using System;
using System.Runtime.InteropServices;
using HandyControl.Tools.Interop;

namespace HandyControl.Data;

[StructLayout(LayoutKind.Sequential)]
public class GifPropertyItemInternal : IDisposable
{
    public int id;
    public int len;
    public short type;
    public IntPtr value = IntPtr.Zero;

    internal GifPropertyItemInternal()
    {
    }

    public byte[] Value
    {
        get
        {
            if (len == 0)
                return null;

            var bytes = new byte[len];

            Marshal.Copy(value,
                bytes,
                0,
                len);
            return bytes;
        }
    }

    public void Dispose()
    {
        Dispose(true);
    }

    ~GifPropertyItemInternal()
    {
        Dispose(false);
    }

    private void Dispose(bool disposing)
    {
        if (value != IntPtr.Zero)
        {
            Marshal.FreeHGlobal(value);
            value = IntPtr.Zero;
        }

        if (disposing)
            GC.SuppressFinalize(this);
    }

    internal static GifPropertyItemInternal ConvertFromPropertyItem(GifPropertyItem propItem)
    {
        var propItemInternal = new GifPropertyItemInternal
        {
            id = propItem.Id,
            len = 0,
            type = propItem.Type
        };

        var propItemValue = propItem.Value;
        if (propItemValue != null)
        {
            var length = propItemValue.Length;
            propItemInternal.len = length;
            propItemInternal.value = Marshal.AllocHGlobal(length);
            Marshal.Copy(propItemValue, 0, propItemInternal.value, length);
        }

        return propItemInternal;
    }

    internal static GifPropertyItem[] ConvertFromMemory(IntPtr propdata, int count)
    {
        var props = new GifPropertyItem[count];

        for (var i = 0; i < count; i++)
        {
            GifPropertyItemInternal propcopy = null;
            try
            {
                propcopy = (GifPropertyItemInternal) InteropMethods.PtrToStructure(propdata,
                    typeof(GifPropertyItemInternal));

                props[i] = new GifPropertyItem
                {
                    Id = propcopy.id,
                    Len = propcopy.len,
                    Type = propcopy.type,
                    Value = propcopy.Value
                };

                // this calls Marshal.Copy and creates a copy of the original memory into a byte array.

                propcopy.value = IntPtr.Zero; // we dont actually own this memory so dont free it.
            }
            finally
            {
                propcopy?.Dispose();
            }

            propdata = (IntPtr) ((long) propdata + Marshal.SizeOf(typeof(GifPropertyItemInternal)));
        }

        return props;
    }
}