// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

#nullable disable

using Microsoft.Win32;

namespace System.Windows.Forms
{
    internal class DisplayInformation
    {
        private static bool s_highContrast;               // whether we are under hight contrast mode
        private static bool s_lowRes;                     // whether we are under low resolution mode
        private static bool s_highContrastSettingValid;   // indicates whether the high contrast setting is correct
        private static bool s_lowResSettingValid;         // indicates whether the low resolution setting is correct
        private static short s_bitsPerPixel;
        private static bool s_dropShadowSettingValid;
        private static bool s_dropShadowEnabled;
        private static bool s_menuAccessKeysUnderlinedValid;
        private static bool s_menuAccessKeysUnderlined;

        static DisplayInformation()
        {
            SystemEvents.UserPreferenceChanging += new UserPreferenceChangingEventHandler(UserPreferenceChanging);
            SystemEvents.DisplaySettingsChanging += new EventHandler(DisplaySettingsChanging);
        }

        public static short BitsPerPixel
        {
            get
            {
                if (s_bitsPerPixel == 0)
                {
                    // we used to iterate through all screens, but
                    // for some reason unused screens can temparily appear
                    // in the AllScreens collection - we would honor the display
                    // setting of an unused screen.
                    // According to EnumDisplayMonitors, a primary screen check should be sufficient
                    s_bitsPerPixel = (short)Screen.PrimaryScreen.BitsPerPixel;
                }
                return s_bitsPerPixel;
            }
        }

        /// <summary>
        ///  Tests to see if the monitor is in low resolution mode (8-bit color depth or less).
        /// </summary>
        public static bool LowResolution
        {
            get
            {
                if (s_lowResSettingValid && !s_lowRes)
                {
                    return s_lowRes;
                }
                // dont cache if we're in low resolution.
                s_lowRes = BitsPerPixel <= 8;
                s_lowResSettingValid = true;
                return s_lowRes;
            }
        }

        /// <summary>
        ///  Tests to see if we are under high contrast mode
        /// </summary>
        public static bool HighContrast
        {
            get
            {
                if (s_highContrastSettingValid)
                {
                    return s_highContrast;
                }
                s_highContrast = SystemInformation.HighContrast;
                s_highContrastSettingValid = true;
                return s_highContrast;
            }
        }

        public static bool IsDropShadowEnabled
        {
            get
            {
                if (s_dropShadowSettingValid)
                {
                    return s_dropShadowEnabled;
                }
                s_dropShadowEnabled = SystemInformation.IsDropShadowEnabled;
                s_dropShadowSettingValid = true;
                return s_dropShadowEnabled;
            }
        }

        // return if mnemonic underlines should always be there regardless of ALT
        public static bool MenuAccessKeysUnderlined
        {
            get
            {
                if (s_menuAccessKeysUnderlinedValid)
                {
                    return s_menuAccessKeysUnderlined;
                }
                s_menuAccessKeysUnderlined = SystemInformation.MenuAccessKeysUnderlined;
                s_menuAccessKeysUnderlinedValid = true;
                return s_menuAccessKeysUnderlined;
            }
        }

        /// <summary>
        ///event handler for change in display setting
        /// </summary>
        private static void DisplaySettingsChanging(object obj, EventArgs ea)
        {
            s_highContrastSettingValid = false;
            s_lowResSettingValid = false;
            s_dropShadowSettingValid = false;
            s_menuAccessKeysUnderlinedValid = false;
        }

        /// <summary>
        ///event handler for change in user preference
        /// </summary>
        private static void UserPreferenceChanging(object obj, UserPreferenceChangingEventArgs e)
        {
            s_highContrastSettingValid = false;
            s_lowResSettingValid = false;
            s_dropShadowSettingValid = false;
            s_bitsPerPixel = 0;

            if (e.Category == UserPreferenceCategory.General)
            {
                s_menuAccessKeysUnderlinedValid = false;
            }
        }
    }
}
