using System;
using System.Text;

namespace Terminal.Gui;

/// <summary>
/// The <see cref="CheckBox"/> <see cref="View"/> shows an on/off toggle that the user can set
/// </summary>
public class CheckBox : View {
	Rune _charNullChecked;
	Rune _charChecked;
	Rune _charUnChecked;
	bool? @_checked;
	bool _allowNullChecked;

	/// <summary>
	///   Toggled event, raised when the <see cref="CheckBox"/>  is toggled.
	/// </summary>
	/// <remarks>
	///   Client code can hook up to this event, it is
	///   raised when the <see cref="CheckBox"/> is activated either with
	///   the mouse or the keyboard. The passed <c>bool</c> contains the previous state. 
	/// </remarks>
	public event EventHandler<ToggleEventArgs> Toggled;

	/// <summary>
	/// Called when the <see cref="Checked"/> property changes. Invokes the <see cref="Toggled"/> event.
	/// </summary>
	public virtual void OnToggled (ToggleEventArgs e)
	{
		Toggled?.Invoke (this, e);
	}

	/// <summary>
	/// Initializes a new instance of <see cref="CheckBox"/> based on the given text, using <see cref="LayoutStyle.Computed"/> layout.
	/// </summary>
	public CheckBox () : this (string.Empty) { }

	/// <summary>
	/// Initializes a new instance of <see cref="CheckBox"/> based on the given text, using <see cref="LayoutStyle.Computed"/> layout.
	/// </summary>
	/// <param name="s">S.</param>
	/// <param name="is_checked">If set to <c>true</c> is checked.</param>
	public CheckBox (string s, bool is_checked = false) : base ()
	{
		SetInitialProperties (s, is_checked);
	}

	/// <summary>
	/// Initializes a new instance of <see cref="CheckBox"/> using <see cref="LayoutStyle.Absolute"/> layout.
	/// </summary>
	/// <remarks>
	///   The size of <see cref="CheckBox"/> is computed based on the
	///   text length. This <see cref="CheckBox"/> is not toggled.
	/// </remarks>
	public CheckBox (int x, int y, string s) : this (x, y, s, false)
	{
	}

	/// <summary>
	/// Initializes a new instance of <see cref="CheckBox"/> using <see cref="LayoutStyle.Absolute"/> layout.
	/// </summary>
	/// <remarks>
	///   The size of <see cref="CheckBox"/> is computed based on the
	///   text length. 
	/// </remarks>
	public CheckBox (int x, int y, string s, bool is_checked) : base (new Rect (x, y, s.Length, 1))
	{
		SetInitialProperties (s, is_checked);
	}

	// TODO: v2 - Remove constructors with parameters
	/// <summary>
	/// Private helper to set the initial properties of the View that were provided via constructors.
	/// </summary>
	/// <param name="s"></param>
	/// <param name="is_checked"></param>
	void SetInitialProperties (string s, bool is_checked)
	{
		_charNullChecked = CM.Glyphs.NullChecked;
		_charChecked = CM.Glyphs.Checked;
		_charUnChecked = CM.Glyphs.UnChecked;
		Checked = is_checked;
		HotKeySpecifier = (Rune)'_';
		CanFocus = true;
		AutoSize = true;
		Text = s;

		OnResizeNeeded ();

		// Things this view knows how to do
		AddCommand (Command.ToggleChecked, () => ToggleChecked ());
		AddCommand (Command.Accept, () => {
			if (!HasFocus) {
				SetFocus ();
			}
			ToggleChecked ();
			return true;
		});

		// Default keybindings for this view
		KeyBindings.Add (Key.Space, Command.ToggleChecked);
	}


	/// <inheritdoc/>
	public override Key HotKey {
		get => base.HotKey;
		set {
			if (value is null || value.KeyCode is KeyCode.Unknown) {
				throw new ArgumentException (nameof (value));
			}

			var prev = base.HotKey;
			if (prev != value) {
				var v = value == KeyCode.Unknown ? Key.Empty: value;
				base.HotKey = TextFormatter.HotKey = v;

				// Also add Alt+HotKey
				if (prev != (Key)KeyCode.Null && KeyBindings.TryGet (prev.WithAlt, out _)) {
					if (v.KeyCode == KeyCode.Null) {
						KeyBindings.Remove (prev.WithAlt);
					} else {
						KeyBindings.Replace (prev.WithAlt, v.WithAlt);
					}
				} else if (v.KeyCode != KeyCode.Null) {
					KeyBindings.Add (v.WithAlt, Command.Accept);
				}
			}
		}
	}

	/// <inheritdoc/>
	protected override void UpdateTextFormatterText ()
	{
		switch (TextAlignment) {
		case TextAlignment.Left:
		case TextAlignment.Centered:
		case TextAlignment.Justified:
			TextFormatter.Text = $"{GetCheckedState ()} {GetFormatterText ()}";
			break;
		case TextAlignment.Right:
			TextFormatter.Text = $"{GetFormatterText ()} {GetCheckedState ()}";
			break;
		}
	}

	Rune GetCheckedState ()
	{
		return Checked switch {
			true => _charChecked,
			false => _charUnChecked,
			var _ => _charNullChecked
		};
	}

	string GetFormatterText ()
	{
		if (AutoSize || string.IsNullOrEmpty (Text) || Frame.Width <= 2) {
			return Text;
		}
		return Text [..Math.Min (Frame.Width - 2, Text.GetRuneCount ())];
	}

	/// <summary>
	///    The state of the <see cref="CheckBox"/>
	/// </summary>
	public bool? Checked {
		get => @_checked;
		set {
			if (value == null && !AllowNullChecked) {
				return;
			}
			@_checked = value;
			UpdateTextFormatterText ();
			OnResizeNeeded ();
		}
	}

	/// <summary>
	/// 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;
		}
	}

	///<inheritdoc/>
	public override void PositionCursor ()
	{
		Move (0, 0);
	}

	bool ToggleChecked ()
	{
		if (!HasFocus) {
			SetFocus ();
		}
		var previousChecked = Checked;
		if (AllowNullChecked) {
			switch (previousChecked) {
			case null:
				Checked = true;
				break;
			case true:
				Checked = false;
				break;
			case false:
				Checked = null;
				break;
			}
		} else {
			Checked = !Checked;
		}

		OnToggled (new ToggleEventArgs (previousChecked, Checked));
		SetNeedsDisplay ();
		return true;
	}

	///<inheritdoc/>
	public override bool MouseEvent (MouseEvent me)
	{
		if (!me.Flags.HasFlag (MouseFlags.Button1Clicked) || !CanFocus)
			return false;

		ToggleChecked ();

		return true;
	}

	///<inheritdoc/>
	public override bool OnEnter (View view)
	{
		Application.Driver.SetCursorVisibility (CursorVisibility.Invisible);

		return base.OnEnter (view);
	}
}