<?php
// application/common/library/Snowflake.php

namespace app\common\library;

class Snowflake
{
    // 起始时间戳（2023-01-01）
    const EPOCH = 1672502400000;

    // 机器ID位数
    const WORKER_ID_BITS = 5;
    const DATACENTER_ID_BITS = 5;
    const SEQUENCE_BITS = 12;

    // 最大值
    const MAX_WORKER_ID = -1 ^ (-1 << self::WORKER_ID_BITS);
    const MAX_DATACENTER_ID = -1 ^ (-1 << self::DATACENTER_ID_BITS);
    const MAX_SEQUENCE = -1 ^ (-1 << self::SEQUENCE_BITS);

    // 移位
    const WORKER_ID_SHIFT = self::SEQUENCE_BITS;
    const DATACENTER_ID_SHIFT = self::SEQUENCE_BITS + self::WORKER_ID_BITS;
    const TIMESTAMP_LEFT_SHIFT = self::SEQUENCE_BITS + self::WORKER_ID_BITS + self::DATACENTER_ID_BITS;

    protected $workerId;
    protected $datacenterId;
    protected $sequence = 0;
    protected $lastTimestamp = -1;

    public function __construct($workerId = 1, $datacenterId = 1)
    {
        if ($workerId > self::MAX_WORKER_ID || $workerId < 0) {
            throw new \Exception("worker Id can't be greater than " . self::MAX_WORKER_ID . " or less than 0");
        }

        if ($datacenterId > self::MAX_DATACENTER_ID || $datacenterId < 0) {
            throw new \Exception("datacenter Id can't be greater than " . self::MAX_DATACENTER_ID . " or less than 0");
        }

        $this->workerId = $workerId;
        $this->datacenterId = $datacenterId;
    }

    public function nextId()
    {
        $timestamp = $this->timeGen();

        if ($timestamp < $this->lastTimestamp) {
            $diff = $this->lastTimestamp - $timestamp;
            throw new \Exception("Clock moved backwards. Refusing to generate id for {$diff} milliseconds");
        }

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

        $this->lastTimestamp = $timestamp;

        return (($timestamp - self::EPOCH) << self::TIMESTAMP_LEFT_SHIFT) |
            ($this->datacenterId << self::DATACENTER_ID_SHIFT) |
            ($this->workerId << self::WORKER_ID_SHIFT) |
            $this->sequence;
    }

    protected function tilNextMillis($lastTimestamp)
    {
        $timestamp = $this->timeGen();
        while ($timestamp <= $lastTimestamp) {
            $timestamp = $this->timeGen();
        }
        return $timestamp;
    }

    protected function timeGen()
    {
        return floor(microtime(true) * 1000);
    }

    /**
     * 解析雪花ID
     * @param int $id
     * @return array
     */
    public static function parseId($id)
    {
        $binary = decbin($id);
        $binary = str_pad($binary, 64, '0', STR_PAD_LEFT);

        $timestamp = bindec(substr($binary, 0, 42));
        $timestamp = $timestamp + self::EPOCH;

        $datacenterId = bindec(substr($binary, 42, 5));
        $workerId = bindec(substr($binary, 47, 5));
        $sequence = bindec(substr($binary, 52, 12));

        return [
            'timestamp' => $timestamp,
            'datacenterId' => $datacenterId,
            'workerId' => $workerId,
            'sequence' => $sequence
        ];
    }

    /**
     * 生成ID（单例模式）
     * @return int
     */
    public static function generate()
    {
        static $instance = null;
        if (!$instance) {
            // 从配置获取workerId和datacenterId
            $workerId = config('snowflake.worker_id') ?: 1;
            $datacenterId = config('snowflake.datacenter_id') ?: 1;
            $instance = new self($workerId, $datacenterId);
        }
        return $instance->nextId();
    }
}