<?php

namespace app\common\library;

/**
 * 雪花算法ID生成器
 * 不依赖数据库，通过配置或自动生成workerId
 * 64位ID结构：0(1位符号位) + 41位时间戳 + 10位工作机器ID + 12位序列号
 */
class Snowflake
{
    // 起始时间戳（2023-01-01 00:00:00），可使用到2089年
    const EPOCH = 1672531200000;

    // 工作机器ID位数
    const WORKER_ID_BITS = 10;

    // 序列号位数
    const SEQUENCE_BITS = 12;

    // 最大工作机器ID
    const MAX_WORKER_ID = (1 << self::WORKER_ID_BITS) - 1;

    // 序列号掩码
    const SEQUENCE_MASK = (1 << self::SEQUENCE_BITS) - 1;

    // 工作机器ID左移位数
    const WORKER_ID_SHIFT = self::SEQUENCE_BITS;

    // 时间戳左移位数
    const TIMESTAMP_LEFT_SHIFT = self::SEQUENCE_BITS + self::WORKER_ID_BITS;

    // 工作机器ID（通过服务器IP生成）
    protected $workerId;

    // 序列号
    protected $sequence = 0;

    // 上次生成ID的时间戳
    protected $lastTimestamp = -1;

    // 单例实例
    protected static $instance = null;

    /**
     * 构造函数私有化，单例模式
     */
    private function __construct()
    {
        $this->workerId = $this->generateWorkerId();
    }

    /**
     * 获取单例实例
     */
    public static function getInstance()
    {
        if (self::$instance === null) {
            self::$instance = new self();
        }
        return self::$instance;
    }

    /**
     * 生成工作机器ID（基于服务器IP）
     */
    protected function generateWorkerId()
    {
        // 方法1：从配置文件中读取
        if (config('snowflake.worker_id')) {
            return config('snowflake.worker_id') & self::MAX_WORKER_ID;
        }

        // 方法2：基于服务器IP生成（推荐）
        $serverIp = $_SERVER['SERVER_ADDR'] ?? '127.0.0.1';
        $ipParts = explode('.', $serverIp);

        // 使用IP后两段生成workerId
        if (count($ipParts) >= 4) {
            $workerId = ($ipParts[2] << 8) | $ipParts[3];
        } else {
            // 如果是IPv6或特殊情况，使用随机数
            $workerId = mt_rand(0, self::MAX_WORKER_ID);
        }

        return $workerId & self::MAX_WORKER_ID;
    }

    /**
     * 生成下一个ID
     */
    public function nextId()
    {
        $timestamp = $this->getCurrentTimestamp();

        // 时钟回拨处理
        if ($timestamp < $this->lastTimestamp) {
            $diff = $this->lastTimestamp - $timestamp;
            throw new \Exception("时钟回拨了 {$diff} 毫秒");
        }

        // 同一毫秒内生成多个ID
        if ($this->lastTimestamp == $timestamp) {
            $this->sequence = ($this->sequence + 1) & self::SEQUENCE_MASK;
            if ($this->sequence == 0) {
                // 序列号用尽，等待下一毫秒
                $timestamp = $this->waitNextMillis($this->lastTimestamp);
            }
        } else {
            $this->sequence = 0;
        }

        $this->lastTimestamp = $timestamp;

        // 组合生成ID
        $id = (($timestamp - self::EPOCH) << self::TIMESTAMP_LEFT_SHIFT)
            | ($this->workerId << self::WORKER_ID_SHIFT)
            | $this->sequence;

        return (string)$id;
    }

    /**
     * 批量生成ID
     */
    public function nextIds($count)
    {
        $ids = [];
        for ($i = 0; $i < $count; $i++) {
            $ids[] = $this->nextId();
        }
        return $ids;
    }

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

    /**
     * 等待到下一毫秒
     */
    protected function waitNextMillis($lastTimestamp)
    {
        $timestamp = $this->getCurrentTimestamp();
        while ($timestamp <= $lastTimestamp) {
            usleep(100); // 休眠100微秒
            $timestamp = $this->getCurrentTimestamp();
        }
        return $timestamp;
    }

    /**
     * 解析雪花ID
     */
    public static function parse($id)
    {
        $id = intval($id);
        return [
            'timestamp' => ($id >> self::TIMESTAMP_LEFT_SHIFT) + self::EPOCH,
            'worker_id' => ($id >> self::WORKER_ID_SHIFT) & self::MAX_WORKER_ID,
            'sequence' => $id & self::SEQUENCE_MASK,
            'generated_at' => date('Y-m-d H:i:s.v', (($id >> self::TIMESTAMP_LEFT_SHIFT) + self::EPOCH) / 1000)
        ];
    }
}