Restructure solution a bit

src/Spectre.Console/Widgets/Panel.cs

@@ -0,0 +1,187 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Spectre.Console.Rendering;
+
+namespace Spectre.Console
+{
+    /// <summary>
+    /// A renderable panel.
+    /// </summary>
+    public sealed class Panel : Renderable, IHasBorder, IExpandable, IPaddable
+    {
+        private const int EdgeWidth = 2;
+
+        private readonly IRenderable _child;
+
+        /// <inheritdoc/>
+        public Border Border { get; set; } = Border.Square;
+
+        /// <inheritdoc/>
+        public bool UseSafeBorder { get; set; } = true;
+
+        /// <inheritdoc/>
+        public Style? BorderStyle { get; set; }
+
+        /// <summary>
+        /// Gets or sets a value indicating whether or not the panel should
+        /// fit the available space. If <c>false</c>, the panel width will be
+        /// auto calculated. Defaults to <c>false</c>.
+        /// </summary>
+        public bool Expand { get; set; }
+
+        /// <summary>
+        /// Gets or sets the padding.
+        /// </summary>
+        public Padding Padding { get; set; } = new Padding(1, 1);
+
+        /// <summary>
+        /// Gets or sets the header.
+        /// </summary>
+        public PanelHeader? Header { get; set; }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Panel"/> class.
+        /// </summary>
+        /// <param name="text">The panel content.</param>
+        public Panel(string text)
+            : this(new Markup(text))
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Panel"/> class.
+        /// </summary>
+        /// <param name="content">The panel content.</param>
+        public Panel(IRenderable content)
+        {
+            _child = content ?? throw new System.ArgumentNullException(nameof(content));
+        }
+
+        /// <inheritdoc/>
+        protected override Measurement Measure(RenderContext context, int maxWidth)
+        {
+            var childWidth = _child.Measure(context, maxWidth);
+            return new Measurement(
+                childWidth.Min + EdgeWidth + Padding.GetHorizontalPadding(),
+                childWidth.Max + EdgeWidth + Padding.GetHorizontalPadding());
+        }
+
+        /// <inheritdoc/>
+        protected override IEnumerable<Segment> Render(RenderContext context, int maxWidth)
+        {
+            var border = Border.GetSafeBorder((context.LegacyConsole || !context.Unicode) && UseSafeBorder);
+            var borderStyle = BorderStyle ?? Style.Plain;
+
+            var paddingWidth = Padding.GetHorizontalPadding();
+            var childWidth = maxWidth - EdgeWidth - paddingWidth;
+
+            if (!Expand)
+            {
+                var measurement = _child.Measure(context, maxWidth - EdgeWidth - paddingWidth);
+                childWidth = measurement.Max;
+            }
+
+            var panelWidth = childWidth + EdgeWidth + paddingWidth;
+            panelWidth = Math.Min(panelWidth, maxWidth);
+
+            var result = new List<Segment>();
+
+            // Panel top
+            AddTopBorder(result, context, border, borderStyle, panelWidth);
+
+            // Split the child segments into lines.
+            var childSegments = _child.Render(context, childWidth);
+            foreach (var line in Segment.SplitLines(childSegments, panelWidth))
+            {
+                result.Add(new Segment(border.GetPart(BorderPart.CellLeft), borderStyle));
+
+                // Left padding
+                if (Padding.Left > 0)
+                {
+                    result.Add(new Segment(new string(' ', Padding.Left)));
+                }
+
+                var content = new List<Segment>();
+                content.AddRange(line);
+
+                // Do we need to pad the panel?
+                var length = line.Sum(segment => segment.CellLength(context.Encoding));
+                if (length < childWidth)
+                {
+                    var diff = childWidth - length;
+                    content.Add(new Segment(new string(' ', diff)));
+                }
+
+                result.AddRange(content);
+
+                // Right padding
+                if (Padding.Right > 0)
+                {
+                    result.Add(new Segment(new string(' ', Padding.Right)));
+                }
+
+                result.Add(new Segment(border.GetPart(BorderPart.CellRight), borderStyle));
+                result.Add(Segment.LineBreak);
+            }
+
+            // Panel bottom
+            AddBottomBorder(result, border, borderStyle, panelWidth);
+
+            return result;
+        }
+
+        private static void AddBottomBorder(List<Segment> result, Border border, Style borderStyle, int panelWidth)
+        {
+            result.Add(new Segment(border.GetPart(BorderPart.FooterBottomLeft), borderStyle));
+            result.Add(new Segment(border.GetPart(BorderPart.FooterBottom, panelWidth - EdgeWidth), borderStyle));
+            result.Add(new Segment(border.GetPart(BorderPart.FooterBottomRight), borderStyle));
+            result.Add(Segment.LineBreak);
+        }
+
+        private void AddTopBorder(List<Segment> segments, RenderContext context, Border border, Style borderStyle, int panelWidth)
+        {
+            segments.Add(new Segment(border.GetPart(BorderPart.HeaderTopLeft), borderStyle));
+
+            if (Header != null)
+            {
+                var leftSpacing = 0;
+                var rightSpacing = 0;
+
+                var headerWidth = panelWidth - (EdgeWidth * 2);
+                var header = Segment.TruncateWithEllipsis(Header.Text, Header.Style ?? borderStyle, context.Encoding, headerWidth);
+
+                var excessWidth = headerWidth - header.CellLength(context.Encoding);
+                if (excessWidth > 0)
+                {
+                    switch (Header.Alignment ?? Justify.Left)
+                    {
+                        case Justify.Left:
+                            leftSpacing = 0;
+                            rightSpacing = excessWidth;
+                            break;
+                        case Justify.Right:
+                            leftSpacing = excessWidth;
+                            rightSpacing = 0;
+                            break;
+                        case Justify.Center:
+                            leftSpacing = excessWidth / 2;
+                            rightSpacing = (excessWidth / 2) + (excessWidth % 2);
+                            break;
+                    }
+                }
+
+                segments.Add(new Segment(border.GetPart(BorderPart.HeaderTop, leftSpacing + 1), borderStyle));
+                segments.Add(header);
+                segments.Add(new Segment(border.GetPart(BorderPart.HeaderTop, rightSpacing + 1), borderStyle));
+            }
+            else
+            {
+                segments.Add(new Segment(border.GetPart(BorderPart.HeaderTop, panelWidth - EdgeWidth), borderStyle));
+            }
+
+            segments.Add(new Segment(border.GetPart(BorderPart.HeaderTopRight), borderStyle));
+            segments.Add(Segment.LineBreak);
+        }
+    }
+}