Kahera POS: A Free Offline Cash Register for Philippine Cafés That Gets Senior Discounts Right

// js/money.js — pure function, amounts in integer centavos
function computeTotals(lines, opts) {
  opts = opts || {};
  var vatReg = opts.vatRegistered !== false;
  var gross = subtotal(lines);
  var diners = clampInt(opts.diners, 1, 99);
  var holders = clampInt(opts.idHolders, 0, diners);
  var kind = (opts.discount === 'senior' || opts.discount === 'pwd') ? opts.discount : 'none';

  var r = {
    gross: gross, items: itemCount(lines), discountKind: 'none', diners: diners, idHolders: 0,
    share: 0, vatRemoved: 0, discount: 0, vatable: 0, vat: 0, vatExemptSales: 0,
    total: gross, vatRegistered: vatReg
  };

  var regular = gross;
  if (kind !== 'none' && holders > 0 && gross > 0) {
    var share = Math.round(gross * holders / diners);
    var base = vatReg ? Math.round(share / (1 + VAT_RATE)) : share;
    var disc = Math.round(base * SC_PWD_RATE);
    regular = gross - share;
    r.discountKind = kind;
    r.idHolders = holders;
    r.share = share;
    r.vatRemoved = share - base;
    r.discount = disc;
    r.vatExemptSales = vatReg ? base : 0;
    r.total = regular + (base - disc);
  }

  if (vatReg) {
    r.vatable = Math.round(regular / (1 + VAT_RATE));
    r.vat = regular - r.vatable;
  }
  return r;
}

// js/app.js — one delegated listener serves every tile, even after re-renders
$('grid').addEventListener('click', function (e) {
  var b = e.target.closest('[data-add]');
  if (b) addItem(b.getAttribute('data-add'));
});

function addItem(id) {
  var m = S.menu.filter(function (x) { return x.id === id; })[0];
  if (!m) return;
  if (!m.available) { toast(m.name + ' is marked sold out'); return; }
  var l = S.cart.lines.filter(function (x) { return x.id === id; })[0];
  if (l) l.qty = Math.min(99, l.qty + 1);
  else S.cart.lines.push({ id: m.id, name: m.name, price: m.price, qty: 1 });
  saveCart(); renderCart(); renderGrid(id);
}

// tests/money.test.js — run with: npm test
const assert = require('assert');
const M = require('../js/money.js');

test('senior, 1 of 4 diners, VAT-registered (₱1,120 bill → ₱1,040)', () => {
  const t = M.computeTotals([{ price: 28000, qty: 4 }], { vatRegistered: true, discount: 'senior', diners: 4, idHolders: 1 });