import SwiftUI

/// Mengen-Erfassung nach dem Scan: mehrere Chargen mit eigenem MHD.
struct CheckInFormView: View {
    let product: Product
    let units: [Unit]
    let locations: [StorageLocation]
    var onDone: (String) -> Void

    @Environment(\.dismiss) private var dismiss

    struct Line: Identifiable {
        let id = UUID()
        var quantity: String = "1"
        var hasDate: Bool = false
        var bestBefore: Date = Date()
    }

    @State private var lines: [Line] = [Line()]
    @State private var unit: String = ""
    @State private var locationId: Int?
    @State private var busy = false
    @State private var error: String?

    /// Einheiten der passenden Art plus das Gebinde des Artikels.
    private var unitOptions: [String] {
        var options = units.filter { $0.kind == product.kind }.map(\.name)
        if let size = product.packageSize, size > 0 {
            options.append(product.packageLabel ?? "Packung")
        }
        return options
    }

    private var packageOptionName: String? {
        guard let size = product.packageSize, size > 0 else { return nil }
        return product.packageLabel ?? "Packung"
    }

    var body: some View {
        Form {
            Section {
                HStack {
                    VStack(alignment: .leading) {
                        Text(product.name).font(.headline)
                        Text("Bestand: \(format(product.stockInArticleUnits)) \(product.articleUnitLabel)")
                            .font(.caption).foregroundStyle(.secondary)
                    }
                    Spacer()
                }
            }

            Section("Einheit") {
                Picker("Einheit", selection: $unit) {
                    ForEach(unitOptions, id: \.self) { Text($0).tag($0) }
                }
                if !locations.isEmpty {
                    Picker("Lagerort", selection: $locationId) {
                        Text("– keiner –").tag(Int?.none)
                        ForEach(locations) { location in
                            Text(location.name).tag(Int?.some(location.id))
                        }
                    }
                }
            }

            Section("Chargen") {
                ForEach($lines) { $line in
                    VStack(alignment: .leading, spacing: 6) {
                        HStack {
                            // Ohne Beschriftung sah die vorbelegte 1 wie eine
                            // Nummerierung der Charge aus.
                            Text("Menge")
                            Spacer(minLength: 12)
                            TextField("Menge", text: $line.quantity)
                                .keyboardType(.decimalPad)
                                .multilineTextAlignment(.trailing)
                                .frame(maxWidth: 110)
                            if lines.count > 1 {
                                Button(role: .destructive) {
                                    lines.removeAll { $0.id == line.id }
                                } label: { Image(systemName: "trash") }
                                .buttonStyle(.borderless)
                            }
                        }
                        Toggle("MHD angeben", isOn: $line.hasDate)
                        if line.hasDate {
                            DatePicker("MHD", selection: $line.bestBefore, displayedComponents: .date)
                        }
                    }
                    .padding(.vertical, 2)
                }
                Button {
                    lines.append(Line())
                } label: {
                    Label("Weitere Charge (anderes MHD)", systemImage: "plus")
                }
            }

            if let error {
                Section { Text(error).foregroundStyle(.red).font(.callout) }
            }

            Section {
                Button(busy ? "Speichern…" : "Einlagern") { Task { await submit() } }
                    .disabled(busy)
            }
        }
        .navigationTitle("Einlagern")
        .navigationBarTitleDisplayMode(.inline)
        .toolbar {
            ToolbarItem(placement: .topBarLeading) { Button("Abbrechen") { dismiss() } }
        }
        .onAppear {
            // Gibt es ein Gebinde, ist das die naheliegende Eingabe.
            unit = packageOptionName ?? product.unitName
        }
    }

    private func format(_ value: Double) -> String {
        value == value.rounded() ? String(Int(value)) : String(format: "%.2f", value)
    }

    private func submit() async {
        error = nil
        let formatter = DateFormatter()
        formatter.dateFormat = "yyyy-MM-dd"

        let payloadLines: [CheckInLine] = lines.compactMap { line in
            guard let quantity = Double(line.quantity.replacingOccurrences(of: ",", with: ".")),
                  quantity > 0 else { return nil }
            return CheckInLine(
                quantity: quantity,
                bestBefore: line.hasDate ? formatter.string(from: line.bestBefore) : nil,
                locationId: locationId
            )
        }
        guard !payloadLines.isEmpty else {
            error = "Bitte mindestens eine Menge angeben."
            return
        }

        busy = true
        defer { busy = false }
        do {
            let response = try await APIClient.shared.checkInBatch(
                BatchCheckInRequest(productId: product.id, unit: unit, lines: payloadLines)
            )
            let total = response.productStock / product.articleUnitFactor
            onDone("Eingelagert. Neuer Bestand: \(format(total)) \(product.articleUnitLabel)")
            dismiss()
        } catch {
            self.error = error.localizedDescription
        }
    }
}