Middleware example

Middleware.swift

class CheckNilMiddleware: Middleware {
  override func check(value: MiddlewareItem) -> MiddlewareItem {
    switch value {
    case .value(let str):
      if str == nil {
        return .error("Значение равно nil")
      }
    default: break
    }
    
    return checkNext(value: value)
  }
}

class CheckCountMiddleware: Middleware {
  private let length: Int
  
  init(length: Int) {
    self.length = length
  }
  
  override func check(value: MiddlewareItem) -> MiddlewareItem {
    switch value {
    case .value(let str):
      if str?.count != length {
        return .error("Длинна должна быть \(length)")
      }
    default: break
    }
    
    return checkNext(value: value)
  }
}

class PhoneFormatterMiddleware: Middleware {
  private let format: String // "+X (XXX) XXX XX-XX"
  
  init(format: String) {
    self.format = format
  }
  
  override func check(value: MiddlewareItem) -> MiddlewareItem {
    switch value {
    case .value(let str):
      if let s = str {
        
        let cleanPhoneNumber = s.components(separatedBy: CharacterSet.decimalDigits.inverted).joined()
        let mask = format
        
        var result = ""
        var index = cleanPhoneNumber.startIndex
        for ch in mask {
          if index == cleanPhoneNumber.endIndex {
            break
          }
          if ch == "X" {
            result.append(cleanPhoneNumber[index])
            index = cleanPhoneNumber.index(after: index)
          } else {
            result.append(ch)
          }
        }
        return .value(result)
      }
    default: break
    }
    
    return checkNext(value: value)
  }
}