package logger

import (
	"encoding/json"
	"fmt"
	"io"
	"os"
	"sync"
	"sync/atomic"
	"time"
)

// Level represents log level.
type Level int

const (
	LevelDebug Level = iota
	LevelInfo
	LevelWarn
	LevelError
)

func (l Level) String() string {
	switch l {
	case LevelDebug:
		return "DEBUG"
	case LevelInfo:
		return "INFO"
	case LevelWarn:
		return "WARN"
	case LevelError:
		return "ERROR"
	default:
		return "INFO"
	}
}

// Logger is a simple JSON logger compatible with Go 1.20.
type Logger struct {
	level  Level
	writer io.Writer
	mu     sync.Mutex
}

// Default is the global default logger.
var Default atomic.Value

func init() {
	Default.Store(&Logger{level: LevelInfo, writer: os.Stderr})
}

func getDefault() *Logger {
	if l, ok := Default.Load().(*Logger); ok && l != nil {
		return l
	}
	return &Logger{level: LevelInfo, writer: os.Stderr}
}

// Init initializes the logger with the specified log level.
func Init(level string) {
	InitWithWriter(level, os.Stdout)
}

// InitWithWriter initializes the logger with the specified log level and writer.
func InitWithWriter(level string, writer io.Writer) {
	var lvl Level
	switch level {
	case "debug":
		lvl = LevelDebug
	case "info":
		lvl = LevelInfo
	case "warn":
		lvl = LevelWarn
	case "error":
		lvl = LevelError
	default:
		lvl = LevelInfo
	}
	if writer == nil {
		writer = os.Stdout
	}
	Default.Store(&Logger{level: lvl, writer: writer})
}

func (l *Logger) log(level Level, msg string, args ...any) {
	if level < l.level {
		return
	}
	record := map[string]any{
		"time":  time.Now().Format(time.RFC3339Nano),
		"level": level.String(),
		"msg":   msg,
	}
	for i := 0; i < len(args)-1; i += 2 {
		key, ok := args[i].(string)
		if !ok {
			continue
		}
		record[key] = args[i+1]
	}
	l.mu.Lock()
	defer l.mu.Unlock()
	data, _ := json.Marshal(record)
	fmt.Fprintln(l.writer, string(data))
}

// Debug logs a message at Debug level.
func Debug(msg string, args ...any) {
	getDefault().log(LevelDebug, msg, args...)
}

// Info logs a message at Info level.
func Info(msg string, args ...any) {
	getDefault().log(LevelInfo, msg, args...)
}

// Warn logs a message at Warn level.
func Warn(msg string, args ...any) {
	getDefault().log(LevelWarn, msg, args...)
}

// Error logs a message at Error level.
func Error(msg string, args ...any) {
	getDefault().log(LevelError, msg, args...)
}

// Fatal logs a message at Error level and exits.
func Fatal(msg string, args ...any) {
	getDefault().log(LevelError, msg, args...)
	os.Exit(1)
}