import Foundation

/// `/api/export/{csv,excel,pdf}` — Pro-only (403 `pro_required` for a
/// free-plan account, surfaced via `APIError.server`). Every route takes the
/// same request body and returns the raw file with its name in
/// `Content-Disposition`; present the returned `Data` via `UIActivityViewController`
/// (share sheet) or write it into a temp file and use `.fileExporter` /
/// `QLPreviewController` — either is fine, this layer just gets you the bytes.
enum ExportAPI {
    enum Format: String {
        case csv, excel, pdf

        var path: String { "/api/export/\(rawValue)" }
        var fallbackExtension: String {
            switch self {
            case .csv: return "csv"
            case .excel: return "xlsx"
            case .pdf: return "pdf"
            }
        }
    }

    struct ExportRequestBody: Encodable {
        let receipts: [Receipt]
        let locale: String
        // Only meaningful for the PDF export (date range on the cover page);
        // harmless to omit for csv/excel, which ignore unknown fields.
        var dateFrom: String?
        var dateTo: String?
    }

    struct ExportResult {
        let data: Data
        let fileName: String
    }

    /// - Parameters:
    ///   - receipts: exactly the receipts to include — the backend does not
    ///     look anything up server-side, it only formats what you send.
    ///   - locale: `"de"` or `"en"`; anything else falls back to German on
    ///     the backend, so just always pass one of the two.
    static func export(
        _ format: Format,
        receipts: [Receipt],
        locale: String = "de",
        dateFrom: String? = nil,
        dateTo: String? = nil
    ) async throws -> ExportResult {
        let body = ExportRequestBody(receipts: receipts, locale: locale, dateFrom: dateFrom, dateTo: dateTo)
        let request = try APIRequest.json(path: format.path, method: .post, body: body)
        let (data, suggestedName) = try await APIClient.shared.sendForFile(request)
        let fileName = suggestedName ?? "Belege_Export.\(format.fallbackExtension)"
        return ExportResult(data: data, fileName: fileName)
    }
}