refactor: migrate logger

backend/logger/logger.go

@@ -0,0 +1,42 @@
+package logger
+
+import (
+	"log/slog"
+	"os"
+)
+
+// LoggerLevel expresses the desired logging verbosity. Unlike a full log-level
+// enum, it only distinguishes between a verbose development mode and a quieter
+// production mode; it is converted to an slog.Level by New.
+type LoggerLevel int
+
+const (
+	// Development enables debug-level output, suitable for local development.
+	Development LoggerLevel = iota
+	// Production limits output to info level and above.
+	Production
+)
+
+// toSlogLevel converts a LoggerLevel into the corresponding slog.Level,
+// defaulting to info for any unrecognized value.
+func toSlogLevel(level LoggerLevel) slog.Level {
+	switch level {
+	case Development:
+		return slog.LevelDebug
+	case Production:
+		return slog.LevelInfo
+	default:
+		return slog.LevelInfo
+	}
+}
+
+// New creates a *slog.Logger that writes to os.Stderr via slog's default
+// TextHandler, with its verbosity driven by the given LoggerLevel. This
+// replaces the legacy module-level singleton LOGGER; callers own the returned
+// logger and thread it through to sub-modules.
+func New(level LoggerLevel) *slog.Logger {
+	handler := slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{
+		Level: toSlogLevel(level),
+	})
+	return slog.New(handler)
+}