/**
 * How a scenario instance's resources are named.
 *
 * A declaration is a KIND; instances are many. Two instances of one declaration hold the
 * same addresses and must never meet, so every resource carries the instance id and
 * nothing is shared between them.
 */

const PREFIX = "mlab";

/** Instance ids are short and sortable — the last one left standing has to be findable. */
export function newInstanceId(scenario: string, now: Date): string {
  const stamp = now.toISOString().replace(/[-:T]/g, "").slice(2, 12);
  return `${scenario}-${stamp}`;
}

/** incus network names are limited to 15 characters, so this hashes rather than truncates. */
export function networkName(instanceId: string, segment: string): string {
  const digest = hash(`${instanceId}/${segment}`);
  return `${PREFIX}${digest}`;
}

export function machineName(instanceId: string, machine: string): string {
  return `${PREFIX}-${instanceId}-${machine}`;
}

export function instanceIdOf(machineName: string, machine: string): string | null {
  const suffix = `-${machine}`;
  if (!machineName.startsWith(`${PREFIX}-`) || !machineName.endsWith(suffix)) return null;
  return machineName.slice(PREFIX.length + 1, machineName.length - suffix.length);
}

export function machinePrefix(instanceId: string): string {
  return `${PREFIX}-${instanceId}-`;
}

/** FNV-1a, rendered base36. Short, stable, and collisions are a naming clash not a leak. */
function hash(text: string): string {
  let h = 0x811c9dc5;
  for (let i = 0; i < text.length; i++) {
    h ^= text.charCodeAt(i);
    h = Math.imul(h, 0x01000193) >>> 0;
  }
  return h.toString(36).padStart(7, "0").slice(0, 7);
}

/**
 * A deterministic MAC for a machine's Nth interface, in the locally-administered range.
 *
 * Set explicitly at creation rather than read back afterwards: incus assigns a MAC at
 * runtime and does not record it in the device config, so querying returns nothing. A
 * derived address is also stable across raises of the same instance, which makes an
 * in-guest match on it reproducible.
 */
export function macFor(instanceId: string, machine: string, index: number): string {
  const digest = hash(`${instanceId}/${machine}/${index}`);
  const octets: string[] = [];
  let value = 0;
  for (let i = 0; i < digest.length; i++) value = (value * 31 + digest.charCodeAt(i)) >>> 0;
  // 02 marks it locally administered, which is what a made-up address is supposed to say.
  octets.push("02");
  for (let i = 0; i < 5; i++) {
    octets.push(((value >>> (i * 5)) & 0xff).toString(16).padStart(2, "0"));
  }
  return octets.join(":");
}