gui-cs.Terminal.Gui/Terminal.Gui/View/Layout/Pos.cs

#nullable enable
namespace Terminal.Gui;

/// <summary>
///     Describes the position of a <see cref="View"/> which can be an absolute value, a percentage, centered, or
///     relative to the ending dimension. Integer values are implicitly convertible to an absolute <see cref="Pos"/>. These
///     objects are created using the static methods Percent, AnchorEnd, and Center. The <see cref="Pos"/> objects can be
///     combined with the addition and subtraction operators.
/// </summary>
/// <remarks>
///     <para>Use the <see cref="Pos"/> objects on the X or Y properties of a view to control the position.</para>
///     <para>
///         These can be used to set the absolute position, when merely assigning an integer value (via the implicit
///         integer to <see cref="Pos"/> conversion), and they can be combined to produce more useful layouts, like:
///         Pos.Center - 3, which would shift the position of the <see cref="View"/> 3 characters to the left after
///         centering for example.
///     </para>
///     <para>
///         Reference coordinates of another view by using the methods Left(View), Right(View), Bottom(View), Top(View).
///         The X(View) and Y(View) are aliases to Left(View) and Top(View) respectively.
///     </para>
///     <para>
///         <list type="table">
///             <listheader>
///                 <term>Pos Object</term> <description>Description</description>
///             </listheader>
///             <item>
///                 <term>
///                     <see cref="Func"/>
///                 </term>
///                 <description>
///                     Creates a <see cref="Pos"/> object that computes the position by executing the provided
///                     function. The function will be called every time the position is needed.
///                 </description>
///             </item>
///             <item>
///                 <term>
///                     <see cref="Pos.Percent(float)"/>
///                 </term>
///                 <description>
///                     Creates a <see cref="Pos"/> object that is a percentage of the width or height of the
///                     SuperView.
///                 </description>
///             </item>
///             <item>
///                 <term>
///                     <see cref="Pos.AnchorEnd()"/>
///                 </term>
///                 <description>
///                     Creates a <see cref="Pos"/> object that is anchored to the end (right side or bottom) of
///                     the dimension, useful to flush the layout from the right or bottom.
///                 </description>
///             </item>
///             <item>
///                 <term>
///                     <see cref="Pos.Center"/>
///                 </term>
///                 <description>Creates a <see cref="Pos"/> object that can be used to center the <see cref="View"/>.</description>
///             </item>
///             <item>
///                 <term>
///                     <see cref="Absolute"/>
///                 </term>
///                 <description>
///                     Creates a <see cref="Pos"/> object that is an absolute position based on the specified
///                     integer value.
///                 </description>
///             </item>
///             <item>
///                 <term>
///                     <see cref="Pos.Left"/>
///                 </term>
///                 <description>
///                     Creates a <see cref="Pos"/> object that tracks the Left (X) position of the specified
///                     <see cref="View"/>.
///                 </description>
///             </item>
///             <item>
///                 <term>
///                     <see cref="Pos.X(View)"/>
///                 </term>
///                 <description>
///                     Creates a <see cref="Pos"/> object that tracks the Left (X) position of the specified
///                     <see cref="View"/>.
///                 </description>
///             </item>
///             <item>
///                 <term>
///                     <see cref="Pos.Top(View)"/>
///                 </term>
///                 <description>
///                     Creates a <see cref="Pos"/> object that tracks the Top (Y) position of the specified
///                     <see cref="View"/>.
///                 </description>
///             </item>
///             <item>
///                 <term>
///                     <see cref="Pos.Y(View)"/>
///                 </term>
///                 <description>
///                     Creates a <see cref="Pos"/> object that tracks the Top (Y) position of the specified
///                     <see cref="View"/>.
///                 </description>
///             </item>
///             <item>
///                 <term>
///                     <see cref="Pos.Right(View)"/>
///                 </term>
///                 <description>
///                     Creates a <see cref="Pos"/> object that tracks the Right (X+Width) coordinate of the
///                     specified <see cref="View"/>.
///                 </description>
///             </item>
///             <item>
///                 <term>
///                     <see cref="Pos.Bottom(View)"/>
///                 </term>
///                 <description>
///                     Creates a <see cref="Pos"/> object that tracks the Bottom (Y+Height) coordinate of the
///                     specified <see cref="View"/>
///                 </description>
///             </item>
///         </list>
///     </para>
/// </remarks>
public abstract class Pos
{
    #region static Pos creation methods

    /// <summary>Creates a <see cref="Pos"/> object that is an absolute position based on the specified integer value.</summary>
    /// <returns>The Absolute <see cref="Pos"/>.</returns>
    /// <param name="position">The value to convert to the <see cref="Pos"/>.</param>
    public static Pos Absolute (int position) { return new PosAbsolute (position); }

    /// <summary>
    ///     Creates a <see cref="Pos"/> object that is anchored to the end (right side or
    ///     bottom) of the SuperView's Content Area, minus the respective size of the View. This is equivalent to using
    ///     <see cref="Pos.AnchorEnd(int)"/>,
    ///     with an offset equivalent to the View's respective dimension.
    /// </summary>
    /// <returns>The <see cref="Pos"/> object anchored to the end (the bottom or the right side) minus the View's dimension.</returns>
    /// <example>
    ///     This sample shows how align a <see cref="Button"/> to the bottom-right the SuperView.
    ///     <code>
    /// anchorButton.X = Pos.AnchorEnd ();
    /// anchorButton.Y = Pos.AnchorEnd ();
    /// </code>
    /// </example>
    public static Pos AnchorEnd () { return new PosAnchorEnd (); }

    /// <summary>
    ///     Creates a <see cref="Pos"/> object that is anchored to the end (right side or bottom) of the SuperView's Content
    ///     Area,
    ///     useful to flush the layout from the right or bottom. See also <see cref="Pos.AnchorEnd()"/>, which uses the view
    ///     dimension to ensure the view is fully visible.
    /// </summary>
    /// <returns>The <see cref="Pos"/> object anchored to the end (the bottom or the right side).</returns>
    /// <param name="offset">The view will be shifted left or up by the amount specified.</param>
    /// <example>
    ///     This sample shows how align a 10 column wide <see cref="Button"/> to the bottom-right the SuperView.
    ///     <code>
    /// anchorButton.X = Pos.AnchorEnd (10);
    /// anchorButton.Y = 1
    /// </code>
    /// </example>
    public static Pos AnchorEnd (int offset)
    {
        if (offset < 0)
        {
            throw new ArgumentException (@"Must be positive", nameof (offset));
        }

        return new PosAnchorEnd (offset);
    }

    /// <summary>Creates a <see cref="Pos"/> object that can be used to center the <see cref="View"/>.</summary>
    /// <returns>The center Pos.</returns>
    /// <example>
    ///     This creates a <see cref="TextView"/> centered horizontally, is 50% of the way down, is 30% the height, and
    ///     is 80% the width of the <see cref="View"/> it added to.
    ///     <code>
    ///  var textView = new TextView () {
    ///     X = Pos.Center (),
    ///     Y = Pos.Percent (50),
    ///     Width = Dim.Percent (80),
    ///     Height = Dim.Percent (30),
    ///  };
    ///  </code>
    /// </example>
    public static Pos Center () { return new PosCenter (); }

    /// <summary>
    ///     Creates a <see cref="Pos"/> object that computes the position by executing the provided function. The function
    ///     will be called every time the position is needed.
    /// </summary>
    /// <param name="function">The function to be executed.</param>
    /// <returns>The <see cref="Pos"/> returned from the function.</returns>
    public static Pos Func (Func<int> function) { return new PosFunc (function); }

    /// <summary>Creates a percentage <see cref="Pos"/> object</summary>
    /// <returns>The percent <see cref="Pos"/> object.</returns>
    /// <param name="percent">A value between 0 and 100 representing the percentage.</param>
    /// <example>
    ///     This creates a <see cref="TextField"/> centered horizontally, is 50% of the way down, is 30% the height, and
    ///     is 80% the width of the <see cref="View"/> it added to.
    ///     <code>
    ///  var textView = new TextField {
    ///      X = Pos.Center (),
    ///      Y = Pos.Percent (50),
    ///      Width = Dim.Percent (80),
    ///      Height = Dim.Percent (30),
    ///  };
    ///  </code>
    /// </example>
    public static Pos Percent (float percent)
    {
        if (percent is < 0 or > 100)
        {
            throw new ArgumentException ("Percent value must be between 0 and 100.");
        }

        return new PosPercent (percent / 100);
    }

    /// <summary>Creates a <see cref="Pos"/> object that tracks the Top (Y) position of the specified <see cref="View"/>.</summary>
    /// <returns>The <see cref="Pos"/> that depends on the other view.</returns>
    /// <param name="view">The <see cref="View"/>  that will be tracked.</param>
    public static Pos Top (View view) { return new PosView (view, Side.Top); }

    /// <summary>Creates a <see cref="Pos"/> object that tracks the Top (Y) position of the specified <see cref="View"/>.</summary>
    /// <returns>The <see cref="Pos"/> that depends on the other view.</returns>
    /// <param name="view">The <see cref="View"/>  that will be tracked.</param>
    public static Pos Y (View view) { return new PosView (view, Side.Top); }

    /// <summary>Creates a <see cref="Pos"/> object that tracks the Left (X) position of the specified <see cref="View"/>.</summary>
    /// <returns>The <see cref="Pos"/> that depends on the other view.</returns>
    /// <param name="view">The <see cref="View"/>  that will be tracked.</param>
    public static Pos Left (View view) { return new PosView (view, Side.Left); }

    /// <summary>Creates a <see cref="Pos"/> object that tracks the Left (X) position of the specified <see cref="View"/>.</summary>
    /// <returns>The <see cref="Pos"/> that depends on the other view.</returns>
    /// <param name="view">The <see cref="View"/>  that will be tracked.</param>
    public static Pos X (View view) { return new PosView (view, Side.Left); }

    /// <summary>
    ///     Creates a <see cref="Pos"/> object that tracks the Bottom (Y+Height) coordinate of the specified
    ///     <see cref="View"/>
    /// </summary>
    /// <returns>The <see cref="Pos"/> that depends on the other view.</returns>
    /// <param name="view">The <see cref="View"/>  that will be tracked.</param>
    public static Pos Bottom (View view) { return new PosView (view, Side.Bottom); }

    /// <summary>
    ///     Creates a <see cref="Pos"/> object that tracks the Right (X+Width) coordinate of the specified
    ///     <see cref="View"/>.
    /// </summary>
    /// <returns>The <see cref="Pos"/> that depends on the other view.</returns>
    /// <param name="view">The <see cref="View"/>  that will be tracked.</param>
    public static Pos Right (View view) { return new PosView (view, Side.Right); }

    #endregion static Pos creation methods

    #region virtual methods

    /// <summary>
    ///     Gets the starting point of an element based on the size of the parent element (typically
    ///     <c>Superview.ContentSize</c>).
    ///     This method is meant to be overridden by subclasses to provide different ways of calculating the starting point.
    ///     This method is used
    ///     internally by the layout system to determine where a View should be positioned.
    /// </summary>
    /// <param name="size">The size of the parent element (typically <c>Superview.ContentSize</c>).</param>
    /// <returns>
    ///     An integer representing the calculated position. The way this position is calculated depends on the specific
    ///     subclass of Pos that is used. For example, PosAbsolute returns a fixed position, PosAnchorEnd returns a
    ///     position that is anchored to the end of the layout, and so on.
    /// </returns>
    internal virtual int GetAnchor (int size) { return 0; }

    /// <summary>
    ///     Calculates and returns the final position of a <see cref="View"/> object. It takes into account the dimension of
    ///     the
    ///     superview and the dimension of the view itself.
    /// </summary>
    /// <remarks>
    /// </remarks>
    /// <param name="superviewDimension">
    ///     The dimension of the superview. This could be the width for x-coordinate calculation or the
    ///     height for y-coordinate calculation.
    /// </param>
    /// <param name="dim">The dimension of the View. It could be the current width or height.</param>
    /// <param name="us">The View that holds this Pos object.</param>
    /// <param name="dimension">Width or Height</param>
    /// <returns>
    ///     The calculated position of the View. The way this position is calculated depends on the specific subclass of Pos
    ///     that
    ///     is used.
    /// </returns>
    internal virtual int Calculate (int superviewDimension, Dim dim, View us, Dimension dimension) { return GetAnchor (superviewDimension); }

    /// <summary>
    ///     Diagnostics API to determine if this Pos object references other views.
    /// </summary>
    /// <returns></returns>
    internal virtual bool ReferencesOtherViews () { return false; }

    #endregion virtual methods

    #region operators

    /// <summary>Adds a <see cref="Terminal.Gui.Pos"/> to a <see cref="Terminal.Gui.Pos"/>, yielding a new <see cref="Pos"/>.</summary>
    /// <param name="left">The first <see cref="Terminal.Gui.Pos"/> to add.</param>
    /// <param name="right">The second <see cref="Terminal.Gui.Pos"/> to add.</param>
    /// <returns>The <see cref="Pos"/> that is the sum of the values of <c>left</c> and <c>right</c>.</returns>
    public static Pos operator + (Pos left, Pos right)
    {
        if (left is PosAbsolute && right is PosAbsolute)
        {
            return new PosAbsolute (left.GetAnchor (0) + right.GetAnchor (0));
        }

        var newPos = new PosCombine (AddOrSubtract.Add, left, right);

        if (left is PosView view)
        {
            view.Target.SetNeedsLayout ();
        }

        return newPos;
    }

    /// <summary>Creates an Absolute <see cref="Pos"/> from the specified integer value.</summary>
    /// <returns>The Absolute <see cref="Pos"/>.</returns>
    /// <param name="n">The value to convert to the <see cref="Pos"/> .</param>
    public static implicit operator Pos (int n) { return new PosAbsolute (n); }

    /// <summary>
    ///     Subtracts a <see cref="Terminal.Gui.Pos"/> from a <see cref="Terminal.Gui.Pos"/>, yielding a new
    ///     <see cref="Pos"/>.
    /// </summary>
    /// <param name="left">The <see cref="Terminal.Gui.Pos"/> to subtract from (the minuend).</param>
    /// <param name="right">The <see cref="Terminal.Gui.Pos"/> to subtract (the subtrahend).</param>
    /// <returns>The <see cref="Pos"/> that is the <c>left</c> minus <c>right</c>.</returns>
    public static Pos operator - (Pos left, Pos right)
    {
        if (left is PosAbsolute && right is PosAbsolute)
        {
            return new PosAbsolute (left.GetAnchor (0) - right.GetAnchor (0));
        }

        var newPos = new PosCombine (AddOrSubtract.Subtract, left, right);

        if (left is PosView view)
        {
            view.Target.SetNeedsLayout ();
        }

        return newPos;
    }

    #endregion operators

}