Add TouchSensor class with events

libs/core/analog.ts

@@ -1,4 +1,12 @@
 namespace input {
+
+    //% shim=pxt::unsafePollForChanges
+    function unsafePollForChanges(
+        periodMs: int32,
+        query: () => int32,
+        changeHandler: (prev: int32, curr: int32) => void
+    ) { }
+
     let analogMM: MMap
 
     /*
@@ -31,8 +39,48 @@ namespace input {
         if (!analogMM) control.fail("no analog sensor")
     }
 
-    export function readAnalogPin6(port: number) {
+    export class TouchSensor {
+        port: number;
+        id: number;
+        private downTime: number;
+
+        constructor(port: number) {
+            this.port = port;
+            this.id = 200 + port;
+            init()
+            unsafePollForChanges(50,
+                () => this.isPressed() ? 1 : 0,
+                (prev, curr) => {
+                    if (prev == curr) return
+                    if (curr) {
+                        this.downTime = control.millis()
+                        control.raiseEvent(this.id, ButtonEvent.Down)
+                    } else {
+                        control.raiseEvent(this.id, ButtonEvent.Up)
+                        let delta = control.millis() - this.downTime
+                        control.raiseEvent(this.id, delta > 500 ? ButtonEvent.LongClick : ButtonEvent.Click)
+                    }
+                })
+        }
+
+        isPressed() {
+            return readAnalogPin6(this.port) > 2500
+        }
+
+        /**
+         * Do something when a touch sensor is clicked, double clicked, etc...
+         * @param button the button that needs to be clicked or used
+         * @param event the kind of button gesture that needs to be detected
+         * @param body code to run when the event is raised
+         */
+        onEvent(ev:ButtonEvent, body: () => void) {
+            control.onEvent(this.id, ev, body)
+        }
+    }
+
+    function readAnalogPin6(port: number) {
         init()
+        port--
         port = Math.clamp(0, 3, port | 0)
         return analogMM.getNumber(NumberFormat.UInt16LE, 2 * (port + 4))
     }