package main

import (
	"fmt"
	"os"
	"sync"
	"time"
)

// SafeWriter 线程安全的Writer封装
type SafeWriter struct {
	writer *os.File
	mu     sync.Mutex // 互斥锁，保护Writer写入
}

// NewSafeWriter 创建SafeWriter实例
func NewSafeWriter(filename string) (*SafeWriter, error) {
	file, err := os.OpenFile(filename,
		os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0644)
	if err != nil {
		return nil, err
	}
	return &SafeWriter{writer: file}, nil
}

// Writef 线程安全的格式化写入
func (w *SafeWriter) Writef(format string, args ...interface{}) error {
	w.mu.Lock()         // 加锁，独占写入权
	defer w.mu.Unlock() // 函数退出自动解锁

	// 拼接日志前缀（时间）+ 格式化内容
	logContent := fmt.Sprintf("[%s] %s\n",
		time.Now().Format("2006-01-02 15:04:05"),
		fmt.Sprintf(format, args...))

	// 写入文件（用WriteString比Fprintf更高效）
	_, err := w.writer.WriteString(logContent)
	return err
}

// Close 关闭文件
func (w *SafeWriter) Close() error {
	return w.writer.Close()
}

func main() {
	writer, err := NewSafeWriter("concurrent.log")
	if err != nil {
		fmt.Printf("SafeWriter创建失败：%v\n", err)
		return
	}
	defer writer.Close()

	var wg sync.WaitGroup
	// 10个goroutine并发写入（每个写10条）
	for i := 0; i < 10; i++ {
		wg.Add(1)
		go func(goroutineID int) {
			defer wg.Done()
			for j := 0; j < 10; j++ {
				writer.Writef("goroutine%d：完成第%d条任务", goroutineID, j)
			}
		}(i)
	}

	wg.Wait()
	fmt.Println("10个goroutine并发写入完成，内容无错乱")
}