Make VT-100 sequences easier to understand

src/Spectre.Console.Tests/Expectations/Widgets/Status/Render.Output.verified.txt

@@ -0,0 +1,10 @@
+[?25l     
+* foo
+     
+     
+- bar
+     
+     
+* baz
+     
+[?25h

src/Spectre.Console.Tests/Unit/AnsiConsoleTests.Cursor.cs

@@ -0,0 +1,52 @@
+using Shouldly;
+using Spectre.Console.Testing;
+using Xunit;
+
+namespace Spectre.Console.Tests.Unit
+{
+    public partial class AnsiConsoleTests
+    {
+        public sealed class Cursor
+        {
+            public sealed class TheMoveMethod
+            {
+                [Theory]
+                [InlineData(CursorDirection.Up, "HelloWorld")]
+                [InlineData(CursorDirection.Down, "HelloWorld")]
+                [InlineData(CursorDirection.Right, "HelloWorld")]
+                [InlineData(CursorDirection.Left, "HelloWorld")]
+                public void Should_Return_Correct_Ansi_Code(CursorDirection direction, string expected)
+                {
+                    // Given
+                    var console = new FakeAnsiConsole(ColorSystem.Standard, AnsiSupport.Yes);
+
+                    // When
+                    console.Write("Hello");
+                    console.Cursor.Move(direction, 2);
+                    console.Write("World");
+
+                    // Then
+                    console.Output.ShouldBe(expected);
+                }
+            }
+
+            public sealed class TheSetPositionMethod
+            {
+                [Fact]
+                public void Should_Return_Correct_Ansi_Code()
+                {
+                    // Given
+                    var console = new FakeAnsiConsole(ColorSystem.Standard, AnsiSupport.Yes);
+
+                    // When
+                    console.Write("Hello");
+                    console.Cursor.SetPosition(5, 3);
+                    console.Write("World");
+
+                    // Then
+                    console.Output.ShouldBe("HelloWorld");
+                }
+            }
+        }
+    }
+}

src/Spectre.Console.Tests/Unit/AnsiConsoleTests.cs

@@ -7,6 +7,23 @@ namespace Spectre.Console.Tests.Unit
 {
     public partial class AnsiConsoleTests
     {
+        [Theory]
+        [InlineData(false, "HelloWorld")]
+        [InlineData(true, "HelloWorld")]
+        public void Should_Clear_Screen(bool home, string expected)
+        {
+            // Given
+            var console = new FakeAnsiConsole(ColorSystem.Standard);
+
+            // When
+            console.Write("Hello");
+            console.Clear(home);
+            console.Write("World");
+
+            // Then
+            console.Output.ShouldBe(expected);
+        }
+
         [Fact]
         public void Should_Combine_Decoration_And_Colors()
         {

src/Spectre.Console.Tests/Unit/StatusTests.cs

@@ -1,13 +1,18 @@
-using Shouldly;
+using System.Threading.Tasks;
 using Spectre.Console.Testing;
+using Spectre.Verify.Extensions;
+using VerifyXunit;
 using Xunit;
 
 namespace Spectre.Console.Tests.Unit
 {
+    [UsesVerify]
+    [ExpectationPath("Widgets/Status")]
     public sealed class StatusTests
     {
         [Fact]
-        public void Should_Render_Status_Correctly()
+        [Expectation("Render")]
+        public Task Should_Render_Status_Correctly()
         {
             // Given
             var console = new FakeAnsiConsole(ColorSystem.TrueColor, width: 10);
@@ -28,16 +33,7 @@ namespace Spectre.Console.Tests.Unit
             });
 
             // Then
-            console.Output
+            return Verifier.Verify(console.Output);
-                .NormalizeLineEndings()
-                .ShouldBe(
-                    "[?25l     \n" +
-                    "* foo\n" +
-                    "          \n" +
-                    "- bar\n" +
-                    "          \n" +
-                    "* baz\n" +
-                    "     [?25h");
         }
     }
 }

src/Spectre.Console/Internal/Backends/Ansi/AnsiBuilder.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Linq;
+using static Spectre.Console.AnsiSequences;
 
 namespace Spectre.Console
 {
@@ -49,9 +50,8 @@ namespace Spectre.Console
                 return text;
             }
 
-            var ansiCodes = string.Join(";", result);
             var ansi = result.Length > 0
-                ? $"\u001b[{ansiCodes}m{text}\u001b[0m"
+                ? $"{SGR(result)}{text}{SGR(0)}"
                 : text;
 
             if (style.Link != null && !_profile.Capabilities.Legacy)
@@ -65,7 +65,7 @@ namespace Spectre.Console
                 }
 
                 var linkId = _linkHasher.GenerateId(link, text);
-                ansi = $"\u001b]8;id={linkId};{link}\u001b\\{ansi}\u001b]8;;\u001b\\";
+                ansi = $"{CSI}]8;id={linkId};{link}{CSI}\\{ansi}{CSI}]8;;{CSI}\\";
             }
 
             return ansi;

src/Spectre.Console/Internal/Backends/Ansi/AnsiConsoleBackend.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Text;
 using Spectre.Console.Rendering;
+using static Spectre.Console.AnsiSequences;
 
 namespace Spectre.Console
 {
@@ -21,11 +22,11 @@ namespace Spectre.Console
 
         public void Clear(bool home)
         {
-            Write(new ControlSequence("\u001b[2J"));
+            Write(new ControlSequence(ED(2)));
 
             if (home)
             {
-                Cursor.SetPosition(0, 0);
+                Write(new ControlSequence(CUP(0, 0)));
             }
         }
 

src/Spectre.Console/Internal/Backends/Ansi/AnsiConsoleCursor.cs

@@ -1,4 +1,5 @@
 using System;
+using static Spectre.Console.AnsiSequences;
 
 namespace Spectre.Console
 {
@@ -15,11 +16,11 @@ namespace Spectre.Console
         {
             if (show)
             {
-                _backend.Write(new ControlSequence("\u001b[?25h"));
+                _backend.Write(new ControlSequence(SM(DECTCEM)));
             }
             else
             {
-                _backend.Write(new ControlSequence("\u001b[?25l"));
+                _backend.Write(new ControlSequence(RM(DECTCEM)));
             }
         }
 
@@ -33,23 +34,23 @@ namespace Spectre.Console
             switch (direction)
             {
                 case CursorDirection.Up:
-                    _backend.Write(new ControlSequence($"\u001b[{steps}A"));
+                    _backend.Write(new ControlSequence(CUU(steps)));
                     break;
                 case CursorDirection.Down:
-                    _backend.Write(new ControlSequence($"\u001b[{steps}B"));
+                    _backend.Write(new ControlSequence(CUD(steps)));
                     break;
                 case CursorDirection.Right:
-                    _backend.Write(new ControlSequence($"\u001b[{steps}C"));
+                    _backend.Write(new ControlSequence(CUF(steps)));
                     break;
                 case CursorDirection.Left:
-                    _backend.Write(new ControlSequence($"\u001b[{steps}D"));
+                    _backend.Write(new ControlSequence(CUB(steps)));
                     break;
             }
         }
 
         public void SetPosition(int column, int line)
         {
-            _backend.Write(new ControlSequence($"\u001b[{line};{column}H"));
+            _backend.Write(new ControlSequence(CUP(line, column)));
         }
     }
 }

src/Spectre.Console/Internal/Backends/Ansi/AnsiSequences.cs

@@ -0,0 +1,169 @@
+using System.Linq;
+
+namespace Spectre.Console
+{
+    internal static class AnsiSequences
+    {
+        /// <summary>
+        /// Introduces a control sequence that uses 8-bit characters.
+        /// </summary>
+        public const string CSI = "\u001b";
+
+        /// <summary>
+        /// Text cursor enable.
+        /// </summary>
+        /// <remarks>
+        /// See <see href="https://vt100.net/docs/vt510-rm/DECRQM.html#T5-8"/>.
+        /// </remarks>
+        public const int DECTCEM = 25;
+
+        /// <summary>
+        /// This control function selects one or more character attributes at the same time.
+        /// </summary>
+        /// <remarks>
+        /// See <see href="https://vt100.net/docs/vt510-rm/SGR.html"/>.
+        /// </remarks>
+        /// <returns>The ANSI escape code.</returns>
+        public static string SGR(params int[] codes)
+        {
+            return CSI + "[" + string.Join(";", codes.Select(c => c.ToString())) + "m";
+        }
+
+        /// <summary>
+        /// This control function selects one or more character attributes at the same time.
+        /// </summary>
+        /// <remarks>
+        /// See <see href="https://vt100.net/docs/vt510-rm/SGR.html"/>.
+        /// </remarks>
+        /// <returns>The ANSI escape code.</returns>
+        public static string SGR(params byte[] codes)
+        {
+            return CSI + "[" + string.Join(";", codes.Select(c => c.ToString())) + "m";
+        }
+
+        /// <summary>
+        /// This control function erases characters from part or all of the display.
+        /// When you erase complete lines, they become single-height, single-width lines,
+        /// with all visual character attributes cleared.
+        /// ED works inside or outside the scrolling margins.
+        /// </summary>
+        /// <remarks>
+        /// See <see href="https://vt100.net/docs/vt510-rm/ED.html"/>.
+        /// </remarks>
+        /// <returns>The ANSI escape code.</returns>
+        public static string ED(int code)
+        {
+            return CSI + $"[{code}J";
+        }
+
+        /// <summary>
+        /// Moves the cursor up a specified number of lines in the same column.
+        /// The cursor stops at the top margin.
+        /// If the cursor is already above the top margin, then the cursor stops at the top line.
+        /// </summary>
+        /// <remarks>
+        /// See <see href="https://vt100.net/docs/vt510-rm/CUU.html"/>.
+        /// </remarks>
+        /// <param name="steps">The number of steps to move up.</param>
+        /// <returns>The ANSI escape code.</returns>
+        public static string CUU(int steps)
+        {
+            return CSI + $"[{steps}A";
+        }
+
+        /// <summary>
+        /// This control function moves the cursor down a specified number of lines in the same column.
+        /// The cursor stops at the bottom margin.
+        /// If the cursor is already below the bottom margin, then the cursor stops at the bottom line.
+        /// </summary>
+        /// <remarks>
+        /// See <see href="https://vt100.net/docs/vt510-rm/CUD.html"/>.
+        /// </remarks>
+        /// <param name="steps">The number of steps to move down.</param>
+        /// <returns>The ANSI escape code.</returns>
+        public static string CUD(int steps)
+        {
+            return CSI + $"[{steps}B";
+        }
+
+        /// <summary>
+        /// This control function moves the cursor to the right by a specified number of columns.
+        /// The cursor stops at the right border of the page.
+        /// </summary>
+        /// <remarks>
+        /// See <see href="https://vt100.net/docs/vt510-rm/CUF.html"/>.
+        /// </remarks>
+        /// <param name="steps">The number of steps to move forward.</param>
+        /// <returns>The ANSI escape code.</returns>
+        public static string CUF(int steps)
+        {
+            return CSI + $"[{steps}C";
+        }
+
+        /// <summary>
+        /// This control function moves the cursor to the left by a specified number of columns.
+        /// The cursor stops at the left border of the page.
+        /// </summary>
+        /// <remarks>
+        /// See <see href="https://vt100.net/docs/vt510-rm/CUB.html"/>.
+        /// </remarks>
+        /// <param name="steps">The number of steps to move backward.</param>
+        /// <returns>The ANSI escape code.</returns>
+        public static string CUB(int steps)
+        {
+            return CSI + $"[{steps}D";
+        }
+
+        /// <summary>
+        /// Moves the cursor to the specified position.
+        /// </summary>
+        /// <param name="line">The line to move to.</param>
+        /// <param name="column">The column to move to.</param>
+        /// <remarks>
+        /// See <see href="https://vt100.net/docs/vt510-rm/CUP.html"/>.
+        /// </remarks>
+        /// <returns>The ANSI escape code.</returns>
+        public static string CUP(int line, int column)
+        {
+            return CSI + $"[{line};{column}H";
+        }
+
+        /// <summary>
+        /// Hides the cursor.
+        /// </summary>
+        /// <remarks>
+        /// See <see href="https://vt100.net/docs/vt510-rm/RM.html"/>.
+        /// </remarks>
+        /// <returns>The ANSI escape code.</returns>
+        public static string RM(int code)
+        {
+            return CSI + $"[?{code}l";
+        }
+
+        /// <summary>
+        /// Shows the cursor.
+        /// </summary>
+        /// <remarks>
+        /// See <see href="https://vt100.net/docs/vt510-rm/SM.html"/>.
+        /// </remarks>
+        /// <returns>The ANSI escape code.</returns>
+        public static string SM(int code)
+        {
+            return CSI + $"[?{code}h";
+        }
+
+        /// <summary>
+        /// This control function erases characters on the line that has the cursor.
+        /// EL clears all character attributes from erased character positions.
+        /// EL works inside or outside the scrolling margins.
+        /// </summary>
+        /// <remarks>
+        /// See <see href="https://vt100.net/docs/vt510-rm/EL.html"/>.
+        /// </remarks>
+        /// <returns>The ANSI escape code.</returns>
+        public static string EL(int code)
+        {
+            return CSI + $"[{code}K";
+        }
+    }
+}

src/Spectre.Console/Rendering/LiveRenderable.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using static Spectre.Console.AnsiSequences;
 
 namespace Spectre.Console.Rendering
 {
@@ -27,7 +28,8 @@ namespace Spectre.Console.Rendering
                     return new ControlSequence(string.Empty);
                 }
 
-                return new ControlSequence("\r" + "\u001b[1A".Repeat(_shape.Value.Height - 1));
+                var linesToMoveUp = _shape.Value.Height - 1;
+                return new ControlSequence("\r" + CUU(linesToMoveUp));
             }
         }
 
@@ -40,7 +42,8 @@ namespace Spectre.Console.Rendering
                     return new ControlSequence(string.Empty);
                 }
 
-                return new ControlSequence("\r\u001b[2K" + "\u001b[1A\u001b[2K".Repeat(_shape.Value.Height - 1));
+                var linesToClear = _shape.Value.Height - 1;
+                return new ControlSequence("\r" + EL(2) + (CUU(1) + EL(2)).Repeat(linesToClear));
             }
         }