ui: Refactor Timer into it's own module.

ui/src/Timer.elm

@@ -0,0 +1,51 @@
+module Timer exposing (Timer, cancel, empty, replace)
+
+{-| Implements an identity to track an asynchronous timer.
+-}
+
+
+type Timer
+    = Empty
+    | Idle Int
+    | Timer Int
+
+
+empty : Timer
+empty =
+    Empty
+
+
+{-| Replaces the provided timer with a newly created one.
+-}
+replace : Timer -> Timer
+replace previous =
+    case previous of
+        Empty ->
+            Timer 0
+
+        Idle index ->
+            Timer (next index)
+
+        Timer index ->
+            Timer (next index)
+
+
+{-| Cancels the provided timer without creating a replacement.
+-}
+cancel : Timer -> Timer
+cancel previous =
+    case previous of
+        Timer index ->
+            Idle index
+
+        _ ->
+            previous
+
+
+next : Int -> Int
+next index =
+    if index > 2 ^ 30 then
+        0
+
+    else
+        index + 1