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/// Enum that contains states for network operation request.
///
/// - initial: Initial state. Before something will happen.
/// - processing: Loading state. When request is started.
/// - done: Result state with result.
/// - failed: Error state with a specific error.
public enum RequestNetworkOperationState<DS: DataSource>: NetworkOperationState {

    case initial
    case processing
    case done(result: DS.ResultType)
    case failed(error: Error)

    public typealias DataSourceType = DS

    public static var initialState: RequestNetworkOperationState<DS> {
        return .initial
    }

    public static func initialLoadingState(after: RequestNetworkOperationState<DS>) -> RequestNetworkOperationState<DS> {
        return .processing
    }

    public static func resultState(result: DS.ResultType,
                                   from: DS,
                                   after: RequestNetworkOperationState<DS>) -> RequestNetworkOperationState<DS> {

        return .done(result: result)
    }

    public static func errorState(error: Error,
                                  after: RequestNetworkOperationState<DS>) -> RequestNetworkOperationState<DS> {

        return .failed(error: error)
    }

    public var isInitialState: Bool {
        switch self {
        case .initial:
            return true
        default:
            return false
        }
    }

    public var result: DS.ResultType? {
        switch self {
        case .done(let result):
            return result
        default:
            return nil
        }
    }

    public var error: Error? {
        switch self {
        case .failed(let error):
            return error
        default:
            return nil
        }
    }

}