Undo/redo (#659)

* immutable crossfilter

* first cut at reducer refactor with cascade model

* add initial redo/undo implementation

* small optimization

* integrate expression with history

* add tests for new reducers and fix a couple of small initialization bugs

* treat tiny lasso selections as a clear

* better function name for clarity

* fix undo for differential expression

* remove logging

* fix regression due to bad merge

* cleanup and comments for clarity

* improve undoable configuration for flexibility

* fix stale comments

* remove debugging code from production build

* rename categoricalSelectionState

* rename file

* improve comments

client/src/reducers/universe.js

@@ -0,0 +1,47 @@
+import _ from "lodash";
+
+import { ControlsHelpers } from "../util/stateManager";
+
+const Universe = (state = null, action, nextSharedState, prevSharedState) => {
+  switch (action.type) {
+    case "initial data load complete (universe exists)": {
+      const { universe } = action;
+      return universe;
+    }
+
+    case "expression load success": {
+      let { varData } = state;
+
+      // Load new expression data into the varData dataframes, if
+      // not already present.
+      _.forEach(action.expressionData, (val, key) => {
+        // If not already in universe.varData, save entire expression column
+        if (!varData.hasCol(key)) {
+          varData = varData.withCol(key, val);
+        }
+      });
+
+      // Prune size of varData "cache" if getting out of hand....
+      const { userDefinedGenes, diffexpGenes } = prevSharedState;
+      const allTheGenesWeNeed = _.uniq(
+        [].concat(
+          userDefinedGenes,
+          diffexpGenes,
+          Object.keys(action.expressionData)
+        )
+      );
+      varData = ControlsHelpers.pruneVarDataCache(varData, allTheGenesWeNeed);
+
+      return {
+        ...state,
+        varData
+      };
+    }
+
+    default: {
+      return state;
+    }
+  }
+};
+
+export default Universe;