using System;
using System.Diagnostics;
using System.IO;
using System.Runtime.InteropServices;
using System.Xml.Linq;

namespace BSO
{
    /// <summary>
    /// Vollbild im Fenster: macht das Spielfenster randlos und so gross wie den Bildschirm. Das exklusive DirectX-9-Vollbild
    /// des Spiels laeuft unter neuen Windows-Versionen schlecht (Alt-Tab, Abstuerze) - so geht Alt-Tab sofort. Nur wenn
    /// das Spiel im Fenstermodus laeuft (Settings.xml: Fullscreen="FALSE"). F11 schaltet zwischen Vollbild und Fenster.
    /// Am schaerfsten ist es, wenn im Spiel die Aufloesung des Bildschirms eingestellt ist (das Bild wird sonst skaliert).
    /// </summary>
    public static class BorderlessWindow
    {
        [StructLayout(LayoutKind.Sequential)] struct Rect { public int Left, Top, Right, Bottom; }
        [StructLayout(LayoutKind.Sequential)] struct MonitorInfo { public int Size; public Rect Monitor, Work; public uint Flags; }

        [DllImport("user32.dll")] static extern nint GetWindowLongPtrW(nint window, int index);
        [DllImport("user32.dll")] static extern nint SetWindowLongPtrW(nint window, int index, nint value);
        [DllImport("user32.dll")] static extern bool GetWindowRect(nint window, out Rect rect);
        [DllImport("user32.dll")] static extern bool GetClientRect(nint window, out Rect rect);
        [DllImport("user32.dll")] static extern bool SetWindowPos(nint window, nint after, int x, int y, int w, int h, uint flags);
        [DllImport("user32.dll")] static extern nint MonitorFromWindow(nint window, uint flags);
        [DllImport("user32.dll")] static extern bool GetMonitorInfoW(nint monitor, ref MonitorInfo info);

        const int GwlStyle = -16, GwlExStyle = -20;
        const long Frame = 0x00C00000 | 0x00040000 | 0x00020000 | 0x00010000; // Titelleiste, Rahmen, Min/Max
        const long ExFrame = 0x1 | 0x100 | 0x200 | 0x20000;                 // Rahmen-Kanten
        const uint MonitorNearest = 2;
        const uint SwpFrameChanged = 0x20, SwpNoZOrder = 0x4, SwpNoOwnerZOrder = 0x200, SwpShowWindow = 0x40;

        static bool checkedSettings, allowed, enabled = true, isBorderless;
        static nint window;
        static long savedStyle, savedExStyle;
        static Rect savedRect;
        static readonly Stopwatch checkClock = new();

        /// <summary>Einmal pro Bild im Hauptthread (dem Thread des Fensters).</summary>
        public static void Update()
        {
            if (!checkedSettings)
            {
                checkedSettings = true;
                allowed = !GameFullscreen();
                if (!allowed) Bootstrap.Log("Spiel laeuft im eigenen Vollbild - BSO-Vollbild bleibt aus");
            }
            if (!allowed) return;

            if (Input.Pressed(Input.F11))
            {
                enabled = !enabled;
                Bootstrap.Log(enabled ? "Vollbild an" : "Vollbild aus (Fenster)");
                if (!enabled && isBorderless) Restore();
            }

            // Jede Sekunde pruefen - das Spiel stellt sein Fenster z.B. nach Aenderungen in den Optionen neu ein
            if (checkClock.IsRunning && checkClock.ElapsedMilliseconds < 1000 && !Input.Pressed(Input.F11)) return;
            checkClock.Restart();
            if (window == 0) window = Process.GetCurrentProcess().MainWindowHandle;
            if (window == 0 || !enabled) return;

            Rect monitor = MonitorRect();
            GetWindowRect(window, out Rect now);
            bool hasFrame = (GetWindowLongPtrW(window, GwlStyle) & Frame) != 0;
            if (isBorderless && !hasFrame && Same(now, monitor)) return;
            MakeBorderless(monitor);
        }

        static void MakeBorderless(Rect monitor)
        {
            long style = GetWindowLongPtrW(window, GwlStyle), exStyle = GetWindowLongPtrW(window, GwlExStyle);
            if ((style & Frame) != 0) // nur das echte Fenster merken, nicht unser randloses
            {
                savedStyle = style;
                savedExStyle = exStyle;
                GetWindowRect(window, out savedRect);
            }
            SetWindowLongPtrW(window, GwlStyle, (nint)(style & ~Frame));
            SetWindowLongPtrW(window, GwlExStyle, (nint)(exStyle & ~ExFrame));
            SetWindowPos(window, 0, monitor.Left, monitor.Top, monitor.Right - monitor.Left, monitor.Bottom - monitor.Top,
                SwpFrameChanged | SwpNoZOrder | SwpNoOwnerZOrder | SwpShowWindow);
            isBorderless = true;

            GetClientRect(window, out Rect client);
            Bootstrap.Log($"Vollbild im Fenster: {client.Right}x{client.Bottom} (Bildschirm {monitor.Right - monitor.Left}x{monitor.Bottom - monitor.Top})");
        }

        static void Restore()
        {
            isBorderless = false;
            if (window == 0 || savedStyle == 0) return;
            SetWindowLongPtrW(window, GwlStyle, (nint)savedStyle);
            SetWindowLongPtrW(window, GwlExStyle, (nint)savedExStyle);
            SetWindowPos(window, 0, savedRect.Left, savedRect.Top, savedRect.Right - savedRect.Left, savedRect.Bottom - savedRect.Top,
                SwpFrameChanged | SwpNoZOrder | SwpNoOwnerZOrder | SwpShowWindow);
        }

        static Rect MonitorRect()
        {
            var info = new MonitorInfo { Size = Marshal.SizeOf<MonitorInfo>() };
            GetMonitorInfoW(MonitorFromWindow(window, MonitorNearest), ref info);
            return info.Monitor;
        }

        static bool Same(Rect a, Rect b) => a.Left == b.Left && a.Top == b.Top && a.Right == b.Right && a.Bottom == b.Bottom;

        /// <summary>Fullscreen-Einstellung des Spiels (%LOCALAPPDATA%\European Bus Simulator 2012\Settings.xml).</summary>
        static bool GameFullscreen()
        {
            try
            {
                string file = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
                    "European Bus Simulator 2012", "Settings.xml");
                string value = (string)XDocument.Load(file).Root?.Element("Graphics")?.Attribute("Fullscreen");
                return string.Equals(value, "TRUE", StringComparison.OrdinalIgnoreCase);
            }
            catch (Exception e)
            {
                Bootstrap.Log("Settings.xml nicht lesbar: " + e.Message);
                return false;
            }
        }
    }
}