fix: prevent duplicate scheduler reminder sends (#270)

backend/src/services/reminder-scheduler.ts

@@ -1,4 +1,4 @@
-import { existsSync, readFileSync, writeFileSync } from "node:fs";
+import { closeSync, existsSync, mkdirSync, openSync, readFileSync, statSync, unlinkSync, writeFileSync } from "node:fs";
 import { resolve } from "node:path";
 import { and, eq } from "drizzle-orm";
 import nodemailer from "nodemailer";
@@ -40,6 +40,56 @@ function escapeHtml(text: string): string {
 const REMINDER_HOUR = parseInt(process.env.REMINDER_HOUR ?? "6", 10); // Default 6:00 AM local time
 
 const reminderStateFile = resolve(getDataDir(), "reminder-state.json");
+const reminderLocksDir = resolve(getDataDir(), "scheduler-locks");
+const LOCK_STALE_MS = 15 * 60 * 1000;
+
+function ensureReminderLocksDir(): void {
+	if (!existsSync(reminderLocksDir)) {
+		mkdirSync(reminderLocksDir, { recursive: true });
+	}
+}
+
+function acquireReminderSendLock(lockKey: string): string | null {
+	ensureReminderLocksDir();
+	const lockFilePath = resolve(reminderLocksDir, `${lockKey}.lock`);
+
+	const tryCreateLock = (): boolean => {
+		try {
+			const fd = openSync(lockFilePath, "wx");
+			closeSync(fd);
+			return true;
+		} catch {
+			return false;
+		}
+	};
+
+	if (tryCreateLock()) {
+		return lockFilePath;
+	}
+
+	try {
+		const stats = statSync(lockFilePath);
+		if (Date.now() - stats.mtimeMs > LOCK_STALE_MS) {
+			unlinkSync(lockFilePath);
+			if (tryCreateLock()) {
+				return lockFilePath;
+			}
+		}
+	} catch {
+		// ignore; lock acquisition fails safely
+	}
+
+	return null;
+}
+
+function releaseReminderSendLock(lockFilePath: string | null): void {
+	if (!lockFilePath) return;
+	try {
+		unlinkSync(lockFilePath);
+	} catch {
+		// ignore release errors
+	}
+}
 
 function loadReminderState(): ReminderState {
 	try {
@@ -565,6 +615,11 @@ async function checkAndSendReminderForUser(
 
 	if (allLowStock.length > 0 && (stockEmailEnabled || stockPushEnabled)) {
 		if (!state.notifiedMedications.includes(userStockNotifiedKey) || settings.repeatDailyReminders) {
+			const stockSendLock = acquireReminderSendLock(userStockNotifiedKey);
+			if (!stockSendLock) {
+				logger.debug(`[Reminder] User ${settings.userId}: stock reminder lock already held, skipping duplicate send`);
+			} else {
+				try {
 					logger.info(
 						`[Reminder] User ${settings.userId}: Sending stock reminder for ${allLowStock.length} medications...`
 					);
@@ -643,11 +698,22 @@ async function checkAndSendReminderForUser(
 						const medNames = allLowStock.map((m) => m.name).join(", ");
 						await updateUserReminderSentTime(settings.userId, "stock", channel, medNames);
 					}
+				} finally {
+					releaseReminderSendLock(stockSendLock);
+				}
+			}
 		}
 	}
 
 	if (allPrescriptionLow.length > 0 && (prescriptionEmailEnabled || prescriptionPushEnabled)) {
 		if (!state.notifiedMedications.includes(userPrescriptionNotifiedKey) || settings.repeatDailyReminders) {
+			const prescriptionSendLock = acquireReminderSendLock(userPrescriptionNotifiedKey);
+			if (!prescriptionSendLock) {
+				logger.debug(
+					`[Reminder] User ${settings.userId}: prescription reminder lock already held, skipping duplicate send`
+				);
+			} else {
+				try {
 					logger.info(
 						`[Reminder] User ${settings.userId}: Sending prescription reminder for ${allPrescriptionLow.length} medications...`
 					);
@@ -695,7 +761,9 @@ async function checkAndSendReminderForUser(
 										: t(tr.prescriptionReminder.subjectMultiple, { count: allPrescriptionLow.length });
 
 								const bodyText =
-							emptyRx.length > 0 ? tr.prescriptionReminder.descriptionEmpty : tr.prescriptionReminder.descriptionLow;
+									emptyRx.length > 0
+										? tr.prescriptionReminder.descriptionEmpty
+										: tr.prescriptionReminder.descriptionLow;
 								const emptyAlert =
 									emptyRx.length === 1
 										? tr.prescriptionReminder.alertEmptySingle
@@ -833,11 +901,16 @@ async function checkAndSendReminderForUser(
 						const medNames = allPrescriptionLow.map((m) => m.name).join(", ");
 						await updateUserReminderSentTime(settings.userId, "prescription", channel, medNames);
 					}
+				} finally {
+					releaseReminderSendLock(prescriptionSendLock);
+				}
+			}
 		}
 	}
 }
 
 let schedulerTimeout: NodeJS.Timeout | null = null;
+let schedulerStarted = false;
 
 function scheduleNextCheck(logger: ServiceLogger): void {
 	const msUntilNext = getMsUntilNextCheck(REMINDER_HOUR);
@@ -862,6 +935,11 @@ function scheduleNextCheck(logger: ServiceLogger): void {
 }
 
 export function startReminderScheduler(logger: ServiceLogger): void {
+	if (schedulerStarted) {
+		logger.info(`[Reminder] Scheduler already started, skipping duplicate start call`);
+		return;
+	}
+	schedulerStarted = true;
 	logger.info(`[Reminder] Starting reminder scheduler (timezone: ${getTimezone()})...`);
 
 	// Check if we need to run immediately (missed today's check)
@@ -881,9 +959,15 @@ export function startReminderScheduler(logger: ServiceLogger): void {
 	logger.info(`[Reminder] Scheduler started - daily check at ${REMINDER_HOUR}:00 ${getTimezone()}`);
 }
 
+export async function runReminderSchedulerNow(logger: ServiceLogger): Promise<void> {
+	logger.info(`[Reminder] Manual trigger: running reminder check now (${getTimezone()})`);
+	await checkAndSendReminder(logger);
+}
+
 export function stopReminderScheduler(): void {
 	if (schedulerTimeout) {
 		clearTimeout(schedulerTimeout);
 		schedulerTimeout = null;
 	}
+	schedulerStarted = false;
 }