Inactive algorithm

shared/algorithms/inactive.ts

@@ -0,0 +1,31 @@
+interface Config {
+  monthsThreshold: number;
+}
+
+const config: Config = {
+  monthsThreshold: 36,
+};
+
+const calculateMonthsBetween = (fyeDate: number, currentDate: Date): number => {
+  const fyeYear = Math.floor(fyeDate / 100);
+  const fyeMonth = fyeDate % 100;
+
+  if (fyeDate < 100000 || fyeDate > 999999 || fyeMonth < 1 || fyeMonth > 12) {
+    throw new Error('fyeDate is expected to be in IRS tax period format YYYYMM');
+  }
+
+  const currentYear = currentDate.getFullYear();
+  const currentMonth = currentDate.getMonth() + 1;
+
+  return (currentYear - fyeYear) * 12 + (currentMonth - fyeMonth);
+};
+
+export const isLikelyInactive = (eobmfStatus: boolean, taxPeriod: number): boolean => {
+  const monthsSinceFye = calculateMonthsBetween(taxPeriod, new Date());
+  if (eobmfStatus === false) {
+    if (monthsSinceFye >= config.monthsThreshold) {
+      return true;
+    }
+  }
+  return false;
+};