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/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]) }
         }
     }