using System.Runtime.InteropServices;
using CursorLang.Core.Interop;

namespace CursorLang.Settings.Interop;

/// <summary>
/// Win32 API for placing the settings window: its own bounds and the work area
/// of the monitor the window is asked to be put on.
/// </summary>
/// <remarks>
/// The bounds are taken from the system rather than from <c>Window.Left/Top/Width/Height</c>:
/// the window height adapts to its content, and WPF converts those properties using the
/// monitor DPI, while the monitor work area comes in pixels. Computing the centre in a
/// single unit is simpler than converting back and forth.
/// </remarks>
internal static class WindowPlacementNative
{
    [DllImport("user32.dll")]
    private static extern bool GetWindowRect(IntPtr hWnd, out PopupWindowNative.Rect lpRect);

    [DllImport("user32.dll")]
    private static extern IntPtr MonitorFromRect(ref PopupWindowNative.Rect lprc, uint dwFlags);

    [DllImport("user32.dll")]
    private static extern bool GetMonitorInfo(IntPtr hMonitor, ref MonitorInfo lpmi);

    [StructLayout(LayoutKind.Sequential)]
    private struct MonitorInfo
    {
        public int cbSize;
        public PopupWindowNative.Rect rcMonitor;
        public PopupWindowNative.Rect rcWork;
        public uint dwFlags;
    }

    private const uint MONITOR_DEFAULTTONEAREST = 2;

    /// <summary>The window bounds in screen pixels — including the frame and the title bar.</summary>
    internal static PopupWindowNative.Rect? TryGetBounds(IntPtr hWnd) =>
        GetWindowRect(hWnd, out PopupWindowNative.Rect bounds) ? bounds : null;

    /// <summary>
    /// The work area — without the taskbar — of the monitor that holds the
    /// rectangle entirely, or at least most of it.
    /// </summary>
    internal static PopupWindowNative.Rect? TryGetWorkAreaNear(PopupWindowNative.Rect rect)
    {
        IntPtr monitor = MonitorFromRect(ref rect, MONITOR_DEFAULTTONEAREST);

        var info = new MonitorInfo { cbSize = Marshal.SizeOf<MonitorInfo>() };
        return GetMonitorInfo(monitor, ref info) ? info.rcWork : null;
    }
}