AppContext.cs

using System.Collections.Generic;

namespace System
{
    public static class AppContext
    {
        [Flags]
        private enum SwitchValueState
        {
            HasFalseValue = 0x1,
            HasTrueValue = 0x2,
            HasLookedForOverride = 0x4,
            UnknownValue = 0x8
        }

        private static readonly Dictionary<string, SwitchValueState> s_switchMap = new Dictionary<string, SwitchValueState>();

        private static volatile bool s_defaultsInitialized = false;

        public static string BaseDirectory => ((string)AppDomain.CurrentDomain.GetData("APP_CONTEXT_BASE_DIRECTORY")) ?? AppDomain.CurrentDomain.BaseDirectory;

        public static string TargetFrameworkName => AppDomain.CurrentDomain.SetupInformation.TargetFrameworkName;

        public static object GetData(string name)
        {
            return AppDomain.CurrentDomain.GetData(name);
        }

        private static void InitializeDefaultSwitchValues()
        {
            lock (s_switchMap)
            {
                if (!s_defaultsInitialized)
                {
                    AppContextDefaultValues.PopulateDefaultValues();
                    s_defaultsInitialized = true;
                }
            }
        }

        public static bool TryGetSwitch(string switchName, out bool isEnabled)
        {
            if (switchName == null)
            {
                throw new ArgumentNullException("switchName");
            }
            if (switchName.Length == 0)
            {
                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyName"), "switchName");
            }
            if (!s_defaultsInitialized)
            {
                InitializeDefaultSwitchValues();
            }
            isEnabled = false;
            lock (s_switchMap)
            {
                if (s_switchMap.TryGetValue(switchName, out SwitchValueState value))
                {
                    if (value == SwitchValueState.UnknownValue)
                    {
                        isEnabled = false;
                        return false;
                    }
                    isEnabled = ((value & SwitchValueState.HasTrueValue) == SwitchValueState.HasTrueValue);
                    if ((value & SwitchValueState.HasLookedForOverride) == SwitchValueState.HasLookedForOverride)
                    {
                        return true;
                    }
                    if (AppContextDefaultValues.TryGetSwitchOverride(switchName, out bool overrideValue))
                    {
                        isEnabled = overrideValue;
                    }
                    s_switchMap[switchName] = (SwitchValueState)(((!isEnabled) ? 1 : 2) | 4);
                    return true;
                }
                if (AppContextDefaultValues.TryGetSwitchOverride(switchName, out bool overrideValue2))
                {
                    isEnabled = overrideValue2;
                    s_switchMap[switchName] = (SwitchValueState)(((!isEnabled) ? 1 : 2) | 4);
                    return true;
                }
                s_switchMap[switchName] = SwitchValueState.UnknownValue;
            }
            return false;
        }

        public static void SetSwitch(string switchName, bool isEnabled)
        {
            if (switchName == null)
            {
                throw new ArgumentNullException("switchName");
            }
            if (switchName.Length == 0)
            {
                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyName"), "switchName");
            }
            if (!s_defaultsInitialized)
            {
                InitializeDefaultSwitchValues();
            }
            SwitchValueState value = (SwitchValueState)(((!isEnabled) ? 1 : 2) | 4);
            lock (s_switchMap)
            {
                s_switchMap[switchName] = value;
            }
        }

        internal static void DefineSwitchDefault(string switchName, bool isEnabled)
        {
            s_switchMap[switchName] = ((!isEnabled) ? SwitchValueState.HasFalseValue : SwitchValueState.HasTrueValue);
        }

        internal static void DefineSwitchOverride(string switchName, bool isEnabled)
        {
            s_switchMap[switchName] = (SwitchValueState)(((!isEnabled) ? 1 : 2) | 4);
        }
    }
}