// 雪花 ID 53-bit 压缩版 (JS Number 安全)
// 移植自 hwt-code (IdGenerator.java) - 与后端 com.ruoyi.common.utils.id.IdGenerator 完全一致
// 53-bit 容量: 2^53-1 = 9007199254740991, JS Number max safe = 2^53-1
//
// 算法:
//   timestamp 40 bits (per 10ms, 2300+ 年可用)
//   machineId 5 bits (0~31)
//   sequence  8 bits (0~255, 每 10ms 重置)
//
// 注意: JS bit-shift 对 32-bit 安全, 53-bit 不会溢出 (32-bit long 范围更大)

const MACHINE_BIT = 5
const SEQUENCE_BIT = 8
const MAX_MACHINE_NUM = -1 ^ (-1 << MACHINE_BIT) // 31
const MAX_SEQUENCE = -1 ^ (-1 << SEQUENCE_BIT)    // 255
const MACHINE_LEFT = SEQUENCE_BIT
const TIMESTMP_LEFT = MACHINE_BIT + SEQUENCE_BIT

let machineId = 0
let sequence = 0
let lastStmp = -1

function initDefaultInstance(id) {
  machineId = id
  sequence = 0
  lastStmp = -1
}

function getTimestamp() {
  return Math.floor(Date.now() / 10) // per 10ms (与后端一致)
}

function getNextTimestamp() {
  let mill = getTimestamp()
  while (mill <= lastStmp) mill = getTimestamp()
  return mill
}

function nextId() {
  let currStmp = getTimestamp()
  if (currStmp < lastStmp) throw new Error('Clock moved backwards. Refusing to generate id')
  if (currStmp === lastStmp) {
    sequence = (sequence + 1) & MAX_SEQUENCE
    if (sequence === 0) currStmp = getNextTimestamp()
  } else {
    sequence = 0
  }
  lastStmp = currStmp
  // JS Number 53-bit 安全
  return Number(BigInt(currStmp) << BigInt(TIMESTMP_LEFT) | BigInt(machineId) << BigInt(MACHINE_LEFT) | BigInt(sequence))
}

function generateId() {
  return nextId()
}

function parseIdTimestamp(id) {
  return new Date(Number(BigInt(id) >> BigInt(TIMESTMP_LEFT)) * 10)
}

export default {
  initDefaultInstance,
  generateId,
  parseIdTimestamp,
}