#!/usr/bin/env python
# -*- coding: utf-8 -*-

import time


class SnowflakeManager(object):
    """
    Twitter的雪花算法实现
    """

    def __init__(self, start_time=1420041600000):
        self.start_time = start_time / 1000  # 以秒为单位
        self.last_timestamp = -1

        # 41 bits时间戳
        self.timestamp_shift = 22
        # 10 bits机器编号
        self.machine_id_shift = 12
        # 12 bits序列号
        self.sequence_shift = 0

        # 41 bits可以表示的最大值，2^41 - 1
        self.max_timestamp = -1 ^ (-1 << self.timestamp_shift)
        # 10 bits可以表示的最大值，2^10 - 1
        self.max_machine_id = -1 ^ (-1 << self.machine_id_shift)
        # 12 bits可以表示的最大值，2^12 - 1
        self.max_sequence = -1 ^ (-1 << self.sequence_shift)

        # 机器编号和序列号暂时不使用，可以通过参数传入
        self.machine_id = 0
        self.sequence = 0

    def next_id(self):
        timestamp = int(time.time())
        if timestamp < self.last_timestamp:
            raise ValueError('Current timestamp is less than last timestamp.')

        if timestamp == self.last_timestamp:
            self.sequence = (self.sequence + 1) & self.max_sequence
            if self.sequence == 0:
                timestamp = self.til_next_millis(self.last_timestamp)
        else:
            self.sequence = 0

        self.last_timestamp = timestamp
        return ((timestamp - int(self.start_time)) << self.timestamp_shift) | (
                self.machine_id << self.machine_id_shift) | self.sequence

    def til_next_millis(self, last_timestamp):
        timestamp = int(time.time())
        while timestamp <= last_timestamp:
            timestamp = int(time.time())
        return timestamp