Introduce data explorer ui reducer

ui/spec/data_explorer/reducers/uiSpec.js

@@ -0,0 +1,40 @@
+import reducer from 'src/data_explorer/reducers/ui';
+
+import {
+  addQuery,
+  deleteQuery,
+} from 'src/data_explorer/actions/view';
+
+const noopAction = () => {
+  return {type: 'NOOP'};
+}
+
+let state = undefined;
+
+describe('DataExplorer.Reducers.UI', () => {
+  it('it sets the default state for UI', () => {
+    const actual = reducer(state, noopAction());
+    const expected = {
+      queryIDs: [],
+    };
+
+    expect(actual).to.deep.equal(expected);
+  });
+
+  it('it can add a query', () => {
+    const actual = reducer(state, addQuery());
+    expect(actual.queryIDs.length).to.equal(1);
+  });
+
+  it('it can delete a query', () => {
+    const queryID = '123';
+    state = {queryIDs: ['456', queryID]};
+
+    const actual = reducer(state, deleteQuery(queryID));
+    const expected = {
+      queryIDs: ['456'],
+    };
+
+    expect(actual).to.deep.equal(expected);
+  });
+});

ui/src/data_explorer/reducers/ui.js

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+const initialState = {
+  queryIDs: [],
+};
+
+export default function ui(state = initialState, action) {
+  switch (action.type) {
+    case 'ADD_QUERY': {
+      const {queryID} = action.payload;
+      const newState = {
+        queryIDs: state.queryIDs.concat(queryID),
+      };
+
+      return {...state, ...newState};
+    }
+
+    case 'DELETE_QUERY': {
+      const {queryID} = action.payload;
+      const newState = {
+        queryIDs: state.queryIDs.filter(id => id !== queryID),
+      };
+
+      return {...state, ...newState};
+    }
+  }
+
+  return state;
+}