package usecase

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

type SystemClock struct{}

func (SystemClock) Now() time.Time {
	return time.Now().UTC()
}

type UUIDGenerator struct{}

func (UUIDGenerator) NewID() (string, error) {
	var value [16]byte
	if _, err := rand.Read(value[:]); err != nil {
		now := uint64(time.Now().UnixNano())
		binary.BigEndian.PutUint64(value[:8], now)
		binary.BigEndian.PutUint64(value[8:], fallbackUUID.Add(1))
	}
	value[6] = (value[6] & 0x0f) | 0x40
	value[8] = (value[8] & 0x3f) | 0x80
	return fmt.Sprintf(
		"%08x-%04x-%04x-%04x-%012x",
		value[0:4],
		value[4:6],
		value[6:8],
		value[8:10],
		value[10:16],
	), nil
}

var fallbackUUID atomic.Uint64