#nullable enable

namespace Terminal.Gui;

/// <summary>
///     A <see cref="MenuItem"/> has title, an associated help text, and an action to execute on activation. MenuItems
///     can also have a checked indicator (see <see cref="Checked"/>).
/// </summary>
public class MenuItem
{
    internal MenuBar _menuBar;

    /// <summary>Initializes a new instance of <see cref="MenuItem"/></summary>
    public MenuItem (Key? shortcutKey = null) : this ("", "", null, null, null, shortcutKey) { }

    /// <summary>Initializes a new instance of <see cref="MenuItem"/>.</summary>
    /// <param name="title">Title for the menu item.</param>
    /// <param name="help">Help text to display.</param>
    /// <param name="action">Action to invoke when the menu item is activated.</param>
    /// <param name="canExecute">Function to determine if the action can currently be executed.</param>
    /// <param name="parent">The <see cref="Parent"/> of this menu item.</param>
    /// <param name="shortcutKey">The <see cref="ShortcutKey"/> keystroke combination.</param>
    public MenuItem (
        string? title,
        string? help,
        Action? action,
        Func<bool>? canExecute = null,
        MenuItem? parent = null,
        Key? shortcutKey = null
    )
    {
        Title = title ?? "";
        Help = help ?? "";
        Action = action!;
        CanExecute = canExecute!;
        Parent = parent!;

        if (Parent is { } && Parent.ShortcutKey != Key.Empty)
        {
            Parent.ShortcutKey = Key.Empty;
        }
        // Setter will ensure Key.Empty if it's null
        ShortcutKey = shortcutKey!;
    }

    private bool _allowNullChecked;
    private MenuItemCheckStyle _checkType;

    private string _title;

    /// <summary>Gets or sets the action to be invoked when the menu item is triggered.</summary>
    /// <value>Method to invoke.</value>
    public Action? Action { get; set; }

    /// <summary>
    ///     Used only if <see cref="CheckType"/> is of <see cref="MenuItemCheckStyle.Checked"/> type. If
    ///     <see langword="true"/> allows <see cref="Checked"/> to be null, true or false. If <see langword="false"/> only
    ///     allows <see cref="Checked"/> to be true or false.
    /// </summary>
    public bool AllowNullChecked
    {
        get => _allowNullChecked;
        set
        {
            _allowNullChecked = value;
            Checked ??= false;
        }
    }

    /// <summary>
    ///     Gets or sets the action to be invoked to determine if the menu can be triggered. If <see cref="CanExecute"/>
    ///     returns <see langword="true"/> the menu item will be enabled. Otherwise, it will be disabled.
    /// </summary>
    /// <value>Function to determine if the action is can be executed or not.</value>
    public Func<bool>? CanExecute { get; set; }

    /// <summary>
    ///     Sets or gets whether the <see cref="MenuItem"/> shows a check indicator or not. See
    ///     <see cref="MenuItemCheckStyle"/>.
    /// </summary>
    public bool? Checked { set; get; }

    /// <summary>
    ///     Sets or gets the <see cref="MenuItemCheckStyle"/> of a menu item where <see cref="Checked"/> is set to
    ///     <see langword="true"/>.
    /// </summary>
    public MenuItemCheckStyle CheckType
    {
        get => _checkType;
        set
        {
            _checkType = value;

            if (_checkType == MenuItemCheckStyle.Checked && !_allowNullChecked && Checked is null)
            {
                Checked = false;
            }
        }
    }

    /// <summary>Gets or sets arbitrary data for the menu item.</summary>
    /// <remarks>This property is not used internally.</remarks>
    public object Data { get; set; }

    /// <summary>Gets or sets the help text for the menu item. The help text is drawn to the right of the <see cref="Title"/>.</summary>
    /// <value>The help text.</value>
    public string Help { get; set; }

    /// <summary>
    ///     Returns <see langword="true"/> if the menu item is enabled. This method is a wrapper around
    ///     <see cref="CanExecute"/>.
    /// </summary>
    public bool IsEnabled () { return CanExecute?.Invoke () ?? true; }

    /// <summary>Gets the parent for this <see cref="MenuItem"/>.</summary>
    /// <value>The parent.</value>
    public MenuItem? Parent { get; set; }

    /// <summary>Gets or sets the title of the menu item .</summary>
    /// <value>The title.</value>
    public string Title
    {
        get => _title;
        set
        {
            if (_title == value)
            {
                return;
            }

            _title = value;
            GetHotKey ();
        }
    }

    /// <summary>
    ///     Toggle the <see cref="Checked"/> between three states if <see cref="AllowNullChecked"/> is
    ///     <see langword="true"/> or between two states if <see cref="AllowNullChecked"/> is <see langword="false"/>.
    /// </summary>
    public void ToggleChecked ()
    {
        if (_checkType != MenuItemCheckStyle.Checked)
        {
            throw new InvalidOperationException ("This isn't a Checked MenuItemCheckStyle!");
        }

        bool? previousChecked = Checked;

        if (AllowNullChecked)
        {
            Checked = previousChecked switch
                      {
                          null => true,
                          true => false,
                          false => null
                      };
        }
        else
        {
            Checked = !Checked;
        }
    }

    /// <summary>Merely a debugging aid to see the interaction with main.</summary>
    internal bool GetMenuBarItem () { return IsFromSubMenu; }

    /// <summary>Merely a debugging aid to see the interaction with main.</summary>
    internal MenuItem GetMenuItem () { return this; }

    /// <summary>Gets if this <see cref="MenuItem"/> is from a sub-menu.</summary>
    internal bool IsFromSubMenu => Parent != null;

    internal int TitleLength => GetMenuBarItemLength (Title);

    // 
    // ┌─────────────────────────────┐
    // │ Quit  Quit UI Catalog  Ctrl+Q │
    // └─────────────────────────────┘
    // ┌─────────────────┐
    // │ ◌ TopLevel Alt+T │
    // └─────────────────┘
    // TODO: Replace the `2` literals with named constants
    internal int Width => 1
                          + // space before Title
                          TitleLength
                          + 2
                          + // space after Title - BUGBUG: This should be 1
                          (Checked == true || CheckType.HasFlag (MenuItemCheckStyle.Checked) || CheckType.HasFlag (MenuItemCheckStyle.Radio)
                               ? 2
                               : 0)
                          + // check glyph + space
                          (Help.GetColumns () > 0 ? 2 + Help.GetColumns () : 0)
                          + // Two spaces before Help
                          (ShortcutTag.GetColumns () > 0
                               ? 2 + ShortcutTag.GetColumns ()
                               : 0); // Pad two spaces before shortcut tag (which are also aligned right)

    private static int GetMenuBarItemLength (string title)
    {
        return title.EnumerateRunes ()
                    .Where (ch => ch != MenuBar.HotKeySpecifier)
                    .Sum (ch => Math.Max (ch.GetColumns (), 1));
    }

    #region Keyboard Handling

    private Key _hotKey = Key.Empty;

    /// <summary>
    ///     The HotKey is used to activate a <see cref="MenuItem"/> with the keyboard. HotKeys are defined by prefixing the
    ///     <see cref="Title"/> of a MenuItem with an underscore ('_').
    ///     <para>
    ///         Pressing Alt-Hotkey for a <see cref="MenuBarItem"/> (menu items on the menu bar) works even if the menu is
    ///         not active. Once a menu has focus and is active, pressing just the HotKey will activate the MenuItem.
    ///     </para>
    ///     <para>
    ///         For example for a MenuBar with a "_File" MenuBarItem that contains a "_New" MenuItem, Alt-F will open the
    ///         File menu. Pressing the N key will then activate the New MenuItem.
    ///     </para>
    ///     <para>See also <see cref="ShortcutKey"/> which enable global key-bindings to menu items.</para>
    /// </summary>
    public Key? HotKey
    {
        get => _hotKey;
        private set
        {
            var oldKey = _hotKey;
            _hotKey = value ?? Key.Empty;
            UpdateHotKeyBinding (oldKey);
        }
    }

    private void GetHotKey ()
    {
        var nextIsHot = false;

        foreach (char x in _title)
        {
            if (x == MenuBar.HotKeySpecifier.Value)
            {
                nextIsHot = true;
            }
            else if (nextIsHot)
            {
                    HotKey = char.ToLower (x);

                    return;
            }
        }

        HotKey = Key.Empty;
    }

    private Key _shortcutKey = Key.Empty;

    /// <summary>
    ///     Shortcut defines a key binding to the MenuItem that will invoke the MenuItem's action globally for the
    ///     <see cref="View"/> that is the parent of the <see cref="MenuBar"/> or <see cref="ContextMenu"/> this
    ///     <see cref="MenuItem"/>.
    ///     <para>
    ///         The <see cref="Key"/> will be drawn on the MenuItem to the right of the <see cref="Title"/> and
    ///         <see cref="Help"/> text. See <see cref="ShortcutTag"/>.
    ///     </para>
    /// </summary>
    public Key? ShortcutKey
    {
        get => _shortcutKey;
        set
        {
            var oldKey = _shortcutKey;
            _shortcutKey = value ?? Key.Empty;
            UpdateShortcutKeyBinding (oldKey);
        }
    }

    /// <summary>Gets the text describing the keystroke combination defined by <see cref="ShortcutKey"/>.</summary>
    public string ShortcutTag => ShortcutKey != Key.Empty ? ShortcutKey!.ToString () : string.Empty;

    internal void AddShortcutKeyBinding (MenuBar menuBar, Key key)
    {
        ArgumentNullException.ThrowIfNull (menuBar);

        _menuBar = menuBar;

        AddOrUpdateShortcutKeyBinding (key);
    }

    private void AddOrUpdateShortcutKeyBinding (Key key)
    {
        if (key != Key.Empty)
        {
            _menuBar.KeyBindings.Remove (key);
        }

        if (ShortcutKey != Key.Empty)
        {
            KeyBinding keyBinding = new ([Command.Select], KeyBindingScope.HotKey, this);
            // Remove an existent ShortcutKey
            _menuBar.KeyBindings.Remove (ShortcutKey!);
            _menuBar.KeyBindings.Add (ShortcutKey!, keyBinding);
        }
    }

    private void UpdateHotKeyBinding (Key oldKey)
    {
        if (_menuBar is null or { IsInitialized: false })
        {
            return;
        }

        if (oldKey != Key.Empty)
        {
            var index = _menuBar.Menus.IndexOf (this);

            if (index > -1)
            {
                _menuBar.KeyBindings.Remove (oldKey.WithAlt);
            }
        }

        if (HotKey != Key.Empty)
        {
            var index = _menuBar.Menus.IndexOf (this);

            if (index > -1)
            {
                _menuBar.KeyBindings.Remove (HotKey!.WithAlt);
                KeyBinding keyBinding = new ([Command.Toggle], KeyBindingScope.HotKey, this);
                _menuBar.KeyBindings.Add (HotKey.WithAlt, keyBinding);
            }
        }
    }

    private void UpdateShortcutKeyBinding (Key oldKey)
    {
        // ReSharper disable once ConditionIsAlwaysTrueOrFalseAccordingToNullableAPIContract
        if (_menuBar is null)
        {
            return;
        }

        AddOrUpdateShortcutKeyBinding (oldKey);
    }

    #endregion Keyboard Handling

    /// <summary>
    /// Removes a <see cref="MenuItem"/> dynamically from the <see cref="Parent"/>.
    /// </summary>
    public virtual void RemoveMenuItem ()
    {
        if (Parent is { })
        {
            MenuItem? []? childrens = ((MenuBarItem)Parent).Children;
            var i = 0;

            foreach (MenuItem? c in childrens!)
            {
                if (c != this)
                {
                    childrens [i] = c;
                    i++;
                }
            }

            Array.Resize (ref childrens, childrens.Length - 1);

            if (childrens.Length == 0)
            {
                ((MenuBarItem)Parent).Children = null;
            }
            else
            {
                ((MenuBarItem)Parent).Children = childrens;
            }
        }

        if (ShortcutKey != Key.Empty)
        {
            // Remove an existent ShortcutKey
            _menuBar.KeyBindings.Remove (ShortcutKey!);
        }
    }
}