import SwiftUI

/// Verwaltungs-Tab: alles, was Stammdaten sind, plus die Serverliste.
struct AdminTabView: View {
    @EnvironmentObject private var session: Session
    @State private var manageShown = false

    var body: some View {
        NavigationStack {
            List {
                Section("Stammdaten") {
                    NavigationLink { LocationsView() } label: {
                        Label("Lagerorte", systemImage: "mappin.and.ellipse")
                    }
                    NavigationLink { UnitsView() } label: {
                        Label("Einheiten", systemImage: "ruler")
                    }
                    NavigationLink { PackageTypesView() } label: {
                        Label("Gebinde", systemImage: "shippingbox")
                    }
                    NavigationLink { CategoriesView() } label: {
                        Label("Kategorien", systemImage: "folder")
                    }
                    NavigationLink { GroupsView() } label: {
                        Label("Gruppen", systemImage: "square.stack.3d.up")
                    }
                    NavigationLink { ShopsView() } label: {
                        Label("Shops", systemImage: "cart")
                    }
                }

                Section("App") {
                    Button {
                        manageShown = true
                    } label: {
                        Label("Server verwalten", systemImage: "server.rack")
                    }
                }

                Section {
                    Button("Abmelden", role: .destructive) { session.logout() }
                } footer: {
                    Text("Benutzer, Einstellungen und Sicherungen bleiben der Web-Oberfläche vorbehalten.")
                }
            }
            .navigationTitle("Verwaltung")
            .sheet(isPresented: $manageShown) { ServerListView() }
        }
    }
}

// MARK: - Gemeinsamer Bauplan

/// Ein Eintrag, wie ihn die Stammdatenliste braucht - unabhaengig davon, ob
/// dahinter ein Lagerort, eine Einheit oder ein Gebinde steckt.
struct MasterDataItem: Identifiable, Equatable {
    let id: Int
    let title: String
    let subtitle: String
    /// Eingebautes laesst sich umbenennen, aber nicht loeschen.
    let isBuiltin: Bool
}

/// Liste mit Anlegen, Umbenennen und Loeschen.
///
/// Alle fuenf Stammdatenbereiche sehen gleich aus und unterscheiden sich nur
/// darin, *wie* geladen und geschrieben wird. Genau das wird hier
/// hereingereicht, statt die Ansicht fuenfmal zu schreiben.
struct MasterDataListView<Editor: View>: View {
    let title: String
    /// Einzahl fuer Meldungen ("Lagerort").
    let singular: String
    let load: () async throws -> [MasterDataItem]
    let delete: ((Int) async throws -> Void)?
    /// Baut den Editor zum Anlegen (`nil`) oder Bearbeiten eines Eintrags.
    @ViewBuilder let editor: (MasterDataItem?, @escaping () -> Void) -> Editor

    @State private var items: [MasterDataItem] = []
    @State private var busy = true
    @State private var error: String?
    @State private var editing: MasterDataItem?
    @State private var addShown = false
    @State private var pendingDeletion: MasterDataItem?

    var body: some View {
        List {
            if let error {
                Section { Text(error).foregroundStyle(.red).font(.callout) }
            }
            ForEach(items) { item in
                Button {
                    editing = item
                } label: {
                    HStack {
                        VStack(alignment: .leading, spacing: 2) {
                            Text(item.title).foregroundStyle(.primary)
                            if !item.subtitle.isEmpty {
                                Text(item.subtitle).font(.caption).foregroundStyle(.secondary)
                            }
                        }
                        Spacer()
                        if item.isBuiltin {
                            Text("eingebaut").font(.caption2).foregroundStyle(.tertiary)
                        }
                    }
                }
                .swipeActions(edge: .trailing) {
                    // Eingebautes bekommt gar nicht erst einen Loeschknopf.
                    if delete != nil && !item.isBuiltin {
                        Button("Löschen", role: .destructive) { pendingDeletion = item }
                    }
                }
            }
            if items.isEmpty && !busy {
                Text("Noch nichts angelegt.").foregroundStyle(.secondary)
            }
        }
        .navigationTitle(title)
        .navigationBarTitleDisplayMode(.inline)
        .toolbar {
            ToolbarItem(placement: .topBarTrailing) {
                Button("Hinzufügen", systemImage: "plus") { addShown = true }
            }
        }
        .sheet(isPresented: $addShown) {
            editor(nil) { Task { await reload() } }
        }
        .sheet(item: $editing) { item in
            editor(item) { Task { await reload() } }
        }
        .confirmationDialog(
            pendingDeletion.map { "„\($0.title)“ löschen?" } ?? "",
            isPresented: Binding(get: { pendingDeletion != nil },
                                 set: { if !$0 { pendingDeletion = nil } }),
            titleVisibility: .visible
        ) {
            Button("Löschen", role: .destructive) {
                if let item = pendingDeletion { Task { await remove(item) } }
                pendingDeletion = nil
            }
            Button("Abbrechen", role: .cancel) { pendingDeletion = nil }
        } message: {
            Text("Wird \(singular.lowercased()) noch verwendet, lehnt der Server das Löschen ab.")
        }
        .refreshable { await reload() }
        .task { await reload() }
    }

    private func reload() async {
        busy = true
        defer { busy = false }
        do {
            items = try await load()
            error = nil
        } catch {
            self.error = error.localizedDescription
        }
    }

    private func remove(_ item: MasterDataItem) async {
        guard let delete else { return }
        do {
            try await delete(item.id)
            error = nil
            await reload()
        } catch {
            // Der Server begruendet die Ablehnung ("wird noch verwendet") -
            // die Meldung unveraendert zeigen.
            self.error = error.localizedDescription
        }
    }
}

// MARK: - Aufklappbarer Baum (Kategorien, Lagerorte)

/// Ein-/ausklappbare Baumliste für hierarchische Stammdaten. Kümmert sich um
/// Baumreihenfolge, Ein-/Ausklappen, Anlegen, Bearbeiten und Löschen. Die
/// Besonderheiten (Kopfzeile mit Filter, Zeilen-Hinweis, Editor) kommen von
/// außen herein, damit Kategorien und Lagerorte dieselbe Mechanik teilen.
struct TreeMasterView<Item: TreeItem, Header: View, Editor: View>: View {
    let title: String
    let singular: String
    let load: () async throws -> [Item]
    let delete: (Int) async throws -> Void
    /// Optionaler kleiner Hinweis am Zeilenende (z. B. der Kategorie-Typ).
    let badge: (Item) -> String?
    /// Nur Einträge, die das erfüllen, werden gezeigt (z. B. der Typ-Filter).
    let include: (Item) -> Bool
    @ViewBuilder let header: () -> Header
    @ViewBuilder let editor: (_ editing: Item?, _ all: [Item], _ done: @escaping () -> Void) -> Editor

    @State private var items: [Item] = []
    @State private var collapsed: Set<Int> = []
    @State private var busy = true
    @State private var error: String?
    @State private var editing: Item?
    @State private var addShown = false
    @State private var pendingDeletion: Item?

    private struct Node: Identifiable {
        let item: Item
        let depth: Int
        var id: Int { item.id }
    }

    private var shown: [Item] { items.filter(include) }

    /// Baumreihenfolge mit Tiefe. Waisen (Elternteil gefiltert/gelöscht) gelten
    /// als oberste Ebene, damit nichts verschwindet.
    private var nodes: [Node] {
        let list = shown
        let ids = Set(list.map(\.id))
        var result: [Node] = []
        func walk(_ n: Item, _ depth: Int) {
            result.append(Node(item: n, depth: depth))
            for child in list.filter({ $0.parentId == n.id }) { walk(child, depth + 1) }
        }
        for root in list.filter({ $0.parentId == nil || !ids.contains($0.parentId!) }) {
            walk(root, 0)
        }
        return result
    }

    private func childCount(_ id: Int) -> Int { shown.filter { $0.parentId == id }.count }

    private var visible: [Node] {
        let parent = Dictionary(uniqueKeysWithValues: shown.map { ($0.id, $0.parentId) })
        func hidden(_ id: Int) -> Bool {
            var p = parent[id] ?? nil
            while let cur = p {
                if collapsed.contains(cur) { return true }
                p = parent[cur] ?? nil
            }
            return false
        }
        return nodes.filter { !hidden($0.item.id) }
    }

    var body: some View {
        VStack(spacing: 0) {
            header()
            List {
                if let error {
                    Section { Text(error).foregroundStyle(.red).font(.callout) }
                }
                ForEach(visible) { node in
                    row(node)
                        .swipeActions(edge: .trailing) {
                            Button("Löschen", role: .destructive) { pendingDeletion = node.item }
                        }
                }
                if shown.isEmpty && !busy {
                    Text("Nichts vorhanden.").foregroundStyle(.secondary)
                }
            }
        }
        .navigationTitle(title)
        .navigationBarTitleDisplayMode(.inline)
        .toolbar {
            ToolbarItem(placement: .topBarTrailing) {
                Button("Hinzufügen", systemImage: "plus") { addShown = true }
            }
        }
        .sheet(isPresented: $addShown) {
            editor(nil, items) { Task { await reload() } }
        }
        .sheet(item: $editing) { item in
            editor(item, items) { Task { await reload() } }
        }
        .confirmationDialog(
            pendingDeletion.map { "„\($0.name)“ löschen?" } ?? "",
            isPresented: Binding(get: { pendingDeletion != nil },
                                 set: { if !$0 { pendingDeletion = nil } }),
            titleVisibility: .visible
        ) {
            Button("Löschen", role: .destructive) {
                if let item = pendingDeletion { Task { await remove(item) } }
                pendingDeletion = nil
            }
            Button("Abbrechen", role: .cancel) { pendingDeletion = nil }
        } message: {
            Text("Wird \(singular.lowercased()) noch verwendet oder hat Untereinträge, entscheidet der Server.")
        }
        .refreshable { await reload() }
        .task { await reload() }
    }

    @ViewBuilder
    private func row(_ node: Node) -> some View {
        let kinder = childCount(node.item.id)
        let zu = collapsed.contains(node.item.id)
        HStack(spacing: 8) {
            if kinder > 0 {
                Button {
                    withAnimation(.easeInOut(duration: 0.15)) { toggle(node.item.id) }
                } label: {
                    Image(systemName: "chevron.right")
                        .font(.caption.weight(.semibold))
                        .foregroundStyle(.secondary)
                        .rotationEffect(.degrees(zu ? 0 : 90))
                        .frame(width: 18)
                }
                .buttonStyle(.plain)
            } else {
                Color.clear.frame(width: 18, height: 1)
            }
            Button {
                editing = node.item
            } label: {
                HStack(spacing: 8) {
                    Text(node.item.name).foregroundStyle(.primary)
                    if zu && kinder > 0 {
                        Text("\(kinder) ausgeblendet").font(.caption2).foregroundStyle(.tertiary)
                    }
                    Spacer()
                    if let hinweis = badge(node.item) {
                        Text(hinweis).font(.caption2).foregroundStyle(.secondary)
                    }
                }
                .contentShape(Rectangle())
            }
            .buttonStyle(.plain)
        }
        .padding(.leading, CGFloat(node.depth) * 16)
    }

    private func toggle(_ id: Int) {
        if collapsed.contains(id) { collapsed.remove(id) } else { collapsed.insert(id) }
    }

    private func reload() async {
        busy = true
        defer { busy = false }
        do {
            items = try await load()
            error = nil
        } catch {
            self.error = error.localizedDescription
        }
    }

    private func remove(_ item: Item) async {
        do {
            try await delete(item.id)
            error = nil
            await reload()
        } catch {
            self.error = error.localizedDescription
        }
    }
}

/// Kleiner Editor fuer alles, was nur einen Namen hat.
struct NameEditor: View {
    @Environment(\.dismiss) private var dismiss

    let title: String
    let label: String
    let initial: String
    let save: (String) async throws -> Void
    let done: () -> Void

    @State private var name: String
    @State private var error: String?
    @State private var busy = false

    init(title: String, label: String = "Name", initial: String = "",
         save: @escaping (String) async throws -> Void, done: @escaping () -> Void) {
        self.title = title
        self.label = label
        self.initial = initial
        self.save = save
        self.done = done
        _name = State(initialValue: initial)
    }

    var body: some View {
        NavigationStack {
            Form {
                Section(label) {
                    TextField(label, text: $name)
                }
                if let error {
                    Section { Text(error).foregroundStyle(.red).font(.callout) }
                }
            }
            .navigationTitle(title)
            .navigationBarTitleDisplayMode(.inline)
            .toolbar {
                ToolbarItem(placement: .topBarLeading) {
                    Button("Abbrechen") { dismiss() }
                }
                ToolbarItem(placement: .topBarTrailing) {
                    Button(busy ? "Sichern…" : "Sichern") { Task { await submit() } }
                        .disabled(busy || name.trimmingCharacters(in: .whitespaces).isEmpty)
                }
            }
        }
    }

    private func submit() async {
        busy = true
        defer { busy = false }
        do {
            try await save(name.trimmingCharacters(in: .whitespaces))
            done()
            dismiss()
        } catch {
            self.error = error.localizedDescription
        }
    }
}

// MARK: - Die fuenf Bereiche

struct LocationsView: View {
    var body: some View {
        TreeMasterView(
            title: "Lagerorte",
            singular: "Der Lagerort",
            load: { try await APIClient.shared.locations() },
            delete: { try await APIClient.shared.deleteLocation(id: $0) },
            badge: { _ in nil },
            include: { _ in true },
            header: { EmptyView() },
            editor: { item, all, done in
                LocationEditor(item: item, all: all, done: done)
            }
        )
    }
}

/// Lagerort anlegen oder bearbeiten: Name **und** übergeordneter Ort. So lässt
/// sich die Hierarchie auch nachträglich ändern (umhängen). Beim Bearbeiten sind
/// der Ort selbst und seine Unterorte als Ziel ausgeschlossen (kein Ring).
struct LocationEditor: View {
    @Environment(\.dismiss) private var dismiss

    let item: StorageLocation?
    let all: [StorageLocation]
    let done: () -> Void

    @State private var name: String
    @State private var parentId: Int?
    @State private var error: String?
    @State private var busy = false

    init(item: StorageLocation?, all: [StorageLocation], done: @escaping () -> Void) {
        self.item = item
        self.all = all
        self.done = done
        _name = State(initialValue: item?.name ?? "")
        _parentId = State(initialValue: item?.parentId)
    }

    private var parentOptions: [StorageLocation] {
        guard let item else { return all }
        let verboten = LocationEditor.descendants(of: item.id, in: all).union([item.id])
        return all.filter { !verboten.contains($0.id) }
    }

    var body: some View {
        NavigationStack {
            Form {
                Section("Name") {
                    TextField("z. B. Keller", text: $name)
                }
                Section {
                    Picker("Übergeordnet", selection: $parentId) {
                        Text("– oberste Ebene –").tag(Int?.none)
                        ForEach(parentOptions) { loc in
                            Text(LocationEditor.pfad(loc, in: all)).tag(Int?.some(loc.id))
                        }
                    }
                } header: {
                    Text("Übergeordneter Lagerort (optional)")
                }
                if let error {
                    Section { Text(error).foregroundStyle(.red).font(.callout) }
                }
            }
            .navigationTitle(item == nil ? "Lagerort anlegen" : "Lagerort bearbeiten")
            .navigationBarTitleDisplayMode(.inline)
            .toolbar {
                ToolbarItem(placement: .topBarLeading) {
                    Button("Abbrechen") { dismiss() }
                }
                ToolbarItem(placement: .topBarTrailing) {
                    Button(busy ? "Sichern…" : "Sichern") { Task { await submit() } }
                        .disabled(busy || name.trimmingCharacters(in: .whitespaces).isEmpty)
                }
            }
        }
    }

    private func submit() async {
        busy = true
        defer { busy = false }
        let n = name.trimmingCharacters(in: .whitespaces)
        do {
            if let item {
                _ = try await APIClient.shared.updateLocation(
                    id: item.id, LocationUpdateRequest(name: n, parentId: parentId))
            } else {
                _ = try await APIClient.shared.createLocation(
                    NewLocationRequest(name: n, parentId: parentId))
            }
            done()
            dismiss()
        } catch {
            self.error = error.localizedDescription
        }
    }

    /// Alle Unterorte (rekursiv) – als Ziel beim Umhängen ausgeschlossen.
    private static func descendants(of id: Int, in all: [StorageLocation]) -> Set<Int> {
        var result: Set<Int> = []
        var stack = [id]
        while let cur = stack.popLast() {
            for kid in all where kid.parentId == cur {
                if result.insert(kid.id).inserted { stack.append(kid.id) }
            }
        }
        return result
    }

    /// "Keller → Regal" – der Pfad macht gleiche Namen im flachen Picker
    /// unterscheidbar.
    private static func pfad(_ loc: StorageLocation, in all: [StorageLocation]) -> String {
        let byId = Dictionary(uniqueKeysWithValues: all.map { ($0.id, $0) })
        var teile = [loc.name]
        var pid = loc.parentId
        while let cur = pid, let parent = byId[cur] {
            teile.insert(parent.name, at: 0)
            pid = parent.parentId
        }
        return teile.joined(separator: " → ")
    }
}

struct UnitsView: View {
    var body: some View {
        MasterDataListView(
            title: "Einheiten",
            singular: "Die Einheit",
            load: {
                try await APIClient.shared.units().map {
                    MasterDataItem(id: $0.id, title: $0.name,
                                   subtitle: "\(UnitsView.artText($0.kind)) · Faktor \(formatAmount($0.factor))",
                                   isBuiltin: $0.isBuiltin)
                }
            },
            delete: { try await APIClient.shared.deleteUnit(id: $0) }
        ) { item, done in
            if let item {
                NameEditor(
                    title: "Einheit umbenennen",
                    initial: item.title,
                    save: { _ = try await APIClient.shared.renameUnit(id: item.id, name: $0) },
                    done: done
                )
            } else {
                NewUnitEditor(done: done)
            }
        }
    }

    private static func artText(_ kind: String) -> String {
        switch kind {
        case "count": return "Anzahl"
        case "weight": return "Gewicht"
        case "volume": return "Volumen"
        default: return kind
        }
    }
}

/// Einheiten brauchen beim Anlegen Art und Faktor - danach stehen beide fest,
/// weil sie in bereits umgerechneten Bestaenden stecken.
struct NewUnitEditor: View {
    @Environment(\.dismiss) private var dismiss
    let done: () -> Void

    @State private var name = ""
    @State private var kind = "weight"
    @State private var factor = "1"
    @State private var error: String?
    @State private var busy = false

    private var faktorWert: Double? {
        Double(factor.replacingOccurrences(of: ",", with: "."))
    }

    var body: some View {
        NavigationStack {
            Form {
                Section("Name") {
                    TextField("z. B. Beutel", text: $name)
                }
                Section("Art") {
                    Picker("Art", selection: $kind) {
                        Text("Anzahl").tag("count")
                        Text("Gewicht").tag("weight")
                        Text("Volumen").tag("volume")
                    }
                    .pickerStyle(.segmented)
                }
                Section {
                    TextField("1", text: $factor).keyboardType(.decimalPad)
                } header: {
                    Text("Faktor")
                } footer: {
                    Text("Wie viele Basiseinheiten ergibt eine Einheit? Ein Kilogramm hat den Faktor 1000, weil die Basiseinheit Gramm ist.")
                }
                if let error {
                    Section { Text(error).foregroundStyle(.red).font(.callout) }
                }
            }
            .navigationTitle("Einheit anlegen")
            .navigationBarTitleDisplayMode(.inline)
            .toolbar {
                ToolbarItem(placement: .topBarLeading) {
                    Button("Abbrechen") { dismiss() }
                }
                ToolbarItem(placement: .topBarTrailing) {
                    Button("Sichern") { Task { await submit() } }
                        .disabled(busy || name.isEmpty || (faktorWert ?? 0) <= 0)
                }
            }
        }
    }

    private func submit() async {
        guard let wert = faktorWert else { return }
        busy = true
        defer { busy = false }
        do {
            _ = try await APIClient.shared.createUnit(
                NewUnitRequest(name: name.trimmingCharacters(in: .whitespaces),
                               kind: kind, factor: wert))
            done()
            dismiss()
        } catch {
            self.error = error.localizedDescription
        }
    }
}

struct PackageTypesView: View {
    var body: some View {
        MasterDataListView(
            title: "Gebinde",
            singular: "Das Gebinde",
            load: {
                try await APIClient.shared.packageTypes().map {
                    MasterDataItem(id: $0.id, title: $0.singular,
                                   subtitle: "Mehrzahl: \($0.plural)", isBuiltin: $0.isBuiltin)
                }
            },
            delete: { try await APIClient.shared.deletePackageType(id: $0) }
        ) { item, done in
            PackageTypeEditor(id: item?.id,
                              singular: item?.title ?? "",
                              plural: item.map { PackageTypesView.plural(from: $0.subtitle) } ?? "",
                              done: done)
        }
    }

    /// Der Untertitel traegt die Mehrzahl - hier wieder heraus.
    private static func plural(from subtitle: String) -> String {
        subtitle.replacingOccurrences(of: "Mehrzahl: ", with: "")
    }
}

/// Gebinde haben Einzahl **und** Mehrzahl (siehe Commit "Gebinde verwalten").
struct PackageTypeEditor: View {
    @Environment(\.dismiss) private var dismiss

    let id: Int?
    let done: () -> Void

    @State private var singular: String
    @State private var plural: String
    @State private var error: String?
    @State private var busy = false

    init(id: Int?, singular: String, plural: String, done: @escaping () -> Void) {
        self.id = id
        self.done = done
        _singular = State(initialValue: singular)
        _plural = State(initialValue: plural)
    }

    var body: some View {
        NavigationStack {
            Form {
                Section("Einzahl") {
                    TextField("z. B. Glas", text: $singular)
                }
                Section {
                    TextField(singular.isEmpty ? "z. B. Gläser" : singular, text: $plural)
                } header: {
                    Text("Mehrzahl")
                } footer: {
                    Text("Ohne Angabe wird die Einzahl verwendet.")
                }
                if let error {
                    Section { Text(error).foregroundStyle(.red).font(.callout) }
                }
            }
            .navigationTitle(id == nil ? "Gebinde anlegen" : "Gebinde bearbeiten")
            .navigationBarTitleDisplayMode(.inline)
            .toolbar {
                ToolbarItem(placement: .topBarLeading) {
                    Button("Abbrechen") { dismiss() }
                }
                ToolbarItem(placement: .topBarTrailing) {
                    Button("Sichern") { Task { await submit() } }
                        .disabled(busy || singular.trimmingCharacters(in: .whitespaces).isEmpty)
                }
            }
        }
    }

    private func submit() async {
        busy = true
        defer { busy = false }
        let einzahl = singular.trimmingCharacters(in: .whitespaces)
        let mehrzahl = plural.trimmingCharacters(in: .whitespaces).isEmpty
            ? einzahl : plural.trimmingCharacters(in: .whitespaces)
        do {
            if let id {
                _ = try await APIClient.shared.updatePackageType(
                    id: id, PackageTypeUpdateRequest(singular: einzahl, plural: mehrzahl))
            } else {
                _ = try await APIClient.shared.createPackageType(
                    NewPackageTypeRequest(singular: einzahl, plural: mehrzahl))
            }
            done()
            dismiss()
        } catch {
            self.error = error.localizedDescription
        }
    }
}

/// Kategorien als ein-/ausklappbarer Baum (wie im Web) mit Typ-Filter
/// Lebensmittel/Gegenstände. Anlegen und Bearbeiten wählen die Verwaltungsart.
struct CategoriesView: View {
    // "" = alle, sonst "food"/"object".
    @State private var typFilter = ""

    var body: some View {
        TreeMasterView(
            title: "Kategorien",
            singular: "Die Kategorie",
            load: { try await APIClient.shared.categories() },
            delete: { try await APIClient.shared.deleteCategory(id: $0) },
            // Typ nur in der „Alle"-Ansicht zeigen – gefiltert wäre er redundant.
            badge: { typFilter == "" ? CategoriesView.typLabel($0.tracking) : nil },
            include: { typFilter == "" || ($0.tracking ?? "food") == typFilter },
            header: {
                Picker("Typ", selection: $typFilter) {
                    Text("Alle").tag("")
                    Text("Lebensmittel").tag("food")
                    Text("Gegenstände").tag("object")
                }
                .pickerStyle(.segmented)
                .padding(.horizontal)
                .padding(.vertical, 8)
            },
            editor: { item, all, done in
                CategoryEditor(item: item, all: all, done: done)
            }
        )
    }

    static func typLabel(_ tracking: String?) -> String {
        tracking == "object" ? "Gegenstand" : "Lebensmittel"
    }
}

/// Kategorie anlegen oder bearbeiten: Name, Verwaltungsart und – beim Anlegen –
/// eine optionale Oberkategorie (Unterkategorie). Bei bestehenden Kategorien
/// führt ein Link zur Verwaltung der eigenen Felder.
struct CategoryEditor: View {
    @Environment(\.dismiss) private var dismiss

    let item: CategoryItem?
    let all: [CategoryItem]
    let done: () -> Void

    @State private var name: String
    @State private var tracking: String
    @State private var parentId: Int?   // nur beim Anlegen
    @State private var error: String?
    @State private var busy = false

    init(item: CategoryItem?, all: [CategoryItem], done: @escaping () -> Void) {
        self.item = item
        self.all = all
        self.done = done
        _name = State(initialValue: item?.name ?? "")
        _tracking = State(initialValue: item?.tracking ?? "object")
        _parentId = State(initialValue: nil)
    }

    // Mit gewählter Oberkategorie erbt die neue Kategorie deren Art – dann ist
    // die Art-Auswahl gegenstandslos.
    private var erbtVonEltern: Bool { item == nil && parentId != nil }

    var body: some View {
        NavigationStack {
            Form {
                Section("Name") {
                    TextField("z. B. Elektronik", text: $name)
                }

                if item == nil {
                    Section {
                        Picker("Übergeordnet", selection: $parentId) {
                            Text("– oberste Ebene –").tag(Int?.none)
                            ForEach(all) { c in
                                Text(CategoryEditor.pfad(c, in: all)).tag(Int?.some(c.id))
                            }
                        }
                    } header: {
                        Text("Übergeordnete Kategorie (optional)")
                    } footer: {
                        Text(erbtVonEltern
                             ? "Erbt die Verwaltungsart der Oberkategorie."
                             : "Ohne Oberkategorie unten die Verwaltungsart wählen.")
                    }
                }

                if !erbtVonEltern {
                    Section {
                        Picker("Art", selection: $tracking) {
                            Text("Lebensmittel").tag("food")
                            Text("Gegenstand").tag("object")
                        }
                        .pickerStyle(.segmented)
                    } header: {
                        Text("Verwaltungsart")
                    } footer: {
                        Text("Lebensmittel: Chargen mit Mindesthaltbarkeit. Gegenstand: Menge je Lagerort bzw. Einzelstücke. Unterkategorien erben die Art.")
                    }
                }

                if let item {
                    Section {
                        NavigationLink {
                            CategoryFieldsView(categoryId: item.id, categoryName: item.name)
                        } label: {
                            Label("Eigene Felder verwalten", systemImage: "tag")
                        }
                    }
                }

                if let error {
                    Section { Text(error).foregroundStyle(.red).font(.callout) }
                }
            }
            .navigationTitle(item == nil ? "Kategorie anlegen" : "Kategorie bearbeiten")
            .navigationBarTitleDisplayMode(.inline)
            .toolbar {
                ToolbarItem(placement: .topBarLeading) {
                    Button("Abbrechen") { dismiss() }
                }
                ToolbarItem(placement: .topBarTrailing) {
                    Button(busy ? "Sichern…" : "Sichern") { Task { await submit() } }
                        .disabled(busy || name.trimmingCharacters(in: .whitespaces).isEmpty)
                }
            }
        }
    }

    private func submit() async {
        busy = true
        defer { busy = false }
        let n = name.trimmingCharacters(in: .whitespaces)
        do {
            if let item {
                _ = try await APIClient.shared.updateCategory(
                    id: item.id, CategoryUpdateRequest(name: n, tracking: tracking))
            } else {
                // Mit Oberkategorie die Art erben (tracking = nil), sonst die
                // gewählte Art.
                _ = try await APIClient.shared.createCategory(
                    NewCategoryRequest(name: n, parentId: parentId,
                                       tracking: parentId == nil ? tracking : nil))
            }
            done()
            dismiss()
        } catch {
            self.error = error.localizedDescription
        }
    }

    private static func pfad(_ c: CategoryItem, in all: [CategoryItem]) -> String {
        let byId = Dictionary(uniqueKeysWithValues: all.map { ($0.id, $0) })
        var teile = [c.name]
        var pid = c.parentId
        while let cur = pid, let parent = byId[cur] {
            teile.insert(parent.name, at: 0)
            pid = parent.parentId
        }
        return teile.joined(separator: " → ")
    }
}

// MARK: - Eigene Felder je Kategorie

/// Eigene Felder einer Kategorie verwalten (anlegen, bearbeiten, löschen). Zeigt
/// nur die *eigenen* Felder – geerbte werden in der Oberkategorie gepflegt.
struct CategoryFieldsView: View {
    let categoryId: Int
    let categoryName: String

    @State private var fields: [FieldDefinition] = []
    @State private var busy = true
    @State private var error: String?
    @State private var editing: FieldDefinition?
    @State private var addShown = false
    @State private var pendingDeletion: FieldDefinition?

    var body: some View {
        List {
            if let error {
                Section { Text(error).foregroundStyle(.red).font(.callout) }
            }
            ForEach(fields) { f in
                Button { editing = f } label: {
                    HStack {
                        VStack(alignment: .leading, spacing: 2) {
                            Text(f.label).foregroundStyle(.primary)
                            Text(CategoryFieldsView.untertitel(f))
                                .font(.caption).foregroundStyle(.secondary)
                        }
                        Spacer()
                        if f.required {
                            Text("Pflicht").font(.caption2).foregroundStyle(.orange)
                        }
                    }
                }
                .swipeActions(edge: .trailing) {
                    Button("Löschen", role: .destructive) { pendingDeletion = f }
                }
            }
            if fields.isEmpty && !busy {
                Text("Noch keine eigenen Felder.").foregroundStyle(.secondary)
            }
        }
        .navigationTitle("Felder: \(categoryName)")
        .navigationBarTitleDisplayMode(.inline)
        .toolbar {
            ToolbarItem(placement: .topBarTrailing) {
                Button("Hinzufügen", systemImage: "plus") { addShown = true }
            }
        }
        .sheet(isPresented: $addShown) {
            FieldEditor(categoryId: categoryId, field: nil) { Task { await reload() } }
        }
        .sheet(item: $editing) { f in
            FieldEditor(categoryId: categoryId, field: f) { Task { await reload() } }
        }
        .confirmationDialog(
            pendingDeletion.map { "„\($0.label)“ löschen?" } ?? "",
            isPresented: Binding(get: { pendingDeletion != nil },
                                 set: { if !$0 { pendingDeletion = nil } }),
            titleVisibility: .visible
        ) {
            Button("Löschen", role: .destructive) {
                if let f = pendingDeletion { Task { await remove(f) } }
                pendingDeletion = nil
            }
            Button("Abbrechen", role: .cancel) { pendingDeletion = nil }
        } message: {
            Text("Die zu diesem Feld erfassten Werte gehen an allen Artikeln verloren.")
        }
        .refreshable { await reload() }
        .task { await reload() }
    }

    private static func untertitel(_ f: FieldDefinition) -> String {
        var teile = [FieldEditor.typLabel(f.fieldType)]
        if f.fieldType == "number", let u = f.unit, !u.isEmpty { teile.append(u) }
        if f.fieldType == "select", !f.options.isEmpty {
            teile.append(f.options.joined(separator: ", "))
        }
        return teile.joined(separator: " · ")
    }

    private func reload() async {
        busy = true
        defer { busy = false }
        do {
            fields = try await APIClient.shared.ownFieldDefinitions(categoryId: categoryId)
            error = nil
        } catch {
            self.error = error.localizedDescription
        }
    }

    private func remove(_ f: FieldDefinition) async {
        do {
            try await APIClient.shared.deleteFieldDefinition(id: f.id)
            error = nil
            await reload()
        } catch {
            self.error = error.localizedDescription
        }
    }
}

/// Eigenes Feld anlegen oder bearbeiten: Name, Typ, (Einheit bei Zahl,
/// Auswahlmöglichkeiten bei Auswahlliste) und Pflicht.
struct FieldEditor: View {
    @Environment(\.dismiss) private var dismiss

    let categoryId: Int
    let field: FieldDefinition?
    let done: () -> Void

    @State private var label: String
    @State private var fieldType: String
    @State private var unit: String
    @State private var options: String   // Komma-getrennt
    @State private var required: Bool
    @State private var error: String?
    @State private var busy = false

    static let typen: [(String, String)] = [
        ("text", "Text (einzeilig)"),
        ("textarea", "Text (mehrzeilig)"),
        ("number", "Zahl (mit Einheit)"),
        ("date", "Datum"),
        ("select", "Auswahlliste"),
        ("boolean", "Ja/Nein"),
    ]

    static func typLabel(_ v: String) -> String { typen.first { $0.0 == v }?.1 ?? v }

    init(categoryId: Int, field: FieldDefinition?, done: @escaping () -> Void) {
        self.categoryId = categoryId
        self.field = field
        self.done = done
        _label = State(initialValue: field?.label ?? "")
        _fieldType = State(initialValue: field?.fieldType ?? "text")
        _unit = State(initialValue: field?.unit ?? "")
        _options = State(initialValue: (field?.options ?? []).joined(separator: ", "))
        _required = State(initialValue: field?.required ?? false)
    }

    var body: some View {
        NavigationStack {
            Form {
                Section("Feldname") {
                    TextField("z. B. Kapazität", text: $label)
                }
                Section("Typ") {
                    Picker("Typ", selection: $fieldType) {
                        ForEach(FieldEditor.typen, id: \.0) { Text($0.1).tag($0.0) }
                    }
                }
                if fieldType == "number" {
                    Section("Einheit (optional)") {
                        TextField("z. B. mAh", text: $unit)
                    }
                }
                if fieldType == "select" {
                    Section {
                        TextField("z. B. S, M, L, XL", text: $options)
                    } header: {
                        Text("Auswahlmöglichkeiten")
                    } footer: {
                        Text("Mit Komma trennen.")
                    }
                }
                Section {
                    Toggle("Pflichtfeld", isOn: $required)
                }
                if let error {
                    Section { Text(error).foregroundStyle(.red).font(.callout) }
                }
            }
            .navigationTitle(field == nil ? "Feld anlegen" : "Feld bearbeiten")
            .navigationBarTitleDisplayMode(.inline)
            .toolbar {
                ToolbarItem(placement: .topBarLeading) {
                    Button("Abbrechen") { dismiss() }
                }
                ToolbarItem(placement: .topBarTrailing) {
                    Button(busy ? "Sichern…" : "Sichern") { Task { await submit() } }
                        .disabled(busy || label.trimmingCharacters(in: .whitespaces).isEmpty)
                }
            }
        }
    }

    private func submit() async {
        busy = true
        defer { busy = false }
        let l = label.trimmingCharacters(in: .whitespaces)
        let u = fieldType == "number" ? unit.trimmingCharacters(in: .whitespaces) : ""
        let opts = fieldType == "select"
            ? options.split(separator: ",").map { $0.trimmingCharacters(in: .whitespaces) }
                .filter { !$0.isEmpty }
            : []
        do {
            if let field {
                _ = try await APIClient.shared.updateFieldDefinition(
                    id: field.id,
                    FieldDefinitionUpdate(label: l, fieldType: fieldType, unit: u,
                                          options: opts, required: required))
            } else {
                _ = try await APIClient.shared.createFieldDefinition(
                    FieldDefinitionCreate(categoryId: categoryId, label: l, fieldType: fieldType,
                                          unit: u, options: opts, required: required))
            }
            done()
            dismiss()
        } catch {
            self.error = error.localizedDescription
        }
    }
}

struct GroupsView: View {
    var body: some View {
        MasterDataListView(
            title: "Gruppen",
            singular: "Die Gruppe",
            load: {
                try await APIClient.shared.groups().map {
                    MasterDataItem(id: $0.id, title: $0.name, subtitle: "", isBuiltin: false)
                }
            },
            delete: { try await APIClient.shared.deleteGroup(id: $0) }
        ) { item, done in
            NameEditor(
                title: item == nil ? "Gruppe anlegen" : "Gruppe umbenennen",
                initial: item?.title ?? "",
                save: { name in
                    if let item {
                        _ = try await APIClient.shared.renameGroup(id: item.id, name: name)
                    } else {
                        _ = try await APIClient.shared.createGroup(
                            NewGroupRequest(name: name, minStock: nil, minStockUnitId: nil))
                    }
                },
                done: done
            )
        }
    }
}

/// Bezugsquellen für „gekauft bei" (nur Gegenstände). Wie im Web pflegbar –
/// Name plus optionale Website.
struct ShopsView: View {
    var body: some View {
        MasterDataListView(
            title: "Shops",
            singular: "Der Shop",
            load: {
                try await APIClient.shared.shops().map {
                    // Die Website steht im Untertitel und wird beim Bearbeiten
                    // wieder daraus gelesen (wie bei den Gebinden die Mehrzahl).
                    MasterDataItem(id: $0.id, title: $0.name,
                                   subtitle: $0.website ?? "", isBuiltin: false)
                }
            },
            delete: { try await APIClient.shared.deleteShop(id: $0) }
        ) { item, done in
            ShopEditor(id: item?.id,
                       name: item?.title ?? "",
                       website: item?.subtitle ?? "",
                       done: done)
        }
    }
}

/// Shops haben Name und optionale Website.
struct ShopEditor: View {
    @Environment(\.dismiss) private var dismiss

    let id: Int?
    let done: () -> Void

    @State private var name: String
    @State private var website: String
    @State private var error: String?
    @State private var busy = false

    init(id: Int?, name: String, website: String, done: @escaping () -> Void) {
        self.id = id
        self.done = done
        _name = State(initialValue: name)
        _website = State(initialValue: website)
    }

    var body: some View {
        NavigationStack {
            Form {
                Section("Name") {
                    TextField("z. B. Digitec", text: $name)
                }
                Section {
                    TextField("https://…", text: $website)
                        .keyboardType(.URL)
                        .textInputAutocapitalization(.never)
                        .autocorrectionDisabled()
                } header: {
                    Text("Website (optional)")
                }
                if let error {
                    Section { Text(error).foregroundStyle(.red).font(.callout) }
                }
            }
            .navigationTitle(id == nil ? "Shop anlegen" : "Shop bearbeiten")
            .navigationBarTitleDisplayMode(.inline)
            .toolbar {
                ToolbarItem(placement: .topBarLeading) {
                    Button("Abbrechen") { dismiss() }
                }
                ToolbarItem(placement: .topBarTrailing) {
                    Button(busy ? "Sichern…" : "Sichern") { Task { await submit() } }
                        .disabled(busy || name.trimmingCharacters(in: .whitespaces).isEmpty)
                }
            }
        }
    }

    private func submit() async {
        busy = true
        defer { busy = false }
        let n = name.trimmingCharacters(in: .whitespaces)
        // Leeres Feld bewusst als "" senden (nicht nil): der Server setzt die
        // Website damit auf leer – so lässt sie sich auch wieder entfernen.
        let w = website.trimmingCharacters(in: .whitespaces)
        do {
            if let id {
                _ = try await APIClient.shared.updateShop(id: id, ShopUpdateRequest(name: n, website: w))
            } else {
                _ = try await APIClient.shared.createShop(NewShopRequest(name: n, website: w))
            }
            done()
            dismiss()
        } catch {
            self.error = error.localizedDescription
        }
    }
}