import SwiftUI

/// Gemeinsame Zahlenformatierung der Listen.
func formatAmount(_ value: Double) -> String {
    value == value.rounded() ? String(Int(value)) : String(format: "%.2f", value)
}

/// Kennzeichnung "Gruppe" an einer Listenzeile.
struct GroupBadge: View {
    var body: some View {
        Text("Gruppe")
            .font(.caption2)
            .padding(.horizontal, 6)
            .padding(.vertical, 2)
            .background(Color.secondary.opacity(0.15))
            .clipShape(Capsule())
            .foregroundStyle(.secondary)
    }
}

/// Zeile mit Symbol links, damit Artikel und Gruppe unterscheidbar sind.
struct ListRow<Trailing: View>: View {
    let systemImage: String
    let title: String
    let subtitle: String
    @ViewBuilder var trailing: Trailing

    var body: some View {
        HStack(spacing: 12) {
            Image(systemName: systemImage)
                .font(.body)
                .foregroundStyle(.secondary)
                .frame(width: 24)
            VStack(alignment: .leading, spacing: 2) {
                HStack(spacing: 6) {
                    Text(title)
                    trailing
                }
                Text(subtitle)
                    .font(.caption).foregroundStyle(.secondary)
            }
        }
    }
}

// MARK: - Einkaufsliste

struct ShoppingListView: View {
    @EnvironmentObject private var display: DisplaySettings

    @State private var items: [ShoppingItem] = []
    @State private var groups: [GroupShoppingItem] = []
    @State private var byLocation: [LocationNeeds] = []
    @State private var busy = true
    @State private var error: String?

    var body: some View {
        List {
            if let error {
                Section { Text(error).foregroundStyle(.red).font(.callout) }
            }
            if !items.isEmpty {
                Section("Artikel unter Mindestbestand") {
                    ForEach(items) { item in
                        ListRow(
                            systemImage: "shippingbox",
                            title: item.name,
                            subtitle: "fehlt \(display.amountText(item.deficit, packageSize: item.packageSize, baseUnit: item.baseUnit))"
                        ) { EmptyView() }
                    }
                }
            }
            if !groups.isEmpty {
                Section("Gruppen unter Mindestbestand") {
                    ForEach(groups) { group in
                        ListRow(
                            systemImage: "square.stack.3d.up",
                            title: group.name,
                            subtitle: "fehlt \(formatAmount(group.deficit)) \(group.unitName) · \(group.productCount) Artikel"
                        ) { GroupBadge() }
                    }
                }
            }
            ForEach(byLocation) { ort in
                Section("Bedarf: \(ort.locationName)") {
                    ForEach(ort.products) { p in
                        ListRow(
                            systemImage: "shippingbox",
                            title: p.name,
                            subtitle: "fehlt \(formatAmount(p.deficit)) \(p.unitLabel)"
                        ) { EmptyView() }
                    }
                    ForEach(ort.groups) { g in
                        ListRow(
                            systemImage: "square.stack.3d.up",
                            title: g.name,
                            subtitle: "fehlt \(formatAmount(g.deficit)) \(g.unitName)"
                        ) { GroupBadge() }
                    }
                }
            }
            if items.isEmpty && groups.isEmpty && byLocation.isEmpty && !busy {
                Text("Nichts einzukaufen – alle Mindestbestände sind gedeckt.")
                    .foregroundStyle(.secondary)
            }
        }
        .navigationTitle("Einkaufsliste")
        .navigationBarTitleDisplayMode(.inline)
        .refreshable { await load() }
        .task { await load() }
    }

    private func load() async {
        busy = true
        defer { busy = false }
        do {
            items = try await APIClient.shared.shoppingList()
            groups = try await APIClient.shared.shoppingGroups()
            byLocation = try await APIClient.shared.shoppingByLocation()
            error = nil
        } catch {
            self.error = error.localizedDescription
        }
    }
}

// MARK: - Bald ablaufend

struct ExpiringView: View {
    @EnvironmentObject private var display: DisplaySettings

    @State private var items: [ExpiringItem] = []
    @State private var busy = true
    @State private var error: String?

    var body: some View {
        List {
            if let error {
                Section { Text(error).foregroundStyle(.red).font(.callout) }
            }
            ForEach(items) { item in
                HStack {
                    VStack(alignment: .leading, spacing: 2) {
                        Text(item.productName)
                        Text("MHD \(display.formatBestBefore(item.bestBefore, precision: item.bestBeforePrecision)) · \(articleAmount(item))")
                            .font(.caption).foregroundStyle(.secondary)
                    }
                    Spacer()
                    Text(restText(item.daysLeft))
                        .font(.caption).bold()
                        .foregroundStyle(item.daysLeft < 0 ? .red : .orange)
                }
            }
            if items.isEmpty && !busy {
                Text("Nichts läuft demnächst ab.").foregroundStyle(.secondary)
            }
        }
        .navigationTitle("Bald ablaufend")
        .navigationBarTitleDisplayMode(.inline)
        .refreshable { await load() }
        .task { await load() }
    }

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

    /// Gebinde ist die Leitangabe, sonst die Produkteinheit.
    private func articleAmount(_ item: ExpiringItem) -> String {
        if let size = item.packageSize, size > 0 {
            return "\(formatAmount(item.quantity / size)) \(item.packageLabel ?? "Packung")"
        }
        let faktor = item.unitFactor == 0 ? 1 : item.unitFactor
        return "\(formatAmount(item.quantity / faktor)) \(item.unitName)"
    }

    private func restText(_ days: Int) -> String {
        if days < 0 { return "abgelaufen" }
        if days == 0 { return "heute" }
        return days == 1 ? "1 Tag" : "\(days) Tage"
    }
}

// MARK: - Produktliste

struct ProductListView: View {
    /// nil = alle, "food" = nur Lebensmittel, "object" = nur Gegenstände.
    /// Getrennte Listen wie im Web (dort über `fixedType`/`p.tracking`).
    var fixedType: String? = nil

    @EnvironmentObject private var session: Session
    @State private var query = ""
    @State private var products: [Product] = []
    @State private var categories: [CategoryItem] = []
    /// nil = alle, 0 = ohne Kategorie, sonst die ID (Unterkategorien zaehlen mit).
    @State private var categoryId: Int?
    @State private var sortMode: SortMode = .nameAsc
    @State private var busy = false
    @State private var showNew = false

    enum SortMode: String, CaseIterable, Identifiable {
        case nameAsc = "Name A–Z"
        case nameDesc = "Name Z–A"
        case updated = "Zuletzt geändert"
        var id: String { rawValue }
    }

    /// Auf den festen Typ gefiltert (clientseitig, wie im Web).
    private var sichtbar: [Product] {
        guard let fixedType else { return products }
        return products.filter { ($0.isObject ? "object" : "food") == fixedType }
    }

    /// Sichtbare Produkte in der gewählten Reihenfolge.
    private var sortiert: [Product] {
        switch sortMode {
        case .nameAsc:
            return sichtbar.sorted { $0.name.localizedCaseInsensitiveCompare($1.name) == .orderedAscending }
        case .nameDesc:
            return sichtbar.sorted { $0.name.localizedCaseInsensitiveCompare($1.name) == .orderedDescending }
        case .updated:
            // ISO-Strings gleichen Formats sind chronologisch vergleichbar; neueste zuerst.
            return sichtbar.sorted { ($0.updatedAt ?? "") > ($1.updatedAt ?? "") }
        }
    }

    /// Nur Kategorien des Listentyps (Lebensmittel-Liste zeigt nur Food-Kategorien usw.).
    private var typKategorien: [CategoryItem] {
        guard let fixedType else { return categories }
        return categories.filter { ($0.tracking ?? "food") == fixedType }
    }

    private var titel: String {
        switch fixedType {
        case "food": return "Lebensmittel"
        case "object": return "Gegenstände"
        default: return "Produkte"
        }
    }

    private var filterLabel: String {
        if categoryId == 0 { return "Ohne Kategorie" }
        if let id = categoryId, let treffer = categories.first(where: { $0.id == id }) {
            return treffer.name
        }
        return "Alle Kategorien"
    }

    var body: some View {
        List {
            Section {
                Menu {
                    Button("Alle Kategorien") { pick(nil) }
                    Button("Ohne Kategorie") { pick(0) }
                    Divider()
                    ForEach(categoryTree()) { eintrag in
                        Button(eintrag.label) { pick(eintrag.item.id) }
                    }
                } label: {
                    HStack {
                        Label("Kategorie", systemImage: "line.3.horizontal.decrease.circle")
                        Spacer()
                        Text(filterLabel).foregroundStyle(.secondary)
                    }
                }
                Picker(selection: $sortMode) {
                    ForEach(SortMode.allCases) { Text($0.rawValue).tag($0) }
                } label: {
                    Label("Sortierung", systemImage: "arrow.up.arrow.down")
                }
                .pickerStyle(.menu)
            }

            Section {
                ForEach(sortiert) { product in
                    NavigationLink {
                        ProductDetailView(product: product)
                    } label: {
                        ProductRow(product: product)
                    }
                }
                if sichtbar.isEmpty && !busy {
                    Text("Keine Treffer").foregroundStyle(.secondary)
                }
            }
        }
        .searchable(text: $query, prompt: "Artikel suchen")
        .onChange(of: query) { _ in Task { await load() } }
        .navigationTitle(titel)
        .navigationBarTitleDisplayMode(.inline)
        .refreshable { await load() }
        .toolbar {
            if session.isAdmin {
                ToolbarItem(placement: .topBarTrailing) {
                    Button { showNew = true } label: {
                        Label("Artikel anlegen", systemImage: "plus")
                    }
                }
            }
        }
        .sheet(isPresented: $showNew) {
            NavigationStack {
                // Ohne Barcode: nur Name + Kategorie nötig. Typ aus der Liste
                // vorbelegen. Nach dem Anlegen schließt sich das Formular und die
                // Liste wird aufgefrischt.
                ProductFormView(prefillBarcode: nil, groupId: nil, initialType: fixedType) { _ in
                    showNew = false
                    Task { await load() }
                }
                .toolbar {
                    ToolbarItem(placement: .topBarLeading) {
                        Button("Abbrechen") { showNew = false }
                    }
                }
            }
        }
        .task {
            categories = (try? await APIClient.shared.categories()) ?? []
            await load()
        }
    }

    private func pick(_ id: Int?) {
        categoryId = id
        Task { await load() }
    }

    /// Kategorien in Baumreihenfolge mit eingerueckter Beschriftung.
    private struct TreeEntry: Identifiable {
        let item: CategoryItem
        let depth: Int
        var id: Int { item.id }
        var label: String { String(repeating: "   ", count: depth) + item.name }
    }

    private func categoryTree() -> [TreeEntry] {
        let liste = typKategorien
        let ids = Set(liste.map(\.id))
        var result: [TreeEntry] = []

        func walk(_ node: CategoryItem, _ depth: Int) {
            result.append(TreeEntry(item: node, depth: depth))
            for child in liste.filter({ $0.parentId == node.id }) {
                walk(child, depth + 1)
            }
        }
        // Waisen (Oberkategorie geloescht) gelten als oberste Ebene.
        for root in liste.filter({ $0.parentId == nil || !ids.contains($0.parentId!) }) {
            walk(root, 0)
        }
        return result
    }

    private func load() async {
        busy = true
        defer { busy = false }
        let geladen = (try? await APIClient.shared.searchProducts(query, categoryId: categoryId)) ?? []
        products = geladen
        // Bilder im Hintergrund sicherstellen – nur fehlende/geänderte werden geholt,
        // damit die Thumbnails auch nach App-Neustart sofort aus dem Cache kommen.
        Task { await ProductImageCache.shared.preload(geladen) }
    }
}

/// Artikelzeile mit Gebinde und Hinweis auf den Mindestbestand.
struct ProductRow: View {
    let product: Product

    var body: some View {
        HStack(spacing: 12) {
            ProductThumb(productId: product.id)
            VStack(alignment: .leading, spacing: 2) {
                Text(product.name)
                Text(bestand)
                    .font(.caption).foregroundStyle(.secondary)
                if let hinweis = mindestbestand {
                    Text(hinweis).font(.caption2).foregroundStyle(farbe)
                }
            }
            Spacer()
        }
    }

    private var bestand: String {
        var text = "\(formatAmount(product.stockInArticleUnits)) \(product.articleUnitLabel)"
        // Bei einem Gebinde die Basismenge dahinter, damit "2 Glas" greifbar wird.
        if let size = product.packageSize, size > 0 {
            text += " · à \(formatAmount(size)) \(DisplaySettings.baseUnitLabel(product.baseUnit))"
        }
        return text
    }

    private var mindestbestand: String? {
        guard let anzeige = product.minStockDisplay else { return nil }
        let einheit = product.minStockUnitLabel ?? ""
        switch product.stockLevel {
        case .below: return "unter Mindestbestand (\(formatAmount(anzeige)) \(einheit))"
        case .close: return "bald nachkaufen (Minimum \(formatAmount(anzeige)) \(einheit))"
        case .ok, .none: return nil
        }
    }

    private var farbe: Color {
        product.stockLevel == .below ? .red : .orange
    }
}