BillTracker/routes/snowball.js

const express = require('express');
const router = express.Router();
const { getDb } = require('../db/database');
const { standardizeError } = require('../middleware/errorFormatter');
const { calculateSnowball, calculateAvalanche } = require('../services/snowballService');

const DEBT_LIKE_CLAUSES = `(
  b.snowball_include = 1
  OR (
    COALESCE(b.snowball_exempt, 0) = 0
    AND (
      LOWER(c.name) LIKE '%credit%'
      OR LOWER(c.name) LIKE '%loan%'
      OR LOWER(c.name) LIKE '%mortgage%'
      OR LOWER(c.name) LIKE '%housing%'
      OR LOWER(c.name) LIKE '%debt%'
    )
  )
)`;

// GET /api/snowball — server-filtered debt bills, pre-sorted by snowball_order
router.get('/', (req, res) => {
  const db = getDb();
  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.user_id = b.user_id
    WHERE b.user_id = ?
      AND b.active = 1
      AND ${DEBT_LIKE_CLAUSES}
    ORDER BY
      CASE WHEN b.snowball_order IS NULL THEN 1 ELSE 0 END ASC,
      b.snowball_order ASC,
      CASE WHEN b.current_balance IS NULL THEN 1 ELSE 0 END ASC,
      b.current_balance ASC
  `).all(req.user.id);

  res.json(bills);
});

// GET /api/snowball/settings — extra monthly payment for this user
router.get('/settings', (req, res) => {
  const db = getDb();
  const user = db.prepare('SELECT snowball_extra_payment FROM users WHERE id = ?').get(req.user.id);
  res.json({ extra_payment: user?.snowball_extra_payment ?? 0 });
});

// PATCH /api/snowball/settings — save extra monthly payment
router.patch('/settings', (req, res) => {
  const { extra_payment } = req.body;
  let val = 0;

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

  const db = getDb();
  db.prepare('UPDATE users SET snowball_extra_payment = ? WHERE id = ?').run(val, req.user.id);
  res.json({ extra_payment: val });
});

// GET /api/snowball/projection — payoff timeline using the snowball math service
router.get('/projection', (req, res) => {
  const db = getDb();

  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.user_id = b.user_id
    WHERE b.user_id = ?
      AND b.active = 1
      AND ${DEBT_LIKE_CLAUSES}
    ORDER BY
      CASE WHEN b.snowball_order IS NULL THEN 1 ELSE 0 END ASC,
      b.snowball_order ASC,
      CASE WHEN b.current_balance IS NULL THEN 1 ELSE 0 END ASC,
      b.current_balance ASC
  `).all(req.user.id);

  const user = db.prepare('SELECT snowball_extra_payment FROM users WHERE id = ?').get(req.user.id);
  const extraPayment = user?.snowball_extra_payment ?? 0;

  const now      = new Date();
  const snowball  = calculateSnowball(bills, extraPayment, now);
  const avalanche = calculateAvalanche(bills, extraPayment, now);

  res.json({ snowball, avalanche });
});

// PATCH /api/snowball/order — batch-save snowball_order positions
router.patch('/order', (req, res) => {
  const items = req.body;
  if (!Array.isArray(items)) {
    return res.status(400).json(standardizeError('Request body must be an array', 'VALIDATION_ERROR'));
  }

  const db = getDb();
  const userId = req.user.id;
  const update = db.prepare('UPDATE bills SET snowball_order = ? WHERE id = ? AND user_id = ?');

  db.transaction((rows) => {
    for (const row of rows) {
      const id = parseInt(row.id, 10);
      const order = parseInt(row.snowball_order, 10);
      if (!Number.isInteger(id) || id <= 0) continue;
      if (!Number.isInteger(order) || order < 0) continue;
      update.run(order, id, userId);
    }
  })(items);

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

module.exports = router;