SetupPublishers.swift

//
//  SetupPublishers.swift
//  RadiantKit
//
//  Created by Leo Dion.
//  Copyright © 2025 BrightDigit.
//
//  Permission is hereby granted, free of charge, to any person
//  obtaining a copy of this software and associated documentation
//  files (the “Software”), to deal in the Software without
//  restriction, including without limitation the rights to use,
//  copy, modify, merge, publish, distribute, sublicense, and/or
//  sell copies of the Software, and to permit persons to whom the
//  Software is furnished to do so, subject to the following
//  conditions:
//
//  The above copyright notice and this permission notice shall be
//  included in all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND,
//  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
//  OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
//  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
//  HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
//  WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
//  FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
//  OTHER DEALINGS IN THE SOFTWARE.
//

#if canImport(Combine)

  import Combine
  import Foundation

  /// Manages the setup and configuration of publishers for an
  /// `ObservableDownloader` instance.
  internal struct SetupPublishers {
    /// Sets up the download publishers for the provided `ObservableDownloader`
    /// instance.
    ///
    /// - Parameter downloader: The `ObservableDownloader` instance to set up the
    /// download publishers for.
    /// - Returns: An array of `AnyCancellable` instances representing the
    /// subscriptions.
    @available(macOS 14.0, iOS 17.0, watchOS 10.0, tvOS 17.0, *)
    @MainActor
    private func setupDownloadPublsihers(
      _ downloader: ObservableDownloader
    ) -> [AnyCancellable] {
      var cancellables = [AnyCancellable]()

      downloader.requestSubject.share()
        .map { downloadRequest -> URLSessionDownloadTask in
          let task = downloader
            .session
            .downloadTask(with: downloadRequest.downloadSourceURL)
          task.resume()
          return task
        }
        .assign(to: \.task, on: downloader)
        .store(in: &cancellables)

      downloader.resumeDataSubject
        .map { resumeData in
          let task = downloader
            .session
            .downloadTask(withResumeData: resumeData)
          task.resume()
          return task
        }
        .assign(to: \.task, on: downloader)
        .store(in: &cancellables)

      return cancellables
    }

    /// Sets up the byte update publishers for the provided
    /// `ObservableDownloader` instance.
    ///
    /// - Parameter downloader: The `ObservableDownloader` instance to set up the
    /// byte update publishers for.
    /// - Returns: An array of `AnyCancellable` instances representing the
    /// subscriptions.
    @available(macOS 14.0, iOS 17.0, watchOS 10.0, tvOS 17.0, *)
    @MainActor
    private func setupByteUpdatPublishers(
      _ downloader: ObservableDownloader
    ) -> [AnyCancellable] {
      var cancellables = [AnyCancellable]()
      let downloadUpdate = downloader.downloadUpdate.share()

      downloadUpdate
        .map(\.totalBytesWritten)
        .assign(to: \.totalBytesWritten, on: downloader)
        .store(in: &cancellables)

      downloadUpdate
        .map(\.totalBytesExpectedToWrite)
        .assign(to: \.totalBytesExpectedToWrite, on: downloader)
        .store(in: &cancellables)

      return cancellables
    }

    /// Calls the `SetupPublishers` struct to set up the necessary publishers for
    /// the provided `ObservableDownloader` instance.
    ///
    /// - Parameter downloader: The `ObservableDownloader` instance to set up the
    /// publishers for.
    /// - Returns: An array of `AnyCancellable` instances representing the
    /// subscriptions.
    @available(macOS 14.0, iOS 17.0, watchOS 10.0, tvOS 17.0, *)
    @MainActor
    internal func callAsFunction(
      downloader: ObservableDownloader
    ) -> [AnyCancellable] {
      var cancellables = [AnyCancellable]()

      let destinationFileURLPublisher = downloader
        .requestSubject
        .share()
        .map(\.destinationFileURL)

      cancellables.append(contentsOf: setupDownloadPublsihers(downloader))

      Publishers.CombineLatest(downloader.locationURLSubject, destinationFileURLPublisher)
        .map { sourceURL, destinationURL in
          Result { try FileManager.default.moveItem(at: sourceURL, to: destinationURL) }
        }
        .receive(on: DispatchQueue.main)
        .sink(receiveValue: downloader.onCompletion)
        .store(in: &cancellables)

      cancellables.append(contentsOf: setupByteUpdatPublishers(downloader))

      return cancellables
    }
  }
#endif