//import Foundation
//
//enum ChangeType {
//    case Address, Port
//}
//
//public class IPMutablePacket {
//    // Support only IPv4 for now
//
//    let version: IPVersion
//    let proto: TransportType
//    let IPHeaderLength: Int
//    var sourceAddress: IPv4Address {
//        get {
//            return IPv4Address(fromBytesInNetworkOrder: payload.bytes.advancedBy(12))
//        }
//        set {
//            setIPv4Address(sourceAddress, newAddress: newValue, at: 12)
//        }
//    }
//    var destinationAddress: IPv4Address {
//        get {
//            return IPv4Address(fromBytesInNetworkOrder: payload.bytes.advancedBy(16))
//        }
//        set {
//            setIPv4Address(destinationAddress, newAddress: newValue, at: 16)
//        }
//    }
//
//    let payload: NSMutableData
//
//    public init(payload: NSData) {
//        let vl = UnsafePointer<UInt8>(payload.bytes).memory
//        version = IPVersion(rawValue: vl >> 4)!
//        IPHeaderLength = Int(vl & 0x0F) * 4
//        let p = UnsafePointer<UInt8>(payload.bytes.advancedBy(9)).memory
//        proto = TransportType(rawValue: p)!
//        self.payload = NSMutableData(data: payload)
//    }
//
//    func updateChecksum(oldValue: UInt16, newValue: UInt16, type: ChangeType) {
//        if type == .Address {
//            updateChecksum(oldValue, newValue: newValue, at: 10)
//        }
//    }
//
//    // swiftlint:disable:next variable_name
//    internal func updateChecksum(oldValue: UInt16, newValue: UInt16, at: Int) {
//        let oldChecksum = UnsafePointer<UInt16>(payload.bytes.advancedBy(at)).memory
//        let oc32 = UInt32(~oldChecksum)
//        let ov32 = UInt32(~oldValue)
//        let nv32 = UInt32(newValue)
//        var newChecksum32 = oc32 &+ ov32 &+ nv32
//        newChecksum32 = (newChecksum32 & 0xFFFF) + (newChecksum32 >> 16)
//        newChecksum32 = (newChecksum32 & 0xFFFF) &+ (newChecksum32 >> 16)
//        var newChecksum = ~UInt16(newChecksum32)
//        payload.replaceBytesInRange(NSRange(location: at, length: 2), withBytes: &newChecksum, length: 2)
//    }
//
//    // swiftlint:disable:next variable_name
//    private func foldChecksum(checksum: UInt32) -> UInt32 {
//        var checksum = checksum
//        while checksum > 0xFFFF {
//            checksum = (checksum & 0xFFFF) + (checksum >> 16)
//        }
//        return checksum
//    }
//
//    // swiftlint:disable:next variable_name
//    private func setIPv4Address(oldAddress: IPv4Address, newAddress: IPv4Address, at: Int) {
//        payload.replaceBytesInRange(NSRange(location: at, length: 4), withBytes: newAddress.bytesInNetworkOrder, length: 4)
//            updateChecksum(UnsafePointer<UInt16>(oldAddress.bytesInNetworkOrder).memory, newValue: UnsafePointer<UInt16>(newAddress.bytesInNetworkOrder).memory, type: .Address)
//            updateChecksum(UnsafePointer<UInt16>(oldAddress.bytesInNetworkOrder).advancedBy(1).memory, newValue: UnsafePointer<UInt16>(newAddress.bytesInNetworkOrder).advancedBy(1).memory, type: .Address)
//        }
//
//}