AlamofireJSONArrayEncoding

import Alamofire

private let kArrayElementKey = "arrayElementKey"

extension Array {
    func asParameter() -> Parameters {
        return [kArrayElementKey: self]
    }
}

/// Convert the parameters into a json array, and it is added as the request body.
/// The array must be sent as parameters using its `asParameters` method.
public struct ArrayEncoding: ParameterEncoding {
    
    /// The options for writing the parameters as JSON data.
    public let options: JSONSerialization.WritingOptions
    
    /// Creates a new instance of the encoding using the given options
    ///
    /// - parameter options: The options used to encode the json. Default is `[]`
    ///
    /// - returns: The new instance
    public init(options: JSONSerialization.WritingOptions = []) {
        self.options = options
    }
    
    public func encode(_ urlRequest: URLRequestConvertible, with parameters: Parameters?) throws -> URLRequest {
        var urlRequest = try urlRequest.asURLRequest()
        
        guard let parameters = parameters, let array = parameters[kArrayElementKey] else {
            return urlRequest
        }
        
        do {
            let data = try JSONSerialization.data(withJSONObject: array, options: options)
            if urlRequest.value(forHTTPHeaderField: "Content-Type") == nil {
                urlRequest.setValue("application/json", forHTTPHeaderField: "Content-Type")
            }
            urlRequest.httpBody = data
        } catch {
            throw AFError.parameterEncodingFailed(reason: AFError.ParameterEncodingFailureReason.jsonEncodingFailed(error: error))
        }
        return urlRequest
    }
}