Add timezone offset to fix bad display

server/lib/statusHistory.ts

@@ -8,26 +8,42 @@ const STATUS_HISTORY_CACHE_TTL = 60; // seconds
 function statusHistoryCacheKey(
     entityType: string,
     entityId: number,
-    days: number
+    days: number,
+    tzOffsetMinutes: number
 ): string {
-    return `statusHistory:${entityType}:${entityId}:${days}`;
+    return `statusHistory:${entityType}:${entityId}:${days}:${tzOffsetMinutes}`;
+}
+
+// Returns the epoch seconds of the most recent local-calendar-day midnight,
+// where "local" is defined by tzOffsetMinutes (minutes to ADD to UTC to get
+// local time, e.g. Australia/Sydney standard time is 600). Defaults to 0
+// (UTC) so callers that don't pass a timezone keep the original behavior.
+function localMidnightSec(tzOffsetMinutes: number): number {
+    const localNow = new Date(Date.now() + tzOffsetMinutes * 60_000);
+    localNow.setUTCHours(0, 0, 0, 0);
+    return Math.floor(localNow.getTime() / 1000) - tzOffsetMinutes * 60;
 }
 
 export async function getCachedStatusHistory(
     entityType: string,
     entityId: number,
-    days: number
+    days: number,
+    tzOffsetMinutes: number = 0
 ): Promise<StatusHistoryResponse> {
-    const cacheKey = statusHistoryCacheKey(entityType, entityId, days);
+    const cacheKey = statusHistoryCacheKey(
+        entityType,
+        entityId,
+        days,
+        tzOffsetMinutes
+    );
     const cached = await cache.get<StatusHistoryResponse>(cacheKey);
     if (cached !== undefined) {
         return cached;
     }
 
-    // Anchor to UTC midnight so the query window aligns with stable calendar days
-    const utcToday = new Date();
-    utcToday.setUTCHours(0, 0, 0, 0);
-    const todayMidnightSec = Math.floor(utcToday.getTime() / 1000);
+    // Anchor to local midnight (UTC when tzOffsetMinutes is 0) so the query
+    // window aligns with stable calendar days for the requesting client
+    const todayMidnightSec = localMidnightSec(tzOffsetMinutes);
     const startSec = todayMidnightSec - days * 86400;
 
     const events = await logsDb
@@ -63,7 +79,8 @@ export async function getCachedStatusHistory(
     const { buckets, totalDowntime } = computeBuckets(
         events,
         days,
-        priorStatus
+        priorStatus,
+        tzOffsetMinutes
     );
     const totalWindow = days * 86400;
     const overallUptime =
@@ -99,11 +116,19 @@ export const statusHistoryQuerySchema = z
         days: z
             .string()
             .optional()
-            .transform((v) => (v ? parseInt(v, 10) : 90))
+            .transform((v) => (v ? parseInt(v, 10) : 90)),
+        // Minutes to add to UTC to get the requesting client's local time
+        // (e.g. Australia/Sydney standard time is 600). Optional and
+        // defaults to 0 (UTC) so older clients keep the prior behavior.
+        tzOffsetMinutes: z
+            .string()
+            .optional()
+            .transform((v) => (v ? parseInt(v, 10) : 0))
     })
     .pipe(
         z.object({
-            days: z.number().int().min(1).max(365)
+            days: z.number().int().min(1).max(365),
+            tzOffsetMinutes: z.number().int().min(-720).max(840)
         })
     );
 
@@ -133,15 +158,15 @@ export function computeBuckets(
         id: number;
     }[],
     days: number,
-    priorStatus: string | null = null
+    priorStatus: string | null = null,
+    tzOffsetMinutes: number = 0
 ): { buckets: StatusHistoryDayBucket[]; totalDowntime: number } {
     const nowSec = Math.floor(Date.now() / 1000);
 
-    // Anchor bucket boundaries to UTC midnight so dates are stable calendar days
-    // and don't drift as the cache expires and is recomputed
-    const utcToday = new Date();
-    utcToday.setUTCHours(0, 0, 0, 0);
-    const todayMidnightSec = Math.floor(utcToday.getTime() / 1000);
+    // Anchor bucket boundaries to local midnight (UTC when tzOffsetMinutes is
+    // 0) so dates are stable calendar days for the requesting client and
+    // don't drift as the cache expires and is recomputed
+    const todayMidnightSec = localMidnightSec(tzOffsetMinutes);
 
     const buckets: StatusHistoryDayBucket[] = [];
     let totalDowntime = 0;
@@ -237,7 +262,13 @@ export function computeBuckets(
                   )
                 : 100;
 
-        const dateStr = new Date(dayStartSec * 1000).toISOString().slice(0, 10);
+        // Shift by the client's offset before formatting so the label reflects
+        // their local calendar date rather than the UTC date of dayStartSec
+        const dateStr = new Date(
+            (dayStartSec + tzOffsetMinutes * 60) * 1000
+        )
+            .toISOString()
+            .slice(0, 10);
 
         const hasAnyData = currentStatus !== null || dayEvents.length > 0;