import SwiftUI

/// Liste aller Einzelstücke (physische Exemplare) über alle Produkte – anders als
/// die Produktliste, die nur die Katalog-Typen zeigt. Such- und Filterfunktion,
/// v.a. nach Lagerort. Tippen öffnet das Einzelstück.
struct ItemListView: View {
    @State private var items: [Item] = []
    @State private var locations: [StorageLocation] = []
    @State private var categories: [CategoryItem] = []
    @State private var query = ""
    @State private var locationFilter: String?   // Lagerort-ID
    @State private var categoryFilter: Int?       // Kategorie-ID (Unterkategorien zählen mit)
    @State private var busy = true
    @State private var error: String?

    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 var catById: [Int: CategoryItem] {
        Dictionary(categories.map { ($0.id, $0) }, uniquingKeysWith: { a, _ in a })
    }

    /// Ist `catId` die Kategorie `target` oder eine ihrer Unterkategorien?
    private func imTeilbaum(_ catId: Int?, target: Int) -> Bool {
        let map = catById
        var cur = catId
        var g = 0
        while let c = cur, g < 50 {
            if c == target { return true }
            cur = map[c]?.parentId
            g += 1
        }
        return false
    }

    /// Kategorien fürs Filter-Menü: alle, die selbst oder als Oberkategorie zu einem
    /// vorhandenen Einzelstück gehören – so ist z.B. auch „Klamotten" wählbar. Baum
    /// mit eingerückter Beschriftung (hierarchisch).
    private var filterKategorien: [TreeEntry] {
        let map = catById
        var relevant = Set<Int>()
        for it in items {
            var cur = it.categoryId
            var g = 0
            while let c = cur, !relevant.contains(c), g < 50 {
                relevant.insert(c)
                cur = map[c]?.parentId
                g += 1
            }
        }
        let liste = categories.filter { relevant.contains($0.id) }
        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) }
        }
        for root in liste.filter({ $0.parentId == nil || !ids.contains($0.parentId!) }) { walk(root, 0) }
        return result
    }

    private var filterKategorieName: String {
        if let id = categoryFilter, let t = categories.first(where: { $0.id == id }) { return t.name }
        return "Alle"
    }

    private var gefiltert: [Item] {
        let q = query.trimmingCharacters(in: .whitespaces).lowercased()
        return items.filter { it in
            if let cat = categoryFilter, !imTeilbaum(it.categoryId, target: cat) { return false }
            if let loc = locationFilter, it.locationId != loc { return false }
            if !q.isEmpty {
                let heu = [it.productName, it.uid, it.note, it.productBrand]
                    .compactMap { $0 }.joined(separator: " ").lowercased()
                if !heu.contains(q) { return false }
            }
            return true
        }
    }

    private var hatFilter: Bool { locationFilter != nil || categoryFilter != nil }

    var body: some View {
        List {
            if !busy && gefiltert.isEmpty {
                Text(items.isEmpty ? "Noch keine Einzelstücke." : "Nichts gefunden.")
                    .foregroundStyle(.secondary)
            }
            ForEach(gefiltert) { it in
                NavigationLink { ItemEditView(item: it) } label: {
                    ItemRow(item: it, locations: locations)
                }
            }
        }
        .searchable(text: $query, prompt: "Produkt, UID oder Notiz")
        .navigationTitle("Einzelstücke")
        .navigationBarTitleDisplayMode(.inline)
        .toolbar { ToolbarItem(placement: .topBarTrailing) { filterMenu } }
        .overlay { if busy && items.isEmpty { ProgressView() } }
        .refreshable { await load() }
        // Auch beim Zurückkommen aus dem Einzelstück neu laden (z.B. Lagerort geändert).
        .onAppear { Task { await load() } }
        .alert("Fehler", isPresented: Binding(get: { error != nil }, set: { if !$0 { error = nil } })) {
            Button("OK", role: .cancel) {}
        } message: { Text(error ?? "") }
    }

    private var filterMenu: some View {
        Menu {
            Menu("Lagerort") {
                check("Alle", locationFilter == nil) { locationFilter = nil }
                ForEach(locations) { loc in
                    check(loc.path(in: locations), locationFilter == loc.id) { locationFilter = loc.id }
                }
            }
            if !filterKategorien.isEmpty {
                Menu("Kategorie") {
                    check("Alle", categoryFilter == nil) { categoryFilter = nil }
                    ForEach(filterKategorien) { e in
                        check(e.label, categoryFilter == e.item.id) { categoryFilter = e.item.id }
                    }
                }
            }
            if hatFilter {
                Divider()
                Button(role: .destructive) { locationFilter = nil; categoryFilter = nil } label: {
                    Label("Filter zurücksetzen", systemImage: "xmark.circle")
                }
            }
        } label: {
            Image(systemName: hatFilter
                  ? "line.3.horizontal.decrease.circle.fill"
                  : "line.3.horizontal.decrease.circle")
        }
    }

    @ViewBuilder
    private func check(_ title: String, _ selected: Bool, _ action: @escaping () -> Void) -> some View {
        Button(action: action) {
            if selected { Label(title, systemImage: "checkmark") } else { Text(title) }
        }
    }

    private func load() async {
        busy = true
        defer { busy = false }
        do {
            items = try await APIClient.shared.allItems()
            locations = (try? await APIClient.shared.locations()) ?? []
            categories = (try? await APIClient.shared.categories()) ?? []
        } catch {
            self.error = error.localizedDescription
        }
    }
}

/// Eine Einzelstück-Zeile: Produktbild, Produktname, UID und Lagerort-Pfad.
struct ItemRow: View {
    let item: Item
    let locations: [StorageLocation]

    var body: some View {
        HStack(spacing: 12) {
            ProductThumb(productId: item.productId)
            VStack(alignment: .leading, spacing: 2) {
                Text(item.productName ?? "—")
                let pfad = locationPath(item.locationId, in: locations)
                HStack(spacing: 6) {
                    Text(item.uid).font(.caption).foregroundStyle(.secondary)
                    if !pfad.isEmpty {
                        Text("· \(pfad)").font(.caption).foregroundStyle(.secondary).lineLimit(1)
                    }
                }
            }
            Spacer()
        }
    }
}