From 939395eea95eb44345e92959773c6289c55fdbfe Mon Sep 17 00:00:00 2001
From: Daniil Korostelev <daniil.korostelev@innogames.com>
Date: Fri, 21 Jun 2024 18:07:39 +0200
Subject: [PATCH] wip

---
 playground/Playground.cs                      | 62 +++++++++----
 .../Runtime/ExternalObservableSource.cs       | 11 +++
 .../Internal/ExternalObservableSource.cs      | 91 +++++++++++++++++++
 src/TinkState/Runtime/Observable.cs           |  7 +-
 4 files changed, 152 insertions(+), 19 deletions(-)
 create mode 100644 src/TinkState/Runtime/ExternalObservableSource.cs
 create mode 100644 src/TinkState/Runtime/Internal/ExternalObservableSource.cs

diff --git a/playground/Playground.cs b/playground/Playground.cs
index 497a760..ac9b441 100644
--- a/playground/Playground.cs
+++ b/playground/Playground.cs
@@ -1,35 +1,61 @@
 using System;
 using System.Diagnostics;
+using System.Threading;
 using System.Threading.Tasks;
+using System.Timers;
 using TinkState;
+using Timer = System.Timers.Timer;
 
 class Playground
 {
-	static async Task Main()
+	static void Main()
 	{
-		var stateA = Observable.State("hello");
-		var stateB = Observable.State("world");
+		var time = CreateTimeObservable();
+		var o = Observable.Auto(() => (time.Value, time.Value.ToShortTimeString()));
+		// var o = time;
 
-		var o = Observable.Auto(async () =>
+		Console.WriteLine(o.Value);
+		Thread.Sleep(2000);
+		Console.WriteLine(o.Value);
+		//
+		// var counter = 0;
+		// IDisposable binding = null;
+		// binding = o.Bind(v =>
+		// {
+		// 	Console.WriteLine($"Current time is: {v}");
+		// 	counter++;
+		// 	if (counter >= 5) binding.Dispose();
+		// });
+
+		Process.GetCurrentProcess().WaitForExit();
+	}
+
+	private static Observable<DateTime> CreateTimeObservable()
+	{
+		var time = Observable.External(() => DateTime.UtcNow);
+
+		var timer = new Timer(1000);
+
+		var timerElapsedHandler = new ElapsedEventHandler((_, _) =>
 		{
-			Console.WriteLine("computing");
-			var a = stateA.Value;
-			await Task.Delay(1000);
-			var b = stateB.Value;
-			return a + " " + b;
+			Console.WriteLine("tick");
+			time.Invalidate();
 		});
 
-		o.Bind(result => Console.WriteLine(result.Status switch
+		time.Subscribed += () =>
 		{
-			AsyncComputeStatus.Loading => "Loading...",
-			AsyncComputeStatus.Done => "Done: " + result.Result,
-			AsyncComputeStatus.Failed => "Failed: " + result.Exception,
-		}));
-
-		await Task.Delay(1500);
+			Console.WriteLine("wakeup");
+			timer.Elapsed += timerElapsedHandler;
+			timer.Start();
+		};
 
-		stateB.Value = "Dan";
+		time.Unsubscribed += () =>
+		{
+			Console.WriteLine("sleep");
+			timer.Elapsed -= timerElapsedHandler;
+			timer.Stop();
+		};
 
-		Process.GetCurrentProcess().WaitForExit();
+		return time;
 	}
 }
diff --git a/src/TinkState/Runtime/ExternalObservableSource.cs b/src/TinkState/Runtime/ExternalObservableSource.cs
new file mode 100644
index 0000000..d7cce3c
--- /dev/null
+++ b/src/TinkState/Runtime/ExternalObservableSource.cs
@@ -0,0 +1,11 @@
+using System;
+
+namespace TinkState
+{
+	public interface ExternalObservableSource<out T> : Observable<T>
+	{
+		event Action Subscribed;
+		event Action Unsubscribed;
+		void Invalidate();
+	}
+}
diff --git a/src/TinkState/Runtime/Internal/ExternalObservableSource.cs b/src/TinkState/Runtime/Internal/ExternalObservableSource.cs
new file mode 100644
index 0000000..61f0511
--- /dev/null
+++ b/src/TinkState/Runtime/Internal/ExternalObservableSource.cs
@@ -0,0 +1,91 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+
+namespace TinkState.Internal
+{
+	class ExternalObservableSource<T> : Dispatcher, TinkState.ExternalObservableSource<T>, DispatchingObservable<T>
+	{
+		public event Action Subscribed;
+		public event Action Unsubscribed;
+
+		readonly Func<T> getter;
+		readonly IEqualityComparer<T> comparer;
+
+		bool isSubscribedTo;
+		bool valid;
+		T last;
+
+		public ExternalObservableSource(Func<T> getter, IEqualityComparer<T> comparer)
+		{
+			this.getter = getter;
+			this.comparer = comparer ?? EqualityComparer<T>.Default;
+		}
+
+		public IDisposable Bind(Action<T> callback, IEqualityComparer<T> comparer = null, Scheduler scheduler = null)
+		{
+			return new Binding<T>(this, callback, comparer, scheduler);
+		}
+
+		public Observable<TOut> Map<TOut>(Func<T, TOut> transform, IEqualityComparer<TOut> comparer = null)
+		{
+			return new TransformObservable<T, TOut>(this, transform, comparer);
+		}
+
+		public IEqualityComparer<T> GetComparer()
+		{
+			return comparer;
+		}
+
+		[DebuggerBrowsable(DebuggerBrowsableState.Never)]
+		public T Value => AutoObservable.Track(this);
+
+		public void Invalidate()
+		{
+			if (valid)
+			{
+				valid = false;
+				Fire();
+			}
+		}
+
+		public T GetCurrentValue()
+		{
+			if (!valid || !isSubscribedTo)
+			{
+				Calculate();
+			}
+			return last;
+		}
+
+		public long GetRevision()
+		{
+			// TODO: auto-observables rely on this so what should we do?
+			return revision;
+		}
+
+		void Calculate()
+		{
+			last = getter();
+			valid = true;
+		}
+
+		protected override void OnStatusChange(bool active)
+		{
+			if (active) WakeUp(); else Sleep();
+		}
+
+		void WakeUp()
+		{
+			isSubscribedTo = true;
+			Calculate();
+			Subscribed?.Invoke();
+		}
+
+		void Sleep()
+		{
+			isSubscribedTo = false;
+			Unsubscribed?.Invoke();
+		}
+	}
+}
diff --git a/src/TinkState/Runtime/Observable.cs b/src/TinkState/Runtime/Observable.cs
index 36fb641..b4c46b0 100644
--- a/src/TinkState/Runtime/Observable.cs
+++ b/src/TinkState/Runtime/Observable.cs
@@ -179,6 +179,11 @@ public static State<T> State<T>(T initialValue, IEqualityComparer<T> comparer =
 			return new Internal.State<T>(initialValue, comparer);
 		}
 
+		public static ExternalObservableSource<T> External<T>(Func<T> getter, IEqualityComparer<T> comparer = null)
+		{
+			return new Internal.ExternalObservableSource<T>(getter, comparer);
+		}
+
 		/// <summary>
 		/// Create an empty observable list.
 		/// </summary>
@@ -220,4 +225,4 @@ public static ObservableDictionary<TKey, TValue> Dictionary<TKey, TValue>()
 		/// </remarks>
 		public static Scheduler Scheduler = Scheduler.Direct;
 	}
-}
\ No newline at end of file
+}