// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Runtime.InteropServices;
using Windows.Win32.System.Com;
 
namespace System.Windows.Forms;
 
/// <summary>
///  Represents an internal class that is used by ComboBox and TextBox AutoCompleteCustomSource property.
///  This class is responsible for initializing the SHAutoComplete COM object and setting options in it.
///  The StringSource contains an array of Strings which is passed to the COM object as the custom source.
/// </summary>
internal unsafe class StringSource : IEnumString.Interface, IManagedWrapper<IEnumString>
{
    private string[] _strings;
    private int _current;
    private int _size;
    private IAutoComplete2* _autoComplete2;
 
    /// <summary>
    ///  Constructor.
    /// </summary>
    public StringSource(string[] strings)
    {
        _strings = strings;
        _size = strings.Length;
 
        PInvokeCore.CoCreateInstance(
            CLSID.AutoComplete,
            pUnkOuter: null,
            CLSCTX.CLSCTX_INPROC_SERVER,
            out _autoComplete2).ThrowOnFailure();
    }
 
    /// <summary>
    ///  This is the method that binds the custom source with the IAutoComplete interface.The "hWndEdit" is the handle
    ///  to the edit Control and the "options' are the options that need to be set in the AUTOCOMPLETE mode.
    /// </summary>
    public bool Bind(IHandle<HWND> edit, AUTOCOMPLETEOPTIONS options)
    {
        if (_autoComplete2 is null || _autoComplete2->SetOptions((uint)options).Failed)
        {
            return false;
        }
 
        _autoComplete2->Init(
            edit.Handle,
            (IUnknown*)ComHelpers.GetComPointer<IEnumString>(this),
            (PCWSTR)null,
            (PCWSTR)null);
 
        GC.KeepAlive(edit.Wrapper);
        return true;
    }
 
    public void ReleaseAutoComplete()
    {
        if (_autoComplete2 is not null)
        {
            _autoComplete2->Release();
            _autoComplete2 = null;
        }
    }
 
    public void RefreshList(string[] newSource)
    {
        Array.Clear(_strings, 0, _size);
        _strings = newSource;
        _current = 0;
        _size = _strings.Length;
    }
 
    public unsafe HRESULT Clone(IEnumString** ppenum)
    {
        if (ppenum is null)
        {
            return HRESULT.E_POINTER;
        }
 
        *ppenum = ComHelpers.GetComPointer<IEnumString>(new StringSource(_strings) { _current = _current });
        return HRESULT.S_OK;
    }
 
    public unsafe HRESULT Next(uint celt, PWSTR* rgelt, [Optional] uint* pceltFetched)
    {
        if (celt < 0)
        {
            return HRESULT.E_INVALIDARG;
        }
 
        uint fetched = 0;
 
        while (_current < _size && celt > 0)
        {
            rgelt[fetched] = (char*)Marshal.StringToCoTaskMemUni(_strings[_current]);
            _current++;
            fetched++;
            celt--;
        }
 
        if (pceltFetched is not null)
        {
            *pceltFetched = fetched;
        }
 
        return celt == 0 ? HRESULT.S_OK : HRESULT.S_FALSE;
    }
 
    public HRESULT Skip(uint celt)
    {
        int newCurrent = _current + (int)celt;
        if (newCurrent >= _size)
        {
            return HRESULT.S_FALSE;
        }
 
        _current = newCurrent;
        return HRESULT.S_OK;
    }
 
    public HRESULT Reset()
    {
        _current = 0;
        return HRESULT.S_OK;
    }
}