PromiseRepository

PromiseRepository.swift

protocol DataPassing: class {
  associatedtype DataSource
  var dataSource: DataSource { get set }
}

protocol PromiseRepository: DataPassing {
  
  func syncCache(_ promise: Promise<DataSource>) -> Promise<DataSource>
}

extension PromiseRepository {
  
  func syncCache(_ promise: Promise<DataSource>) -> Promise<DataSource> {
    promise.done(on: DispatchQueue.global(), { [weak self] in
      self?.dataSource = $0
    }).cauterize()
    return promise
  }
}

TestRepository.swift

import PromiseKit

class HistoryRepository: PromiseRepository {
  
  struct DataSource {
    var history: History?
    var error: Error?
  }
  
  var dataSource: DataSource = .init(history: nil, error: nil)
  
  public func getHistory() -> Promise<DataSource> {
    let response = Promise(resolver: { seal in
      seal.fulfill(History(id: 1, title: "test", isFollow: true))
    })
      .map({ history -> DataSource in
        var newDataSource = self.dataSource
        newDataSource.history = history
        newDataSource.error = nil
        return newDataSource
      })
      .recover({ error -> Promise<DataSource> in
        var newDataSource = self.dataSource
        newDataSource.history = nil
        newDataSource.error = error
        return Promise.value(newDataSource)
      })
    
    return syncCache(response)
  }
}