package logging

import (
	"errors"
	"log/slog"
	"os"
	"path/filepath"

	"github.com/lmittmann/tint"
)

// ---------- Standard log handling (terminal or file based) ----------

// Logger state shared by the terminal and file loggers.
var (
	// logLevel is the minimum level logged, read by whichever handler is
	// installed, so changing it takes effect immediately.
	logLevel slog.LevelVar
	// fileLogger is the log file opened by LogToFile, or nil when logging
	// to the terminal.
	fileLogger *os.File
)

// SetLevel sets the logging level without logging the change.
func SetLevel(level slog.Level) {
	logLevel.Set(level)
}

// EnableDebug lowers the logging level to debug, if it isn't already, and
// logs that it did.
func EnableDebug() {
	if logLevel.Level() > slog.LevelDebug {
		logLevel.Set(slog.LevelDebug)
		slog.Debug("Debug logging enabled")
	}
}

// LogToFile sends all logging to logfile as JSON, replacing the default slog
// logger. The file is created if needed and appended to; any log file opened
// by an earlier call is closed.
func LogToFile(logfile string) error {
	closeErr := Shutdown()

	// Open the log file
	var err error
	fileLogger, err = os.OpenFile(
		filepath.Clean(logfile), os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0o600,
	)
	if err != nil {
		return errors.Join(err, closeErr)
	}

	opts := &slog.HandlerOptions{
		Level: &logLevel,
	}
	handler := slog.NewJSONHandler(fileLogger, opts)
	logger := slog.New(handler)
	slog.SetDefault(logger)

	return closeErr
}

// Shutdown closes the log file opened by LogToFile, if any.
func Shutdown() error {
	var err error = nil
	if fileLogger != nil {
		err = (*fileLogger).Close()
		fileLogger = nil
	}
	return err
}

// LogToTerminal sends all logging to stdout as coloured text, replacing the
// default slog logger.
func LogToTerminal() {
	opts := &tint.Options{
		Level:      &logLevel,
		TimeFormat: "*",
	}
	handler := tint.NewTextHandler(os.Stdout, opts)
	logger := slog.New(handler)
	slog.SetDefault(logger)
}

// IsJSONHandler reports whether h writes JSON, as the file logger does.
func IsJSONHandler(h slog.Handler) bool {
	_, ok := h.(*slog.JSONHandler)
	return ok
}

// IsFileLogger reports whether logging currently goes to a file.
func IsFileLogger() bool {
	return fileLogger != nil
}

// IsDebugEnabled reports whether debug messages are logged.
func IsDebugEnabled() bool {
	return logLevel.Level() <= slog.LevelDebug
}