<?php
namespace app\common\library;

/**
 * 雪花算法ID生成器
 */
class Snowflake
{
    // 起始时间戳（2023-01-01 00:00:00）
    const EPOCH = 1672531200000;

    // 机器ID位数
    const MACHINE_BITS = 10;

    // 序列号位数
    const SEQUENCE_BITS = 12;

    // 最大机器ID
    const MAX_MACHINE_ID = -1 ^ (-1 << self::MACHINE_BITS);

    // 最大序列号
    const MAX_SEQUENCE = -1 ^ (-1 << self::SEQUENCE_BITS);

    // 机器ID左移位数
    const MACHINE_SHIFT = self::SEQUENCE_BITS;

    // 时间戳左移位数
    const TIMESTAMP_SHIFT = self::SEQUENCE_BITS + self::MACHINE_BITS;

    // 机器ID（0-1023）
    private $machineId;

    // 最后时间戳
    private $lastTimestamp = -1;

    // 序列号
    private $sequence = 0;

    /**
     * 构造函数
     * @param int $machineId 机器ID
     */
    public function __construct($machineId = 1)
    {
        if ($machineId < 0 || $machineId > self::MAX_MACHINE_ID) {
            throw new \InvalidArgumentException("机器ID必须在0-" . self::MAX_MACHINE_ID . "之间");
        }

        $this->machineId = $machineId;
    }

    /**
     * 生成ID
     * @return string
     */
    public function generateId()
    {
        $timestamp = $this->getTimestamp();

        if ($timestamp < $this->lastTimestamp) {
            throw new \Exception("时钟回拨异常");
        }

        if ($timestamp == $this->lastTimestamp) {
            $this->sequence = ($this->sequence + 1) & self::MAX_SEQUENCE;
            if ($this->sequence == 0) {
                $timestamp = $this->waitNextMillis($this->lastTimestamp);
            }
        } else {
            $this->sequence = 0;
        }

        $this->lastTimestamp = $timestamp;

        return (($timestamp - self::EPOCH) << self::TIMESTAMP_SHIFT) |
            ($this->machineId << self::MACHINE_SHIFT) |
            $this->sequence;
    }

    /**
     * 获取当前毫秒时间戳
     * @return int
     */
    private function getTimestamp()
    {
        return (int)(microtime(true) * 1000);
    }

    /**
     * 等待下一毫秒
     * @param int $lastTimestamp
     * @return int
     */
    private function waitNextMillis($lastTimestamp)
    {
        $timestamp = $this->getTimestamp();
        while ($timestamp <= $lastTimestamp) {
            usleep(100); // 休眠100微秒
            $timestamp = $this->getTimestamp();
        }
        return $timestamp;
    }

    /**
     * 解析ID
     * @param string $id
     * @return array
     */
    public static function parseId($id)
    {
        $timestamp = ($id >> self::TIMESTAMP_SHIFT) + self::EPOCH;
        $machineId = ($id >> self::MACHINE_SHIFT) & self::MAX_MACHINE_ID;
        $sequence = $id & self::MAX_SEQUENCE;

        return [
            'timestamp' => $timestamp,
            'machine_id' => $machineId,
            'sequence' => $sequence,
            'generate_time' => date('Y-m-d H:i:s', $timestamp / 1000)
        ];
    }
}