AsyncAction implementation for Suas that read from disk in the background

DiskReadAsyncAction.swift

/// Callback called when Disk IO read operation completes
public typealias DiskReadActionCompletionBlock = (Data?, DispatchFunction) -> Void


/// Disk Read `AsyncAction` implementation to read data from the disk asynchronously. Requires `AsyncMiddleware` to be added to the store.
///
/// # Example
///
/// ```
/// let action = DiskReadAsyncAction(path: ...) { data, dispatch in
///   // Dispatch a new action
///   dispatch(DataFetchedAction(data))
/// }
/// ```
public struct DiskReadAsyncAction: AsyncAction {
  static let defaultDispatchQueue = DispatchQueue(label: "DISK_READ_ASYNC_ACTION")

  private let path: String
  private let fileManager: FileManager
  private let dispatchQueue: DispatchQueue
  private let completionBlock: DiskReadActionCompletionBlock

  /// Create a Read DiskIO AsyncAction
  ///
  /// - Parameters:
  ///   - path: path to read from disk
  ///   - fileManager: (optional) the file manager to use. When not passed it defaults to `FileManager.default`
  ///   - dispatchQueue: (optional) the dispatch queue to use when accessing disk. When not passed it defaults to `DispatchQueue(label: "IOMIDDLEWARE_IO_QUEUE")
  ///   - completionBlock: callback to call when data is read from disk. In this block `dispatch` is used to dispatch new actions
  /// - Returns: an async action to dispatch
  public init(path: String,
              fileManager: FileManager = .default,
              dispatchQueue: DispatchQueue = defaultDispatchQueue,
              completionBlock: @escaping DiskReadActionCompletionBlock) {
    self.path = path
    self.fileManager = fileManager
    self.dispatchQueue = dispatchQueue
    self.completionBlock = completionBlock
  }

  public func execute(getState: @escaping GetStateFunction, dispatch: @escaping DispatchFunction) {
    // Perform action on a background thread
    dispatchQueue.async {
      if
        let data = self.fileManager.contents(atPath: self.path) {
        // When data is loaded call the block
        self.completionBlock(data, dispatch)
      }
    }
  }

}