URLSession+cacheThenDataTaskPublisher.swift

import Foundation
import Combine

extension URLSession {
  func cacheThenDataTaskPublisher(
    for urlRequest: URLRequest
  ) -> some Publisher {
    let cacheDataTaskPublisher = configuration.urlCache?
      .cachedResponse(for: urlRequest)
      .map {
        Just((data: $0.data, response: $0.response)).eraseToAnyPublisher()
      } ?? Empty().eraseToAnyPublisher()
        
    return Publishers.Merge(
      cacheDataTaskPublisher.mapError { switch $0 {} },
      dataTaskPublisher(for: urlRequest)
    )
    .removeDuplicates(by: { $0.data == $1.data })
  }
}