// Copyright 2023 magnifier Author.
//
// 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.
//
// |--------------|------------------|---------------|--------------------|
// | 1 Bit Unused | 41 Bit Timestamp | 10 Bit NodeID | 12 Bit Sequence ID |
// |--------------|------------------|---------------|--------------------|
package snow

import (
	"math/rand"
	"sync"
	"time"
)

type Snow struct {
	// Epoch indicate start time, in milliseconds
	epoch    time.Time
	node     int64
	sequence int64
	mu       sync.Mutex
}

func New(epoch time.Time, node int64) *Snow {
	if epoch.IsZero() {
		epoch = time.Date(2022, 1, 1, 0, 0, 0, 0, time.UTC)
	}
	if node == 0 {
		node = rand.Int63() % 0x3ff
	}
	return &Snow{
		epoch: epoch,
		node:  node,
	}
}

func (g *Snow) Next() int64 {
	g.mu.Lock()
	defer g.mu.Unlock()

	g.sequence = (g.sequence + 1) % 0xfff
	return (time.Since(g.epoch).Milliseconds() << 22) | (g.node << 12) | g.sequence
}

func (g *Snow) Parse(id int64) (time.Time, int64, int64) {
	seq := id & 0xfff
	node := id >> 12 & 0x3ff
	return time.UnixMilli(id>>22 + g.epoch.UnixMilli()), node, seq
}

func (g *Snow) At(moment time.Time) int64 {
	return moment.Sub(g.epoch).Milliseconds() << 22
}