From 76b9d95ddf60af56b6b083d8747e316c354c8509 Mon Sep 17 00:00:00 2001
From: "Frank A. Krueger" <fak@praeclarum.org>
Date: Wed, 14 Jun 2017 23:10:58 -0700
Subject: [PATCH] Add Events

---
 Ooui/Button.cs       |  5 ++++
 Ooui/EventTarget.cs  | 56 ++++++++++++++++++++++++++++++++++++++++++--
 Ooui/Message.cs      | 16 +++++++++++++
 Tests/ButtonTests.cs | 19 +++++++++++++++
 4 files changed, 94 insertions(+), 2 deletions(-)

diff --git a/Ooui/Button.cs b/Ooui/Button.cs
index 45c9279..8027c6b 100644
--- a/Ooui/Button.cs
+++ b/Ooui/Button.cs
@@ -16,6 +16,11 @@ namespace Ooui
             set => SetProperty (ref val, value, "value");
         }
 
+        public event EventHandler Clicked {
+            add => AddEventListener ("onclick", value);
+            remove => RemoveEventListener ("onclick", value);
+        }
+
         public Button ()
         {
         }
diff --git a/Ooui/EventTarget.cs b/Ooui/EventTarget.cs
index 465da3f..9dc5bd9 100644
--- a/Ooui/EventTarget.cs
+++ b/Ooui/EventTarget.cs
@@ -6,12 +6,15 @@ namespace Ooui
 {
     public abstract class EventTarget
     {
+        readonly List<Message> stateMessages = new List<Message> ();
+
+        readonly Dictionary<string, List<EventHandler>> eventListeners =
+            new Dictionary<string, List<EventHandler>> ();
+
         public string Id { get; private set; } = GenerateId ();
 
         public Mapping Mapping { get; private set; }
 
-        readonly List<Message> stateMessages = new List<Message> ();
-
         public event Action<Message> MessageSent;
 
         public IEnumerable<Message> StateMessages => stateMessages;
@@ -21,6 +24,36 @@ namespace Ooui
             Mapping = Mapping.Get (GetType ());
         }
 
+        public void AddEventListener (string eventType, EventHandler handler)
+        {
+            if (eventType == null) return;
+            if (handler == null) return;
+
+            var sendListen = false;
+
+            List<EventHandler> handlers;
+            if (!eventListeners.TryGetValue (eventType, out handlers)) {
+                handlers = new List<EventHandler> ();
+                eventListeners[eventType] = handlers;
+                sendListen = true;
+            }
+            handlers.Add (handler);
+
+            if (sendListen)
+                SendListen (eventType);
+        }
+
+        public void RemoveEventListener (string eventType, EventHandler handler)
+        {
+            if (eventType == null) return;
+            if (handler == null) return;
+
+            List<EventHandler> handlers;
+            if (eventListeners.TryGetValue (eventType, out handlers)) {
+                handlers.Remove (handler);
+            }
+        }
+
         protected bool SetProperty<T> (ref T backingStore, T newValue, string attributeName, [System.Runtime.CompilerServices.CallerMemberName] string propertyName = "")
         {
             if (!backingStore.Equals (newValue)) {
@@ -73,6 +106,15 @@ namespace Ooui
             });
         }
 
+        protected void SendListen (string eventType)
+        {
+            Send (new Message {
+                MessageType = MessageType.Listen,
+                TargetId = Id,
+                Key = eventType,
+            });
+        }
+
         public virtual void Receive (Message message)
         {
             if (message == null)
@@ -110,11 +152,21 @@ namespace Ooui
                         ReplaceStateMessage (old, message);
                     }
                     break;
+                case MessageType.Listen:
+                    SaveStateMessage (message);
+                    break;
             }
         }
 
         protected virtual void TriggerEventFromMessage (Message message)
         {
+            List<EventHandler> handlers;
+            if (eventListeners.TryGetValue (message.Key, out handlers)) {
+                var args = EventArgs.Empty;
+                foreach (var h in handlers) {
+                    h.Invoke (this, args);
+                }
+            }
         }
     }
 }
diff --git a/Ooui/Message.cs b/Ooui/Message.cs
index 1d52e07..8546c81 100644
--- a/Ooui/Message.cs
+++ b/Ooui/Message.cs
@@ -26,6 +26,18 @@ namespace Ooui
             set => v = FixupValue (value);
         }
 
+        public static Message Listen (string targetId, string eventType) => new Message {
+            MessageType = MessageType.Listen,
+            TargetId = targetId,
+            Key = eventType,
+        };
+
+        public static Message Event (string targetId, string eventType) => new Message {
+            MessageType = MessageType.Event,
+            TargetId = targetId,
+            Key = eventType,
+        };
+
         static object FixupValue (object v)
         {
             if (v is Array a) {
@@ -60,5 +72,9 @@ namespace Ooui
         Set,
         [EnumMember(Value = "call")]
         Call,
+        [EnumMember(Value = "listen")]
+        Listen,
+        [EnumMember(Value = "event")]
+        Event,
     }
 }
diff --git a/Tests/ButtonTests.cs b/Tests/ButtonTests.cs
index 778d011..00cf2cf 100644
--- a/Tests/ButtonTests.cs
+++ b/Tests/ButtonTests.cs
@@ -21,5 +21,24 @@ namespace Tests
             var b = new Button ("Hello World!");
             Assert.AreEqual ("Hello World!", b.Text);
         }
+
+        [TestMethod]
+        public void Clicked ()
+        {
+            var b = new Button ("Hello World!");
+            var clicked = false;
+            var listened = false;
+            b.MessageSent += m => {
+                listened = listened || (m.MessageType == MessageType.Listen);
+            };
+            Assert.IsFalse (listened);
+            b.Clicked += (s, e) => {
+                clicked = true;
+            };
+            Assert.IsTrue (listened);
+            Assert.IsFalse (clicked);
+            b.Receive (Message.Event (b.Id, "onclick"));
+            Assert.IsTrue (clicked);
+        }
     }
 }