Add status to portfolios

 - Also improve reflex code

 - Also document

use-case-2/frontend/src/Frontend/Portfolio.hs

@@ -57,29 +57,56 @@ portfolioDashboard wid = do
       -- recurring event used to poll for wallet balance
       pollingEvent <- tickLossyFromPostBuildTime 10
       requesting_ $ (Api_CallFunds (ContractInstanceId wid)) <$ (leftmost [pb, () <$ pollingEvent])
-      fmap (switch . current) $ prerender (return never) $ do
+      -- prerender separates the code which can be run on the backend (to
+      -- prerender), from the code that is run on the frontend. We don't use the
+      -- browser way of listening to the websocket on the backend (though in
+      -- principle we could listen to the websocket a different way), and so we
+      -- return a "never firing" event on the backend to both branches return
+      -- the same type.
+      --
+      -- the prerender will splice together the server-rendered and
+      -- client-animated versions, wrapping the result value in a "dynamic", so
+      -- we have "dynamic of an event of a maybe", hence the DEM in the name of
+      -- the variable.
+      respDEM <- prerender (return never) $ do
         -- incorporate the use of PAB's websockets to display the wallet's current Ada Balance
         ws <- jsonWebSocket ("ws://localhost:8080/ws/" <> wid) (def :: WebSocketConfig t Aeson.Value)
         -- filter for websocket events relevent to funds that contain the "Funds" tag and "NewObservableState" tag
-        let fundsEvent = wsFilterFunds $ _webSocket_recv ws
-        widgetHold_ blank $ ffor fundsEvent $ \(mIncomingFundsWebSocketData :: Maybe Aeson.Value) -> case mIncomingFundsWebSocketData of
-          Nothing -> return ()
+        pure $ wsFilterFunds $ _webSocket_recv ws
+      -- Squash together the dynamic and event into a single dynamic, but with
+      -- an extra maybe. The outer maybe is 'Nothing' when we have yet to hear a
+      -- response, and 'Just' once we have a result. That means once the dynamic
+      -- becomes an outer 'Just', it should never go back to being an outer
+      -- 'Nothing'.
+      respDMM <- holdDyn Nothing $ fmap Just $ switch $ current respDEM
+      -- "factor" the dynamic of maybe so that the innerside has it's own
+      -- dynamic, and when we change from one "Just ..." to another "Just ...",
+      -- only the inner dynamic changes. This doesn't make much of difference
+      -- here, but is good practice in general to minimize DOM changes. (You can compare React's virtual DOM, but we are deduping on the *input* rather than *output* side, which is more efficient.)
+      respDMDM <- maybeDyn respDMM
+      dyn_ $ ffor respDMDM $ \case
+        Nothing -> text "Waiting for response from PAB..."
+        Just respDM -> dyn_ $ ffor respDM $ \case
+          Nothing -> text "error: missing key in JSON from PAB."
           Just fundsWebSocketData -> do
             let currencyDetails = fundsWebSocketData ^. key "contents" . key "Right" . key "contents" . key "getValue" . _Array
-            elClass "table" "table" $ do
-              elClass "thead" "thead-primary" $ el "tr" $ do
-                elAttr "th" ("scope" =: "col") $ text "Token Name"
-                elAttr "th" ("scope" =: "col") $ text "Balance"
-              let formattedTokenDetails = Map.filter
-                    -- Note: If token names change, this hash will need to change. Otherwise, the token balances will not be found.
-                    (\(_,cs) -> cs == "4195b7e88acc9a061b21f962266770d2e676f76f2a686f6fa15ac155f383c9ad") $
-                    parseTokensToMap currencyDetails
-              el"tbody" $ do
-                forM_ (Map.toList formattedTokenDetails) $ \(tokenName, (tokenBalance,_)) -> do
-                  el "tr" $ do
-                    el "td" $ text $ T.pack $ show tokenName
-                    el "td" $ text $ T.pack $ show tokenBalance
-              return ()
-            return ()
-        return never
+            let formattedTokenDetails = Map.filter
+                  -- Note: If token names change, this hash will need to change. Otherwise, the token balances will not be found.
+                  (\(_,cs) -> cs == "4195b7e88acc9a061b21f962266770d2e676f76f2a686f6fa15ac155f383c9ad") $
+                  parseTokensToMap currencyDetails
+            if Map.null formattedTokenDetails
+              then
+                text "PAB reports empty portfolio, this probably means it is still loading, rather than there actually being an empty portfolio."
+              else do
+                elClass "table" "table" $ do
+                  elClass "thead" "thead-primary" $ el "tr" $ do
+                    elAttr "th" ("scope" =: "col") $ text "Token Name"
+                    elAttr "th" ("scope" =: "col") $ text "Balance"
+                  el "tbody" $ do
+                    forM_ (Map.toList formattedTokenDetails) $ \(tokenName, (tokenBalance,_)) -> do
+                      el "tr" $ do
+                        el "td" $ text $ T.pack $ show tokenName
+                        el "td" $ text $ T.pack $ show tokenBalance
+                  return ()
+                return ()
   return ()