BillTracker/client/lib/money.js

// Currency formatting for the client, mirroring the server's utils/money.js.
//
// The API sends money in two units: bill / summary values are serialized as
// DOLLARS (the server calls fromCents before responding), while raw bank
// transaction amounts arrive as integer CENTS. So there are two entry points —
// formatUSD(dollars) and formatCentsUSD(cents) — matching the server's
// formatUSD / formatCentsUSD split. USD / en-US throughout (the app is USD-only,
// and this matches the server). Inputs are coerced defensively so null, '',
// undefined, or NaN never render as "$NaN".

const DASH = '—';

function toNumber(value) {
  const n = Number(value);
  if (!Number.isFinite(n)) return 0;
  return n === 0 ? 0 : n; // normalize -0 → +0 so it never renders as "-$0.00"
}

function isBlank(value) {
  return value === null || value === undefined || value === '';
}

/**
 * Format a DOLLAR amount → "$1,234.56".
 * @param {number|string|null} dollars
 * @param {{ whole?: boolean, dash?: boolean }} [opts]
 *   whole — drop the cents ("$1,235"); dash — render blank input as "—" not "$0.00".
 */
export function formatUSD(dollars, { whole = false, dash = false } = {}) {
  if (dash && isBlank(dollars)) return DASH;
  return toNumber(dollars).toLocaleString('en-US', {
    style: 'currency',
    currency: 'USD',
    minimumFractionDigits: whole ? 0 : 2,
    maximumFractionDigits: whole ? 0 : 2,
  });
}

/** Whole-dollar convenience → "$1,235". */
export function formatUSDWhole(dollars, opts = {}) {
  return formatUSD(dollars, { ...opts, whole: true });
}

/**
 * Format an integer-CENTS amount (e.g. a bank transaction) → "$12.34".
 * @param {number|string|null} cents
 * @param {{ signed?: boolean, dash?: boolean, currency?: string }} [opts]
 *   signed — prefix "+"/"-" (income vs expense); dash — blank input → "—";
 *   currency — ISO code (defaults USD).
 */
export function formatCentsUSD(cents, { signed = false, dash = false, currency = 'USD' } = {}) {
  if (dash && isBlank(cents)) return DASH;
  const c = toNumber(cents);
  const body = (Math.abs(c) / 100).toLocaleString('en-US', {
    style: 'currency',
    currency: currency || 'USD',
    minimumFractionDigits: 2,
    maximumFractionDigits: 2,
  });
  if (signed) return (c < 0 ? '-' : '+') + body;
  return (c < 0 ? '-' : '') + body;
}

/**
 * Shared form validator for a non-negative money field (dollars). Blank is
 * allowed (returns ''); otherwise the value must parse to a number ≥ 0. Returns
 * '' when valid, or an error string labelled for the field. Zero is allowed —
 * these are non-negative, not strictly-positive, amounts.
 * @param {number|string|null} val
 * @param {string} [label] — field name for the message (e.g. "Amount", "Balance")
 */
export function validateNonNegativeMoney(val, label = 'Amount') {
  if (val === '' || val === null || val === undefined) return '';
  const num = parseFloat(val);
  if (isNaN(num) || num < 0) return `${label} must be a non-negative number`;
  return '';
}