type HighResolutionTime = [number, number]

// Converts an hrtime array (as returned from process.hrtime) to nanoseconds.
//
// ONLY CALL THIS ON VALUES REPRESENTING DELTAS, NOT ON THE RAW RETURN VALUE
// FROM process.hrtime() WITH NO ARGUMENTS.
//
// The entire point of the hrtime data structure is that the JavaScript Number
// type can't represent all int64 values without loss of precision:
// Number.MAX_SAFE_INTEGER nanoseconds is about 104 days. Calling this function
// on a duration that represents a value less than 104 days is fine. Calling
// this function on an absolute time (which is generally roughly time since
// system boot) is not a good idea.
function durationHrTimeToNanos(hrtimeList: HighResolutionTime) {
  return hrtimeList[0] * 1e9 + hrtimeList[1]
}

const IS_BROWSER = typeof window === 'object'
// global.performance = require('perf_hooks'), (global as any).performance.now
// (time?: [number, number]) => [window.performance.now]
const performanceNow = IS_BROWSER ? window.performance.now : process.hrtime

/**
 * @description generate timestamp or delta
 * @see http://nodejs.org/api/process.html#process_process_hrtime
 */
function hrtimeBrowser(previousTimestamp?: HighResolutionTime): HighResolutionTime {
  const clockTime = performanceNow.call(performance) * 1e-3
  let seconds = Math.floor(clockTime)
  let nanoseconds = Math.floor((clockTime % 1) *1e9)
  if (previousTimestamp) {
    seconds = seconds - previousTimestamp[0]
    nanoseconds = nanoseconds - previousTimestamp[1]
    if (nanoseconds < 0) {
      seconds--
      nanoseconds += 1e9
    }
  }
  return [seconds, nanoseconds]
}

function hrtime(previousTimestamp?: HighResolutionTime): HighResolutionTime {
  if (IS_BROWSER) {
    return hrtimeBrowser(previousTimestamp)
  } else {
    return process.hrtime(previousTimestamp)
  }
}


import { isObj } from 'exotic'
function toISOString(date?: Date) {
  if (isObj(date) === true) {
    return (date as Date).toISOString()
  } else {
    return 'xx-xx-xxx'
  }
}

export class Timer {
  public startWallTime?: Date
  public endWallTime?: Date
  public startHrTime?: HighResolutionTime
  public duration?: HighResolutionTime

  public static init() {
    const timer = new Timer()
    timer.start()
    return timer
  }
  public start() {
    this.startHrTime = hrtime()
    this.startWallTime = new Date()
  }
  public end() {
    this.duration = hrtime(this.startHrTime)
    this.endWallTime = new Date()
  }
  public toString() {
    if (this.duration === undefined) {
      return 'unfinished'
    } else {
      return durationHrTimeToNanos(this.duration)
    }
  }
  public toJSON() {
    return {
      durationInNanoSeconds: this.toString(),
      startTime: toISOString(this.startWallTime),
      endTime: toISOString(this.endWallTime),
    }
  }
}