package idgen

import (
	"sync"
	"time"
)

var (
	lock       sync.Mutex
	ts         uint64 = uint64(time.Now().Unix())
	counter    uint64 = 1
	counterMax uint64 = 1 << 28
)

// Next can generate ~268M ints per second for ~1000 years.
func Next() uint64 {
	lock.Lock()
	defer lock.Unlock()

	tt := uint64(time.Now().Unix())
	if tt > ts {
		ts = tt
		counter = 1
	} else {
		counter++
		if counter == counterMax {
			panic("Too many IDs.")
		}
	}

	return ts<<28 + counter
}