// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Collections;
using Windows.Win32.System.Com;

/// <summary>
///  The <see cref="ComWrappers"/> implementation for WinForm's COM interop usages.
/// </summary>
internal unsafe partial class WinFormsComWrappers : ComWrappers
{
    internal static WinFormsComWrappers Instance { get; } = new();

    private WinFormsComWrappers() { }

    internal static void PopulateIUnknownVTable(IUnknown.Vtbl* unknown)
    {
        GetIUnknownImpl(out nint fpQueryInterface, out nint fpAddRef, out nint fpRelease);
        unknown->QueryInterface_1 = (delegate* unmanaged[Stdcall]<IUnknown*, Guid*, void**, HRESULT>)fpQueryInterface;
        unknown->AddRef_2 = (delegate* unmanaged[Stdcall]<IUnknown*, uint>)fpAddRef;
        unknown->Release_3 = (delegate* unmanaged[Stdcall]<IUnknown*, uint>)fpRelease;
    }

    protected override unsafe ComInterfaceEntry* ComputeVtables(object obj, CreateComInterfaceFlags flags, out int count)
    {
        if (obj is not IManagedWrapper vtables)
        {
            Debug.Fail("object does not implement IManagedWrapper");
            count = 0;
            return null;
        }

        ComInterfaceTable table = vtables.GetComInterfaceTable();
        count = table.Count;

        return table.Entries;
    }

    protected override object CreateObject(IntPtr externalComObject, CreateObjectFlags flags)
    {
        throw new NotImplementedException();
    }

    protected override void ReleaseObjects(IEnumerable objects)
    {
        throw new NotImplementedException();
    }

    /// <summary>
    ///  For the given <paramref name="this"/> pointer unwrap the associated managed object and use it to
    ///  invoke <paramref name="func"/>.
    /// </summary>
    /// <remarks>
    ///  <para>
    ///   Handles exceptions and converts to <see cref="HRESULT"/>.
    ///  </para>
    /// </remarks>
    internal static HRESULT UnwrapAndInvoke<TThis, TInterface>(TThis* @this, Func<TInterface, HRESULT> func)
        where TThis : unmanaged
        where TInterface : class
    {
        try
        {
            TInterface? @object = ComInterfaceDispatch.GetInstance<TInterface>((ComInterfaceDispatch*)@this);
            return @object is null ? HRESULT.COR_E_OBJECTDISPOSED : func(@object);
        }
        catch (Exception ex)
        {
            return ex;
        }
    }

    internal static TReturnType UnwrapAndInvoke<TThis, TInterface, TReturnType>(TThis* @this, Func<TInterface, TReturnType> func)
        where TThis : unmanaged
        where TInterface : class
        where TReturnType : unmanaged
    {
        try
        {
            TInterface? @object = ComInterfaceDispatch.GetInstance<TInterface>((ComInterfaceDispatch*)@this);
            return @object is null ? default : func(@object);
        }
        catch (Exception ex)
        {
            Debug.Fail($"Exception thrown in UnwrapAndInvoke {ex.Message}.");
            return default;
        }
    }

    /// <summary>
    ///  For the given <paramref name="this"/> pointer unwrap the associated managed object and use it to
    ///  invoke <paramref name="action"/>.
    /// </summary>
    /// <inheritdoc cref="UnwrapAndInvoke{TThis, TInterface}(TThis*, Func{TInterface, HRESULT})"/>
    internal static HRESULT UnwrapAndInvoke<TThis, TInterface>(TThis* @this, Action<TInterface> action)
        where TThis : unmanaged
        where TInterface : class
    {
        try
        {
            TInterface? @object = ComInterfaceDispatch.GetInstance<TInterface>((ComInterfaceDispatch*)@this);
            if (@object is null)
            {
                return HRESULT.COR_E_OBJECTDISPOSED;
            }

            action(@object);
            return HRESULT.S_OK;
        }
        catch (Exception ex)
        {
            return ex;
        }
    }
}
