package common

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

// IDGenerator 简单的 ID 生成器（类似 Snowflake）
type IDGenerator struct {
	mu        sync.RWMutex
	lastTime  int64
	sequence  int64
	machineID int64
}

var (
	defaultGenerator *IDGenerator
	once             sync.Once
)

// GetIDGenerator 获取默认生成器单例
func GetIDGenerator() *IDGenerator {
	once.Do(func() {
		defaultGenerator = &IDGenerator{
			machineID: 1,
		}
	})
	return defaultGenerator
}

// Lazy initialize on first access
func getInstance() *IDGenerator {
	if defaultGenerator == nil {
		once.Do(func() {
			defaultGenerator = &IDGenerator{
				machineID: 1,
			}
		})
	}
	return defaultGenerator
}

// GenerateStringID 全局辅助函数：生成 string 类型 ID
func GenerateStringID() string {
	gen := getInstance()
	if gen == nil {
		// Fallback: create new instance if singleton fails
		gen = &IDGenerator{machineID: 1}
	}
	return gen.NextIDStr()
}

// GenerateLongID 全局辅助函数：生成 long 类型 ID
func GenerateLongID() int64 {
	gen := getInstance()
	if gen == nil {
		gen = &IDGenerator{machineID: 1}
	}
	return gen.NextID()
}

// NextID 生成下一个 64 位整数 ID
func (g *IDGenerator) NextID() int64 {
	g.mu.Lock()
	defer g.mu.Unlock()

	now := time.Now().UnixMilli()

	if now == g.lastTime {
		g.sequence = (g.sequence + 1) & 4095
		if g.sequence == 0 {
			for now <= g.lastTime {
				now = time.Now().UnixMilli()
			}
		}
	} else {
		g.sequence = 0
	}

	g.lastTime = now
	return now*10000 + g.sequence
}

// NextIDStr 生成字符串类型的 ID
func (g *IDGenerator) NextIDStr() string {
	id := g.NextID()
	return strconv.FormatInt(id, 10)
}