using System.Runtime.InteropServices;

namespace Pilz.Updating.Client.Gui;

internal static class BaseFeatures
{
    [DllImport("user32")]
    private static extern uint SendMessage(IntPtr hWnd, uint msg, uint wParam, uint lParam);

    private const int BCM_FIRST = 0x1600; // Normal button
    private const int BCM_SETSHIELD = BCM_FIRST + 0xC; // Elevated button

    public static void AddShieldToButton(Button b)
    {
        b.FlatStyle = FlatStyle.System;
        SendMessage(b.Handle, BCM_SETSHIELD, 0, 0xFFFFFFFFU);
    }

    // Return a bitmap containing the UAC shield.
    private static Bitmap shield_bm = null;

    public static Bitmap GetUacShieldImage()
    {
        if (shield_bm is object)
        {
            return shield_bm;
        }

        const int WID = 50;
        const int HGT = 50;
        const int MARGIN = 4;

        // Make the button. For some reason, it must
        // have text or the UAC shield won't appear.
        var btn = new Button
        {
            Text = " ",
            Size = new Size(WID, HGT)
        };
        AddShieldToButton(btn);

        // Draw the button onto a bitmap.
        var bm = new Bitmap(WID, HGT);
        btn.Refresh();
        btn.DrawToBitmap(bm, new Rectangle(0, 0, WID, HGT));

        // Find the part containing the shield.
        int min_x = WID;
        int max_x = 0;
        int min_y = HGT;
        int max_y = 0;

        // Fill on the left.
        int y = MARGIN;
        while (y < HGT - MARGIN)
        {
            // Get the leftmost pixel's color.
            var target_color = bm.GetPixel(MARGIN, y);

            // Fill in with this color as long as we see the target.
            int x = MARGIN;
            while (x < WID - MARGIN)
            {
                // See if this pixel is part of the shield.
                if (bm.GetPixel(x, y).Equals(target_color))
                {
                    // It's not part of the shield.
                    // Clear the pixel.
                    bm.SetPixel(x, y, Color.Transparent);
                }
                else
                {
                    // It's part of the shield.
                    if (min_y > y)
                    {
                        min_y = y;
                    }

                    if (min_x > x)
                    {
                        min_x = x;
                    }

                    if (max_y < y)
                    {
                        max_y = y;
                    }

                    if (max_x < x)
                    {
                        max_x = x;
                    }
                }

                x += 1;
            }

            y += 1;
        }

        // Clip out the shield part.
        int shield_wid = max_x - min_x + 1;
        int shield_hgt = max_y - min_y + 1;
        shield_bm = new Bitmap(shield_wid, shield_hgt);
        var shield_gr = Graphics.FromImage(shield_bm);
        shield_gr.DrawImage(bm, 0, 0, new Rectangle(min_x, min_y, shield_wid, shield_hgt), GraphicsUnit.Pixel);

        // Return the shield.
        return shield_bm;
    }
}