using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;

namespace GUI
{
	public class UTF8Marshaler : ICustomMarshaler
	{
		static UTF8Marshaler _instance;

		public IntPtr MarshalManagedToNative(object managedObj)
		{
			if(managedObj == null) {
				return IntPtr.Zero;
			}
			if(!(managedObj is string)) {
				throw new MarshalDirectiveException("UTF8Marshaler must be used on a string.");
			}

			// not null terminated
			byte[] strbuf = Encoding.UTF8.GetBytes((string)managedObj);
			IntPtr buffer = Marshal.AllocHGlobal(strbuf.Length + 1);
			Marshal.Copy(strbuf, 0, buffer, strbuf.Length);

			// write the terminating null
			Marshal.WriteByte(buffer + strbuf.Length, 0);
			return buffer;
		}

		public object MarshalNativeToManaged(IntPtr pNativeData)
		{
			return GetStringFromIntPtr(pNativeData);
		}

		public void CleanUpNativeData(IntPtr pNativeData)
		{
			//Marshal.FreeHGlobal(pNativeData);
		}

		public void CleanUpManagedData(object managedObj)
		{
		}

		public int GetNativeDataSize()
		{
			return -1;
		}

		public static ICustomMarshaler GetInstance(string cookie)
		{
			if(_instance == null) {
				return _instance = new UTF8Marshaler();
			}
			return _instance;
		}

		public static string GetStringFromIntPtr(IntPtr pNativeData)
		{
			int offset = 0;
			byte b = 0;
			do {
				b = Marshal.ReadByte(pNativeData, offset);
				offset++;
			} while(b != 0);

			int length = offset - 1;

			// should not be null terminated
			byte[] strbuf = new byte[length];
			// skip the trailing null
			Marshal.Copy((IntPtr)pNativeData, strbuf, 0, length);
			string data = Encoding.UTF8.GetString(strbuf);
			return data;
		}
	}
}