[explore] Split large reducer logic in ExploreViewContainer (#3088)

* split reducer logic for ExploreViewContainer

* fix saveModal component and unit tests

* revert changes in SaveModal_spec.
will make another commit just to improve test coverage for SaveModal component.

* remove comment-out code

* fix merge confilicts

superset/assets/javascripts/explore/reducers/chartReducer.js

@@ -0,0 +1,72 @@
+/* eslint camelcase: 0 */
+import { now } from '../../modules/dates';
+import * as actions from '../actions/chartActions';
+import { QUERY_TIMEOUT_THRESHOLD } from '../../constants';
+
+export default function chartReducer(state = {}, action) {
+  const actionHandlers = {
+    [actions.CHART_UPDATE_SUCCEEDED]() {
+      return Object.assign(
+        {},
+        state,
+        {
+          chartStatus: 'success',
+          queryResponse: action.queryResponse,
+        },
+      );
+    },
+    [actions.CHART_UPDATE_STARTED]() {
+      return Object.assign({}, state,
+        {
+          chartStatus: 'loading',
+          chartUpdateEndTime: null,
+          chartUpdateStartTime: now(),
+          queryRequest: action.queryRequest,
+          latestQueryFormData: action.latestQueryFormData,
+        });
+    },
+    [actions.CHART_UPDATE_STOPPED]() {
+      return Object.assign({}, state,
+        {
+          chartStatus: 'stopped',
+          chartAlert: 'Updating chart was stopped',
+        });
+    },
+    [actions.CHART_RENDERING_FAILED]() {
+      return Object.assign({}, state, {
+        chartStatus: 'failed',
+        chartAlert: 'An error occurred while rendering the visualization: ' + action.error,
+      });
+    },
+    [actions.CHART_UPDATE_TIMEOUT]() {
+      return Object.assign({}, state, {
+        chartStatus: 'failed',
+        chartAlert: '<strong>Query timeout</strong> - visualization query are set to timeout at ' +
+        `${QUERY_TIMEOUT_THRESHOLD / 1000} seconds. ` +
+        'Perhaps your data has grown, your database is under unusual load, ' +
+        'or you are simply querying a data source that is to large to be processed within the timeout range. ' +
+        'If that is the case, we recommend that you summarize your data further.',
+      });
+    },
+    [actions.CHART_UPDATE_FAILED]() {
+      return Object.assign({}, state, {
+        chartStatus: 'failed',
+        chartAlert: action.queryResponse ? action.queryResponse.error : 'Network error.',
+        chartUpdateEndTime: now(),
+        queryResponse: action.queryResponse,
+      });
+    },
+    [actions.UPDATE_CHART_STATUS]() {
+      const newState = Object.assign({}, state, { chartStatus: action.status });
+      if (action.status === 'success' || action.status === 'failed') {
+        newState.chartUpdateEndTime = now();
+      }
+      return newState;
+    },
+  };
+
+  if (action.type in actionHandlers) {
+    return actionHandlers[action.type]();
+  }
+  return state;
+}