#nullable enable
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;

namespace Terminal.Gui.App;

public static partial class Application // Run (Begin -> Run -> Layout/Draw -> End -> Stop)
{
    /// <summary>Gets or sets the key to quit the application.</summary>
    [ConfigurationProperty (Scope = typeof (SettingsScope))]
    public static Key QuitKey
    {
        get => Keyboard.QuitKey;
        set => Keyboard.QuitKey = value;
    }

    /// <summary>Gets or sets the key to activate arranging views using the keyboard.</summary>
    [ConfigurationProperty (Scope = typeof (SettingsScope))]
    public static Key ArrangeKey
    {
        get => Keyboard.ArrangeKey;
        set => Keyboard.ArrangeKey = value;
    }

    // When `End ()` is called, it is possible `RunState.Toplevel` is a different object than `Top`.
    // This variable is set in `End` in this case so that `Begin` correctly sets `Top`.
    private static Toplevel? _cachedRunStateToplevel;

    /// <summary>
    ///     Notify that a new <see cref="RunState"/> was created (<see cref="Begin(Toplevel)"/> was called). The token is
    ///     created in <see cref="Begin(Toplevel)"/> and this event will be fired before that function exits.
    /// </summary>
    /// <remarks>
    ///     If <see cref="EndAfterFirstIteration"/> is <see langword="true"/> callers to <see cref="Begin(Toplevel)"/>
    ///     must also subscribe to <see cref="NotifyStopRunState"/> and manually dispose of the <see cref="RunState"/> token
    ///     when the application is done.
    /// </remarks>
    public static event EventHandler<RunStateEventArgs>? NotifyNewRunState;

    /// <summary>Notify that an existent <see cref="RunState"/> is stopping (<see cref="End(RunState)"/> was called).</summary>
    /// <remarks>
    ///     If <see cref="EndAfterFirstIteration"/> is <see langword="true"/> callers to <see cref="Begin(Toplevel)"/>
    ///     must also subscribe to <see cref="NotifyStopRunState"/> and manually dispose of the <see cref="RunState"/> token
    ///     when the application is done.
    /// </remarks>
    public static event EventHandler<ToplevelEventArgs>? NotifyStopRunState;

    /// <summary>Building block API: Prepares the provided <see cref="Toplevel"/> for execution.</summary>
    /// <returns>
    ///     The <see cref="RunState"/> handle that needs to be passed to the <see cref="End(RunState)"/> method upon
    ///     completion.
    /// </returns>
    /// <param name="toplevel">The <see cref="Toplevel"/> to prepare execution for.</param>
    /// <remarks>
    ///     This method prepares the provided <see cref="Toplevel"/> for running with the focus, it adds this to the list
    ///     of <see cref="Toplevel"/>s, lays out the SubViews, focuses the first element, and draws the <see cref="Toplevel"/>
    ///     in the screen. This is usually followed by executing the <see cref="RunLoop"/> method, and then the
    ///     <see cref="End(RunState)"/> method upon termination which will undo these changes.
    /// </remarks>
    public static RunState Begin (Toplevel toplevel)
    {
        ArgumentNullException.ThrowIfNull (toplevel);

        // Ensure the mouse is ungrabbed.
        if (Mouse.MouseGrabView is { })
        {
            Mouse.UngrabMouse ();
        }

        var rs = new RunState (toplevel);

#if DEBUG_IDISPOSABLE
        if (View.EnableDebugIDisposableAsserts && Top is { } && toplevel != Top && !TopLevels.Contains (Top))
        {
            // This assertion confirm if the Top was already disposed
            Debug.Assert (Top.WasDisposed);
            Debug.Assert (Top == _cachedRunStateToplevel);
        }
#endif

        lock (TopLevels)
        {
            if (Top is { } && toplevel != Top && !TopLevels.Contains (Top))
            {
                // If Top was already disposed and isn't on the Toplevels Stack,
                // clean it up here if is the same as _cachedRunStateToplevel
                if (Top == _cachedRunStateToplevel)
                {
                    Top = null;
                }
                else
                {
                    // Probably this will never hit
                    throw new ObjectDisposedException (Top.GetType ().FullName);
                }
            }

            // BUGBUG: We should not depend on `Id` internally.
            // BUGBUG: It is super unclear what this code does anyway.
            if (string.IsNullOrEmpty (toplevel.Id))
            {
                var count = 1;
                var id = (TopLevels.Count + count).ToString ();

                while (TopLevels.Count > 0 && TopLevels.FirstOrDefault (x => x.Id == id) is { })
                {
                    count++;
                    id = (TopLevels.Count + count).ToString ();
                }

                toplevel.Id = (TopLevels.Count + count).ToString ();

                TopLevels.Push (toplevel);
            }
            else
            {
                Toplevel? dup = TopLevels.FirstOrDefault (x => x.Id == toplevel.Id);

                if (dup is null)
                {
                    TopLevels.Push (toplevel);
                }
            }
        }

        if (Top is null)
        {
            Top = toplevel;
        }

        if ((Top?.Modal == false && toplevel.Modal)
            || (Top?.Modal == false && !toplevel.Modal)
            || (Top?.Modal == true && toplevel.Modal))
        {
            if (toplevel.Visible)
            {
                if (Top is { HasFocus: true })
                {
                    Top.HasFocus = false;
                }

                // Force leave events for any entered views in the old Top
                if (GetLastMousePosition () is { })
                {
                    RaiseMouseEnterLeaveEvents (GetLastMousePosition ()!.Value, new ());
                }

                Top?.OnDeactivate (toplevel);
                Toplevel previousTop = Top!;

                Top = toplevel;
                Top.OnActivate (previousTop);
            }
        }

        // View implements ISupportInitializeNotification which is derived from ISupportInitialize
        if (!toplevel.IsInitialized)
        {
            toplevel.BeginInit ();
            toplevel.EndInit (); // Calls Layout
        }

        // Try to set initial focus to any TabStop
        if (!toplevel.HasFocus)
        {
            toplevel.SetFocus ();
        }

        toplevel.OnLoaded ();

        ApplicationImpl.Instance.LayoutAndDraw (true);

        if (PositionCursor ())
        {
            Driver?.UpdateCursor ();
        }

        NotifyNewRunState?.Invoke (toplevel, new (rs));

        return rs;
    }

    /// <summary>
    ///     Calls <see cref="View.PositionCursor"/> on the most focused view.
    /// </summary>
    /// <remarks>
    ///     Does nothing if there is no most focused view.
    ///     <para>
    ///         If the most focused view is not visible within it's superview, the cursor will be hidden.
    ///     </para>
    /// </remarks>
    /// <returns><see langword="true"/> if a view positioned the cursor and the position is visible.</returns>
    internal static bool PositionCursor ()
    {
        // Find the most focused view and position the cursor there.
        View? mostFocused = Navigation?.GetFocused ();

        // If the view is not visible or enabled, don't position the cursor
        if (mostFocused is null || !mostFocused.Visible || !mostFocused.Enabled)
        {
            var current = CursorVisibility.Invisible;
            Driver?.GetCursorVisibility (out current);

            if (current != CursorVisibility.Invisible)
            {
                Driver?.SetCursorVisibility (CursorVisibility.Invisible);
            }

            return false;
        }

        // If the view is not visible within it's superview, don't position the cursor
        Rectangle mostFocusedViewport = mostFocused.ViewportToScreen (mostFocused.Viewport with { Location = Point.Empty });

        Rectangle superViewViewport =
            mostFocused.SuperView?.ViewportToScreen (mostFocused.SuperView.Viewport with { Location = Point.Empty }) ?? Driver!.Screen;

        if (!superViewViewport.IntersectsWith (mostFocusedViewport))
        {
            return false;
        }

        Point? cursor = mostFocused.PositionCursor ();

        Driver!.GetCursorVisibility (out CursorVisibility currentCursorVisibility);

        if (cursor is { })
        {
            // Convert cursor to screen coords
            cursor = mostFocused.ViewportToScreen (mostFocused.Viewport with { Location = cursor.Value }).Location;

            // If the cursor is not in a visible location in the SuperView, hide it
            if (!superViewViewport.Contains (cursor.Value))
            {
                if (currentCursorVisibility != CursorVisibility.Invisible)
                {
                    Driver.SetCursorVisibility (CursorVisibility.Invisible);
                }

                return false;
            }

            // Show it
            if (currentCursorVisibility == CursorVisibility.Invisible)
            {
                Driver.SetCursorVisibility (mostFocused.CursorVisibility);
            }

            return true;
        }

        if (currentCursorVisibility != CursorVisibility.Invisible)
        {
            Driver.SetCursorVisibility (CursorVisibility.Invisible);
        }

        return false;
    }

    /// <summary>
    ///     Runs the application by creating a <see cref="Toplevel"/> object and calling
    ///     <see cref="Run(Toplevel, Func{Exception, bool})"/>.
    /// </summary>
    /// <remarks>
    ///     <para>Calling <see cref="Init"/> first is not needed as this function will initialize the application.</para>
    ///     <para>
    ///         <see cref="Shutdown"/> must be called when the application is closing (typically after Run> has returned) to
    ///         ensure resources are cleaned up and terminal settings restored.
    ///     </para>
    ///     <para>
    ///         The caller is responsible for disposing the object returned by this method.
    ///     </para>
    /// </remarks>
    /// <returns>The created <see cref="Toplevel"/> object. The caller is responsible for disposing this object.</returns>
    [RequiresUnreferencedCode ("AOT")]
    [RequiresDynamicCode ("AOT")]
    public static Toplevel Run (Func<Exception, bool>? errorHandler = null, IConsoleDriver? driver = null)
    {
        return ApplicationImpl.Instance.Run (errorHandler, driver);
    }

    /// <summary>
    ///     Runs the application by creating a <see cref="Toplevel"/>-derived object of type <c>T</c> and calling
    ///     <see cref="Run(Toplevel, Func{Exception, bool})"/>.
    /// </summary>
    /// <remarks>
    ///     <para>Calling <see cref="Init"/> first is not needed as this function will initialize the application.</para>
    ///     <para>
    ///         <see cref="Shutdown"/> must be called when the application is closing (typically after Run> has returned) to
    ///         ensure resources are cleaned up and terminal settings restored.
    ///     </para>
    ///     <para>
    ///         The caller is responsible for disposing the object returned by this method.
    ///     </para>
    /// </remarks>
    /// <param name="errorHandler"></param>
    /// <param name="driver">
    ///     The <see cref="IConsoleDriver"/> to use. If not specified the default driver for the platform will
    ///     be used. Must be <see langword="null"/> if <see cref="Init"/> has already been called.
    /// </param>
    /// <returns>The created T object. The caller is responsible for disposing this object.</returns>
    [RequiresUnreferencedCode ("AOT")]
    [RequiresDynamicCode ("AOT")]
    public static T Run<T> (Func<Exception, bool>? errorHandler = null, IConsoleDriver? driver = null)
        where T : Toplevel, new()
    {
        return ApplicationImpl.Instance.Run<T> (errorHandler, driver);
    }

    /// <summary>Runs the Application using the provided <see cref="Toplevel"/> view.</summary>
    /// <remarks>
    ///     <para>
    ///         This method is used to start processing events for the main application, but it is also used to run other
    ///         modal <see cref="View"/>s such as <see cref="Dialog"/> boxes.
    ///     </para>
    ///     <para>
    ///         To make a <see cref="Run(Toplevel,System.Func{System.Exception,bool})"/> stop execution, call
    ///         <see cref="Application.RequestStop"/>.
    ///     </para>
    ///     <para>
    ///         Calling <see cref="Run(Toplevel,System.Func{System.Exception,bool})"/> is equivalent to calling
    ///         <see cref="Begin(Toplevel)"/>, followed by <see cref="RunLoop(RunState)"/>, and then calling
    ///         <see cref="End(RunState)"/>.
    ///     </para>
    ///     <para>
    ///         Alternatively, to have a program control the main loop and process events manually, call
    ///         <see cref="Begin(Toplevel)"/> to set things up manually and then repeatedly call
    ///         <see cref="RunLoop(RunState)"/> with the wait parameter set to false. By doing this the
    ///         <see cref="RunLoop(RunState)"/> method will only process any pending events, timers handlers and then
    ///         return control immediately.
    ///     </para>
    ///     <para>
    ///         When using <see cref="Run{T}"/> or
    ///         <see cref="Run(System.Func{System.Exception,bool},IConsoleDriver)"/>
    ///         <see cref="Init"/> will be called automatically.
    ///     </para>
    ///     <para>
    ///         RELEASE builds only: When <paramref name="errorHandler"/> is <see langword="null"/> any exceptions will be
    ///         rethrown. Otherwise, if <paramref name="errorHandler"/> will be called. If <paramref name="errorHandler"/>
    ///         returns <see langword="true"/> the <see cref="RunLoop(RunState)"/> will resume; otherwise this method will
    ///         exit.
    ///     </para>
    /// </remarks>
    /// <param name="view">The <see cref="Toplevel"/> to run as a modal.</param>
    /// <param name="errorHandler">
    ///     RELEASE builds only: Handler for any unhandled exceptions (resumes when returns true,
    ///     rethrows when null).
    /// </param>
    public static void Run (Toplevel view, Func<Exception, bool>? errorHandler = null) { ApplicationImpl.Instance.Run (view, errorHandler); }

    /// <summary>Adds a timeout to the application.</summary>
    /// <remarks>
    ///     When time specified passes, the callback will be invoked. If the callback returns true, the timeout will be
    ///     reset, repeating the invocation. If it returns false, the timeout will stop and be removed. The returned value is a
    ///     token that can be used to stop the timeout by calling <see cref="RemoveTimeout(object)"/>.
    /// </remarks>
    public static object? AddTimeout (TimeSpan time, Func<bool> callback) { return ApplicationImpl.Instance.AddTimeout (time, callback); }

    /// <summary>Removes a previously scheduled timeout</summary>
    /// <remarks>The token parameter is the value returned by <see cref="AddTimeout"/>.</remarks>
    /// Returns
    /// <see langword="true"/>
    /// if the timeout is successfully removed; otherwise,
    /// <see langword="false"/>
    /// .
    /// This method also returns
    /// <see langword="false"/>
    /// if the timeout is not found.
    public static bool RemoveTimeout (object token) { return ApplicationImpl.Instance.RemoveTimeout (token); }

    /// <summary>Runs <paramref name="action"/> on the thread that is processing events</summary>
    /// <param name="action">the action to be invoked on the main processing thread.</param>
    public static void Invoke (Action action) { ApplicationImpl.Instance.Invoke (action); }

    /// <summary>
    ///     Causes any Toplevels that need layout to be laid out. Then draws any Toplevels that need display. Only Views that
    ///     need to be laid out (see <see cref="View.NeedsLayout"/>) will be laid out.
    ///     Only Views that need to be drawn (see <see cref="View.NeedsDraw"/>) will be drawn.
    /// </summary>
    /// <param name="forceRedraw">
    ///     If <see langword="true"/> the entire View hierarchy will be redrawn. The default is <see langword="false"/> and
    ///     should only be overriden for testing.
    /// </param>
    public static void LayoutAndDraw (bool forceRedraw = false)
    {
        ApplicationImpl.Instance.LayoutAndDraw (forceRedraw);
    }

    /// <summary>This event is raised on each iteration of the main loop.</summary>
    /// <remarks>See also <see cref="Timeout"/></remarks>
    public static event EventHandler<IterationEventArgs>? Iteration;

    /// <summary>
    ///     Set to true to cause <see cref="End"/> to be called after the first iteration. Set to false (the default) to
    ///     cause the application to continue running until Application.RequestStop () is called.
    /// </summary>
    public static bool EndAfterFirstIteration { get; set; }

    /// <summary>Building block API: Runs the main loop for the created <see cref="Toplevel"/>.</summary>
    /// <param name="state">The state returned by the <see cref="Begin(Toplevel)"/> method.</param>
    public static void RunLoop (RunState state)
    {
        ArgumentNullException.ThrowIfNull (state);
        ObjectDisposedException.ThrowIf (state.Toplevel is null, "state");

        var firstIteration = true;

        for (state.Toplevel.Running = true; state.Toplevel?.Running == true;)
        {
            if (EndAfterFirstIteration && !firstIteration)
            {
                return;
            }

            firstIteration = RunIteration (ref state, firstIteration);
        }

        // Run one last iteration to consume any outstanding input events from Driver
        // This is important for remaining OnKeyUp events.
        RunIteration (ref state, firstIteration);
    }

    /// <summary>Run one application iteration.</summary>
    /// <param name="state">The state returned by <see cref="Begin(Toplevel)"/>.</param>
    /// <param name="firstIteration">
    ///     Set to <see langword="true"/> if this is the first run loop iteration.
    /// </param>
    /// <returns><see langword="false"/> if at least one iteration happened.</returns>
    public static bool RunIteration (ref RunState state, bool firstIteration = false)
    {
        ApplicationImpl appImpl = (ApplicationImpl)ApplicationImpl.Instance;
        appImpl.Coordinator?.RunIteration ();

        return false;
    }

    /// <summary>Stops the provided <see cref="Toplevel"/>, causing or the <paramref name="top"/> if provided.</summary>
    /// <param name="top">The <see cref="Toplevel"/> to stop.</param>
    /// <remarks>
    ///     <para>This will cause <see cref="Application.Run(Toplevel, Func{Exception, bool})"/> to return.</para>
    ///     <para>
    ///         Calling <see cref="RequestStop(Toplevel)"/> is equivalent to setting the
    ///         <see cref="Toplevel.Running"/>
    ///         property on the currently running <see cref="Toplevel"/> to false.
    ///     </para>
    /// </remarks>
    public static void RequestStop (Toplevel? top = null) { ApplicationImpl.Instance.RequestStop (top); }

    /// <summary>
    ///     Building block API: completes the execution of a <see cref="Toplevel"/> that was started with
    ///     <see cref="Begin(Toplevel)"/> .
    /// </summary>
    /// <param name="runState">The <see cref="RunState"/> returned by the <see cref="Begin(Toplevel)"/> method.</param>
    public static void End (RunState runState)
    {
        ArgumentNullException.ThrowIfNull (runState);

        if (Popover?.GetActivePopover () as View is { Visible: true } visiblePopover)
        {
            ApplicationPopover.HideWithQuitCommand (visiblePopover);
        }

        runState.Toplevel.OnUnloaded ();

        // End the RunState.Toplevel
        // First, take it off the Toplevel Stack
        if (TopLevels.TryPop (out Toplevel? topOfStack))
        {
            if (topOfStack != runState.Toplevel)
            {
                // If the top of the stack is not the RunState.Toplevel then
                // this call to End is not balanced with the call to Begin that started the RunState
                throw new ArgumentException ("End must be balanced with calls to Begin");
            }
        }

        // Notify that it is closing
        runState.Toplevel?.OnClosed (runState.Toplevel);

        if (TopLevels.TryPeek (out Toplevel? newTop))
        {
            Top = newTop;
            Top?.SetNeedsDraw ();
        }

        if (runState.Toplevel is { HasFocus: true })
        {
            runState.Toplevel.HasFocus = false;
        }

        if (Top is { HasFocus: false })
        {
            Top.SetFocus ();
        }

        _cachedRunStateToplevel = runState.Toplevel;

        runState.Toplevel = null;
        runState.Dispose ();

        LayoutAndDraw (true);
    }
    internal static void RaiseIteration ()
    {
        Iteration?.Invoke (null, new ());
    }
}