/** Format a number as a MATLAB literal that round-trips exactly and reads well. */
export function formatNumber(x: number): string {
  if (!Number.isFinite(x)) return x > 0 ? "Inf" : x < 0 ? "-Inf" : "NaN";
  if (x === 0) return "0";
  const ax = Math.abs(x);
  if (Number.isInteger(x) && ax < 1e6) return String(x);
  if (ax >= 1e5 || ax < 1e-4) {
    // shortest exponential form that round-trips, written like 200e9 rather than 2e+11
    for (let p = 0; p <= 16; p++) {
      const s = x.toExponential(p);
      if (Number(s) === x) return tidyExponential(s);
    }
    return tidyExponential(x.toExponential());
  }
  return String(x);
}

function tidyExponential(s: string): string {
  const [mant, expo] = s.split("e");
  const e = Number(expo);
  // Prefer engineering-style exponents (multiples of 3) when the mantissa stays short
  const shift = ((e % 3) + 3) % 3;
  if (shift !== 0) {
    const mNum = Number(mant) * Math.pow(10, shift);
    const mStr = String(Number(mNum.toPrecision(15)));
    if (mStr.length <= 8) return `${mStr}e${e - shift}`;
  }
  return `${mant}e${e}`;
}

export function formatString(s: string): string {
  return `'${s.replace(/'/g, "''")}'`;
}

export function formatVector(v: readonly number[]): string {
  return `[${v.map(formatNumber).join(" ")}]`;
}