package main


import "fmt"
import "os"
import "io"
import "bufio"
import "io/ioutil"

func main() {
	
	myfile := "debug.txt"
	
	test_write_file(myfile)
	
	test_read_file(myfile)
	
	test_open_or_create_file()
	
	test_bufio()
	
	test_ioutil();
	
}

/*写文件内容*/
func test_write_file(filename string) {
	fp, err := os.Create(filename)
	if (err != nil) {
		fmt.Println(err)
		return
	}
	for i := 0; i < 10; i++ {
		ourstr := fmt.Sprintf("%s:%d\n", "Hello World", i)
		fp.WriteString(ourstr)
		fp.Write([]byte("abcd\n"))
	}
	fp.Close()
}

/*读取文件内容*/
func test_read_file(filename string) {
	fp, err := os.Open(filename)
	if err != nil {
		fmt.Println(err)
	}
	defer fp.Close()
	buf := make([]byte, 1024)
	for {
		n, _ := fp.Read(buf)
		if n == 0 {
			break
		}
		os.Stdout.Write(buf)
	}
}

/*同时使用os.Open与os.Create操作文件*/
func test_open_or_create_file() {
	openFile := "log.txt"
	fo, err := os.Open(openFile)
	if err != nil {
		fmt.Println(err)
	}
	defer fo.Close()
	
	createFile := "log_new.txt" 
	fc, err := os.Create(createFile)
	if err != nil {
		fmt.Println(err)
	}
	defer fc.Close()
	
	buf := make([]byte, 1024)
	for {
		rn, err := fo.Read(buf)
		if err != nil && err != io.EOF {
			fmt.Println(err)
			panic(err)
		}
		fmt.Println(rn)
		if rn == 0 {
			break
		}
		
		wn, err := fc.Write(buf[: rn])
		if err != nil {
			fmt.Println(err)
			panic(err)
		}
		if wn != rn {
			fmt.Println("err writing")
			panic("err writing")
		}
	}
}

/*用bufio库*/
func test_bufio() {
	ofile := "log.txt"
	fo, err := os.Open(ofile)
	if err != nil {
		panic(err)
	}
	defer fo.Close()

	r := bufio.NewReader(fo) 
	
	cfile := "output.txt"
	fc, err := os.Create(cfile)
	if err != nil {
		panic(err)
	}
	defer fc.Close()
	w := bufio.NewWriter(fc) 
	
	buf := make([]byte, 1024)
	for {
		fmt.Println("start")
		rn, err := r.Read(buf)
		if err != nil && err != io.EOF {
			panic(err)
		}
		if rn == 0 {
			break
		}
		
		wn, err := w.Write(buf[: rn])
		if err != nil {
			panic(err)
		}
		if wn != rn {
			panic("err writing")
		}
	}
	err = w.Flush()
	if err != nil {
		panic(err)
	}
}

/*用ioutil库*/
func test_ioutil() {
	b, err := ioutil.ReadFile("log.txt")
	if err != nil {
		panic(err)
	}
	
	err = ioutil.WriteFile("out.txt", b, 0644)
	if err != nil {
		panic(err)
	}
}