import Io from "../Io.js";
import JavaTypes from "./JavaTypes.js";
import TimeUnits, { TimerUnit } from "./TimeUnits.js";

/**
 * Allows checkpointing of generic objects.
 */
export default class Checkpoint {
  checkpointName: string;
  interval: number | undefined = undefined;
  currentObject: object | undefined = undefined;
  timestamp: number | undefined = undefined;

  constructor(checkpointName: string) {
    this.checkpointName = checkpointName;
  }

  /**
   * Monitors the given object. If there is a saved filed from a previous execution, returns the saved object instead.
   *
   * @returns The object that will be monitored
   */
  monitor(object: object) {
    // Check if saved data already exists
    const checkpointFilename = this.getCheckpointFile();
    if (Io.isFile(checkpointFilename)) {
      this.currentObject = Io.readJson(checkpointFilename) as object;
    } else {
      this.currentObject = object;
    }

    return this.currentObject;
  }

  save() {
    // If no interval, manual checking
    if (this.interval === undefined) {
      this.saveManual();
      return;
    }

    const systemClass = JavaTypes.System;

    // Time interval is defined
    // If no timestamp yet, do nothing and record time
    if (this.timestamp === undefined) {
      this.timestamp = systemClass.nanoTime();
      return;
    }

    // Get timestamp, check if passed interval
    const currentTime = systemClass.nanoTime();
    const passedTime = currentTime - this.timestamp;

    // If passed more time than the set interval, save object and update timestamp
    if (passedTime > this.interval) {
      this.saveManual();
      this.timestamp = currentTime;
    }
  }

  setInterval(interval: number, timeUnit: TimerUnit = TimerUnit.SECONDS) {
    this.interval = new TimeUnits(timeUnit).toNanos(interval);
  }

  stop() {
    // Delete checkpoint
    Io.deleteFile(this.getCheckpointFile());

    // Clean state
    this.currentObject = undefined;
    this.timestamp = undefined;
  }

  /**
   * Saves the current object.
   */
  private saveManual() {
    Io.writeJson(this.getCheckpointFile(), this.currentObject);
  }

  /**
   * @returns The checkpoint file for the object being monitored
   */
  private getCheckpointFile() {
    return `checkpoint_${this.checkpointName}.json`;
  }
}