Refactor code saving data

Move the code dealing with saving and loading data to server/database to
gather it all up into one place.

server/database.ts

@@ -0,0 +1,44 @@
+import { readFile, writeFile } from "node:fs/promises";
+import { Schedule } from "~/shared/types/schedule";
+
+// For this demo I'm just storing the runtime data in JSON files. When making
+// this into proper application this should be replaced with an actual database.
+
+const schedulePath = "schedule.json"
+const subscriptionsPath = "push-subscriptions.json"
+
+export async function readSchedule() {
+	let schedule: Schedule;
+	try {
+		schedule = JSON.parse(await readFile(schedulePath, "utf-8"));
+	} catch (err: any) {
+		if (err.code !== "ENOENT")
+			throw err;
+		// Use an empty schedule if nothing is stored yet.
+		schedule = {
+			locations: [],
+			events: [],
+		}
+	}
+	return schedule;;
+}
+
+export async function writeSchedule(schedule: Schedule) {
+	await writeFile(schedulePath, JSON.stringify(schedule, undefined, "\t") + "\n", "utf-8");
+}
+
+export async function readSubscriptions() {
+	let subscriptions: PushSubscriptionJSON[];
+	try {
+		subscriptions = JSON.parse(await readFile(subscriptionsPath, "utf-8"));
+	} catch (err: any) {
+		if (err.code !== "ENOENT")
+			throw err;
+		subscriptions = [];
+	}
+	return subscriptions;;
+}
+
+export async function writeSubscriptions(subscriptions: PushSubscriptionJSON[]) {
+	await writeFile(subscriptionsPath, JSON.stringify(subscriptions, undefined, "\t") + "\n", "utf-8");
+}