import SwiftUI

/// Whose day to show: a teacher or a room.
enum SearchTarget: Hashable {
    case teacher(String)
    case room(String)

    var title: String {
        switch self {
        case .teacher(let name): name
        case .room(let room): "Аудитория \(room)"
        }
    }
}

/// "Кто где": teachers and rooms across every timetable of the university, only online.
struct SearchView: View {
    @Environment(AppModel.self) private var model
    @Environment(Router.self) private var router
    @State private var hits: DirectorySearch?
    @State private var error: String?
    @State private var retries = 0

    var body: some View {
        NavigationStack {
            List {
                if let error {
                    Banner(text: error, offline: true, onRetry: { self.error = nil; retries += 1 })
                        .listRowBackground(Color.clear)
                        .listRowInsets(EdgeInsets())
                }
                if let hits, router.searchQuery.trimmed.count >= 2 {
                    if !hits.teachers.isEmpty {
                        Section("Преподаватели") {
                            ForEach(hits.teachers, id: \.name) { t in
                                NavigationLink(value: SearchTarget.teacher(t.name)) {
                                    VStack(alignment: .leading, spacing: 2) {
                                        Text(t.name).font(.body.weight(.medium))
                                        Text(([t.faculties.compactMap(facultyShort).joined(separator: ", ")].filter { !$0.isEmpty } + ["\(t.count) \(plural(t.count, "занятие", "занятия", "занятий"))"]).joined(separator: " · "))
                                            .font(.subheadline).foregroundStyle(.secondary)
                                    }
                                }
                            }
                        }
                    }
                    if !hits.rooms.isEmpty {
                        Section("Аудитории") {
                            ForEach(hits.rooms, id: \.room) { r in
                                NavigationLink(value: SearchTarget.room(r.room)) {
                                    Label("Аудитория \(r.room)", systemImage: "door.left.hand.open")
                                }
                            }
                        }
                    }
                    if hits.teachers.isEmpty && hits.rooms.isEmpty {
                        EmptyState(title: "Никого не нашли", text: "Ни преподавателя, ни аудитории с таким названием в расписаниях каталога.", symbol: "magnifyingglass")
                            .listRowBackground(Color.clear)
                    }
                } else if error == nil {
                    EmptyState(
                        title: "Кто где",
                        text: "Найдите преподавателя или аудиторию — покажем занятия на выбранный день по всем расписаниям университета.",
                        symbol: "binoculars"
                    )
                    .listRowBackground(Color.clear)
                }
            }
            .navigationTitle("Поиск")
            .navigationDestination(for: SearchTarget.self) { DirectoryDayView(target: $0) }
        }
        .task(id: "\(router.searchQuery)|\(retries)") {
            let q = router.searchQuery.trimmed
            guard q.count >= 2 else { hits = nil; return }
            try? await Task.sleep(for: .milliseconds(250))
            guard !Task.isCancelled else { return }
            do {
                hits = try await model.api.searchDirectory(q)
                error = nil
            } catch is CancellationError {
            } catch {
                self.error = error.localizedDescription
            }
        }
    }
}

/// A teacher's or room's lessons on a day, with a glass strip of dates.
struct DirectoryDayView: View {
    @Environment(AppModel.self) private var model
    var target: SearchTarget
    @State private var date = CivilDate.today().weekday == 7 ? CivilDate.today().adding(days: 1) : CivilDate.today()
    @State private var day: DirectoryDay?
    @State private var error: String?
    @State private var loading = false
    @State private var retries = 0
    @State private var bells: [Bell] = []

    var body: some View {
        ScrollView {
            LazyVStack(alignment: .leading, spacing: 12) {
                if let error {
                    Banner(text: error, offline: true, onRetry: { self.error = nil; retries += 1 })
                }
                if loading && day == nil {
                    ProgressView().frame(maxWidth: .infinity).padding(.top, 60)
                } else if let day {
                    if day.lessons.isEmpty {
                        EmptyState(title: "Занятий нет", text: "По расписаниям каталога в этот день здесь пусто.", symbol: "calendar.badge.checkmark")
                            .padding(.top, 40)
                    }
                    ForEach(Array(day.lessons.enumerated()), id: \.offset) { _, l in
                        DirectoryLessonCard(lesson: l, target: target, bells: bells)
                    }
                    Text(coverageNote(day.coverage))
                        .font(.footnote)
                        .foregroundStyle(.secondary)
                        .padding(.top, 8)
                }
            }
            .padding(16)
            .readableWidth()
        }
        .safeAreaBar(edge: .top, spacing: 0) {
            DateStrip(selected: $date).padding(.horizontal, 12).padding(.bottom, 6).readableWidth()
        }
        .background(Color(.systemGroupedBackground))
        .navigationTitle(target.title)
        .navigationSubtitle(date.weekdayName + ", " + date.longLabel)
        .navigationBarTitleDisplayMode(.inline)
        .task { if bells.isEmpty { bells = (try? await model.api.calendar().bells) ?? model.timetable?.bells ?? [] } }
        .task(id: "\(date.iso)|\(retries)") {
            loading = true
            defer { loading = false }
            do {
                day = switch target {
                case .teacher(let name): try await model.api.teacherDay(name, date: date)
                case .room(let room): try await model.api.roomDay(room, date: date)
                }
                error = nil
            } catch is CancellationError {
            } catch {
                self.error = error.localizedDescription
            }
        }
    }

    private func coverageNote(_ c: Coverage) -> String {
        var s = "По расписаниям из Word: учтено \(c.documents) из \(c.total) документов каталога \(c.year)."
        if !c.failed.isEmpty { s += " Не распознано: \(c.failed.count)." }
        if !c.withoutSemester.isEmpty { s += " Без дат (нет семестра в таблице недель): \(c.withoutSemester.count)." }
        return s
    }
}

private struct DirectoryLessonCard: View {
    var lesson: DirectoryLesson
    var target: SearchTarget
    var bells: [Bell]

    var body: some View {
        let pair = bells.first { $0.start == lesson.start }?.pair
        WithSubjectColor(subject: lesson.subject) { c in
            VStack(alignment: .leading, spacing: 6) {
                Text(lesson.subject).font(.headline)
                Text(lesson.start + (lesson.end.map { " → \($0)" } ?? "") + (pair.map { " · \($0) пара" } ?? "")).font(.body.monospacedDigit())
                FlowLayout(spacing: 14) {
                    if case .teacher = target {
                        Meta(symbol: "mappin.and.ellipse", text: lesson.distance ? "Дистанционно" : withPlace(lesson.rooms.joined(separator: ", ") + (lesson.moved ? " (перенос)" : ""), lesson.place) ?? "")
                    } else if !lesson.teachers.isEmpty {
                        Meta(symbol: "person", text: lesson.teachers.joined(separator: ", "))
                    }
                    if !lesson.groups.isEmpty { Meta(symbol: "person.3", text: lesson.groups.joined(separator: ", ")) }
                }
                FlowLayout(spacing: 6) {
                    if !lesson.type.isEmpty { Tag(text: lesson.type, foreground: c.onSoft, background: c.onSoft.opacity(0.12)) }
                    if lesson.uncertain { Tag(text: "Сверьте недели", foreground: .red, background: .red.opacity(0.14)) }
                }
            }
            .foregroundStyle(c.onSoft)
            .padding(.horizontal, 18).padding(.vertical, 14)
            .frame(maxWidth: .infinity, alignment: .leading)
            .background(c.soft, in: .rect(cornerRadius: 22, style: .continuous))
        }
    }
}

/// Seven days around the chosen one in a glass strip; arrows step a week.
struct DateStrip: View {
    @Binding var selected: CivilDate

    var body: some View {
        let monday = selected.monday
        let today = CivilDate.today()
        HStack(spacing: 2) {
            Button("Предыдущая неделя", systemImage: "chevron.left") { withAnimation(.smooth) { selected = selected.adding(days: -7) } }
                .labelStyle(.iconOnly).frame(width: 30)
            ForEach(0..<7, id: \.self) { i in
                let d = monday.adding(days: i)
                let isSelected = d == selected
                Button { withAnimation(.smooth) { selected = d } } label: {
                    VStack(spacing: 3) {
                        Text(d.shortWeekday).font(.caption2.weight(.medium)).foregroundStyle(d == today ? Color.brand : .secondary)
                        Text("\(d.day)")
                            .font(.callout.weight(isSelected ? .bold : .regular))
                            .foregroundStyle(isSelected ? Color.onBrand : .primary)
                            .frame(width: 32, height: 32)
                            .background { if isSelected { Circle().fill(Color.brand) } }
                    }
                    .frame(maxWidth: .infinity)
                    .contentShape(.rect)
                }
                .buttonStyle(.plain)
                .accessibilityLabel(d.weekdayName + ", " + d.longLabel)
            }
            Button("Следующая неделя", systemImage: "chevron.right") { withAnimation(.smooth) { selected = selected.adding(days: 7) } }
                .labelStyle(.iconOnly).frame(width: 30)
        }
        .padding(.vertical, 8)
        .padding(.horizontal, 4)
        .glassEffect(.regular.interactive(), in: .rect(cornerRadius: 26, style: .continuous))
    }
}