improve auto-scroll for doc panel

marlowe-playground-client/src/Simulation.purs

@@ -14,6 +14,7 @@ import Data.BigInteger (BigInteger, fromString, fromInt)
 import Data.Either (Either(..), note)
 import Data.Enum (toEnum, upFromIncluding)
 import Data.HeytingAlgebra (not, (&&))
+import Data.Int (toNumber)
 import Data.Lens (_Just, assign, modifying, over, preview, to, use, view, (^.))
 import Data.Lens.Index (ix)
 import Data.Lens.NonEmptyList (_Head)
@@ -65,7 +66,7 @@ import Monaco (IMarker, isError, isWarning)
 import Monaco (getModel, getMonaco, setTheme, setValue) as Monaco
 import Network.RemoteData (RemoteData(..), _Success)
 import Network.RemoteData as RemoteData
-import Prelude (class Show, Unit, add, bind, bottom, const, discard, eq, flip, identity, mempty, one, pure, show, unit, zero, ($), (/=), (<$>), (<<<), (<>), (=<<), (==), (>))
+import Prelude (class Show, Unit, add, bind, bottom, const, discard, eq, flip, identity, mempty, one, pure, show, unit, zero, ($), (/=), (<$>), (<<<), (<>), (=<<), (==), (>), (-), (<))
 import Servant.PureScript.Ajax (AjaxError, errorToString)
 import Servant.PureScript.Settings (SPSettings_)
 import Simulation.BottomPanel (bottomPanel)
@@ -82,6 +83,7 @@ import Web.DOM.HTMLCollection as WC
 import Web.HTML as Web
 import Web.HTML.HTMLDocument (toDocument)
 import Web.HTML.Window as W
+import Web.HTML.Window as Window
 import WebSocket (WebSocketRequestMessage(..))
 
 mkComponent :: forall m. MonadEffect m => MonadAff m => SPSettings_ SPParams_ -> H.Component HTML Query Unit Message m
@@ -371,11 +373,15 @@ scrollHelpPanel =
     window <- Web.window
     document <- toDocument <$> W.document window
     mSidePanel <- WC.item 0 =<< D.getElementsByClassName "sidebar-composer" document
-    case mSidePanel of
-      Nothing -> pure unit
-      Just sidePanel -> do
-        scrollHeight <- E.scrollHeight sidePanel
-        setScrollTop scrollHeight sidePanel
+    mDocPanel <- WC.item 0 =<< D.getElementsByClassName "documentation-panel" document
+    case mSidePanel, mDocPanel of
+      Just sidePanel, Just docPanel -> do
+        sidePanelHeight <- E.scrollHeight sidePanel
+        docPanelHeight <- E.scrollHeight docPanel
+        let
+          availableHeight = sidePanelHeight - docPanelHeight - 100.0
+        setScrollTop availableHeight sidePanel
+      _, _ -> pure unit
 
 editorSetValue :: forall m. String -> HalogenM State Action ChildSlots Message m Unit
 editorSetValue contents = void $ query _editorSlot unit (Monaco.SetText contents unit)