package alert

import (
	"crypto/rand"
	"encoding/hex"
	"sync/atomic"
	"time"
)

// ulidLike returns a 26-char time-sortable ID. Layout:
//   - first 10 hex chars: unix ms (fits in 40 bits, padded)
//   - next 16 hex chars:  random
// Not a real ULID, but good enough for log ordering and broker keys.
func ulidLike() string {
	now := time.Now().UTC().UnixMilli()
	var msBuf [8]byte
	for i := 7; i >= 0; i-- {
		msBuf[i] = byte(now)
		now >>= 8
	}
	var rnd [8]byte
	if _, err := rand.Read(rnd[:]); err != nil {
		// crypto/rand should never fail; if it does, fall back to atomic counter
		// so we still produce a unique ID.
		fb := atomic.AddUint64(&fallbackCounter, 1)
		for i := 7; i >= 0; i-- {
			rnd[i] = byte(fb)
			fb >>= 8
		}
	}
	return hex.EncodeToString(msBuf[:])[:10] + hex.EncodeToString(rnd[:])
}

var fallbackCounter uint64