Extract payday calculation logic to shared utility module

lib/utils/payday.ts

@@ -0,0 +1,52 @@
+import { HOURS_IN_DAY, MINUTES_IN_HOUR, SECONDS_IN_MINUTE, MS_IN_SEC } from './consts';
+
+/**
+ * Milliseconds in day. Needs for calculating difference between dates in days.
+ */
+const MILLISECONDS_IN_DAY = HOURS_IN_DAY * MINUTES_IN_HOUR * SECONDS_IN_MINUTE * MS_IN_SEC;
+
+/**
+ * Returns difference between now and payday in days
+ *
+ * Pay day is calculated by formula: paidUntil date or last charge date + 1 month
+ *
+ * @param date - last charge date
+ * @param paidUntil - paid until date
+ * @param isDebug - flag for debug purposes
+ */
+export function daysBeforePayday(date: Date, paidUntil: Date = null, isDebug = false): number {
+  const expectedPayDay = paidUntil ? new Date(paidUntil) : new Date(date);
+
+  if (isDebug) {
+    expectedPayDay.setDate(date.getDate() + 1);
+  } else if (!paidUntil) {
+    expectedPayDay.setMonth(date.getMonth() + 1);
+  }
+
+  const now = new Date().getTime();
+
+  return Math.floor((expectedPayDay.getTime() - now) / MILLISECONDS_IN_DAY);
+}
+
+/**
+ * Returns difference between payday and now in days
+ *
+ * Pay day is calculated by formula: paidUntil date or last charge date + 1 month
+ *
+ * @param date - last charge date
+ * @param paidUntil - paid until date
+ * @param isDebug - flag for debug purposes
+ */
+export function daysAfterPayday(date: Date, paidUntil: Date = null, isDebug = false): number {
+  const expectedPayDay = paidUntil ? new Date(paidUntil) : new Date(date);
+
+  if (isDebug) {
+    expectedPayDay.setDate(date.getDate() + 1);
+  } else if (!paidUntil) {
+    expectedPayDay.setMonth(date.getMonth() + 1);
+  }
+
+  const now = new Date().getTime();
+
+  return Math.floor((now - expectedPayDay.getTime()) / MILLISECONDS_IN_DAY);
+}