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package id
import (
"crypto/rand"
"encoding/hex"
"fmt"
"strings"
"sync"
"time"
)
const (
PrefixSession = "ses"
PrefixMessage = "msg"
PrefixUser = "usr"
PrefixPart = "prt"
)
const length = 26
var (
lastTimestamp int64
counter int64
mu sync.Mutex
)
type Prefix string
const (
Session Prefix = PrefixSession
Message Prefix = PrefixMessage
User Prefix = PrefixUser
Part Prefix = PrefixPart
)
func ValidatePrefix(id string, prefix Prefix) bool {
return strings.HasPrefix(id, string(prefix))
}
func Ascending(prefix Prefix, given ...string) string {
return generateID(prefix, false, given...)
}
func Descending(prefix Prefix, given ...string) string {
return generateID(prefix, true, given...)
}
func generateID(prefix Prefix, descending bool, given ...string) string {
if len(given) > 0 && given[0] != "" {
if !strings.HasPrefix(given[0], string(prefix)) {
panic(fmt.Sprintf("ID %s does not start with %s", given[0], string(prefix)))
}
return given[0]
}
return generateNewID(prefix, descending)
}
func randomBase62(length int) string {
const chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
result := make([]byte, length)
bytes := make([]byte, length)
rand.Read(bytes)
for i := 0; i < length; i++ {
result[i] = chars[bytes[i]%62]
}
return string(result)
}
func generateNewID(prefix Prefix, descending bool) string {
mu.Lock()
defer mu.Unlock()
currentTimestamp := time.Now().UnixMilli()
if currentTimestamp != lastTimestamp {
lastTimestamp = currentTimestamp
counter = 0
}
counter++
now := uint64(currentTimestamp)*0x1000 + uint64(counter)
if descending {
now = ^now
}
timeBytes := make([]byte, 6)
for i := 0; i < 6; i++ {
timeBytes[i] = byte((now >> (40 - 8*i)) & 0xff)
}
return string(prefix) + "_" + hex.EncodeToString(timeBytes) + randomBase62(length-12)
}
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