缓存数据

数据缓存可以简单将数据缓存到沙盒，结合RSA或者其他加密，可以将数据安全地缓存在本地，而不用操作较为复杂的数据库。

demo

enum CacheManagerPath {
    case demoCache
    case none

    var directory: String {
      if case . demoCache = self {
          return "demoCache"
      }

      return ""
    }

    var path: String {
      if case . demoCache = self {
          return "userId.txt"
      }

      return ""
    }
}

protocol CacheManagerProtocol {
     var filePath: CacheManagerPath { get }
     func write(_ data: Data?) throws
     func read<T: Codable>() throws -> T
     func remove()
}


extension CacheManagerProtocol {
     func write(_ data: Data?)  {
        do {
            let fileUrl = try fileUrl(by: filePath.path)
            try createDirectories(in: fileUrl.deletingLastPathComponent())
            if let data = data {
                   try data.write(to: fileUrl, option: .atomic)       
            } else {
                   let emptyData = Data()
                   try emptyData.write(to: fileUrl, options: .atomic)
            }
        } catch {}
    }

    func read<T: Codable>() throws -> T {
        let fileUrl = try fileUrl(by: filePath.path)
        let data = try Data(contentsOf: fileUrl)

        return try JSONDecoder().decode(T.self, from: data)
    }

    func remove() {
    //  remove all the directory
      do {
          let fileUrl = try fileUrl(by: filePath.directory)
          try FileManager.default.removeItem(at: fileUrl)
      } catch {}
    }

    private func createDirectories(in url: URL) throws {
        do {
            try FileManager.default.createDirectory(at: url, withIntermediateDirectories: true)
        } catch {}
    }

    private func fileUrl(by fileName: String) throws -> URL {
        return try FileManager.default.url(for: .applicationSupportDirectory, in: .userDomainMask, appropriateFor: nil, create: false).appendingPathComponent(fileName)

    }
}

class CacheManager: CacheManagerProtocol {
  var filePath: CacheManagerPath

  init(filePath: CacheManagerPath) {
      self.filePath = filePath
  }
}

protocol TestDemoProtocol {
  var localStore: CacheManager { get }
  func saveToCache(response: Sample)
  ...

}

class TestDemo: TestDemoProtocol {
  init(localStore: CacheManager = CacheManager(filePath: . demoCache)) {
    self. localStore = localStore
   }

   func saveToCache(response: Sample) {
      let data = try JSONEncoder().encode(response)
      try localStore.write(data)
  }
}