import SwiftUI

/// Presented from `ReceiptsListView`'s toolbar. Exports the given receipts as
/// CSV, XLSX, or PDF via `ExportAPI`, writes the result to a temp file (so
/// the receiving app sees the right filename/extension), and hands it to the
/// iOS share sheet.
struct ExportSheet: View {
    let receipts: [Receipt]

    @Environment(\.dismiss) private var dismiss
    @State private var isExporting = false
    @State private var errorMessage: String?
    @State private var shareFile: ShareFile?

    var body: some View {
        NavigationStack {
            VStack(spacing: ZenithSpacing.sm) {
                if receipts.isEmpty {
                    Text("Keine Belege zum Exportieren.")
                        .zenithBodyStyle(color: .zenithMuted)
                        .padding(.top, 40)
                } else {
                    Text("\(receipts.count) Beleg\(receipts.count == 1 ? "" : "e") exportieren")
                        .zenithHeadlineMdStyle()
                        .padding(.top, ZenithSpacing.md)

                    VStack(spacing: ZenithSpacing.xs) {
                        exportButton(title: "Als CSV exportieren", systemImage: "tablecells", format: .csv)
                        exportButton(title: "Als Excel exportieren", systemImage: "tablecells.fill", format: .excel)
                        exportButton(title: "Als PDF exportieren", systemImage: "doc.richtext", format: .pdf)
                    }
                    .padding(.horizontal, ZenithSpacing.sm)
                }

                if isExporting {
                    ProgressView()
                }

                if let errorMessage {
                    Text(errorMessage)
                        .zenithBodySmStyle(color: .zenithError)
                        .multilineTextAlignment(.center)
                        .padding(.horizontal, ZenithSpacing.sm)
                }

                Spacer()
            }
            .background(Color.zenithBg.ignoresSafeArea())
            .navigationTitle("Exportieren")
            .navigationBarTitleDisplayMode(.inline)
            .toolbar {
                ToolbarItem(placement: .cancellationAction) {
                    Button("Fertig") { dismiss() }
                        .buttonStyle(.zenithPlain)
                }
            }
            .sheet(item: $shareFile) { file in
                ShareSheet(activityItems: [file.url])
            }
        }
    }

    private func exportButton(title: String, systemImage: String, format: ExportAPI.Format) -> some View {
        Button {
            Task { await export(format) }
        } label: {
            Label(title, systemImage: systemImage)
                .frame(maxWidth: .infinity)
        }
        .buttonStyle(.zenithPrimary)
        .disabled(isExporting)
    }

    private func export(_ format: ExportAPI.Format) async {
        isExporting = true
        errorMessage = nil
        defer { isExporting = false }
        do {
            let result = try await ExportAPI.export(format, receipts: receipts, locale: "de")
            let tempURL = FileManager.default.temporaryDirectory.appendingPathComponent(result.fileName)
            try result.data.write(to: tempURL, options: .atomic)
            shareFile = ShareFile(url: tempURL)
        } catch let apiError as APIError {
            if case .server(let code, _, _) = apiError, code == "pro_required" {
                errorMessage = "Export ist Pro-Nutzern vorbehalten."
            } else {
                errorMessage = apiError.localizedDescription
            }
        } catch {
            errorMessage = error.localizedDescription
        }
    }
}

/// Wraps a temp-file URL so it can drive `.sheet(item:)`.
private struct ShareFile: Identifiable {
    let url: URL
    var id: String { url.absoluteString }
}