APIError.swift

struct APIError: NetworkError {

    let json: JSON

    let apiCode: Int?

    let message: String?

    let httpResponse: HTTPURLResponse

    var statusCode: Int {
        return httpResponse.statusCode
    }

    init?(json: JSON, httpResponse: HTTPURLResponse) {
        guard let errorJSON = json["error"] as? [String: Any] else {
            return nil
        }
        let apiCode = errorJSON["errorCode"] as? Int
        let message = errorJSON["errorMessage"] as? String ?? json["errorMessage"] as? String
        self.init(json: json, apiCode: apiCode, message: message, httpResponse: httpResponse)
    }

    init(json: JSON, apiCode: Int?, message: String?, httpResponse: HTTPURLResponse) {
        self.json = json
        self.apiCode = apiCode
        self.message = message
        self.httpResponse = httpResponse
    }
}

extension APIError: LocalizedError, CustomNSError {
    var errorDescription: String? {
        return message
    }

    var errorCode: Int {
        return apiCode ?? -1
    }
}