feat: implement changes tracking for university documents

- Added a new data structure `ScheduleChanges` to represent changes when a university document is republished.
- Implemented methods to read and write changes to a local JSON file.
- Enhanced the `Repository` class to detect changes between the current and fresh timetable versions.
- Updated the `MainViewModel` to expose changes to the UI and handle marking changes as seen.
- Created UI components for displaying changes in both Home and Settings screens.
- Added support for changes in iOS views, including a new `ChangesCard` and `ChangesSheet`.
- Implemented logic to compare timetable versions and identify added, removed, and changed lessons.

ios/PSUSchedule/AppModel.swift

@@ -24,6 +24,8 @@ final class AppModel {
     private(set) var exams: ExamsResponse?
     private(set) var allNotes: [Note]
     private(set) var allMarks: [Mark]
+    /** What changed when the university republished a document, per document and group. */
+    private(set) var allChanges: [ScheduleChanges]
     private(set) var status = Status()
     /** Moves every half minute while the app is open: the clock "Идёт · ещё 20 мин" counts from. */
     private(set) var now = Date()
@@ -39,6 +41,7 @@ final class AppModel {
         exams = Storage.read(ExamsResponse.self, "exams.json")
         allNotes = Storage.read([Note].self, "notes.json") ?? []
         allMarks = Storage.read([Mark].self, "attendance.json") ?? []
+        allChanges = Storage.read([ScheduleChanges].self, "changes.json") ?? []
         Task { [weak self] in
             while !Task.isCancelled {
                 try? await Task.sleep(for: .seconds(30))
@@ -62,6 +65,21 @@ final class AppModel {
         t.slots(on: date, subgroup: subgroup, hidden: hidden)
     }
 
+    /** The open group's last republished document: what changed for it. */
+    var changes: ScheduleChanges? {
+        guard let t = timetable else { return nil }
+        return allChanges.first { $0.document == t.document.id && $0.group == t.group }
+    }
+
+    /** The overview's card was opened or closed: the record stays for "Последние изменения". */
+    func markChangesSeen(_ record: ScheduleChanges) {
+        guard !record.seen else { return }
+        for i in allChanges.indices where allChanges[i].document == record.document && allChanges[i].group == record.group {
+            allChanges[i].seen = true
+        }
+        Storage.write(allChanges, "changes.json")
+    }
+
     /** Upcoming exams of the open group, soonest first; the cache of another group is ignored. */
     var upcomingExams: [Exam] {
         guard let t = timetable, let e = exams, e.group == t.group else { return [] }
@@ -110,6 +128,11 @@ final class AppModel {
         status.loading = true
         do {
             let fresh = try await block()
+            // Also in a background refresh: the card waits for the student on the overview.
+            if let record = ScheduleChanges.between(timetable, fresh) {
+                allChanges = Array(([record] + allChanges.filter { $0.document != record.document || $0.group != record.group }).prefix(12))
+                Storage.write(allChanges, "changes.json")
+            }
             timetable = fresh
             Storage.write(fresh, "timetable.json")
             lastFailed = nil

ios/PSUSchedule/Views/ChangesView.swift

@@ -0,0 +1,114 @@
+import SwiftUI
+
+extension ScheduleChanges: Identifiable {
+    var id: String { "\(document)|\(group)|\(at.timeIntervalSince1970)" }
+}
+
+/**
+ * The overview's card after the university republished the group's document: how many lessons
+ * changed, "Показать" for the list, and a close button. Both mark the record as seen.
+ */
+struct ChangesCard: View {
+    var record: ScheduleChanges
+    var onShow: () -> Void
+    var onClose: () -> Void
+
+    var body: some View {
+        HStack(alignment: .top, spacing: 14) {
+            Image(systemName: "arrow.triangle.2.circlepath.doc.on.clipboard")
+                .font(.body.weight(.semibold))
+                .foregroundStyle(Color.onBrand)
+                .frame(width: 40, height: 40)
+                .background(Color.brand, in: .circle)
+                .accessibilityHidden(true)
+            VStack(alignment: .leading, spacing: 4) {
+                Text("Расписание обновлено · \(changesLabel(record.count))").font(.headline)
+                Text("Для \(record.group)" + (fileDateLabel(record.to).map { " · файл от \($0)" } ?? ""))
+                    .font(.subheadline).foregroundStyle(.secondary)
+                Button("Показать", action: onShow)
+                    .buttonStyle(.glassProminent)
+                    .padding(.top, 6)
+            }
+            .frame(maxWidth: .infinity, alignment: .leading)
+            Button("Скрыть сообщение об изменениях", systemImage: "xmark", action: onClose)
+                .labelStyle(.iconOnly)
+                .buttonStyle(.glass)
+                .buttonBorderShape(.circle)
+        }
+        .card(padding: 18)
+    }
+}
+
+/// The list behind the card: changed, added and removed lessons, as in the PWA.
+struct ChangesSheet: View {
+    @Environment(\.dismiss) private var dismiss
+    var record: ScheduleChanges
+
+    var body: some View {
+        NavigationStack {
+            List {
+                Section {
+                    Text("\(record.group) · \(record.name.replacingOccurrences(of: #"\.docx?$"#, with: "", options: [.regularExpression, .caseInsensitive]))"
+                        + (fileDateLabel(record.to).map { " · файл от \($0)" } ?? "")
+                        + ". Сравнение с прошлой версией, сохранённой на этом устройстве.")
+                        .font(.subheadline).foregroundStyle(.secondary)
+                }
+                if !record.changed.isEmpty {
+                    Section("Изменено · \(record.changed.count)") {
+                        ForEach(record.changed, id: \.self) { change in
+                            VStack(alignment: .leading, spacing: 4) {
+                                when(change.after)
+                                Text(change.after.lesson.subject).font(.headline)
+                                ForEach(change.fields, id: \.self) { f in
+                                    (Text("\(f.label): ").foregroundStyle(.secondary)
+                                        + Text(f.from).strikethrough().foregroundStyle(.secondary)
+                                        + Text("  →  ").foregroundStyle(.secondary)
+                                        + Text(f.to))
+                                        .font(.subheadline)
+                                        .accessibilityLabel("\(f.label): было \(f.from), стало \(f.to)")
+                                }
+                                if change.fields.isEmpty {
+                                    Text("Изменился текст ячейки Word").font(.subheadline).foregroundStyle(.secondary)
+                                }
+                            }
+                            .padding(.vertical, 2)
+                        }
+                    }
+                }
+                if !record.added.isEmpty {
+                    Section("Добавлено · \(record.added.count)") {
+                        ForEach(record.added, id: \.self) { row in
+                            item(row, details: [row.lesson.type, row.lesson.teachers.joined(separator: ", "),
+                                                row.lesson.rooms.map { "ауд. \($0)" }.joined(separator: ", "), row.lesson.condition])
+                        }
+                    }
+                }
+                if !record.removed.isEmpty {
+                    Section("Удалено · \(record.removed.count)") {
+                        ForEach(record.removed, id: \.self) { row in
+                            item(row, removed: true, details: [row.lesson.type, row.lesson.condition])
+                        }
+                    }
+                }
+                Section {} footer: { Text("Сверяйтесь с документом Word: при сомнениях он главнее.") }
+            }
+            .navigationTitle("Изменения")
+            .toolbar { ToolbarItem(placement: .confirmationAction) { Button("Готово", systemImage: "checkmark") { dismiss() } } }
+        }
+    }
+
+    private func when(_ row: ChangedLesson) -> some View {
+        let day = row.date.flatMap { CivilDate($0) }.map { "\($0.shortWeekday), \($0.longLabel)" } ?? dayName(row.day)
+        return Text(day + " · " + row.lesson.start).font(.subheadline.weight(.semibold)).foregroundStyle(Color.brand)
+    }
+
+    private func item(_ row: ChangedLesson, removed: Bool = false, details: [String]) -> some View {
+        VStack(alignment: .leading, spacing: 4) {
+            when(row).foregroundStyle(removed ? .secondary : Color.brand)
+            Text(row.lesson.subject).font(.headline).strikethrough(removed).foregroundStyle(removed ? .secondary : .primary)
+            let text = details.filter { !$0.trimmed.isEmpty }.joined(separator: " · ")
+            if !text.isEmpty { Text(text).font(.subheadline).foregroundStyle(.secondary) }
+        }
+        .padding(.vertical, 2)
+    }
+}

ios/PSUSchedule/Views/HomeView.swift

@@ -9,6 +9,7 @@ struct HomeView: View {
     @State private var details: LessonRef?
     @State private var editor: EditorRequest?
     @State private var session = false
+    @State private var changes: ScheduleChanges?
 
     var body: some View {
         NavigationStack {
@@ -26,6 +27,7 @@ struct HomeView: View {
         .sheet(item: $details) { LessonDetails(ref: $0).presentationDetents([.medium, .large]) }
         .sheet(item: $editor) { NoteEditor(request: $0) }
         .sheet(isPresented: $session) { SessionSheet(exams: model.upcomingExams).presentationDetents([.medium, .large]) }
+        .sheet(item: $changes) { ChangesSheet(record: $0).presentationDetents([.medium, .large]) }
     }
 
     @ViewBuilder private var content: some View {
@@ -75,6 +77,16 @@ struct HomeView: View {
         let next = (1...7).lazy.map { today.adding(days: $0) }.map { ($0, model.slots(t, on: $0)) }.first { !$0.1.isEmpty }
         return VStack(alignment: .leading, spacing: 16) {
             StatusBanner()
+            // The university republished the document: what changed for the group, until seen.
+            if let record = model.changes, !record.seen {
+                ChangesCard(record: record, onShow: {
+                    changes = record
+                    model.markChangesSeen(record)
+                }, onClose: {
+                    withAnimation { model.markChangesSeen(record) }
+                })
+                .transition(.opacity.combined(with: .scale(scale: 0.96)))
+            }
             WeekReport(timetable: t)
             SessionCard(timetable: t) { session = true }
             DayTitle(label: "Сегодня", date: today)

ios/PSUSchedule/Views/SettingsView.swift

@@ -3,6 +3,7 @@ import SwiftUI
 struct SettingsView: View {
     @Environment(AppModel.self) private var model
     @Environment(\.dismiss) private var dismiss
+    @State private var changes: ScheduleChanges?
 
     var body: some View {
         let s = model.settings
@@ -63,6 +64,13 @@ struct SettingsView: View {
                 Section {
                     LabeledContent("Документ", value: model.timetable?.document.name ?? "Группа не выбрана")
                     if let sem = model.timetable?.semester { LabeledContent("Семестр", value: sem.label) }
+                    // The last republication of the document, also after its card was closed.
+                    if let record = model.changes {
+                        Button { changes = record } label: {
+                            LabeledContent("Последние изменения", value: changesLabel(record.count) + " · " + CivilDate(record.at).longLabel)
+                                .foregroundStyle(.primary)
+                        }
+                    }
                     LabeledContent("Сервер", value: model.api.base.absoluteString)
                 } header: {
                     Text("О расписании")
@@ -73,6 +81,7 @@ struct SettingsView: View {
             .navigationTitle("Настройки")
             .navigationBarTitleDisplayMode(.inline)
             .toolbar { ToolbarItem(placement: .confirmationAction) { Button("Готово", systemImage: "checkmark") { dismiss() } } }
+            .sheet(item: $changes) { ChangesSheet(record: $0).presentationDetents([.medium, .large]) }
         }
     }
 

ios/Shared/Changes.swift

@@ -0,0 +1,151 @@
+import Foundation
+
+// What changed for the group when the university republished its document, as the PWA reports it
+// (shared/lessons.js diffSchedules) and the Android client's Changes.kt: the new timetable is
+// compared with the copy on the device.
+
+/// A Word row of the timetable: a weekday's lesson, or a lesson on its own date.
+struct ChangedLesson: Codable, Hashable {
+    var day: Int
+    var date: String?
+    var lesson: Lesson
+}
+
+struct FieldChange: Codable, Hashable {
+    var label: String
+    var from: String
+    var to: String
+}
+
+struct LessonChange: Codable, Hashable {
+    var before: ChangedLesson
+    var after: ChangedLesson
+    var fields: [FieldChange]
+}
+
+struct ScheduleChanges: Codable, Hashable {
+    var document: String
+    var group: String
+    var name: String
+    /// When the change was found.
+    var at: Date
+    /// Dates of the two versions of the file, as the server sends them.
+    var from: String?
+    var to: String?
+    var added: [ChangedLesson] = []
+    var removed: [ChangedLesson] = []
+    var changed: [LessonChange] = []
+    /// The card on the overview was opened or closed.
+    var seen = false
+
+    var count: Int { added.count + removed.count + changed.count }
+
+    /**
+     * Compares a newer version of the same document with the copy on the device: only a
+     * republished file counts, not a new parser or another document of the group.
+     */
+    static func between(_ previous: Timetable?, _ fresh: Timetable, now: Date = Date()) -> ScheduleChanges? {
+        guard let previous, previous.document.id == fresh.document.id, previous.group == fresh.group,
+              let was = previous.document.modified, let then = fresh.document.modified, was != then
+        else { return nil }
+        let (added, removed, changed) = diff(previous, fresh)
+        let record = ScheduleChanges(
+            document: fresh.document.id, group: fresh.group, name: fresh.document.name, at: now,
+            from: was, to: then, added: added, removed: removed, changed: changed
+        )
+        return record.count > 0 ? record : nil
+    }
+}
+
+/// "3 изменения".
+func changesLabel(_ n: Int) -> String { "\(n) \(plural(n, "изменение", "изменения", "изменений"))" }
+
+/// The date of a file version as the server sends it ("Mon, 19 Oct 2026 08:00:00 GMT").
+func fileDateLabel(_ value: String?) -> String? {
+    guard let value else { return nil }
+    let f = DateFormatter()
+    f.locale = Locale(identifier: "en_US_POSIX")
+    f.dateFormat = "EEE, dd MMM yyyy HH:mm:ss zzz"
+    return f.date(from: value).map { CivilDate($0).longLabel }
+}
+
+/**
+ * The timetable's rows: the weekly Word rows, plus lessons printed with their own date (the
+ * server's key then starts with that date). Dates computed from week marks are not compared one
+ * by one, or one changed mark would read as a dozen changes.
+ */
+private func rows(_ t: Timetable) -> [ChangedLesson] {
+    let weekly = t.weekly.flatMap { d in d.lessons.map { ChangedLesson(day: d.day, date: nil, lesson: $0) } }
+    var seen = Set<String>()
+    let dated = t.days.flatMap { d in
+        d.lessons.filter { $0.key.range(of: #"^\d{4}-\d{2}-\d{2}\|"#, options: .regularExpression) != nil }
+            .map { ChangedLesson(day: d.weekday, date: d.date, lesson: $0) }
+    }.filter { seen.insert($0.lesson.key).inserted }
+    return weekly + dated
+}
+
+private func norm(_ s: String) -> String {
+    s.lowercased().split(whereSeparator: \.isWhitespace).joined(separator: " ")
+}
+
+/// Looser identity for pairing a lesson whose day, time or week mark changed.
+private func looseKey(_ l: Lesson) -> String {
+    [norm(l.subject), l.variant, l.subgroup ?? "", norm(l.type)].joined(separator: "|")
+}
+
+private func whenLabel(_ row: ChangedLesson) -> String {
+    row.date.flatMap { CivilDate($0) }.map { "\($0.weekdayName), \($0.longLabel)" } ?? dayName(row.day)
+}
+
+private func fields(_ a: ChangedLesson, _ b: ChangedLesson) -> [FieldChange] {
+    let pairs: [(String, String, String)] = [
+        ("День", whenLabel(a), whenLabel(b)),
+        ("Начало", a.lesson.start, b.lesson.start),
+        ("Окончание", a.lesson.end ?? "", b.lesson.end ?? ""),
+        ("Недели", a.lesson.condition, b.lesson.condition),
+        ("Вид занятия", a.lesson.type, b.lesson.type),
+        ("Преподаватель", a.lesson.teachers.joined(separator: ", "), b.lesson.teachers.joined(separator: ", ")),
+        ("Аудитория", a.lesson.rooms.joined(separator: ", "), b.lesson.rooms.joined(separator: ", ")),
+    ]
+    let shown = { (s: String) in s.trimmed.isEmpty ? "не указано" : s }
+    return pairs.filter { $0.1.trimmed != $0.2.trimmed }.map { FieldChange(label: $0.0, from: shown($0.1), to: shown($0.2)) }
+}
+
+private func order(_ a: ChangedLesson, _ b: ChangedLesson) -> Bool {
+    ((a.date ?? ""), a.day, a.lesson.start) < ((b.date ?? ""), b.day, b.lesson.start)
+}
+
+/// Added, removed and changed rows between two versions of the group's timetable.
+private func diff(_ before: Timetable, _ after: Timetable) -> ([ChangedLesson], [ChangedLesson], [LessonChange]) {
+    var old: [String: [ChangedLesson]] = [:]
+    var order0: [String] = []
+    for row in rows(before) {
+        if old[row.lesson.key] == nil { order0.append(row.lesson.key) }
+        old[row.lesson.key, default: []].append(row)
+    }
+    var changed: [LessonChange] = []
+    var unmatched: [ChangedLesson] = []
+    for row in rows(after) {
+        if var list = old[row.lesson.key], !list.isEmpty {
+            let was = list.removeFirst()
+            old[row.lesson.key] = list
+            let f = fields(was, row)
+            if !f.isEmpty { changed.append(LessonChange(before: was, after: row, fields: f)) }
+        } else {
+            unmatched.append(row)
+        }
+    }
+    var left = order0.flatMap { old[$0] ?? [] }
+    // Pair the rest by subject on the same day first, then by subject alone (moved to another day).
+    for sameDay in [true, false] {
+        for row in unmatched {
+            guard let index = left.firstIndex(where: {
+                looseKey($0.lesson) == looseKey(row.lesson) && (!sameDay || ($0.date ?? "\($0.day)") == (row.date ?? "\(row.day)"))
+            }) else { continue }
+            let was = left.remove(at: index)
+            if let i = unmatched.firstIndex(of: row) { unmatched.remove(at: i) }
+            changed.append(LessonChange(before: was, after: row, fields: fields(was, row)))
+        }
+    }
+    return (unmatched.sorted(by: order), left.sorted(by: order), changed.sorted { order($0.after, $1.after) })
+}