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fix(ics): resolve Windows TZIDs from Outlook published calendars #1913

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fix(ics): resolve Windows TZIDs from Outlook published calendars #1913

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104 changes: 84 additions & 20 deletions src/services/ICSSubscriptionService.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@ import type { InterpolationValues, TranslationKey } from "../i18n";
import { stringifyUnknown } from "../utils/stringUtils";
import { createTaskNotesLogger } from "../utils/tasknotesLogger";
import { publishUserNotice } from "../core/userNotices";
import { resolveTzidToIANA, wallTimeInZoneToUtcIso } from "../utils/icsTimezoneFallback";

const tasknotesLogger = createTaskNotesLogger({ tag: "Services/ICSSubscriptionService" });

Expand Down Expand Up @@ -98,12 +99,21 @@ export class ICSSubscriptionService extends EventEmitter {
* For timed events, uses toUnixTime() which correctly handles all timezones.
* For all-day events, preserves the date without time conversion.
*
* When ical.js can't resolve a TZID (no matching VTIMEZONE in the feed and
* no IANA tzdata in ical.js itself), it demotes the time to "floating",
* and `toUnixTime()` then misinterprets the wall clock as UTC. To recover,
* the caller can pass the raw TZID parameter from the source property; if
* it maps to a known IANA zone (directly or via the Windows TZID alias
* table), Intl.DateTimeFormat is used to compute the correct UTC instant.
*
* This fixes issues with:
* - Non-IANA timezones (e.g., TZID=Zurich without VTIMEZONE)
* - Floating time events
* - Outlook/Exchange timezone formats
* - Outlook/Exchange feeds that reference Windows TZIDs without
* inlining a VTIMEZONE block for every referenced zone.
* - Events with IANA TZIDs that have no accompanying VTIMEZONE.
* - Non-IANA timezones (e.g., TZID=Zurich without VTIMEZONE).
* - All-day events (date-only output, no zone math).
*/
private icalTimeToISOString(icalTime: ICAL.Time): string {
private icalTimeToISOString(icalTime: ICAL.Time, rawTzid?: string | null): string {
// For all-day events, return date-only string (YYYY-MM-DD)
// This preserves the calendar date semantics without timezone ambiguity
// per iCalendar RFC 5545 specification for VALUE=DATE events
Expand All @@ -114,15 +124,36 @@ export class ICSSubscriptionService extends EventEmitter {
return `${year}-${month}-${day}`;
}

// For timed events, use toUnixTime() which correctly converts to UTC
// This handles all timezone cases properly, including:
// - Events with proper VTIMEZONE definitions
// - Events with non-IANA TZIDs (treated as floating)
// - Floating time events
// Fallback path: when ical.js fell back to floating but the source
// property had a TZID that resolves to a known IANA zone, compute
// the UTC instant from the wall clock using Intl tzdata.
const zoneTzid = icalTime.zone?.tzid;
if (zoneTzid === "floating" || zoneTzid === undefined) {
const iana = resolveTzidToIANA(rawTzid);
if (iana) {
return wallTimeInZoneToUtcIso(icalTime, iana);
}
}

// Normal path: ical.js has a registered timezone for this Time
// (either from a VTIMEZONE in the feed or because the time is UTC),
// so toUnixTime() gives the correct instant.
const unixTime = icalTime.toUnixTime();
return new Date(unixTime * 1000).toISOString();
}

/**
* Extract the raw TZID parameter from a property (e.g. DTSTART, DTEND).
* Returns null when the property is missing or has no TZID parameter
* (which means the value is either UTC, date-only, or floating by intent).
*/
private rawTzidOf(vevent: ICAL.Component, propName: string): string | null {
const prop = vevent.getFirstProperty(propName);
if (!prop) return null;
const tzid = prop.getParameter("tzid");
return typeof tzid === "string" ? tzid : null;
}

constructor(plugin: TaskNotesPlugin) {
super();
this.plugin = plugin;
Expand Down Expand Up @@ -469,9 +500,18 @@ export class ICSSubscriptionService extends EventEmitter {
return; // Skip events without start date
}

// Capture the raw TZID parameters so icalTimeToISOString can
// fall back to Intl-based resolution for floating times whose
// TZID was a Windows (Outlook) zone name or any other IANA
// name not present in the calendar's VTIMEZONE blocks.
const startTzidRaw = this.rawTzidOf(vevent, "dtstart");
const endTzidRaw = this.rawTzidOf(vevent, "dtend");

const isAllDay = startDate.isDate;
const startISO = this.icalTimeToISOString(startDate);
const endISO = endDate ? this.icalTimeToISOString(endDate) : undefined;
const startISO = this.icalTimeToISOString(startDate, startTzidRaw);
const endISO = endDate
? this.icalTimeToISOString(endDate, endTzidRaw ?? startTzidRaw)
: undefined;

// Generate unique ID
const uid = event.uid || `${subscriptionId}-${events.length}`;
Expand Down Expand Up @@ -549,16 +589,30 @@ export class ICSSubscriptionService extends EventEmitter {
// Use the modified event instead
const modifiedStart = modifiedEvent.startDate;
const modifiedEnd = modifiedEvent.endDate;
const modifiedVevent: ICAL.Component | undefined =
(modifiedEvent as { component?: ICAL.Component }).component;
const modStartTzidRaw = modifiedVevent
? this.rawTzidOf(modifiedVevent, "dtstart")
: null;
const modEndTzidRaw = modifiedVevent
? this.rawTzidOf(modifiedVevent, "dtend")
: null;

if (modifiedStart) {
events.push({
id: instanceId,
subscriptionId: subscriptionId,
title: modifiedEvent.summary || summary,
description: modifiedEvent.description || description,
start: this.icalTimeToISOString(modifiedStart),
start: this.icalTimeToISOString(
modifiedStart,
modStartTzidRaw
),
end: modifiedEnd
? this.icalTimeToISOString(modifiedEnd)
? this.icalTimeToISOString(
modifiedEnd,
modEndTzidRaw ?? modStartTzidRaw
)
: undefined,
allDay: modifiedStart.isDate,
location: modifiedEvent.location || location,
Expand All @@ -567,15 +621,25 @@ export class ICSSubscriptionService extends EventEmitter {
visibleInstanceCount++;
}
} else {
// Use the original recurring event instance
const instanceStart = this.icalTimeToISOString(occurrence);
// Use the original recurring event instance.
// The iterator emits ICAL.Time values that share the
// startDate's TZID, so pass startTzidRaw for fallback.
const instanceStart = this.icalTimeToISOString(
occurrence,
startTzidRaw
);
let instanceEnd = endISO;

if (endDate && startDate) {
// Calculate duration using Unix timestamps for accuracy
const duration = endDate.toUnixTime() - startDate.toUnixTime();
const instanceEndTime = occurrence.toUnixTime() + duration;
instanceEnd = new Date(instanceEndTime * 1000).toISOString();
if (endISO && startISO && !isAllDay) {
// Derive duration from the already-resolved ISO
// strings so the fallback path stays consistent
// across the start and end of an instance.
const durationMs =
new Date(endISO).getTime() -
new Date(startISO).getTime();
instanceEnd = new Date(
new Date(instanceStart).getTime() + durationMs
).toISOString();
}

events.push({
Expand Down
7 changes: 6 additions & 1 deletion src/types/ical.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@ declare module 'ical.js' {
export class Component {
constructor(jcal: unknown);
getAllSubcomponents(name: string): Component[];
getFirstProperty(name: string): Property | null;
getFirstPropertyValue(name: string): unknown;
getAllProperties(name: string): Property[];
addSubcomponent(component: Component): Component;
Expand All @@ -31,6 +32,10 @@ declare module 'ical.js' {
iterator(startDate?: Time): EventIterator;
}

export interface TimezoneRef {
tzid?: string;
}

export class Time {
constructor();
isDate: boolean;
Expand All @@ -40,7 +45,7 @@ declare module 'ical.js' {
hour: number;
minute: number;
second: number;
zone: unknown;
zone: TimezoneRef | null | undefined;
fromJSDate(date: Date): void;
toJSDate(): Date;
toUnixTime(): number;
Expand Down
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