--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Implab/Diagnostics/TextListenerBase.cs	Tue Apr 15 17:52:09 2014 +0400
@@ -0,0 +1,99 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace Implab.Diagnostics {
+    public abstract class TextListenerBase : ServiceLocator, IEventTextFormatter<object>, IEventTextFormatter<TraceEvent> {
+
+        readonly Dictionary<object, Action> m_subscriptions = new Dictionary<object, Action>();
+
+        protected TextListenerBase() {
+            Register(this);
+        }
+
+        public void Subscribe(Type eventType) {
+            if (eventType == null)
+                throw new ArgumentNullException("eventType");
+            GetType().GetMethod("Subscribe", new Type[0]).MakeGenericMethod(eventType).Invoke(this, null);
+        }
+
+        public void Subscribe<TEvent>() {
+            Subscribe<TEvent>(LogChannel<TEvent>.Default);
+        }
+
+        public void Subscribe<TEvent>(LogChannel<TEvent> channel) {
+            if (channel == null)
+                throw new ArgumentNullException("channel");
+
+            lock (m_subscriptions) {
+                AssertNotDisposed();
+
+                var formatter = GetService<IEventTextFormatter<TEvent>>();
+
+                EventHandler<ValueEventArgs<TEvent>> handler = (sender, args) => {
+                    WriteEntry((TraceContext)sender, formatter.Format((TraceContext)sender, args.Value));
+                };
+
+                if (m_subscriptions.ContainsKey(channel))
+                    return;
+
+                channel.Events += handler;
+
+                Action unsubscribe = () => {
+                    channel.Events -= handler;
+                };
+
+                m_subscriptions.Add(channel, unsubscribe);
+            }
+        }
+
+        public void Unsubscribe<TEvent>(LogChannel<TEvent> channel) {
+            if (channel == null)
+                throw new ArgumentNullException("channel");
+
+            lock (m_subscriptions) {
+                Action subscription;
+                if (m_subscriptions.TryGetValue(channel, out subscription)) {
+                    subscription();
+                    m_subscriptions.Remove(channel);
+                }
+            }
+        }
+
+        public void UnsubscribeAll() {
+            lock (m_subscriptions) {
+                foreach (var subscription in m_subscriptions.Values)
+                    subscription();
+                m_subscriptions.Clear();
+            }
+        }
+
+        protected abstract void WriteEntry(TraceContext context, EventText text);
+        
+        public EventText Format(TraceContext context, object data) {
+            return new EventText {
+                indent = context.CurrentOperation.Level,
+                content = data.ToString()
+            };
+        }
+
+        public EventText Format(TraceContext context, TraceEvent data) {
+            var level = context.CurrentOperation.Level;
+            if (data.EventType == TraceEventType.OperationCompleted || data.EventType == TraceEventType.OperationStarted)
+                level--;
+
+            return new EventText {
+                indent = level,
+                content = data.ToString()
+            };
+        }
+
+        protected override void Dispose(bool disposing) {
+            if (disposing) {
+                UnsubscribeAll();
+            }
+            base.Dispose(disposing);
+        }
+    }
+}