Move inactivity notice validation to separate exported function

functions/api/inactivity/validate.ts

@@ -0,0 +1,49 @@
+function errorResponse(error: string, status = 400): Response {
+  return new Response(JSON.stringify({ error }), {
+    headers: {
+      "content-type": "application/json",
+    },
+    status,
+  });
+}
+
+export default function (
+  selectedDepartments: string[],
+  end: any,
+  reason: any,
+  start: any,
+  userDepartments?: string[],
+): void | Response {
+  if (!userDepartments)
+    return errorResponse("Not part of any departments", 403);
+
+  if (
+    !Array.isArray(selectedDepartments) ||
+    !selectedDepartments.length ||
+    typeof end !== "string" ||
+    typeof reason !== "string" ||
+    typeof start !== "string"
+  )
+    return errorResponse("Invalid notice");
+
+  if (!selectedDepartments.every((dept) => userDepartments.includes(dept)))
+    return errorResponse(
+      "Cannot file an inactivity notice in a department you are not part of",
+      403,
+    );
+
+  const endDate = new Date(end);
+  const now = new Date();
+  const startDate = new Date(start);
+
+  if (
+    isNaN(endDate.getFullYear()) ||
+    isNaN(startDate.getFullYear()) ||
+    endDate.getFullYear() < now.getFullYear() ||
+    endDate.getFullYear() > now.getFullYear() + 1 ||
+    startDate.getFullYear() < now.getFullYear() ||
+    startDate.getFullYear() > now.getFullYear() + 1 ||
+    endDate.valueOf() < startDate.valueOf()
+  )
+    return errorResponse("Dates are invalid");
+}