplicateCheckStmt.get(req.user.id, bill_id, paid_date, parsedAmt);
      if (isDuplicate) {
        skipped.push({ bill_id, paid_date, amount: fromCents(parsedAmt) });
        continue;
      }
      
      const billRow = getBillForBalance.get(bill_id, req.user.id);
      if (!billRow) {
        errors.push({ item, error: `Bill ${bill_id} not found` });
        continue;
      }

      const balCalc = computeBalanceDelta(billRow, parsedAmt);
      const r = insert.run(bill_id, parsedAmt, paid_date, method || null, notes || null, balCalc?.balance_delta ?? null, balCalc?.interest_delta ?? null, payment_source);
      applyBalanceDelta(db, bill_id, balCalc);

      created.push(serializePayment(db.prepare('SELECT * FROM payments WHERE id = ?').get(r.lastInsertRowid)));
    }
  });

  runBulk();
  res.status(201).json({ created, skipped, errors });
});

// PUT /api/payments/:id
router.put('/:id', (req, res) => {
  const db = getDb();
  const existing = db.prepare(`SELECT p.* FROM payments p JOIN bills b ON b.id = p.bill_id WHERE p.id = ? AND p.${SQL_NOT_DELETED} AND b.user_id = ? AND b.deleted_at IS NULL`).get(req.params.id, req.user.id);
  if (!existing) return res.status(404).json(standardizeError('Payment not found', 'NOT_FOUND', 'id'));
  if (isTransactionLinkedPayment(existing)) return rejectTransactionLinkedPayment(res);

  const { amount, paid_date, method, notes, payment_source } = req.body;
  const validation = validatePaymentInput(
    { amount, paid_date, payment_source },
    { requireBillId: false, requireAmount: false, requirePaidDate: false },
  );
  if (validation.error) {
    return res.status(400).json(standardizeError(validation.error, 'VALIDATION_ERROR', validation.field));
  }

  const nextAmount = validation.normalized.amount ?? existing.amount;
  const nextPaidDate = validation.normalized.paid_date ?? existing.paid_date;
  const nextPaymentSource = validation.normalized.payment_source ?? existing.payment_source ?? 'manual';
  let nextBalanceDelta = existing.balance_delta;

  const bill = db.prepare('SELECT * FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(existing.bill_id, req.user.id);
  let nextInterestDelta = existing.interest_delta ?? null;
  if (bill) {
    // Reverse only the *payment* portion of the stored delta (not the interest component)
    // so that interest already charged this month is not double-counted. For legacy rows
    // where interest_delta is NULL, fall back to reversing the full delta as before.
    const interestPortion = existing.interest_delta ?? 0;
    const paymentPortion  = existing.balance_delta != null ? existing.balance_delta - interestPortion : null;
    let restoredBalance = bill.current_balance;
    if (paymentPortion != null && bill.current_balance != null) {
      restoredBalance = Math.max(0, bill.current_balance - paymentPortion);
    }

    // interest_accrued_month is still set to this month (if interest was charged) so
    // computeBalanceDelta will skip interest when the payment is within the same month,
    // and charge a fresh month of interest if editing into a new calendar month.
    const balCalc = computeBalanceDelta({ ...bill, current_balance: restoredBalance }, nextAmount);
    nextBalanceDelta  = balCalc?.balance_delta ?? null;
    nextInterestDelta = balCalc?.interest_delta ?? null;
    if (balCalc) {
      applyBalanceDelta(db, existing.bill_id, balCalc);
    } else if (paymentPortion != null && restoredBalance != null) {
      db.prepare("UPDATE bills SET current_balance = ?, updated_at = datetime('now') WHERE id = ?")
        .run(restoredBalance, existing.bill_id);
    }
  }

  const { autopay_failure } = req.body;
  const nextAutopayFailure = autopay_failure !== undefined ? (autopay_failure ? 1 : 0) : existing.autopay_failure;

  db.prepare(`
    UPDATE payments SET
      amount = ?, paid_date = ?, method = ?, notes = ?, balance_delta = ?, interest_delta = ?,
      payment_source = ?, autopay_failure = ?, updated_at = datetime('now')
    WHERE id = ?
      AND bill_id IN (SELECT id FROM bills WHERE user_id = ? AND deleted_at IS NULL)
  `).run(
    nextAmount,
    nextPaidDate,
    method    !== undefined ? (method || null)  : existing.method,
    notes     !== undefined ? (notes  || null)  : existing.notes,
    nextBalanceDelta,
    nextInterestDelta,
    nextPaymentSource,
    nextAutopayFailure,
    req.params.id,
    req.user.id,
  );

  res.json(serializePayment(db.prepare(`SELECT p.* FROM payments p JOIN bills b ON b.id = p.bill_id WHERE p.id = ? AND p.${SQL_NOT_DELETED} AND b.user_id = ? AND b.deleted_at IS NULL`).get(req.params.id, req.user.id)));
});

// DELETE /api/payments/:id — soft delete (sets deleted_at)
router.delete('/:id', (req, res) => {
  const db = getDb();
  const payment = db.prepare(`SELECT p.* FROM payments p JOIN bills b ON b.id = p.bill_id WHERE p.id = ? AND p.${SQL_NOT_DELETED} AND b.user_id = ? AND b.deleted_at IS NULL`).get(req.params.id, req.user.id);
  if (!payment) return res.status(404).json(standardizeError('Payment not found', 'NOT_FOUND', 'id'));
  if (isTransactionLinkedPayment(payment)) return rejectTransactionLinkedPayment(res);

  // Reverse any balance delta that was stored when this payment was created.
  // If this payment was the one that charged interest this month, clear
  // interest_accrued_month so the next payment can re-accrue correctly.
  if (!payment.accounting_excluded && payment.balance_delta != null) {
    const bill = db.prepare('SELECT current_balance FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(payment.bill_id, req.user.id);
    if (bill?.current_balance != null) {
      const restored = Math.max(0, bill.current_balance - payment.balance_delta);
      db.prepare(`
        UPDATE bills
        SET current_balance        = ?,
            interest_accrued_month = CASE WHEN ? THEN NULL ELSE interest_accrued_month END,
            updated_at             = datetime('now')
        WHERE id = ?
      `).run(restored, payment.interest_delta != null ? 1 : 0, payment.bill_id);
    }
  }

  db.prepare("UPDATE payments SET deleted_at = datetime('now') WHERE id = ? AND bill_id IN (SELECT id FROM bills WHERE user_id = ? AND deleted_at IS NULL)").run(req.params.id, req.user.id);
  res.json({ success: true });
});

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

  // Re-apply the balance delta (undo the reversal done on delete).
  // If this payment originally charged interest, restore interest_accrued_month
  // to the month of the payment so future same-month payments skip interest.
  if (!payment.accounting_excluded && payment.balance_delta != null) {
    const bill = db.prepare('SELECT current_balance FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(payment.bill_id, req.user.id);
    if (bill?.current_balance != null) {
      const reapplied    = Math.max(0, bill.current_balance + payment.balance_delta);
      const interestMonth = payment.interest_delta != null ? (payment.paid_date?.slice(0, 7) ?? null) : null;
      db.prepare(`
        UPDATE bills
        SET current_balance        = ?,
            interest_accrued_month = CASE WHEN ? IS NOT NULL THEN ? ELSE interest_accrued_month END,
            updated_at             = datetime('now')
        WHERE id = ?
      `).run(reapplied, interestMonth, interestMonth, payment.bill_id);
    }
  }

  db.prepare('UPDATE payments SET deleted_at = NULL WHERE id = ? AND bill_id IN (SELECT id FROM bills WHERE user_id = ? AND deleted_at IS NULL)').run(req.params.id, req.user.id);
  res.json(serializePayment(db.prepare(`SELECT p.* FROM payments p JOIN bills b ON b.id = p.bill_id WHERE p.id = ? AND p.${SQL_NOT_DELETED} AND b.user_id = ? AND b.deleted_at IS NULL`).get(req.params.id, req.user.id)));
});

// PATCH /api/payments/:id/attribute-to-month
// Changes only the paid_date of a provider_sync payment to move it into the
// correct billing period when it posted just after month end.
// Does not touch the amount or balance_delta.
router.patch('/:id/attribute-to-month', (req, res) => {
  const db = getDb();
  const paymentId = parseInt(req.params.id, 10);
  if (!Number.isInteger(paymentId) || paymentId < 1) {
    return res.status(400).json(standardizeError('Invalid payment id', 'VALIDATION_ERROR'));
  }

  const { paid_date } = req.body;
  if (!paid_date || !/^\d{4}-\d{2}-\d{2}$/.test(paid_date)) {
    return res.status(400).json(standardizeError('paid_date must be YYYY-MM-DD', 'VALIDATION_ERROR', 'paid_date'));
  }
  // Validate it is a real calendar date
  const newDate = new Date(paid_date + 'T00:00:00Z');
  if (isNaN(newDate.getTime()) || newDate.toISOString().slice(0, 10) !== paid_date) {
    return res.status(400).json(standardizeError('paid_date is not a valid calendar date', 'VALIDATION_ERROR', 'paid_date'));
  }

  try {
    const payment = db.prepare(`
      SELECT p.* FROM payments p
      JOIN bills b ON b.id = p.bill_id
      WHERE p.id = ? AND p.${SQL_NOT_DELETED} AND b.user_id = ? AND b.deleted_at IS NULL
    `).get(paymentId, req.user.id);

    if (!payment) return res.status(404).json(standardizeError('Payment not found', 'NOT_FOUND'));

    // Only allow date-only reclassification for provider_sync payments
    if (payment.payment_source !== 'provider_sync' && payment.payment_source !== 'auto_match') {
      return res.status(409).json(standardizeError(
        'Only bank-synced payments can be reclassified to a different month',
        'RECLASSIFY_ONLY_SYNC',
      ));
    }

    // Sanity check: new date must be in the month immediately before the original date
    const orig = new Date(payment.paid_date + 'T00:00:00');
    const origYM = orig.getFullYear() * 12 + orig.getMonth();
    const newYM  = newDate.getFullYear() * 12 + newDate.getMonth();
    if (newYM !== origYM - 1) {
      return res.status(400).json(standardizeError(
        'The new paid_date must be in the month immediately before the original payment date',
        'VALIDATION_ERROR', 'paid_date',
      ));
    }

    db.transaction(() => {
      db.prepare("UPDATE payments SET paid_date = ?, updated_at = datetime('now') WHERE id = ?")
        .run(paid_date, paymentId);

      const bill = db.prepare('SELECT * FROM bills WHERE id = ? AND user_id = ? AND deleted_at IS NULL')
        .get(payment.bill_id, req.user.id);
      if (bill) markProvisionalManualPaymentsOverridden(db, bill, { ...payment, paid_date });
    })();

    res.json(serializePayment(db.prepare(`SELECT p.* FROM payments p JOIN bills b ON b.id = p.bill_id WHERE p.id = ? AND p.${SQL_NOT_DELETED} AND b.user_id = ? AND b.deleted_at IS NULL`).get(paymentId, req.user.id)));
  } catch (err) {
    console.error('[payments] attribute-to-month error:', err.message);
    res.status(500).json(standardizeError('Failed to reclassify payment date', 'DB_ERROR'));
  }
});

module.exports = router;