export type DurationMsParseOptions = {
  defaultUnit?: "ms" | "s" | "m" | "h" | "d";
};

const DURATION_MULTIPLIERS: Record<string, number> = {
  ms: 1,
  s: 1000,
  m: 60_000,
  h: 3_600_000,
  d: 86_400_000,
};

export function parseDurationMs(raw: string, opts?: DurationMsParseOptions): number {
  const trimmed = String(raw ?? "")
    .trim()
    .toLowerCase();
  if (!trimmed) {
    throw new Error("invalid duration (empty)");
  }

  // Fast path for a single token (supports default unit for bare numbers).
  const single = /^(\d+(?:\.\d+)?)(ms|s|m|h|d)?$/.exec(trimmed);
  if (single) {
    const value = Number(single[1]);
    if (!Number.isFinite(value) || value < 0) {
      throw new Error(`invalid duration: ${raw}`);
    }
    const unit = (single[2] ?? opts?.defaultUnit ?? "ms") as "ms" | "s" | "m" | "h" | "d";
    const ms = Math.round(value * DURATION_MULTIPLIERS[unit]);
    if (!Number.isFinite(ms)) {
      throw new Error(`invalid duration: ${raw}`);
    }
    return ms;
  }

  // Composite form (e.g. "1h30m", "2m500ms"); each token must include a unit.
  let totalMs = 0;
  let consumed = 0;
  const tokenRe = /(\d+(?:\.\d+)?)(ms|s|m|h|d)/g;
  for (const match of trimmed.matchAll(tokenRe)) {
    const [full, valueRaw, unitRaw] = match;
    const index = match.index ?? -1;
    if (!full || !valueRaw || !unitRaw || index < 0) {
      throw new Error(`invalid duration: ${raw}`);
    }
    if (index !== consumed) {
      throw new Error(`invalid duration: ${raw}`);
    }
    const value = Number(valueRaw);
    if (!Number.isFinite(value) || value < 0) {
      throw new Error(`invalid duration: ${raw}`);
    }
    const multiplier = DURATION_MULTIPLIERS[unitRaw];
    if (!multiplier) {
      throw new Error(`invalid duration: ${raw}`);
    }
    totalMs += value * multiplier;
    consumed += full.length;
  }

  if (consumed !== trimmed.length || consumed === 0) {
    throw new Error(`invalid duration: ${raw}`);
  }

  const ms = Math.round(totalMs);
  if (!Number.isFinite(ms)) {
    throw new Error(`invalid duration: ${raw}`);
  }
  return ms;
}