import type { RealTime } from "@deadhead/sim";

/** The engine's only source of time (CR-014): injected, so tests use a fixed one. */
export interface Clock {
  now(): RealTime;
}

/**
 * The device clock (decision 0.5.88): device time plus a dev-only offset,
 * clamped so it never runs backward. Setting the device clock back leaves
 * the game at the last time it saw; setting it forward is accepted.
 */
export class DeviceClock implements Clock {
  #lastSeen: RealTime;
  #offsetMs: number;

  constructor(
    /** Device time; Date.now outside tests. */
    private readonly deviceNow: () => RealTime = () => Date.now(),
    options: { lastTimeSeen?: RealTime; offsetMs?: number } = {},
  ) {
    this.#lastSeen = options.lastTimeSeen ?? 0;
    this.#offsetMs = options.offsetMs ?? 0;
  }

  now(): RealTime {
    this.#lastSeen = Math.max(this.deviceNow() + this.#offsetMs, this.#lastSeen);
    return this.#lastSeen;
  }

  /** The latest time handed out, stored in the save (CR-014 §2). */
  get lastTimeSeen(): RealTime {
    return this.#lastSeen;
  }

  /** After loading a save: never hand out a time before the one it last saw. */
  restore(lastTimeSeen: RealTime): void {
    this.#lastSeen = Math.max(this.#lastSeen, lastTimeSeen);
  }

  get offsetMs(): number {
    return this.#offsetMs;
  }

  /** Developer tool: move the game forward (never back). */
  advance(ms: number): void {
    if (ms < 0) throw new RangeError("The clock only moves forward");
    this.#offsetMs += ms;
  }
}