package util

import (
	"crypto/rand"
	"fmt"
	"time"
)

// UUID7 generates a UUIDv7-like identifier (time-ordered, random suffix).
// Format: 32 hex chars, e.g. "01972a8b4c3d8000a1b2c3d4e5f6a7b8".
func UUID7() string {
	var b [16]byte
	if _, err := rand.Read(b[:]); err != nil {
		panic("uuid7: rand: " + err.Error())
	}

	// Set version 7 bits.
	b[6] = (b[6] & 0x0f) | 0x70
	b[8] = (b[8] & 0x3f) | 0x80

	// Encode timestamp in first 6 bytes for rough time-ordering.
	now := time.Now().UnixMilli()
	b[0] = byte(now >> 40)
	b[1] = byte(now >> 32)
	b[2] = byte(now >> 24)
	b[3] = byte(now >> 16)
	b[4] = byte(now >> 8)
	b[5] = byte(now)

	return fmt.Sprintf("%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x",
		b[0], b[1], b[2], b[3], b[4], b[5], b[6], b[7],
		b[8], b[9], b[10], b[11], b[12], b[13], b[14], b[15])
}