Change how months are subtracted in SearchManager

src/backend/model/database/SearchManager.ts

@@ -779,7 +779,7 @@ export class SearchManager {
                 break;
 
               case DatePatternFrequency.months_ago:
-                to.setUTCMonth(to.getUTCMonth() - tq.agoNumber);
+                to.setTime(Utils.addMonthToDate(to, -1 * tq.agoNumber).getTime());
                 break;
 
               case DatePatternFrequency.years_ago:

src/common/Utils.ts

@@ -220,6 +220,19 @@ export class Utils {
     return dayOfYear;
   }
 
+  //Adding months to a date differently from standard JS
+  //this function makes sure that if date is the 31st and you add a month, you will get the last day of the next month
+  //so adding or subtracting a month from 31st of march will give 30th of april or 28th of february respectively (29th on leap years).
+  static addMonthToDate(date: Date, numMonths: number) {
+    let result = new Date(date)
+    const expectedMonth = ((date.getMonth() + numMonths) % 12 + 12) % 12; //inner %12 + 12 makes correct handling of negative months
+    result.setMonth(result.getMonth() + numMonths);
+    if (result.getMonth() !== expectedMonth) {
+      result.setDate(0);
+    }
+    return result;
+  }
+
   static renderDataSize(size: number): string {
     const postFixes = ['B', 'KB', 'MB', 'GB', 'TB'];
     let index = 0;