package logger

import (
	"io"
	"log/slog"
	"os"
	"strings"
)

// Config holds the logger configuration
type Config struct {
	ServiceName   string
	Environment   string // APP_ENV 기준
	LevelOverride string
	Output        io.Writer
}

func IsProductionLikeEnv(appEnv string) bool {
	env := strings.ToLower(strings.TrimSpace(appEnv))
	return env == "prod" || env == "production" || env == "stage" || env == "staging"
}

// Init initializes the global logger with slog.
// It detects the environment to switch between TextHandler (dev) and JSONHandler (prod).
func Init(cfg Config) {
	var handler slog.Handler
	output := cfg.Output
	if output == nil {
		output = os.Stdout
	}

	opts := &slog.HandlerOptions{
		Level: ResolveBackendLogLevel(cfg.Environment, cfg.LevelOverride),
		// Customize attributes (Time format)
		ReplaceAttr: func(groups []string, a slog.Attr) slog.Attr {
			if a.Key == slog.TimeKey {
				return slog.String(a.Key, a.Value.Time().Format("2006-01-02 15:04:05"))
			}
			return a
		},
	}

	// Adjust level and format based on environment
	env := strings.ToLower(cfg.Environment)
	if env == "dev" || env == "local" || env == "development" {
		handler = slog.NewTextHandler(output, opts)
	} else {
		// Production defaults to JSON
		handler = slog.NewJSONHandler(output, opts)
	}

	// Create logger with common attributes
	logger := slog.New(handler).With(
		slog.String("svc", cfg.ServiceName),
	)

	// Set as global default logger
	slog.SetDefault(logger)
}

func ResolveBackendLogLevel(appEnv, override string) slog.Level {
	switch strings.ToLower(strings.TrimSpace(override)) {
	case "debug":
		return slog.LevelDebug
	case "info":
		return slog.LevelInfo
	case "warn", "warning":
		return slog.LevelWarn
	case "error":
		return slog.LevelError
	}

	env := strings.ToLower(strings.TrimSpace(appEnv))
	if env == "dev" || env == "local" || env == "development" {
		return slog.LevelDebug
	}
	return slog.LevelInfo
}