import SwiftUI

private let plainPeriod = #/^(осенний|весенний) семестр$|^расписание из word$/#.ignoresCase()

private func describe(_ faculty: String, _ course: String, _ form: String = "", _ period: String = "") -> String {
    var parts: [String] = []
    if let f = facultyShort(faculty) { parts.append(f) }
    if !course.isEmpty { parts.append(course) }
    let form = form.replacingOccurrences(of: " форма", with: "").lowercased()
    if !form.isEmpty { parts.append(form) }
    if !period.isEmpty && (try? plainPeriod.wholeMatch(in: period)) == nil { parts.append(period.lowercased()) }
    return parts.joined(separator: " · ")
}

/**
 * Picking a group: search by number across the whole catalog, recent groups, the catalog by
 * faculty and course, and the subgroup of the open group. Students think in groups, not files.
 */
struct GroupsView: View {
    @Environment(AppModel.self) private var model
    @Environment(\.dismiss) private var dismiss
    /** A step of the onboarding: its own header, and the subgroup is asked on a page of its own. */
    var onboarding: Bool
    var onOpened: () -> Void

    @State private var query = ""
    @State private var faculty = ""
    @State private var course = ""
    @State private var data: GroupsResponse?
    @State private var error: String?
    @State private var retries = 0
    @State private var opening: String?
    @State private var askSubgroup: [String]?

    var body: some View {
        let current = model.settings.current
        let searching = query.trimmed.count >= 2
        List {
            if onboarding || current == nil {
                VStack(alignment: .leading, spacing: 6) {
                    Text("Найдите свою группу").font(.largeTitle.bold())
                    Text("Расписание откроется сразу и будет доступно без интернета.").foregroundStyle(.secondary)
                }
                .listRowBackground(Color.clear)
                .listRowInsets(EdgeInsets(top: 8, leading: 4, bottom: 4, trailing: 4))
            }
            Section {
                HStack(spacing: 10) {
                    Image(systemName: "magnifyingglass").foregroundStyle(.secondary)
                    TextField("Номер группы, например 23-БА", text: $query)
                        .textInputAutocapitalization(.characters)
                        .autocorrectionDisabled()
                        .submitLabel(.search)
                    if !query.isEmpty {
                        Button("Очистить", systemImage: "xmark.circle.fill") { query = "" }
                            .labelStyle(.iconOnly).foregroundStyle(.secondary).buttonStyle(.plain)
                    }
                }
                .padding(.horizontal, 16)
                .padding(.vertical, 12)
                .glassEffect(.regular.interactive(), in: .capsule)
                .listRowBackground(Color.clear)
                .listRowInsets(EdgeInsets())
            }
            if let error {
                Banner(text: error, offline: true, onRetry: { self.error = nil; retries += 1 })
                    .listRowBackground(Color.clear).listRowInsets(EdgeInsets())
            }
            if let message = model.status.message {
                Banner(text: message, offline: model.status.offline, onClose: { model.dismissMessage() }, onRetry: model.status.offline ? { Task { await model.retry() } } : nil)
                    .listRowBackground(Color.clear).listRowInsets(EdgeInsets())
            }

            if searching {
                let results = data?.results ?? []
                if !results.isEmpty {
                    Section("Найдено: \(results.count)") { rows(results) }
                } else if data != nil {
                    EmptyState(title: "Группа не найдена", text: "Группы «\(query.trimmed)» нет в каталоге \(data?.year ?? ""). Проверьте номер.", symbol: "magnifyingglass")
                        .listRowBackground(Color.clear)
                }
            } else {
                if let current, !onboarding {
                    Section("Сейчас открыта") {
                        GroupRow(group: current.group, subtitle: describe(current.faculty, current.course))
                        if let subgroups = model.timetable?.subgroups, !subgroups.isEmpty {
                            Picker("Подгруппа", selection: Binding(get: { model.subgroup }, set: { model.setSubgroup($0) })) {
                                Text("Все").tag(String?.none)
                                ForEach(subgroups, id: \.self) { Text($0.replacingOccurrences(of: "Подгруппа ", with: "")).tag(Optional($0)) }
                            }
                            .pickerStyle(.segmented)
                        }
                    }
                }
                let recent = model.settings.recent.filter { $0.key != current?.key }
                if !recent.isEmpty {
                    Section("Недавние") {
                        ForEach(recent, id: \.key) { g in
                            Button { Task { await model.open(g); opened() } } label: {
                                GroupRow(group: g.group, subtitle: describe(g.faculty, g.course), chevron: true)
                            }
                            .foregroundStyle(.primary)
                        }
                    }
                }
                if let d = data {
                    Section {
                        VStack(alignment: .leading, spacing: 10) {
                            Text("Факультет").font(.subheadline.weight(.semibold)).foregroundStyle(.secondary)
                            FlowLayout(spacing: 8) {
                                ForEach(d.facets.faculties, id: \.name) { f in
                                    Chip(label: facultyShort(f.name) ?? f.name, on: faculty == f.name) {
                                        faculty = faculty == f.name ? "" : f.name
                                        course = ""
                                    }
                                }
                            }
                            if !faculty.isEmpty {
                                Text("Курс").font(.subheadline.weight(.semibold)).foregroundStyle(.secondary).padding(.top, 4)
                                FlowLayout(spacing: 8) {
                                    ForEach(d.facets.courses, id: \.name) { c in
                                        Chip(label: c.name, on: course == c.name) { course = course == c.name ? "" : c.name }
                                    }
                                }
                            } else {
                                Text("Выберите факультет или введите номер группы. Всего в каталоге \(d.total) групп.")
                                    .font(.subheadline).foregroundStyle(.secondary)
                            }
                        }
                        .padding(.vertical, 6)
                        if !faculty.isEmpty { rows(d.results) }
                    } header: {
                        Text("Каталог \(d.year)")
                    }
                } else if error == nil {
                    ProgressView().frame(maxWidth: .infinity).listRowBackground(Color.clear)
                }
            }
        }
        .listStyle(.insetGrouped)
        .scrollDismissesKeyboard(.interactively)
        .navigationTitle(onboarding ? "" : "Группы")
        .navigationBarTitleDisplayMode(.inline)
        .toolbar {
            if !onboarding && current != nil {
                ToolbarItem(placement: .confirmationAction) { Button("Готово", systemImage: "checkmark") { dismiss() } }
            }
        }
        .task(id: "\(query)|\(faculty)|\(course)|\(retries)") {
            if !query.isEmpty { try? await Task.sleep(for: .milliseconds(250)) }
            guard !Task.isCancelled else { return }
            do {
                data = try await model.api.groups(query: query.trimmed, faculty: faculty, course: course)
                error = nil
            } catch is CancellationError {
            } catch {
                self.error = error.localizedDescription
            }
        }
        .alert("Ваша подгруппа", isPresented: Binding(get: { askSubgroup != nil }, set: { if !$0 { askSubgroup = nil } })) {
            ForEach(askSubgroup ?? [], id: \.self) { s in
                Button(s) { model.setSubgroup(s); askSubgroup = nil; onOpened() }
            }
            Button("Все подгруппы") { model.setSubgroup(nil); askSubgroup = nil; onOpened() }
            Button("Позже", role: .cancel) { askSubgroup = nil; onOpened() }
        } message: {
            Text("В группе \(model.timetable?.group ?? "") занятия делятся на подгруппы. Выберите свою — чужие пары скроются из расписания, виджетов и напоминаний. Изменить можно в разделе «Группы».")
        }
        .onAppear { if faculty.isEmpty { faculty = current?.faculty ?? "" } }
    }

    @ViewBuilder private func rows(_ results: [GroupResult]) -> some View {
        ForEach(results) { r in
            Button {
                opening = r.id
                Task {
                    let ok = await model.open(r)
                    opening = nil
                    if ok { opened() }
                }
            } label: {
                GroupRow(group: r.group, subtitle: describe(r.faculty, r.course, r.form, r.period), chevron: opening != r.id, busy: opening == r.id)
            }
            .foregroundStyle(.primary)
            .disabled(opening != nil)
        }
    }

    /// A group with subgroups asks which one is yours, unless you already chose it.
    private func opened() {
        let subgroups = model.timetable?.subgroups ?? []
        if !subgroups.isEmpty && model.subgroup == nil && !onboarding {
            askSubgroup = subgroups
        } else {
            onOpened()
        }
    }
}

private struct GroupRow: View {
    @Environment(\.palette) private var palette
    @Environment(\.colorScheme) private var scheme
    var group: String
    var subtitle: String
    var chevron = false
    var busy = false

    var body: some View {
        let label = String(group.split(separator: "-").dropFirst().first ?? Substring(group)).prefix(3)
        let c = palette.color(String(label), dark: scheme == .dark)
        HStack(spacing: 14) {
            Text(label.uppercased())
                .font(.footnote.weight(.bold))
                .foregroundStyle(c.onStrong)
                .frame(width: 40, height: 40)
                .background(c.strong, in: .circle)
            VStack(alignment: .leading, spacing: 2) {
                Text(group).font(.headline)
                Text(subtitle).font(.subheadline).foregroundStyle(.secondary)
            }
            Spacer()
            if busy { ProgressView() } else if chevron { Image(systemName: "chevron.right").font(.footnote.weight(.semibold)).foregroundStyle(.tertiary) }
        }
        .contentShape(.rect)
    }
}

private struct Chip: View {
    var label: String
    var on: Bool
    var action: () -> Void
    var body: some View {
        Button(action: action) {
            HStack(spacing: 4) {
                if on { Image(systemName: "checkmark").font(.caption.weight(.bold)) }
                Text(label).font(.subheadline.weight(.medium))
            }
            .padding(.horizontal, 12)
            .padding(.vertical, 7)
            .foregroundStyle(on ? Color.onBrand : .primary)
            .background(on ? Color.brand : Color(.tertiarySystemFill), in: .capsule)
        }
        .buttonStyle(.plain)
        .accessibilityAddTraits(on ? .isSelected : [])
    }
}