add websocket endpoint /api/workout/:id/subscribe.

src/api/workout.js

@@ -174,5 +174,45 @@ module.exports = function workoutRouter(repo) {
     }
   });
 
+  router.ws("/:id/subscribe", (ws, req) => {
+    console.log("HELLO!")
+
+    const workout = workouts.find(w => w.id === req.params.id);
+    if (workout == null) {
+      ws.send(JSON.stringify({error: "workout not found"}));
+      ws.close();
+    }
+
+    workout.listMeasurements().then((list) => {
+      ws.send(JSON.stringify({workoutStatusBackfill: list}));
+    }).catch(err => {
+      ws.send(JSON.stringify({error: `could not list measurements: ${err.message || err}`}));
+      ws.close();
+    });
+
+    const handler = (workotuStatus) => {
+      workotuStatus = {...workotuStatus};
+      delete workotuStatus.id;
+    
+      ws.send(JSON.stringify({workotuStatus}))
+    }
+    
+    workout.events.on("workoutStatus", handler);
+
+    ws.onclose = () => {
+      workout.events.removeListener("workoutStatus", handler);
+      ws.removeAllListeners();
+    };
+
+    ws.send(JSON.stringify({
+      workout: {
+        id: workout.id,
+        bike: workout.bike,
+        program: workout.program,
+        date: workout.date,
+      },
+    }));
+  })
+
   return router;
 }