// Copyright 2019 The Vearch Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
// implied. See the License for the specific language governing
// permissions and limitations under the License.

package uuid

import (
	"strconv"
	"sync"
	"time"
)

// timeGenerator is for tests.
type timeGenerator struct {
	sync.Mutex
	// ensure clock moves forward
	lastTimestamp int64
}

func NewTimeGenerator() Generator {
	return &timeGenerator{lastTimestamp: time.Now().UnixNano()}
}

func (g *timeGenerator) GetUUID() string {
	cur := time.Now().UnixNano()

	g.Lock()
	if cur == g.lastTimestamp {
		cur++
	}
	g.lastTimestamp = cur
	g.Unlock()

	return strconv.FormatInt(cur, 10)
}