package idgen

import (
	"crypto/rand"
	"encoding/base32"
	"sync"
	"time"
)

var encoding = base32.StdEncoding.WithPadding(base32.NoPadding)

// Creates a new, random token from 20 random bytes, encoded as base32.
func NewToken() string {
	buf := make([]byte, 20)
	rand.Read(buf) // Guaranteed not to return an error.
	return encoding.EncodeToString(buf)
}

var (
	lock   sync.Mutex
	ts     int64 = time.Now().Unix()
	seq    int64 = 0
	seqMax int64 = 1 << 20
)

// NextID can generate ~1M int64s per second.
//
// nodeID must be in [0, 63]. The counter is shared across all nodeIDs within a
// process, so IDs are not guaranteed to be sequential.
func NextID(nodeID int64) int64 {
	if nodeID < 0 || nodeID >= 64 {
		panic("nodeID out of range [0, 63]")
	}

	for {
		if id := nextID(nodeID); id != 0 {
			return id
		}
		time.Sleep(100 * time.Millisecond)
	}
}

func nextID(nodeID int64) int64 {
	lock.Lock()
	defer lock.Unlock()

	tt := time.Now().Unix()
	if tt > ts {
		ts = tt
		seq = 1
	} else {
		seq++
		if seq >= seqMax {
			return 0
		}
	}

	return (ts << 26) + (nodeID << 20) + seq
}

func SplitID(id int64) (unixTime, nodeID, counter int64) {
	counter = id & (0x00000000000FFFFF)
	nodeID = (id >> 20) & (0x000000000000003F)
	unixTime = id >> 26
	return
}