fix timezone for publish date mutation (#149)

src/datasources/product-api.ts

@@ -537,15 +537,18 @@ export class ProductAPI extends BaseSQLDataSource {
       promises.push(promise);
     }
 
-    const pd = info.publishingDate;
-    const publishingDate = new Date(
-      pd.getFullYear(),
-      pd.getMonth(),
-      pd.getDate(),
-      0,
-      0,
-      0,
-    );
+    const publishingDate = info.publishingDate;
+    // Some notes about timezone here:
+    // If client sets YYYY-MM-10T00:00:00.000+02 (which admin does) the timestamp
+    // here will be YYYY-MM-09T22:00:00.000Z since JS internal Dates are always in UTC and will be
+    // sent like the string above from client to graphql server.
+    // Some functions on the Date object however is local timezone dependent. setHours is one of them.
+    // So as long as we correctly set timezone for node to be Europe/Paris to match
+    // database server the publishDate above (in UTC) can be YYYY-MM-09T22:00:00.000Z and setHours will not (incorrectly)
+    // set it to YYYY-MM-09T00:00:00.000Z but but instead keep it as YYYY-MM-09T22:00:00.000Z since that is hour, minute
+    // second 0 of YYYY-MM-10 with the local timezone.
+    publishingDate.setHours(0, 0, 0);
+
     promises.push(
       this.knex
         .table('product-products')