feat(worker/pr): readable cron schedule

lib/workers/repository/update/pr/body/config-description.spec.ts

@@ -53,9 +53,21 @@
     it('renders UTC as the default timezone', () => {
       const res = getPrConfigDescription({
         ...config,
-        schedule: ['* 1 * * * *'],
+        schedule: ['* 1 * * *'],
+      });
+      expect(res).toContain(
+        'Between 01:00 AM and 01:59 AM ( * 1 * * * ) (UTC)',
+      );
+    });
+
+    it('summarizes cron schedules', () => {
+      const res = getPrConfigDescription({
+        ...config,
+        schedule: ['* 1 * * *', '* * 2 * 1'],
       });
-      expect(res).toContain(`"* 1 * * * *" (UTC)`);
+      expect(res).toContain(
+        'Between 01:00 AM and 01:59 AM ( * 1 * * * ), On day 2 of the month, and on Monday ( * * 2 * 1 ) (UTC)',
+      );
     });
 
     it('renders undefined schedule', () => {

lib/workers/repository/update/pr/body/config-description.ts

@@ -1,3 +1,6 @@
+import { CronPattern } from 'croner';
+import cronstrue from 'cronstrue';
+import { capitalize } from '../../../../../../tools/docs/utils';
 import { emojify } from '../../../../../util/emoji';
 import type { BranchConfig } from '../../../../types';
 
@@ -51,7 +54,8 @@
 ): string {
   let scheduleString = '';
   if (schedule && schedule[0] !== 'at any time') {
-    scheduleString += `"${String(schedule)}"`;
+    scheduleString =
+      getReadableCronSchedule(schedule) ?? `"${String(schedule)}"`;
     if (timezone) {
       scheduleString += ` in timezone ${timezone}`;
     } else {
@@ -62,3 +66,28 @@
   }
   return scheduleString;
 }
+
+/**
+ * Return human-readable cron schedule summary if the schedule is a valid cron
+ * else return null
+ */
+function getReadableCronSchedule(scheduleText: string[]): string | null {
+  // assuming if one schedule is cron the others in the array will be cron too
+  try {
+    new CronPattern(scheduleText[0]); // validate cron
+    return scheduleText
+      .map(
+        (cron) =>
+          capitalize(
+            cronstrue
+              .toString(cron, {
+                throwExceptionOnParseError: false,
+              })
+              .replace('Every minute, ', ''),
+          ) + ` (${cron})`,
+      )
+      .join(', ');
+  } catch {
+    return null;
+  }
+}