app/ui/src/format.js

// Display formatting ONLY — no business arithmetic happens in the UI.
// Every number shown comes from the engine via the API.

export const fmtMillions = (v) =>
  v == null || Number.isNaN(Number(v)) ? '—' : `$${Number(v).toFixed(1)}m`;

export const fmtPct = (v, dp = 2) =>
  v == null || Number.isNaN(Number(v)) ? '—' : `${(Number(v) * 100).toFixed(dp)}%`;

export const fmtRatio = (v) =>
  v == null || Number.isNaN(Number(v)) ? '—' : `${Number(v).toFixed(3)}×`;

export const fmtSignedM = (v) =>
  v == null || Number.isNaN(Number(v))
    ? '—'
    : `${Number(v) >= 0 ? '+' : '−'}$${Math.abs(Number(v)).toFixed(1)}m`;

export const fmtTime = (ms) => {
  const d = new Date(ms);
  const p = (n) => String(n).padStart(2, '0');
  return `${p(d.getHours())}:${p(d.getMinutes())}:${p(d.getSeconds())}`;
};

// A "*_pct" field is already 0-100 scale (per the contract's convention) —
// never re-multiply it.
export const fmtPctScale = (v, dp = 1) =>
  v == null || Number.isNaN(Number(v)) ? '—' : `${Number(v).toFixed(dp)}%`;

export const fmtNum = (v, dp = 0) =>
  v == null || Number.isNaN(Number(v))
    ? '—'
    : Number(v).toLocaleString(undefined, {
        minimumFractionDigits: dp,
        maximumFractionDigits: dp,
      });

export const fmtHazard = (v) =>
  v == null || Number.isNaN(Number(v)) ? '—' : Number(v).toFixed(4);

export const fmtSigned = (v, dp = 1) =>
  v == null || Number.isNaN(Number(v))
    ? '—'
    : `${Number(v) >= 0 ? '+' : '−'}${Math.abs(Number(v)).toFixed(dp)}`;

// Exhibit-footer "run <date>" stamp (FINAL_SPEC §5.2) — the client's own
// clock; the app has no server-side "as-of build" timestamp endpoint.
export const runDate = () => new Date().toISOString().slice(0, 10);