using System;
using System.Runtime.InteropServices;
using System.Text;

namespace Foodsoft.Alpm
{
    internal readonly struct UTF8InMarshaler : ICustomMarshaler
    {
        private static readonly UTF8InMarshaler _instance = default;


        public void CleanUpManagedData(object managedObj) { }

        public void CleanUpNativeData(IntPtr pNativeData)
        {
            if (pNativeData == IntPtr.Zero)
                return;
            Marshal.FreeHGlobal(pNativeData);
        }

        public int GetNativeDataSize() => -1;

        public unsafe IntPtr MarshalManagedToNative(object? managedObj)
        {
            if (managedObj is null) return IntPtr.Zero;

            var s = (string) managedObj;

            var nb = Encoding.UTF8.GetMaxByteCount(s.Length);

            var pMem = Marshal.AllocHGlobal(nb + 1);
            var pbMem = (byte*) pMem;

            int nbWritten;
            fixed (char* firstChar = s)
            {
                nbWritten = Encoding.UTF8.GetBytes(firstChar, s.Length, pbMem, nb);
            }

            pbMem[nbWritten] = 0;
            return pMem;
        }

        public object MarshalNativeToManaged(IntPtr pNativeData)
        {
            return Marshal.PtrToStringUTF8(pNativeData)!;
        }

        // ReSharper disable once UnusedMember.Local
        // ReSharper disable once UnusedParameter.Local
        private static ICustomMarshaler GetInstance(string cookie)
        {
            return _instance;
        }
    }
}