layout change UI (#776)

* add layout to schema

* add layout choice action and reducer

* multi layout UI

* update unit tests

* add missing file

* update test schema

* fix duplicate test id

* fix tabs

* PR lint

* fix pytest

client/src/reducers/layoutChoice.js

@@ -0,0 +1,50 @@
+/*
+we have a UI heuristic to pick the default layout, based on assumptions
+about commonly used names.  Preferentially, pick in the following order:
+
+  1. "umap"
+  2. "tsne"
+  3. "pca"
+  4. give up, use the first available
+*/
+function bestDefaultLayout(layouts) {
+  const preferredNames = ["umap", "tsne", "pca"];
+  const idx = preferredNames.findIndex(name => layouts.indexOf(name) !== -1);
+  if (idx !== -1) return preferredNames[idx];
+  return layouts[0];
+}
+
+const LayoutChoice = (
+  state = {
+    available: [], // all available choices
+    current: undefined, // name of the current layout, eg, 'umap'
+    currentDimNames: [] // dimension name
+  },
+  action,
+  nextSharedState
+) => {
+  switch (action.type) {
+    case "initial data load complete (universe exists)":
+    case "reset World to eq Universe": {
+      // set default to default
+      const { schema } = nextSharedState.world;
+      const available = schema.layout.obs.map(v => v.name);
+      const current = bestDefaultLayout(available);
+      const currentDimNames = schema.layout.obsByName[current].dims;
+      return { available, current, currentDimNames };
+    }
+
+    case "set layout choice": {
+      const { schema } = nextSharedState.world;
+      const current = action.layoutChoice;
+      const currentDimNames = schema.layout.obsByName[current].dims;
+      return { ...state, current, currentDimNames };
+    }
+
+    default: {
+      return state;
+    }
+  }
+};
+
+export default LayoutChoice;