fix: use correct month numbers from 0 to 11

src/app.ts

@@ -1,6 +1,7 @@
 /* eslint-disable unicorn/no-process-exit */
 import { Range, RecurrenceRule, scheduleJob } from 'node-schedule';
 
+import { MAX_MONTH } from './constants';
 import {
   CHANNEL_ID,
   JOB_HOUR,
@@ -11,10 +12,20 @@ import {
 import { logger } from './logger';
 import { run } from './run';
 
+const formatMonth = (month: number) => {
+  const formatted = month - 1;
+  if (formatted < 0) return 0;
+  if (formatted > MAX_MONTH) return MAX_MONTH;
+  return formatted;
+};
+
 const rule = new RecurrenceRule();
 rule.hour = JOB_HOUR;
 rule.minute = 0;
-rule.month = new Range(JOB_MONTH_START, JOB_MONTH_END);
+rule.month = new Range(
+  formatMonth(JOB_MONTH_START),
+  formatMonth(JOB_MONTH_END),
+);
 rule.tz = TZ;
 
 const job = scheduleJob(rule, run);

src/constants.ts

@@ -3,6 +3,7 @@ export const FIRST_MESSAGE_DAYS = 4;
 export const FIRST_NOTIFICATION_DAYS = 2;
 export const JANUARY = 1;
 export const LAST_NOTIFICATION_DAYS = 1;
+export const MAX_MONTH = 11;
 export const SATURDAY = 6;
 export const SATURDAY_DIFF = 1;
 export const SUNDAY = 0;