Update filters to hide ancestral nodes before last common ancestor

Before this commit, filters determined visibility by:
1. Finding all terminal nodes in view window that match the filters and
mark them as visible.
2. Recursively marking all parent nodes of these terminal nodes visible,
all the way up to the root of the tree.

This commit adds an additional step to hide ancestral nodes before
the last common ancestor of visible terminal nodes. Starting from
the root of the tree, recursively hide each node if it does not have
more than one child node that is visible.

src/util/treeVisibilityHelpers.js

@@ -93,6 +93,21 @@ const makeParentVisible = (visArray, node) => {
   makeParentVisible(visArray, node.parent);
 };
 
+/* Recursively hide nodes that do not have more than one child node in
+ * the param visArray.
+ * Relies on visArray having been updated by `makeParentVisible` */
+const hideNodeIfOnlyOneChildVisible = (visArray, node) => {
+  if (!node.hasChildren) {
+    return; // Terminal node without children
+  }
+  const visibleChildren = node.children.filter((child) => visArray[child.arrayIdx])
+  if (visibleChildren.length > 1) {
+    return; // This is the common ancestor of visible children
+  }
+  visArray[node.arrayIdx] = false;
+  visibleChildren.forEach((child) => hideNodeIfOnlyOneChildVisible(visArray, child))
+}
+
 /* calcVisibility
 USES:
 inView: attribute of phyloTree.nodes, but accessible through redux.tree.nodes[idx].shell.inView
@@ -154,6 +169,9 @@ export const calcVisibility = (tree, controls, dates) => {
       for (let i = 0; i < idxsOfFilteredTips.length; i++) {
         makeParentVisible(filtered, tree.nodes[idxsOfFilteredTips[i]]);
       }
+      /* Recursivley hide ancestor nodes that are not the last common
+       * ancestor of selected nodes, starting from the root of the tree */
+      hideNodeIfOnlyOneChildVisible(filtered, tree.nodes[0]);
     }
     /* intersect the various arrays contributing to visibility */
     const visibility = tree.nodes.map((node, idx) => {