n0mbers/src/utils.ts

import { utcToZonedTime } from 'date-fns-tz'

import { BXL_TZ, GAME_STARTING_DATE } from '@/globals'

export function getCurrentDate(): Date {
  return utcToZonedTime(new Date(), BXL_TZ)
}

export function getCurrentSessionKey(): string {
  const now = getCurrentDate()
  // https://stackoverflow.com/a/28149561
  const tzoffset = now.getTimezoneOffset() * 60000
  const localISOTime = new Date(now.getTime() - tzoffset).toISOString()
  return localISOTime.slice(0, 10)
}

/**
 *
 * @param a
 * @param b
 * @returns Percentage rounded to 2 decimals
 */
export function percentageDiff(a: number, b: number): number {
  return Math.round(((a - b) / ((a + b) / 2)) * 100) / 100
}

// #region RNG

export let random = Math.random

/**
 *
 * @param min inclusive
 * @param max exclusive
 * @returns
 */
export function randRange(min: number, max: number, rnd = random): number {
  return Math.floor(rnd() * (max - min) + min)
}

export function randItem<T>(items: T[], rnd = random): T {
  return items[Math.floor(rnd() * items.length)]
}

export function setMathPRNG(): void {
  random = Math.random
}

export function setDailyPRNG(): void {
  random = initDailyPRNG()
}

/**
 * Shuffles an array in place and returns it
 * @param array
 * @returns
 */
export function shuffle<T>(array: T[]): T[] {
  let currentIndex = array.length
  let randomIndex: number

  // While there remain elements to shuffle...
  while (currentIndex !== 0) {
    // Pick a remaining element...
    randomIndex = Math.floor(random() * currentIndex)
    currentIndex--

    // And swap it with the current element.
    ;[array[currentIndex], array[randomIndex]] = [
      array[randomIndex],
      array[currentIndex],
    ]
  }

  return array
}

function initDailyPRNG(): () => number {
  // Prefix the seed when in dev to avoid spoiling myself while working on it
  const prefix = import.meta.env.DEV ? 'dev-' : ''
  const hashed = hashStr(prefix + getCurrentSessionKey())
  return mulberry32(hashed)
}

function mulberry32(a: number) {
  return function () {
    let t = (a += 0x6d2b79f5)
    t = Math.imul(t ^ (t >>> 15), t | 1)
    t ^= t + Math.imul(t ^ (t >>> 7), t | 61)
    return ((t ^ (t >>> 14)) >>> 0) / 4294967296
  }
}

/**
 * https://stackoverflow.com/a/7616484
 * @param val
 * @returns
 */
function hashStr(val: string): number {
  let hash = 0
  if (val.length === 0) {
    return 0
  }
  for (let i = 0; i < val.length; ++i) {
    hash = (hash << 5) - hash + val[i].charCodeAt(0)
    hash |= 0
  }
  return hash
}

// #endregion RNG