CalendarrKit

Shared code between Calendarr (iOS / Mac Catalyst) and other apps from the same developer team that want to read the user's calendar.

CalendarrCore depends on Foundation only — no SwiftUI, no UIKit, no AppKit — so it compiles for iOS, Mac Catalyst and native macOS from one source. That constraint is load-bearing: swift build against the native macOS SDK is what catches a UIKit import before it reaches a consumer, because a Mac Catalyst build would compile it happily.

What a reading app gets

import CalendarrCore

let store = SnapshotStore()          // uses CalendarrAppGroup.current

switch store.read() {
case .ok(let snap):
    snap.events          // [SnapshotEvent]
    snap.theme           // the colours Calendarr is currently rendering with
    snap.writtenAt       // "as of 14:32"
    snap.coverageStart   // see "Coverage" below
    snap.coverageEnd
case .neverWritten:      // Calendarr has never run here → "open Calendarr once"
case .loggedOut:         // signed out → "sign in to Calendarr", discard old events
case .incompatible:      // Calendarr is newer than this package → "update the app"
case .unreadable(let why): // almost always a wrong App Group; log `why`
}

store.readCalendars()    // [SnapshotCalendar] for a filter UI

React to changes without polling:

let token = SnapshotChangeNotifier.observe { /* hop to your actor, read again */ }
// keep `token` alive; releasing it removes the observer

Also reload on window activation — the notification is a best-effort signal, and missing one should leave you slightly stale, never wrong.

Coverage — the part that bites

The snapshot is not the whole calendar. Outside coverageStart..<coverageEnd it carries no information, which is not the same as "no events". Rendering an empty March because it is outside the window produces a screen that looks correct and is false. Use snapshot.covers(date) and grey out what you cannot speak for.

Window	~7 days back, ~42 days ahead, frozen at write time
Cap	500 events, sorted by start
Filters	hidden and "banished" calendars are already excluded — you see the user's filtered view
Scope	personal only; group overlays are never published, deliberately
Dropped	notes, url, source, creator, privacy, read-only, reminders, recurrence

What remains is enough to display a calendar and deliberately not enough to edit one or reason about permissions.

Setup for a consuming app

Same developer team (PP34X97WS3) is required — that is what makes the container and the keychain group shared.

<key>com.apple.security.app-sandbox</key><true/>
<key>com.apple.security.application-groups</key>
<array><string>PP34X97WS3.group.com.scarriffleservices.calendarr</string></array>

The Team ID prefix is mandatory on macOS and forbidden on iOS. CalendarrAppGroup.current resolves the right one; it must match the entitlement byte for byte, or containerURL(…) returns nil and every read silently yields nothing.

Never sign in from a consuming app. Credentials, 2FA and token storage belong to Calendarr alone.

Wire format rules

widget-cache.json, widget-calendars.json and session.json live in the group container and are read by apps that ship on independent schedules.

1. Filenames do not change within a major version, so an older build keeps reading after the writer updates.
2. Readers refuse schemaVersion > maxSupportedSchema instead of guessing.
3. Writers only ever add optional fields. Never rename, remove or retype one.
4. A breaking change means a new major version and a new filename, with the old file still written for one full release cycle.
5. The package version is the contract: CalendarrKit 1.x ⇔ snapshot schema 2. Depend on .upToNextMajor(from: "1.0.0").

Rule 3 is why the six colour values sit flat at the top level instead of nested under theme, which would read better: a v1 reader requires them flat, so nesting would have broken every older build on the first v2 write. theme is a computed view over them. SnapshotSchemaTests pins this down in both directions.

Verify

DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer swift build   # native macOS — catches UIKit leaks
DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer swift test