package main
import "log"
func main() {
	log.Print("Print")
	log.Printf("Printf: %s", "print")
	log.Println("Println")
	log.Fatal("Fatal")
	log.Fatalf("Fatalf: %s", "fatal")
	log.Fatalln("Fatalln")
	log.Panic("Panic")
	log.Panicf("Panicf: %s", "panic")
	log.Panicln("Panicln")
}

logger := log.New(os.Stdout, "[Debug] - ", log.Lshortfile)

package main

import (
	"log"
	"os"
)

func main() {
	logger := log.New(os.Stdout, "[Debug] - ", log.Lshortfile)
	logger.Println("custom logger")
}

package main

import (
	"log"
	"os"
)

func main() {
	// 準備日志文件
	logFile, _ := os.Create("demo.log")
	defer func() { _ = logFile.Close() }()

	// 初始化日志對象
	logger := log.New(logFile, "[Debug] - ", log.Lshortfile|log.Lmsgprefix)
	logger.Print("Print")
	logger.Println("Println")

	// 修改日志配置
	logger.SetOutput(os.Stdout)
	logger.SetPrefix("[Info] - ")
	logger.SetFlags(log.Ldate|log.Ltime|log.LUTC)
	logger.Print("Print")
	logger.Println("Println")
}

func Print(v ...any) {
	if atomic.LoadInt32(&std.isDiscard) != 0 {
		return
	}
	std.Output(2, fmt.Sprint(v...))
}
func Printf(format string, v ...any) {
	if atomic.LoadInt32(&std.isDiscard) != 0 {
		return
	}
	std.Output(2, fmt.Sprintf(format, v...))
}
func Println(v ...any) {
	if atomic.LoadInt32(&std.isDiscard) != 0 {
		return
	}
	std.Output(2, fmt.Sprintln(v...))
}
func Fatal(v ...any) {
	std.Output(2, fmt.Sprint(v...))
	os.Exit(1)
}
func Fatalf(format string, v ...any) {
	std.Output(2, fmt.Sprintf(format, v...))
	os.Exit(1)
}
func Fatalln(v ...any) {
	std.Output(2, fmt.Sprintln(v...))
	os.Exit(1)
}
func Panic(v ...any) {
	s := fmt.Sprint(v...)
	std.Output(2, s)
	panic(s)
}
func Panicf(format string, v ...any) {
	s := fmt.Sprintf(format, v...)
	std.Output(2, s)
	panic(s)
}
func Panicln(v ...any) {
	s := fmt.Sprintln(v...)
	std.Output(2, s)
	panic(s)
}

var std = New(os.Stderr, "", LstdFlags)
func New(out io.Writer, prefix string, flag int) *Logger {
	l := &Logger{out: out, prefix: prefix, flag: flag}
	if out == io.Discard {
		l.isDiscard = 1
	}
	return l
}

type Logger struct {
	mu        sync.Mutex // 鎖，保證并發(fā)情況下對其屬性操作是原子性的
	prefix    string     // 日志前綴，即 Lmsgprefix 參數(shù)值
	flag      int        // 日志屬性，用來控制日志輸出格式
	out       io.Writer  // 日志輸出位置，實現(xiàn)了 io.Writer 接口即可，如 文件、os.Stderr
	buf       []byte     // 存儲日志輸出內(nèi)容
	isDiscard int32      // 當 out = io.Discard 是，此值為 1
}

const (
	Ldate         = 1 << iota     // the date in the local time zone: 2009/01/23
	Ltime                         // the time in the local time zone: 01:23:23
	Lmicroseconds                 // microsecond resolution: 01:23:23.123123.  assumes Ltime.
	Llongfile                     // full file name and line number: /a/b/c/d.go:23
	Lshortfile                    // final file name element and line number: d.go:23. overrides Llongfile
	LUTC                          // if Ldate or Ltime is set, use UTC rather than the local time zone
	Lmsgprefix                    // move the "prefix" from the beginning of the line to before the message
	LstdFlags     = Ldate | Ltime // initial values for the standard logger
)

func (l *Logger) Output(calldepth int, s string) error {
	now := time.Now() // 獲取當前時間
	var file string
	var line int
	// 加鎖，保證并發(fā)安全
	l.mu.Lock()
	defer l.mu.Unlock()
	// 通過位運算來判斷是否需要獲取文件名和行號
	if l.flag&(Lshortfile|Llongfile) != 0 {
		// 運行 runtime.Caller 獲取文件名和行號比較耗時，所以先釋放鎖
		l.mu.Unlock()
		var ok bool
		_, file, line, ok = runtime.Caller(calldepth)
		if !ok {
			file = "???"
			line = 0
		}
		// 獲取到文件行號后再次加鎖，保證下面代碼并發(fā)安全
		l.mu.Lock()
	}
	// 清空上次緩存的內(nèi)容
	l.buf = l.buf[:0]
	// 格式化日志頭信息（如：日期時間、文件名和行號、前綴）并寫入 buf
	l.formatHeader(&l.buf, now, file, line)
	// 追加日志內(nèi)容到 buf
	l.buf = append(l.buf, s...)
	// 保證輸出日志以 \n 結(jié)尾
	if len(s) == 0 || s[len(s)-1] != '\n' {
		l.buf = append(l.buf, '\n')
	}
	// 調(diào)用 Logger 對象的 out 屬性的 Write 方法輸出日志
	_, err := l.out.Write(l.buf)
	return err
}

func (l *Logger) formatHeader(buf *[]byte, t time.Time, file string, line int) {
	// 如果沒有設(shè)置 Lmsgprefix 屬性，將日志前綴內(nèi)容設(shè)置到行首
	if l.flag&Lmsgprefix == 0 {
		*buf = append(*buf, l.prefix...)
	}
	// 判斷是否設(shè)置了日期時間相關(guān)的屬性
	if l.flag&(Ldate|Ltime|Lmicroseconds) != 0 {
		// 是否設(shè)置 UTC 時間
		if l.flag&LUTC != 0 {
			t = t.UTC()
		}
		// 是否設(shè)置日期
		if l.flag&Ldate != 0 {
			year, month, day := t.Date()
			itoa(buf, year, 4)
			*buf = append(*buf, '/')
			itoa(buf, int(month), 2)
			*buf = append(*buf, '/')
			itoa(buf, day, 2)
			*buf = append(*buf, ' ')
		}
		// 是否設(shè)置時間
		if l.flag&(Ltime|Lmicroseconds) != 0 {
			hour, min, sec := t.Clock()
			itoa(buf, hour, 2)
			*buf = append(*buf, ':')
			itoa(buf, min, 2)
			*buf = append(*buf, ':')
			itoa(buf, sec, 2)
			if l.flag&Lmicroseconds != 0 {
				*buf = append(*buf, '.')
				itoa(buf, t.Nanosecond()/1e3, 6)
			}
			*buf = append(*buf, ' ')
		}
	}
	// 是否設(shè)置文件名和行號
	if l.flag&(Lshortfile|Llongfile) != 0 {
		if l.flag&Lshortfile != 0 {
			short := file
			for i := len(file) - 1; i > 0; i-- {
				if file[i] == '/' {
					short = file[i+1:]
					break
				}
			}
			file = short
		}
		*buf = append(*buf, file...)
		*buf = append(*buf, ':')
		itoa(buf, line, -1)
		*buf = append(*buf, ": "...)
	}
	// 如果設(shè)置了 Lmsgprefix 屬性，將日志前綴內(nèi)容放到日志頭信息最后，也就是緊挨著日志內(nèi)容前面
	if l.flag&Lmsgprefix != 0 {
		*buf = append(*buf, l.prefix...)
	}
}

func itoa(buf *[]byte, i int, wid int) {
	// Assemble decimal in reverse order.
	var b [20]byte
	bp := len(b) - 1
	for i >= 10 || wid > 1 {
		wid--
		q := i / 10
		b[bp] = byte('0' + i - q*10)
		bp--
		i = q
	}
	// i < 10
	b[bp] = byte('0' + i)
	*buf = append(*buf, b[bp:]...)
}

func (l *Logger) Print(v ...any) {
	if atomic.LoadInt32(&l.isDiscard) != 0 {
		return
	}
	l.Output(2, fmt.Sprint(v...))
}

func (l *Logger) Printf(format string, v ...any) {
	if atomic.LoadInt32(&l.isDiscard) != 0 {
		return
	}
	l.Output(2, fmt.Sprintf(format, v...))
}

func (l *Logger) Println(v ...any) {
	if atomic.LoadInt32(&l.isDiscard) != 0 {
		return
	}
	l.Output(2, fmt.Sprintln(v...))
}

func (l *Logger) Fatal(v ...any) {
	l.Output(2, fmt.Sprint(v...))
	os.Exit(1)
}

func (l *Logger) Fatalf(format string, v ...any) {
	l.Output(2, fmt.Sprintf(format, v...))
	os.Exit(1)
}

func (l *Logger) Fatalln(v ...any) {
	l.Output(2, fmt.Sprintln(v...))
	os.Exit(1)
}

func (l *Logger) Panic(v ...any) {
	s := fmt.Sprint(v...)
	l.Output(2, s)
	panic(s)
}

func (l *Logger) Panicf(format string, v ...any) {
	s := fmt.Sprintf(format, v...)
	l.Output(2, s)
	panic(s)
}

func (l *Logger) Panicln(v ...any) {
	s := fmt.Sprintln(v...)
	l.Output(2, s)
	panic(s)
}

func Caller(skip int) (pc uintptr, file string, line int, ok bool)

func (l *Logger) Flags() int {
	l.mu.Lock()
	defer l.mu.Unlock()
	return l.flag
}

func (l *Logger) SetFlags(flag int) {
	l.mu.Lock()
	defer l.mu.Unlock()
	l.flag = flag
}

func (l *Logger) Prefix() string {
	l.mu.Lock()
	defer l.mu.Unlock()
	return l.prefix
}

func (l *Logger) SetPrefix(prefix string) {
	l.mu.Lock()
	defer l.mu.Unlock()
	l.prefix = prefix
}

func (l *Logger) Writer() io.Writer {
	l.mu.Lock()
	defer l.mu.Unlock()
	return l.out
}

func (l *Logger) SetOutput(w io.Writer) {
	l.mu.Lock()
	defer l.mu.Unlock()
	l.out = w
	isDiscard := int32(0)
	if w == io.Discard {
		isDiscard = 1
	}
	atomic.StoreInt32(&l.isDiscard, isDiscard)
}

func Default() *Logger { return std }

func SetOutput(w io.Writer) {
	std.SetOutput(w)
}

func Flags() int {
	return std.Flags()
}

func SetFlags(flag int) {
	std.SetFlags(flag)
}

func Prefix() string {
	return std.Prefix()
}

func SetPrefix(prefix string) {
	std.SetPrefix(prefix)
}

func Writer() io.Writer {
	return std.Writer()
}

func Output(calldepth int, s string) error {
	return std.Output(calldepth+1, s) // +1 for this frame.
}

loggerDebug = log.New(os.Stdout, "[Debug]", log.LstdFlags)
loggerInfo = log.New(os.Stdout, "[Info]", log.LstdFlags)
loggerWarn = log.New(os.Stdout, "[Warn]", log.LstdFlags)
loggerError = log.New(os.Stdout, "[Error]", log.LstdFlags)