idgen.go

package well

import (
	"crypto/rand"
	"encoding/binary"
	"sync/atomic"
)

var hexData = [...]byte{
	'0', '0', '0', '1', '0', '2', '0', '3', '0', '4', '0', '5', '0', '6', '0', '7', '0', '8', '0', '9', '0', 'a', '0', 'b', '0', 'c', '0', 'd', '0', 'e', '0', 'f',
	'1', '0', '1', '1', '1', '2', '1', '3', '1', '4', '1', '5', '1', '6', '1', '7', '1', '8', '1', '9', '1', 'a', '1', 'b', '1', 'c', '1', 'd', '1', 'e', '1', 'f',
	'2', '0', '2', '1', '2', '2', '2', '3', '2', '4', '2', '5', '2', '6', '2', '7', '2', '8', '2', '9', '2', 'a', '2', 'b', '2', 'c', '2', 'd', '2', 'e', '2', 'f',
	'3', '0', '3', '1', '3', '2', '3', '3', '3', '4', '3', '5', '3', '6', '3', '7', '3', '8', '3', '9', '3', 'a', '3', 'b', '3', 'c', '3', 'd', '3', 'e', '3', 'f',
	'4', '0', '4', '1', '4', '2', '4', '3', '4', '4', '4', '5', '4', '6', '4', '7', '4', '8', '4', '9', '4', 'a', '4', 'b', '4', 'c', '4', 'd', '4', 'e', '4', 'f',
	'5', '0', '5', '1', '5', '2', '5', '3', '5', '4', '5', '5', '5', '6', '5', '7', '5', '8', '5', '9', '5', 'a', '5', 'b', '5', 'c', '5', 'd', '5', 'e', '5', 'f',
	'6', '0', '6', '1', '6', '2', '6', '3', '6', '4', '6', '5', '6', '6', '6', '7', '6', '8', '6', '9', '6', 'a', '6', 'b', '6', 'c', '6', 'd', '6', 'e', '6', 'f',
	'7', '0', '7', '1', '7', '2', '7', '3', '7', '4', '7', '5', '7', '6', '7', '7', '7', '8', '7', '9', '7', 'a', '7', 'b', '7', 'c', '7', 'd', '7', 'e', '7', 'f',
	'8', '0', '8', '1', '8', '2', '8', '3', '8', '4', '8', '5', '8', '6', '8', '7', '8', '8', '8', '9', '8', 'a', '8', 'b', '8', 'c', '8', 'd', '8', 'e', '8', 'f',
	'9', '0', '9', '1', '9', '2', '9', '3', '9', '4', '9', '5', '9', '6', '9', '7', '9', '8', '9', '9', '9', 'a', '9', 'b', '9', 'c', '9', 'd', '9', 'e', '9', 'f',
	'a', '0', 'a', '1', 'a', '2', 'a', '3', 'a', '4', 'a', '5', 'a', '6', 'a', '7', 'a', '8', 'a', '9', 'a', 'a', 'a', 'b', 'a', 'c', 'a', 'd', 'a', 'e', 'a', 'f',
	'b', '0', 'b', '1', 'b', '2', 'b', '3', 'b', '4', 'b', '5', 'b', '6', 'b', '7', 'b', '8', 'b', '9', 'b', 'a', 'b', 'b', 'b', 'c', 'b', 'd', 'b', 'e', 'b', 'f',
	'c', '0', 'c', '1', 'c', '2', 'c', '3', 'c', '4', 'c', '5', 'c', '6', 'c', '7', 'c', '8', 'c', '9', 'c', 'a', 'c', 'b', 'c', 'c', 'c', 'd', 'c', 'e', 'c', 'f',
	'd', '0', 'd', '1', 'd', '2', 'd', '3', 'd', '4', 'd', '5', 'd', '6', 'd', '7', 'd', '8', 'd', '9', 'd', 'a', 'd', 'b', 'd', 'c', 'd', 'd', 'd', 'e', 'd', 'f',
	'e', '0', 'e', '1', 'e', '2', 'e', '3', 'e', '4', 'e', '5', 'e', '6', 'e', '7', 'e', '8', 'e', '9', 'e', 'a', 'e', 'b', 'e', 'c', 'e', 'd', 'e', 'e', 'e', 'f',
	'f', '0', 'f', '1', 'f', '2', 'f', '3', 'f', '4', 'f', '5', 'f', '6', 'f', '7', 'f', '8', 'f', '9', 'f', 'a', 'f', 'b', 'f', 'c', 'f', 'd', 'f', 'e', 'f', 'f',
}

var (
	defaultGenerator = NewIDGenerator()
)

// IDGenerator generates ID suitable for request tracking.
type IDGenerator struct {
	seed [16]byte
	n    uint64
}

// NewIDGenerator creates a new IDGenerator.
func NewIDGenerator() *IDGenerator {
	g := new(IDGenerator)
	_, err := rand.Read(g.seed[:])
	if err != nil {
		panic(err)
	}
	return g
}

// Generate generates an ID.
// Multiple goroutines can safely call this.
func (g *IDGenerator) Generate() string {
	var nb [8]byte
	n := atomic.AddUint64(&g.n, 1)
	binary.LittleEndian.PutUint64(nb[:], n)

	id := g.seed
	for i, b := range nb {
		id[i] ^= b
	}

	var strbuf [36]byte
	for i := 0; i < 4; i++ {
		strbuf[i*2] = hexData[int(id[i])*2]
		strbuf[i*2+1] = hexData[int(id[i])*2+1]
	}
	strbuf[8] = '-'
	for i := 4; i < 6; i++ {
		strbuf[i*2+1] = hexData[int(id[i])*2]
		strbuf[i*2+2] = hexData[int(id[i])*2+1]
	}
	strbuf[13] = '-'
	for i := 6; i < 8; i++ {
		strbuf[i*2+2] = hexData[int(id[i])*2]
		strbuf[i*2+3] = hexData[int(id[i])*2+1]
	}
	strbuf[18] = '-'
	for i := 8; i < 10; i++ {
		strbuf[i*2+3] = hexData[int(id[i])*2]
		strbuf[i*2+4] = hexData[int(id[i])*2+1]
	}
	strbuf[23] = '-'
	for i := 10; i < 16; i++ {
		strbuf[i*2+4] = hexData[int(id[i])*2]
		strbuf[i*2+5] = hexData[int(id[i])*2+1]
	}
	return string(strbuf[:])
}

// GenerateID genereates an ID using the default generator.
// Multiple goroutines can safely call this.
func GenerateID() string {
	return defaultGenerator.Generate()
}