feat(mensa): show the canteen menu on Today

App/AppContainer.swift

@@ -20,6 +20,7 @@ final class AppContainer {
     let studIPAnnouncementService: any StudIPAnnouncementService
     let announcementRepository: any AnnouncementRepository
     let studIPScheduleService: any StudIPScheduleService
+    let canteenService: any CanteenService
     let studIPAccountStore: any StudIPAccountStore
     let courseFileRepository: any CourseFileRepository
     let backupArchiver: any BackupArchiving
@@ -55,6 +56,7 @@ final class AppContainer {
         studIPService = studIPClient
         studIPAnnouncementService = studIPClient
         studIPScheduleService = studIPClient
+        canteenService = OpenMensaClient()
         if inMemory {
             preferences = InMemoryStudyPreferences()
             studIPAccountStore = InMemoryStudIPAccountStore()
@@ -147,6 +149,10 @@ final class AppContainer {
         StudyTimerViewModel(repository: studySessionRepository, settings: preferences, scheduler: notificationScheduler)
     }
 
+    func makeMensaViewModel() -> MensaViewModel {
+        MensaViewModel(service: canteenService, settings: preferences)
+    }
+
     func makeAssignmentsViewModel() -> AssignmentsViewModel {
         AssignmentsViewModel(repository: assignmentRepository)
     }

App/StudyAppApp.swift

@@ -19,6 +19,7 @@ struct StudyAppApp: App {
     @State private var examsViewModel: ExamsViewModel
     @State private var announcementsViewModel: AnnouncementsViewModel
     @State private var studyTimerViewModel: StudyTimerViewModel
+    @State private var mensaViewModel: MensaViewModel
     @State private var updater = AppUpdater()
     @AppStorage(ViewPreferences.appearanceKey) private var appearance = AppAppearance.standard
     @AppStorage(ViewPreferences.showsMenuBarItemKey) private var showsMenuBarItem = true
@@ -88,6 +89,7 @@ struct StudyAppApp: App {
             _examsViewModel = State(initialValue: exams)
             _announcementsViewModel = State(initialValue: announcements)
             _studyTimerViewModel = State(initialValue: studyTimer)
+            _mensaViewModel = State(initialValue: container.makeMensaViewModel())
         } catch {
             fatalError("Datenbank konnte nicht geöffnet werden: \(error)")
         }
@@ -106,6 +108,7 @@ struct StudyAppApp: App {
                 examsViewModel: examsViewModel,
                 announcementsViewModel: announcementsViewModel,
                 studyTimerViewModel: studyTimerViewModel,
+                mensaViewModel: mensaViewModel,
                 makeSlidesViewModel: { moduleID in
                     container.makeSlidesViewModel(moduleID: moduleID)
                 },
@@ -176,7 +179,8 @@ struct StudyAppApp: App {
                 updater: updater,
                 studIP: studIPViewModel,
                 backup: backupViewModel,
-                notifications: notificationsViewModel
+                notifications: notificationsViewModel,
+                mensa: mensaViewModel
             )
             .tint(Theme.accent)
             .preferredColorScheme(appearance.colorScheme)
@@ -240,6 +244,8 @@ struct StudyAppApp: App {
             try? await Task.sleep(for: .seconds(300))
             await calendarViewModel.refreshStaleSubscriptions()
             await studIPViewModel.syncIfDue()
+            // Switches to tomorrow's menu after lunch; cached, so usually no request.
+            await mensaViewModel.refresh()
             // Picks up new or moved lectures and assignments.
             await notificationsViewModel.refresh()
         }

Data/Mensa/OpenMensaClient.swift

@@ -0,0 +1,45 @@
+import Foundation
+
+/// Loads canteens and menus from the OpenMensa API v2. No account is needed.
+struct OpenMensaClient: CanteenService {
+    static let baseURL = URL(string: "https://openmensa.org/api/v2/")!
+
+    var session: URLSession = .shared
+    var calendar: Calendar = .current
+
+    func canteens(nearLatitude latitude: Double, longitude: Double, radius: Double) async throws -> [Canteen] {
+        let data = try await get("canteens", query: [
+            URLQueryItem(name: "near[lat]", value: String(latitude)),
+            URLQueryItem(name: "near[lng]", value: String(longitude)),
+            URLQueryItem(name: "near[dist]", value: String(radius)),
+        ])
+        return try OpenMensaParser.canteens(data)
+    }
+
+    func menu(canteenID: Int, on date: Date) async throws -> CanteenMenu {
+        let day = OpenMensaParser.dayString(date, calendar: calendar)
+        let isClosed = try OpenMensaParser.isClosed(try await get("canteens/\(canteenID)/days/\(day)"))
+        let meals = isClosed ? [] : try OpenMensaParser.meals(try await get("canteens/\(canteenID)/days/\(day)/meals"))
+        return CanteenMenu(canteenID: canteenID, date: date, isClosed: isClosed, meals: meals)
+    }
+
+    private func get(_ path: String, query: [URLQueryItem] = []) async throws -> Data {
+        var components = URLComponents(url: Self.baseURL.appendingPathComponent(path), resolvingAgainstBaseURL: false)
+        if !query.isEmpty { components?.queryItems = query }
+        guard let url = components?.url else { throw MensaError.unavailable }
+        var request = URLRequest(url: url)
+        request.timeoutInterval = 20
+        request.setValue("application/json", forHTTPHeaderField: "Accept")
+        let data: Data
+        let response: URLResponse
+        do {
+            (data, response) = try await session.data(for: request)
+        } catch {
+            throw MensaError.offline
+        }
+        guard let http = response as? HTTPURLResponse else { throw MensaError.unavailable }
+        // OpenMensa answers 404 for days without a published menu.
+        guard (200...299).contains(http.statusCode) else { throw MensaError.unavailable }
+        return data
+    }
+}

Data/Mensa/OpenMensaParser.swift

@@ -0,0 +1,55 @@
+import Foundation
+
+/// Reads OpenMensa API v2 responses (https://openmensa.org/api/v2).
+enum OpenMensaParser {
+    private struct CanteenDTO: Decodable {
+        let id: Int
+        let name: String
+        let city: String?
+        let address: String?
+    }
+
+    private struct DayDTO: Decodable {
+        let closed: Bool
+    }
+
+    private struct MealDTO: Decodable {
+        struct Prices: Decodable {
+            let students: Double?
+        }
+
+        let id: Int
+        let name: String
+        let category: String?
+        let prices: Prices?
+        let notes: [String]?
+    }
+
+    static func canteens(_ data: Data) throws -> [Canteen] {
+        try JSONDecoder().decode([CanteenDTO].self, from: data).map {
+            Canteen(id: $0.id, name: $0.name, city: $0.city ?? "", address: $0.address ?? "")
+        }
+    }
+
+    static func isClosed(_ data: Data) throws -> Bool {
+        try JSONDecoder().decode(DayDTO.self, from: data).closed
+    }
+
+    static func meals(_ data: Data) throws -> [Meal] {
+        try JSONDecoder().decode([MealDTO].self, from: data).map {
+            Meal(
+                id: $0.id,
+                name: $0.name,
+                category: $0.category ?? "Essen",
+                studentPrice: $0.prices?.students,
+                notes: $0.notes ?? []
+            )
+        }
+    }
+
+    /// OpenMensa addresses days as `yyyy-MM-dd` in the canteen's (German) time zone.
+    static func dayString(_ date: Date, calendar: Calendar) -> String {
+        let components = calendar.dateComponents([.year, .month, .day], from: date)
+        return String(format: "%04d-%02d-%02d", components.year ?? 0, components.month ?? 0, components.day ?? 0)
+    }
+}

Data/Preferences/UserDefaultsStudyPreferences.swift

@@ -13,6 +13,7 @@ final class UserDefaultsStudyPreferences: StudySettingsStore, ReadingProgressSto
         static let lastAutoOpenedLecture = "autopilot.lastHandledLecture"
         static let automaticBackups = "backup.automatic"
         static let importsStudIPTimetable = "studip.importsTimetable"
+        static let canteenID = "mensa.canteenID"
         static let notificationSettings = "notifications.settings"
         static let studyTimerSettings = "studyTimer.settings"
         static func lastPage(_ documentID: UUID) -> String { "reading.page.\(documentID.uuidString)" }
@@ -67,6 +68,11 @@ final class UserDefaultsStudyPreferences: StudySettingsStore, ReadingProgressSto
         set { defaults.set(newValue, forKey: Key.importsStudIPTimetable) }
     }
 
+    var canteenID: Int? {
+        get { defaults.object(forKey: Key.canteenID) as? Int }
+        set { defaults.set(newValue, forKey: Key.canteenID) }
+    }
+
     /// Stored as JSON; unreadable or missing data falls back to the defaults.
     var notificationSettings: NotificationSettings {
         get {

Domain/Entities/Mensa.swift

@@ -0,0 +1,52 @@
+import Foundation
+
+/// A canteen listed by OpenMensa.
+struct Canteen: Identifiable, Hashable, Codable, Sendable {
+    let id: Int
+    var name: String
+    var city: String
+    var address: String
+}
+
+/// One dish on a canteen's menu.
+struct Meal: Identifiable, Hashable, Sendable {
+    let id: Int
+    var name: String
+    /// e.g. „Pasta“, „Vegetarisch“, „Pizza“.
+    var category: String
+    /// Price for students in euros, if the canteen publishes one.
+    var studentPrice: Double?
+    /// Hints such as „vegan“ or allergens.
+    var notes: [String]
+}
+
+/// The menu of one canteen on one day.
+struct CanteenMenu: Equatable, Sendable {
+    let canteenID: Int
+    let date: Date
+    var isClosed: Bool
+    var meals: [Meal]
+
+    /// Meals grouped by category, in the order the canteen lists them.
+    var mealsByCategory: [(category: String, meals: [Meal])] {
+        var order: [String] = []
+        var groups: [String: [Meal]] = [:]
+        for meal in meals {
+            if groups[meal.category] == nil { order.append(meal.category) }
+            groups[meal.category, default: []].append(meal)
+        }
+        return order.map { ($0, groups[$0] ?? []) }
+    }
+}
+
+enum MensaError: LocalizedError, Equatable {
+    case offline
+    case unavailable
+
+    var errorDescription: String? {
+        switch self {
+        case .offline: "Der Mensaplan ist gerade nicht erreichbar. Bist du online?"
+        case .unavailable: "Für diesen Tag gibt es keinen Speiseplan."
+        }
+    }
+}

Domain/Repositories/CanteenService.swift

@@ -0,0 +1,10 @@
+import Foundation
+
+/// Port to a canteen menu source (OpenMensa).
+@MainActor
+protocol CanteenService {
+    /// Canteens within `radius` kilometres of a coordinate.
+    func canteens(nearLatitude latitude: Double, longitude: Double, radius: Double) async throws -> [Canteen]
+    /// The menu of a canteen on a day. Throws `MensaError.unavailable` when the canteen publishes nothing for it.
+    func menu(canteenID: Int, on date: Date) async throws -> CanteenMenu
+}

Domain/Repositories/StudyPreferences.swift

@@ -20,6 +20,8 @@ protocol StudySettingsStore: AnyObject {
     var automaticBackups: Bool { get set }
     /// Import the dates of linked Stud.IP courses into the calendar during a Stud.IP sync.
     var importsStudIPTimetable: Bool { get set }
+    /// OpenMensa canteen shown on „Heute“; `nil` hides the menu.
+    var canteenID: Int? { get set }
     var notificationSettings: NotificationSettings { get set }
     var studyTimerSettings: StudyTimerSettings { get set }
 }
@@ -48,6 +50,7 @@ final class InMemoryStudyPreferences: StudySettingsStore, ReadingProgressStore {
     var lastAutoOpenedLecture: String?
     var automaticBackups = true
     var importsStudIPTimetable = false
+    var canteenID: Int?
     var notificationSettings = NotificationSettings()
     var studyTimerSettings = StudyTimerSettings()
     private var pages: [UUID: Int] = [:]

Domain/UseCases/MensaUseCases.swift

@@ -0,0 +1,40 @@
+import Foundation
+
+/// Which day's menu is worth showing: after lunch is over, the next day's.
+enum MensaSchedule {
+    /// Hot meals are served until about 14:15; afterwards the next day is more useful.
+    static let lunchEndHour = 15
+
+    static func menuDay(for now: Date, calendar: Calendar = .current) -> Date {
+        let today = calendar.startOfDay(for: now)
+        guard calendar.component(.hour, from: now) >= lunchEndHour else { return today }
+        return calendar.date(byAdding: .day, value: 1, to: today) ?? today
+    }
+}
+
+/// Canteens of the Studierendenwerk Oldenburg area, nearest first.
+enum MensaLocation {
+    /// University of Oldenburg, campus Haarentor.
+    static let oldenburgLatitude = 53.1478
+    static let oldenburgLongitude = 8.1814
+    static let searchRadius = 15.0
+}
+
+/// Loads a menu and keeps it for the rest of the day, so „Heute“ does not ask the server on every visit.
+@MainActor
+final class LoadCanteenMenuUseCase {
+    private let service: any CanteenService
+    private var cache: [String: CanteenMenu] = [:]
+
+    init(service: any CanteenService) {
+        self.service = service
+    }
+
+    func callAsFunction(canteenID: Int, day: Date) async throws -> CanteenMenu {
+        let key = "\(canteenID)-\(day.timeIntervalSince1970)"
+        if let cached = cache[key] { return cached }
+        let menu = try await service.menu(canteenID: canteenID, on: day)
+        cache = [key: menu]
+        return menu
+    }
+}