// 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 System.Collections.Generic;
using System.Threading;
using static Interop;

namespace System.Windows.Forms
{
    /// <summary>
    ///  Implements keyboard ToolTips for controls with a <see cref="ToolTip"/> set on them.
    ///
    ///  A keyboard ToolTip is shown when a user focuses a control using keyboard keys such as Tab, arrow keys etc.
    ///  This state machine attempts to simulate the mouse ToolTip behavior.
    /// </summary>
    /// <remarks>
    ///  The control should be focused with keyboard for an amount of time specified with TTDT_INITIAL flag to make
    ///  the keyboard ToolTip appear. <see href="https://docs.microsoft.com/windows/win32/controls/ttm-getdelaytime">TTM_GETDELAYTIME message (Microsoft Docs)</see>
    ///
    ///  Once visible, the keyboard ToolTip will be demonstrated for an amount of time specified with TTDT_AUTOPOP
    ///  flag. The ToolTip will disappear afterwards. If the keyboard ToolTip is visible and the focus moves from
    ///  one ToolTip-enabled control to another, the keyboard ToolTip will be shown after a time interval specified
    ///  with TTDT_RESHOW flag has passed.
    /// </remarks>
    internal sealed partial class KeyboardToolTipStateMachine
    {
        public static KeyboardToolTipStateMachine Instance
        {
            get
            {
                if (s_instance is null)
                {
                    s_instance = new KeyboardToolTipStateMachine();
                }

                return s_instance;
            }
        }

        [ThreadStatic]
        private static KeyboardToolTipStateMachine s_instance;

        private readonly ToolToTipDictionary _toolToTip = new();

        private SmState _currentState = SmState.Hidden;
        private IKeyboardToolTip _currentTool;
        private readonly InternalStateMachineTimer _timer = new();
        private SendOrPostCallback _refocusDelayExpirationCallback;

        private readonly WeakReference<IKeyboardToolTip> _lastFocusedTool = new(null);

        private KeyboardToolTipStateMachine()
        {
        }

        private SmState Transition(IKeyboardToolTip tool, ToolTip tooltip, SmEvent @event)
            => (_currentState, @event) switch
            {
                (SmState.Hidden, SmEvent.FocusedTool) => SetupInitShowTimer(tool, tooltip),
                (SmState.Hidden, SmEvent.LeftTool) => _currentState, // OK
                (SmState.ReadyForInitShow, SmEvent.FocusedTool) => _currentState, // unlikely: focus without leave
                (SmState.ReadyForInitShow, SmEvent.LeftTool) => FullFsmReset(),
                (SmState.ReadyForInitShow, SmEvent.InitialDelayTimerExpired) => ShowToolTip(tool, tooltip),

                (SmState.Shown, SmEvent.FocusedTool) => _currentState, // unlikely: focus without leave
                (SmState.Shown, SmEvent.LeftTool) => HideAndStartWaitingForRefocus(tool, tooltip),
                (SmState.Shown, SmEvent.AutoPopupDelayTimerExpired) => FullFsmReset(),

                (SmState.WaitForRefocus, SmEvent.FocusedTool) => SetupReshowTimer(tool, tooltip),
                (SmState.WaitForRefocus, SmEvent.LeftTool) => _currentState, // OK
                (SmState.WaitForRefocus, SmEvent.RefocusWaitDelayExpired) => FullFsmReset(),

                (SmState.ReadyForReshow, SmEvent.FocusedTool) => _currentState, // unlikely: focus without leave
                (SmState.ReadyForReshow, SmEvent.LeftTool) => StartWaitingForRefocus(tool),
                (SmState.ReadyForReshow, SmEvent.ReshowDelayTimerExpired) => ShowToolTip(tool, tooltip),

                // This is what we would have thrown historically
                (_, _) => throw new KeyNotFoundException()
            };

        public void ResetStateMachine(ToolTip toolTip)
        {
            Reset(toolTip);
        }

        public void Hook(IKeyboardToolTip tool, ToolTip toolTip)
        {
            if (tool.AllowsToolTip())
            {
                StartTracking(tool, toolTip);
                tool.OnHooked(toolTip);
            }
        }

        public void NotifyAboutMouseEnter(IKeyboardToolTip sender)
        {
            if (IsToolTracked(sender) && sender.ShowsOwnToolTip())
            {
                Reset(null);
            }
        }

        private bool IsToolTracked(IKeyboardToolTip sender)
        {
            return _toolToTip[sender] != null;
        }

        public void NotifyAboutLostFocus(IKeyboardToolTip sender)
        {
            if (IsToolTracked(sender) && sender.ShowsOwnToolTip())
            {
                Transit(SmEvent.LeftTool, sender);
                if (_currentTool is null)
                {
                    _lastFocusedTool.SetTarget(null);
                }
            }
        }

        public void NotifyAboutGotFocus(IKeyboardToolTip sender)
        {
            if (IsToolTracked(sender) && sender.ShowsOwnToolTip() && sender.IsBeingTabbedTo())
            {
                Transit(SmEvent.FocusedTool, sender);
                if (_currentTool == sender)
                {
                    _lastFocusedTool.SetTarget(sender);
                }
            }
        }

        public void Unhook(IKeyboardToolTip tool, ToolTip toolTip)
        {
            if (tool.AllowsToolTip())
            {
                StopTracking(tool, toolTip);
                tool.OnUnhooked(toolTip);
            }
        }

        public void NotifyAboutFormDeactivation(ToolTip sender)
        {
            OnFormDeactivation(sender);
        }

        internal IKeyboardToolTip LastFocusedTool
        {
            get
            {
                if (_lastFocusedTool.TryGetTarget(out IKeyboardToolTip tool))
                {
                    return tool;
                }

                return Control.FromHandle(User32.GetFocus());
            }
        }

        private SmState HideAndStartWaitingForRefocus(IKeyboardToolTip tool, ToolTip toolTip)
        {
            toolTip.HideToolTip(_currentTool);
            return StartWaitingForRefocus(tool);
        }

        private SmState StartWaitingForRefocus(IKeyboardToolTip tool)
        {
            ResetTimer();
            _currentTool = null;
            SendOrPostCallback expirationCallback = null;
            _refocusDelayExpirationCallback = expirationCallback = (object toolObject) =>
            {
                if (_currentState == SmState.WaitForRefocus && _refocusDelayExpirationCallback == expirationCallback)
                {
                    Transit(SmEvent.RefocusWaitDelayExpired, (IKeyboardToolTip)toolObject);
                }
            };
            SynchronizationContext.Current.Post(expirationCallback, tool);
            return SmState.WaitForRefocus;
        }

        private SmState SetupReshowTimer(IKeyboardToolTip tool, ToolTip toolTip)
        {
            _currentTool = tool;
            ResetTimer();
            StartTimer(toolTip.GetDelayTime(ComCtl32.TTDT.RESHOW),
                GetOneRunTickHandler((Timer sender) => Transit(SmEvent.ReshowDelayTimerExpired, tool)));
            return SmState.ReadyForReshow;
        }

        private SmState ShowToolTip(IKeyboardToolTip tool, ToolTip toolTip)
        {
            string toolTipText = tool.GetCaptionForTool(toolTip);
            int autoPopDelay = toolTip.GetDelayTime(ComCtl32.TTDT.AUTOPOP);
            if (!_currentTool.IsHoveredWithMouse())
            {
                toolTip.ShowKeyboardToolTip(toolTipText, _currentTool, autoPopDelay);
            }

            StartTimer(autoPopDelay,
                GetOneRunTickHandler((Timer sender) => Transit(SmEvent.AutoPopupDelayTimerExpired, _currentTool)));
            return SmState.Shown;
        }

        private SmState SetupInitShowTimer(IKeyboardToolTip tool, ToolTip toolTip)
        {
            _currentTool = tool;
            ResetTimer();
            StartTimer(toolTip.GetDelayTime(ComCtl32.TTDT.INITIAL),
                GetOneRunTickHandler((Timer sender) => Transit(SmEvent.InitialDelayTimerExpired, _currentTool)));

            return SmState.ReadyForInitShow;
        }

        private void StartTimer(int interval, EventHandler eventHandler)
        {
            _timer.Interval = interval;
            _timer.Tick += eventHandler;
            _timer.Start();
        }

        private EventHandler GetOneRunTickHandler(Action<Timer> handler)
        {
            void wrapper(object sender, EventArgs eventArgs)
            {
                _timer.Stop();
                _timer.Tick -= wrapper;
                handler(_timer);
            }

            return wrapper;
        }

        private void Transit(SmEvent @event, IKeyboardToolTip source)
        {
            bool fullFsmResetRequired = false;
            try
            {
                ToolTip toolTip = _toolToTip[source];
                if ((_currentTool is null || _currentTool.CanShowToolTipsNow()) && toolTip != null)
                {
                    _currentState = Transition(source, toolTip, @event);
                }
                else
                {
                    fullFsmResetRequired = true;
                }
            }
            catch
            {
                fullFsmResetRequired = true;
                throw;
            }
            finally
            {
                if (fullFsmResetRequired)
                {
                    FullFsmReset();
                }
            }
        }

        private SmState FullFsmReset()
        {
            if (_currentState == SmState.Shown && _currentTool != null)
            {
                ToolTip currentToolTip = _toolToTip[_currentTool];
                if (currentToolTip != null)
                {
                    currentToolTip.HideToolTip(_currentTool);
                }
            }

            ResetTimer();
            _currentTool = null;
            return _currentState = SmState.Hidden;
        }

        private void ResetTimer()
        {
            _timer.ClearTimerTickHandlers();
            _timer.Stop();
        }

        private void Reset(ToolTip toolTipToReset)
        {
            if (toolTipToReset is null || (_currentTool != null && _toolToTip[_currentTool] == toolTipToReset))
            {
                FullFsmReset();
            }
        }

        private void StartTracking(IKeyboardToolTip tool, ToolTip toolTip)
        {
            _toolToTip[tool] = toolTip;
        }

        private void StopTracking(IKeyboardToolTip tool, ToolTip toolTip)
        {
            _toolToTip.Remove(tool, toolTip);
        }

        private void OnFormDeactivation(ToolTip sender)
        {
            if (_currentTool != null && _toolToTip[_currentTool] == sender)
            {
                FullFsmReset();
            }
        }

        private enum SmEvent : byte
        {
            FocusedTool,
            LeftTool,
            InitialDelayTimerExpired, // internal
            ReshowDelayTimerExpired, // internal
            AutoPopupDelayTimerExpired, // internal
            RefocusWaitDelayExpired // internal
        }

        private enum SmState : byte
        {
            Hidden,
            ReadyForInitShow,
            Shown,
            ReadyForReshow,
            WaitForRefocus
        }
    }
}
