using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;
using WhiteMagic.Native;

namespace WhiteMagic.Windows;

/// <summary>
/// Factory for enumerating and locating <see cref="RemoteWindow"/> instances.
/// </summary>
public static class WindowFactory
{
    /// <summary>Enumerates all top-level windows.</summary>
    public static unsafe IEnumerable<RemoteWindow> GetWindows()
    {
        var handles = new List<IntPtr>();
        GCHandle gch = GCHandle.Alloc(handles);
        try
        {
            delegate* unmanaged[Stdcall]<IntPtr, IntPtr, int> callback = &EnumWindowsCallback;
            NativeMethods.EnumWindows((nint)callback, GCHandle.ToIntPtr(gch));
        }
        finally
        {
            gch.Free();
        }

        return handles.Select(static h => new RemoteWindow(h));
    }

    /// <summary>Returns all top-level windows with the specified class name.</summary>
    public static IEnumerable<RemoteWindow> GetWindowsByClassName(string className)
    {
        if (className is null)
            throw new ArgumentNullException(nameof(className));

        return GetWindows().Where(w => w.ClassName.Equals(className, StringComparison.Ordinal));
    }

    /// <summary>Returns all top-level windows owned by the specified process.</summary>
    public static IEnumerable<RemoteWindow> GetWindowsByProcessId(int processId)
    {
        return GetWindows().Where(w => w.ProcessId == (uint)processId);
    }

    /// <summary>Returns the first top-level window with the specified class name.</summary>
    public static RemoteWindow? GetWindowByClassName(string className)
    {
        return GetWindowsByClassName(className).FirstOrDefault();
    }

    /// <summary>
    /// Returns the main window of a process. When <see cref="Process.MainWindowHandle"/>
    /// is unavailable, falls back to the first enumerated window owned by the process.
    /// </summary>
    public static RemoteWindow? GetMainWindow(System.Diagnostics.Process process)
    {
        if (process is null)
            throw new ArgumentNullException(nameof(process));

        if (process.MainWindowHandle != IntPtr.Zero)
            return new RemoteWindow(process.MainWindowHandle);

        return GetWindowsByProcessId(process.Id).FirstOrDefault();
    }

    [UnmanagedCallersOnly(CallConvs = new[] { typeof(CallConvStdcall) })]
    private static int EnumWindowsCallback(IntPtr hWnd, IntPtr lParam)
    {
        var handles = (List<IntPtr>)GCHandle.FromIntPtr(lParam).Target!;
        handles.Add(hWnd);
        return 1; // Continue enumeration.
    }
}