/*----------------------------------------------------------------
// Copyright (C) 2025 Beijing All rights reserved.
//
// Author: huachangmiao
// Create Date: 2025/04/11
// Module Describe:
//----------------------------------------------------------------*/
using System;
using System.Runtime.InteropServices;
using System.Text;

namespace LeviathanVideo.Abstractions
{

    public class UTF8Marshaler : ICustomMarshaler
    {
        private static readonly UTF8Marshaler Instance = new UTF8Marshaler();

        public virtual object MarshalNativeToManaged(IntPtr pNativeData) => FromNative(Encoding.UTF8, pNativeData);

        public virtual IntPtr MarshalManagedToNative(object managedObj)
        {
            if (managedObj == null)
                return IntPtr.Zero;

            if (!(managedObj is string str))
                throw new MarshalDirectiveException($"{GetType().Name} must be used on a string.");

            return FromManaged(Encoding.UTF8, str);
        }

        public virtual void CleanUpNativeData(IntPtr pNativeData)
        {
            //Free anything allocated by MarshalManagedToNative
            //This is called after the native function call completes

            if (pNativeData != IntPtr.Zero)
                Marshal.FreeHGlobal(pNativeData);
        }

        public void CleanUpManagedData(object managedObj)
        {
            //Free anything allocated by MarshalNativeToManaged
            //This is called after the native function call completes
        }

        public int GetNativeDataSize() => -1; // Not a value type

        public static ICustomMarshaler GetInstance(string cookie) => Instance;

        public static unsafe string FromNative(Encoding encoding, IntPtr pNativeData) => FromNative(encoding, (byte*)pNativeData);

        public static unsafe string FromNative(Encoding encoding, byte* pNativeData)
        {
            if (pNativeData == null)
                return null;

            var start = pNativeData;
            var walk = start;

            // Find the end of the string
            while (*walk != 0) walk++;

            if (walk == start)
                return string.Empty;

            return new string((sbyte*)pNativeData, 0, (int)(walk - start), encoding);
        }

        public static unsafe IntPtr FromManaged(Encoding encoding, string value)
        {
            if (encoding == null || value == null)
                return IntPtr.Zero;

            var length = encoding.GetByteCount(value);
            var buffer = (byte*)Marshal.AllocHGlobal(length + 1).ToPointer();

            if (length > 0)
            {
                fixed (char* pValue = value)
                {
                    encoding.GetBytes(pValue, value.Length, buffer, length);
                }
            }

            buffer[length] = 0;

            return new IntPtr(buffer);
        }
    }
}