fix: Calendar Heatmap day offset (#24989)

superset-frontend/plugins/legacy-plugin-chart-calendar/src/vendor/cal-heatmap.js

@@ -296,8 +296,21 @@ var CalHeatMap = function () {
     // Used mainly to convert the datas if they're not formatted like expected
     // Takes the fetched "data" object as argument, must return a json object
     // formatted like {timestamp:count, timestamp2:count2},
-    afterLoadData: function (data) {
-      return data;
+    afterLoadData: function (timestamps) {
+      // See https://github.com/wa0x6e/cal-heatmap/issues/126#issuecomment-373301803
+      const stdTimezoneOffset = date => {
+        const jan = new Date(date.getFullYear(), 0, 1);
+        const jul = new Date(date.getFullYear(), 6, 1);
+        return Math.max(jan.getTimezoneOffset(), jul.getTimezoneOffset());
+      };
+      const offset = stdTimezoneOffset(new Date()) * 60;
+      let results = {};
+      for (let timestamp in timestamps) {
+        const value = timestamps[timestamp];
+        timestamp = parseInt(timestamp, 10);
+        results[timestamp + offset] = value;
+      }
+      return results;
     },
 
     // Callback triggered after calling and completing update().