add proper logger, saves to file as well

AscNet.Logging/ThreadSafeStreamWriter.cs

@@ -0,0 +1,60 @@
+namespace AscNet.Logging
+{
+    public class ThreadSafeStreamWriter : IDisposable
+    {
+        private static ThreadSafeStreamWriter? _instance;
+
+        private static StreamWriter _writer;
+
+        private bool disposedValue;
+
+        // TODO: add support for configuring
+        private string _logFilePath = "log.log";
+
+        private object _lock = new object();
+
+        public ThreadSafeStreamWriter()
+        {
+            _writer = new StreamWriter(_logFilePath, true);
+#if !RELEASE
+            _writer.AutoFlush = true;
+#endif
+        }
+
+        public static ThreadSafeStreamWriter Instance
+        {
+            get
+            {
+                return _instance ??= new ThreadSafeStreamWriter();
+            }
+        }
+
+        public void AppendLine(string line)
+        {
+            lock (_lock)
+            {
+                _writer.WriteLine(line);
+            }
+        }
+
+        protected virtual void Dispose(bool disposing)
+        {
+            if (!disposedValue)
+            {
+                if (disposing)
+                {
+                    _writer.Flush();
+                    _writer.Close();
+                    _writer.Dispose();
+                }
+                disposedValue = true;
+            }
+        }
+
+        public void Dispose()
+        {
+            Dispose(disposing: true);
+            GC.SuppressFinalize(this);
+        }
+    }
+}