[tree] make fewer first-tree calls to the API

When a child doesn't have children, avoid API first-tree calls.

src/Gargantext/Components/Forest/Tree.purs

@@ -90,9 +90,13 @@ type NSCommon =
   , handed    :: Handed
   , session   :: Session  )
 
--- The annoying 'render' here is busting a cycle in the low tech
--- way. This function is only called by functions in this module, so
--- we just have to careful in what we pass.
+-- | The annoying 'render' here is busting a cycle in the low tech
+--   way. This function is only called by functions in this module, so
+--   we just have to careful in what we pass.
+--   Without the 'render' function though, we get a 'tree' cpt that
+--   depends on a 'renderTreeChildren' component, which itself depends
+--   on 'tree'. This results in PS 'CycleInDeclaration' compilation
+--   error.
 type ChildLoaderProps =
   ( id     :: ID
   , render :: R2.Leaf TreeProps
@@ -109,7 +113,6 @@ type PerformActionProps =
 -- | Loads and renders the tree starting at the given root node id.
 treeLoader :: R2.Leaf ( key :: String | LoaderProps )
 treeLoader = R2.leaf treeLoaderCpt
-
 treeLoaderCpt :: R.Component ( key :: String | LoaderProps )
 treeLoaderCpt = R2.hereComponent here "treeLoader" hCpt where
 -- treeLoaderCpt :: R.Memo LoaderProps
@@ -155,7 +158,6 @@ getNodeTreeFirstLevel session nodeId = get session $ GR.TreeFirstLevel (Just nod
 
 tree :: R2.Leaf TreeProps
 tree props = R.createElement treeCpt props []
-
 treeCpt :: R.Component TreeProps
 treeCpt = here.component "tree" cpt where
   cpt p@{ frontends
@@ -255,8 +257,42 @@ renderTreeChildrenCpt = here.component "renderTreeChildren" cpt where
 
     where
       nodeProps = RecordE.pick p :: Record NodeProps
-      renderChild (NTree (LNode {id: cId}) _) = childLoader props [] where
-        props = Record.merge nodeProps { id: cId, render, root }
+      -- | | If a child doesn't have children, avoid normal
+      -- |   'childLoader' which queries API for first-level data (there
+      -- |   is nothing new here) and render the child immediately.
+      renderChild tree'@(NTree (LNode {id: cId}) []) = childDummyLoader renderProps []
+        where
+          renderProps = Record.merge nodeProps { id: cId, render, root, tree: tree' } :: Record ChildDummyLoaderProps
+      renderChild (NTree (LNode {id: cId}) _children) = childLoader renderProps []
+        where
+          renderProps = Record.merge nodeProps { id: cId, render, root } :: Record ChildLoaderProps
+
+type ChildDummyLoaderProps =
+  ( tree   :: FTree
+  | ChildLoaderProps
+  )
+
+
+-- | A "dummy" loader: this is because for nodes without children, we
+-- | don't want to make the API call.
+childDummyLoader :: R2.Component ChildDummyLoaderProps
+childDummyLoader = R.createElement childDummyLoaderCpt
+childDummyLoaderCpt :: R.Component ChildDummyLoaderProps
+childDummyLoaderCpt = R2.hereComponent here "childDummyLoader" hCpt where
+  hCpt hp p@{ reloadTree
+            , render
+            , root
+            , tree: tree' } _ = do
+    { reloadRoot } <- Store.use
+    reload <- T.useBox T2.newReload
+
+    pure $ paint reload tree'
+
+    where
+      paint reload tree' = render (Record.merge base extra) where
+        base = nodeProps { reload = reload }
+        extra = { root, tree: tree' }
+        nodeProps = RecordE.pick p :: Record NodeProps
 
 
 childLoader :: R2.Component ChildLoaderProps