Terminal.Gui/Tests/UnitTestsParallelizable/Text/RuneTests.cs

using System.Buffers;
using System.Globalization;
using System.Text;

namespace TextTests;

public class RuneTests
{
    [Fact]
    public void Cast_To_Char_Surrogate_Pair_Return_UTF16 ()
    {
        Assert.NotEqual ("𝔹", $"{new Rune (unchecked ((char)0x1d539))}");
        Assert.Equal ("픹", $"{new Rune (unchecked ((char)0x1d539))}");
        Assert.Equal ("픹", $"{new Rune (0xd539)}");
        Assert.Equal ("𝔹", $"{new Rune (0x1d539)}");
    }

    [Fact]
    public void Equals_ToRuneList ()
    {
        List<List<Rune>> a = new () { "First line.".ToRuneList () };
        List<List<Rune>> b = new () { "First line.".ToRuneList (), "Second line.".ToRuneList () };
        List<Rune> c = new (a [0]);
        List<Rune> d = a [0];

        Assert.Equal (a [0], b [0]);

        // Not the same reference
        Assert.False (a [0] == b [0]);
        Assert.NotEqual (a [0], b [1]);
        Assert.False (a [0] == b [1]);

        Assert.Equal (c, a [0]);
        Assert.False (c == a [0]);
        Assert.Equal (c, b [0]);
        Assert.False (c == b [0]);
        Assert.NotEqual (c, b [1]);
        Assert.False (c == b [1]);

        Assert.Equal (d, a [0]);

        // Is the same reference
        Assert.True (d == a [0]);
        Assert.Equal (d, b [0]);
        Assert.False (d == b [0]);
        Assert.NotEqual (d, b [1]);
        Assert.False (d == b [1]);

        Assert.True (a [0].SequenceEqual (b [0]));
        Assert.False (a [0].SequenceEqual (b [1]));

        Assert.True (c.SequenceEqual (a [0]));
        Assert.True (c.SequenceEqual (b [0]));
        Assert.False (c.SequenceEqual (b [1]));

        Assert.True (d.SequenceEqual (a [0]));
        Assert.True (d.SequenceEqual (b [0]));
        Assert.False (d.SequenceEqual (b [1]));
    }

    [Fact]
    public void GetColumns_GetRuneCount ()
    {
        PrintTextElementCount ('\u00e1'.ToString (), "á", 1, 1, 1, 1);
        PrintTextElementCount ("\u0061\u0301", "á", 1, 2, 2, 1);
        PrintTextElementCount ("\u0061\u0301", "á", 1, 2, 2, 1);
        PrintTextElementCount ("\u0065\u0301", "é", 1, 2, 2, 1);
        PrintTextElementCount ("\U0001f469\U0001f3fd\u200d\U0001f692", "👩🏽‍🚒", 2, 4, 7, 1);
        PrintTextElementCount ("\ud801\udccf", "𐓏", 1, 1, 2, 1);
        PrintTextElementCount ("\U0001F468\u200D\U0001F469\u200D\U0001F467\u200D\U0001F466", "👨‍👩‍👧‍👦", 2, 7, 11, 1);
        PrintTextElementCount ("\U0001f469\u200d\U0001f692", "👩‍🚒", 2, 3, 5, 1);
        PrintTextElementCount ("\u0068\u0069", "hi", 2, 2, 2, 2);
    }

    [Theory]
    [InlineData (
                    "\u2615\ufe0f",
                    "☕️",
                    2,
                    2,
                    2
                )] // \ufe0f forces it to be rendered as a colorful image as compared to a monochrome text variant.
    [InlineData (
                    "\u1107\u1165\u11b8",
                    "법",
                    3,
                    2,
                    1
                )] // the letters 법 join to form the Korean word for "rice:" U+BC95 법 (read from top left to bottom right)
    [InlineData ("\U0001F468\u200D\U0001F469\u200D\U0001F467", "👨‍👩‍👧", 8, 2, 8)] // Man, Woman and Girl emoji.
    //[InlineData ("\u0915\u093f", "कि", 2, 2, 2)] // Hindi कि with DEVANAGARI LETTER KA and DEVANAGARI VOWEL SIGN I
    [InlineData (
                    "\u0e4d\u0e32",
                    "ํา",
                    2,
                    1,
                    2
                )] // Decomposition: ํ (U+0E4D) - า (U+0E32) = U+0E33 ำ Thai Character Sara Am
    [InlineData ("\u0e33", "ำ", 1, 1, 1)] // Decomposition: ํ (U+0E4D) - า (U+0E32) = U+0E33 ำ Thai Character Sara Am
    public void GetColumns_String_Without_SurrogatePair (
        string code,
        string str,
        int codeLength,
        int columns,
        int stringLength
    )
    {
        Assert.Equal (str, code.Normalize ());
        Assert.Equal (codeLength, code.Length);

        //Assert.Equal (columns, code.EnumerateRunes ().Sum (x => x.GetColumns ()));
        Assert.Equal (columns, str.GetColumns ());
        Assert.Equal (stringLength, str.Length);
    }

    [Theory]
    [InlineData (new [] { '\ud83e', '\ude01' }, "🨁", 1, 2, 4)] // Neutral Chess Queen
    [InlineData (new [] { '\udb43', '\udfe1' }, "󠿡", 1, 2, 4)] // Undefined Character
    [InlineData (new [] { '\ud83c', '\udf55' }, "🍕", 2, 2, 4)] // 🍕 Slice of Pizza
    [InlineData (new [] { '\ud83e', '\udd16' }, "🤖", 2, 2, 4)] // 🤖 Robot Face
    [InlineData (new [] { '\ud83e', '\udde0' }, "🧠", 2, 2, 4)] // 🧠 Brain
    [InlineData (new [] { '\ud801', '\udc21' }, "𐐡", 1, 2, 4)] // 𐐡 Deseret Capital Letter Er
    [InlineData (new [] { '\ud83c', '\udf39' }, "🌹", 2, 2, 4)] // 🌹 Rose
    [InlineData (new [] { '\uD83D', '\uDC7E' }, "👾", 2, 2, 4)] //   U+1F47E alien monster (CodepointWidth::Wide)
    [InlineData (
                    new [] { '\uD83D', '\uDD1C' },
                    "🔜",
                    2,
                    2,
                    4
                )] //  🔜 Soon With Rightwards Arrow Above (CodepointWidth::Wide)
    public void GetColumns_Utf16_Encode (char [] code, string str, int columns, int stringLength, int utf8Length)
    {
        var rune = new Rune (code [0], code [1]);
        Assert.Equal (str, rune.ToString ());
        Assert.Equal (columns, rune.GetColumns ());
        Assert.Equal (stringLength, rune.ToString ().Length);
        Assert.Equal (utf8Length, rune.Utf8SequenceLength);
        Assert.True (Rune.IsValid (rune.Value));
    }

    [Theory]
    [InlineData ("\U0001fa01", "🨁", 1, 2)] // Neutral Chess Queen
    [InlineData ("\U000e0fe1", "󠿡", 1, 2)] // Undefined Character
    [InlineData ("\U0001F355", "🍕", 2, 2)] // 🍕 Slice of Pizza
    [InlineData ("\U0001F916", "🤖", 2, 2)] // 🤖 Robot Face
    [InlineData ("\U0001f9e0", "🧠", 2, 2)] // 🧠 Brain
    [InlineData ("\U00010421", "𐐡", 1, 2)] // 𐐡 Deseret Capital Letter Er
    [InlineData ("\U0001f339", "🌹", 2, 2)] // 🌹 Rose
    //[InlineData ("\uFE20FE21", "", 1, 1)]   // Combining Ligature Left Half - U+fe20 -https://github.com/microsoft/terminal/blob/main/src/types/unicode_width_overrides.xml
    // Combining Ligature Right Half - U+fe21 -https://github.com/microsoft/terminal/blob/main/src/types/unicode_width_overrides.xml
    public void GetColumns_Utf32_Encode (string code, string str, int columns, int stringLength)
    {
        OperationStatus operationStatus = Rune.DecodeFromUtf16 (code, out Rune rune, out int charsConsumed);
        Assert.Equal (OperationStatus.Done, operationStatus);
        Assert.Equal (str, rune.ToString ());
        Assert.Equal (columns, rune.GetColumns ());
        Assert.Equal (stringLength, rune.ToString ().Length);
        Assert.Equal (charsConsumed, rune.Utf16SequenceLength);
        Assert.True (Rune.IsValid (rune.Value));

        // with DecodeRune
        (Rune nrune, int size) = code.DecodeRune ();
        Assert.Equal (str, nrune.ToString ());
        Assert.Equal (columns, nrune.GetColumns ());
        Assert.Equal (stringLength, nrune.ToString ().Length);
        Assert.Equal (size, nrune.Utf8SequenceLength);

        for (var x = 0; x < code.Length - 1; x++)
        {
            Assert.Equal (nrune.Value, char.ConvertToUtf32 (code [x], code [x + 1]));
            Assert.True (RuneExtensions.EncodeSurrogatePair (code [x], code [x + 1], out Rune result));
            Assert.Equal (rune, result);
        }

        Assert.True (Rune.IsValid (nrune.Value));
    }

    [Theory]
    [InlineData (new byte [] { 0xf0, 0x9f, 0xa8, 0x81 }, "🨁", 1, 2)] // Neutral Chess Queen
    [InlineData (new byte [] { 0xf3, 0xa0, 0xbf, 0xa1 }, "󠿡", 1, 2)] // Undefined Character
    [InlineData (new byte [] { 0xf0, 0x9f, 0x8d, 0x95 }, "🍕", 2, 2)] // 🍕 Slice of Pizza
    [InlineData (new byte [] { 0xf0, 0x9f, 0xa4, 0x96 }, "🤖", 2, 2)] // 🤖 Robot Face
    [InlineData (new byte [] { 0xf0, 0x90, 0x90, 0xa1 }, "𐐡", 1, 2)] // 𐐡 Deseret Capital Letter Er
    [InlineData (new byte [] { 0xf0, 0x9f, 0x8c, 0xb9 }, "🌹", 2, 2)] // 🌹 Rose
    public void GetColumns_Utf8_Encode (byte [] code, string str, int columns, int stringLength)
    {
        OperationStatus operationStatus = Rune.DecodeFromUtf8 (code, out Rune rune, out int bytesConsumed);
        Assert.Equal (OperationStatus.Done, operationStatus);
        Assert.Equal (str, rune.ToString ());
        Assert.Equal (columns, rune.GetColumns ());
        Assert.Equal (stringLength, rune.ToString ().Length);
        Assert.Equal (bytesConsumed, rune.Utf8SequenceLength);
        Assert.True (Rune.IsValid (rune.Value));
    }

    [Theory]
    [InlineData (0, "\0", 0, 1, 1)]
    [InlineData ('\u1dc0', "᷀", 0, 1, 3)] // ◌᷀ Combining Dotted Grave Accent
    [InlineData ('\u20D0', "⃐", 0, 1, 3)] // ◌⃐ Combining Left Harpoon Above
    [InlineData (1, "\u0001", -1, 1, 1)]
    [InlineData (2, "\u0002", -1, 1, 1)]
    [InlineData (31, "\u001f", -1, 1, 1)] // non printable character - Information Separator One
    [InlineData (127, "\u007f", -1, 1, 1)] // non printable character - Delete
    [InlineData (32, " ", 1, 1, 1)] // space
    [InlineData ('a', "a", 1, 1, 1)]
    [InlineData ('b', "b", 1, 1, 1)]
    [InlineData (123, "{", 1, 1, 1)] // { Left Curly Bracket
    [InlineData ('\u231c', "⌜", 1, 1, 3)] // ⌜ Top Left Corner

    // BUGBUG: These are CLEARLY wide glyphs, but GetColumns() returns 1
    // However, most terminals treat these as narrow and they overlap the next cell when drawn (including Windows Terminal)
    [InlineData (
                    '\u1161',
                    "ᅡ",
                    0,
                    1,
                    3
                )] // ᅡ Hangul Jungseong A - Unicode Hangul Jamo for join with column width equal to 0 alone.
    [InlineData ('\u2103', "℃", 1, 1, 3)] // ℃ Degree Celsius
    [InlineData ('\u2501', "━", 1, 1, 3)] // ━ Box Drawings Heavy Horizontal
    [InlineData ('\u25a0', "■", 1, 1, 3)] // ■ Black Square
    [InlineData ('\u25a1', "□", 1, 1, 3)] // □ White Square
    [InlineData ('\u277f', "❿", 1, 1, 3)] //Dingbat Negative Circled Number Ten - ❿ U+277f 
    [InlineData (
                    '\u4dc0',
                    "䷀",
                    2,
                    1,
                    3
                )]  // ䷀Hexagram For The Creative Heaven -  U+4dc0 - https://github.com/microsoft/terminal/blob/main/src/types/unicode_width_overrides.xml
                    // See https://github.com/microsoft/terminal/issues/19389

    [InlineData ('\ud7b0', "ힰ", 0, 1, 3)] // ힰ ┤Hangul Jungseong O-Yeo - ힰ U+d7b0')]
    [InlineData ('\uf61e', "", 1, 1, 3)] // Private Use Area
    [InlineData ('\u23f0', "⏰", 2, 1, 3)] // Alarm Clock - ⏰ U+23f0
    [InlineData ('\u1100', "ᄀ", 2, 1, 3)] // ᄀ Hangul Choseong Kiyeok
    [InlineData ('\u1150', "ᅐ", 2, 1, 3)] // ᅐ Hangul Choseong Ceongchieumcieuc
    [InlineData ('\u2615', "☕", 2, 1, 3)] // ☕ Hot Beverage
    [InlineData ('\u231a', "⌚", 2, 1, 3)] // ⌚ Watch
    [InlineData ('\u231b', "⌛", 2, 1, 3)] // ⌛ Hourglass

    // From WindowsTerminal's CodepointWidthDetector tests (https://github.com/microsoft/terminal/blob/main/src/types/CodepointWidthDetector.cpp)
    //static constexpr std::wstring_view emoji = L"\xD83E\xDD22"; // U+1F922 nauseated face
    //static constexpr std::wstring_view ambiguous = L"\x414"; // U+0414 cyrillic capital de

    //{ 0x414, L"\x414", CodepointWidth::Narrow }, // U+0414 cyrillic capital de
    [InlineData ('\u0414', "Д", 1, 1, 2)] // U+0414 cyrillic capital de

    //{ 0x1104, L"\x1104", CodepointWidth::Wide }, // U+1104 hangul choseong ssangtikeut
    [InlineData ('\u1104', "ᄄ", 2, 1, 3)]

    //{ 0x306A, L"\x306A", CodepointWidth::Wide }, // U+306A hiragana na な
    [InlineData (0x306A, "な", 2, 1, 3)]

    //{ 0x30CA, L"\x30CA", CodepointWidth::Wide }, // U+30CA katakana na ナ
    [InlineData (0x30CA, "ナ", 2, 1, 3)]

    //{ 0x72D7, L"\x72D7", CodepointWidth::Wide }, // U+72D7
    [InlineData (0x72D7, "狗", 2, 1, 3)]
    public void GetColumns_With_Single_Code (int code, string str, int columns, int stringLength, int utf8Length)
    {
        var rune = new Rune (code);
        Assert.Equal (str, rune.ToString ());
        Assert.Equal (columns, rune.GetColumns ());
        Assert.Equal (stringLength, rune.ToString ().Length);
        Assert.Equal (utf8Length, rune.Utf8SequenceLength);
        Assert.True (Rune.IsValid (rune.Value));
    }

    // IsCombiningMark tests
    [Theory]
    [InlineData (0x0338, true)] // Combining Long Solidus Overlay (U+0338) (e.g. ≠)
    [InlineData (0x0300, true)] // Combining Grave Accent
    [InlineData (0x0301, true)] // Combining acute accent (é)
    [InlineData (0x0302, true)] // Combining Circumflex Accent
    [InlineData (0x0328, true)] //  Combining ogonek (a small hook or comma shape) U+0328
    [InlineData (0x00E9, false)] // Latin Small Letter E with Acute, Unicode U+00E9 é 
    [InlineData (0x0061, false)] // Latin Small Letter A is U+0061.
    [InlineData (
                    '\uFE20',
                    true
                )] // Combining Ligature Left Half - U+fe20 -https://github.com/microsoft/terminal/blob/main/src/types/unicode_width_overrides.xml
    [InlineData (
                    '\uFE21',
                    true
                )] // Combining Ligature Right Half - U+fe21 -https://github.com/microsoft/terminal/blob/main/src/types/unicode_width_overrides.xml
    public void IsCombiningMark (int codepoint, bool expected)
    {
        var rune = new Rune (codepoint);
        Assert.Equal (expected, rune.IsCombiningMark ());
    }

    [Theory]
    [InlineData (0x0338)] // Combining Long Solidus Overlay (U+0338) (e.g. ≠)
    [InlineData (0x0300)] // Combining Grave Accent
    [InlineData (0x0301)] // Combining acute accent (é)
    [InlineData (0x0302)] // Combining Circumflex Accent
    [InlineData (0x0061)] // Combining ogonek (a small hook or comma shape)
    [InlineData (
                    '\uFE20'
                )] // Combining Ligature Left Half - U+fe20 -https://github.com/microsoft/terminal/blob/main/src/types/unicode_width_overrides.xml
    [InlineData (
                    '\uFE21'
                )] // Combining Ligature Right Half - U+fe21 -https://github.com/microsoft/terminal/blob/main/src/types/unicode_width_overrides.xml
    public void MakePrintable_Combining_Character_Is_Not_Printable (int code)
    {
        var rune = new Rune (code);
        Rune actual = rune.MakePrintable ();
        Assert.Equal (code, actual.Value);
    }

    [Theory]
    [InlineData (0x0000001F, 0x241F)]
    [InlineData (0x0000007F, 0x247F)]
    [InlineData (0x0000009F, 0x249F)]
    [InlineData (0x0001001A, 0x1001A)]
    public void MakePrintable_Converts_Control_Chars_To_Proper_Unicode (int code, int expected)
    {
        Rune actual = ((Rune)code).MakePrintable ();
        Assert.Equal (expected, actual.Value);
    }

    [Theory]
    [InlineData (0x20)]
    [InlineData (0x7E)]
    [InlineData (0xA0)]
    [InlineData (0x010020)]
    public void MakePrintable_Does_Not_Convert_Ansi_Chars_To_Unicode (int code)
    {
        Rune actual = ((Rune)code).MakePrintable ();
        Assert.Equal (code, actual.Value);
    }

    [Theory]
    [InlineData (
                    "01234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789",
                    200,
                    200,
                    200
                )]
    [InlineData (
                    "01234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n",
                    201,
                    200,
                    199
                )] // has a '\n' newline
    [InlineData (
                    "\t01234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n",
                    202,
                    200,
                    198
                )] // has a '\t' and a '\n' newline
    public void Rune_ColumnWidth_Versus_String_ConsoleWidth (string text, int stringLength, int strCols, int runeCols)
    {
        Assert.Equal (stringLength, text.Length);
        Assert.Equal (stringLength, text.GetRuneCount ());
        Assert.Equal (strCols, text.GetColumns ());
        int sumRuneWidth = text.EnumerateRunes ().Sum (x => x.GetColumns ());
        Assert.Equal (runeCols, sumRuneWidth);
    }

    [Theory]
    [InlineData (0x12345678)]
    [InlineData ('\ud801')]
    public void Rune_Exceptions_Integers (int code) { Assert.Throws<ArgumentOutOfRangeException> (() => new Rune (code)); }

    [Theory]
    // Control characters (should be mapped to Control Pictures)
    [InlineData ('\u0000', 0x2400)]  // NULL → ␀
    [InlineData ('\u0009', 0x2409)]  // TAB → ␉
    [InlineData ('\u000A', 0x240A)]  // LF → ␊
    [InlineData ('\u000D', 0x240D)]  // CR → ␍

    // Printable characters (should remain unchanged)
    [InlineData ('A', 'A')]
    [InlineData (' ', ' ')]
    [InlineData ('~', '~')]
    public void MakePrintable_ReturnsExpected (char inputChar, int expectedCodePoint)
    {
        // Arrange
        Rune input = new Rune (inputChar);

        // Act
        Rune result = input.MakePrintable ();

        // Assert
        Assert.Equal (expectedCodePoint, result.Value);
    }

    [Fact]
    public void MakePrintable_SupplementaryRune_RemainsUnchanged ()
    {
        // Arrange: supplementary character outside BMP (not a control)
        Rune input = new Rune (0x1F600); // 😀 grinning face emoji

        // Act
        Rune result = input.MakePrintable ();

        // Assert
        Assert.Equal (input.Value, result.Value);
    }

    [Theory]
    [InlineData (new [] { '\ud799', '\udc21' })]
    public void Rune_Exceptions_Utf16_Encode (char [] code)
    {
        Assert.False (RuneExtensions.EncodeSurrogatePair (code [0], code [1], out Rune rune));
        Assert.Throws<ArgumentOutOfRangeException> (() => new Rune (code [0], code [1]));
    }

    /// <summary>
    ///     Shows the difference between using Wcwidth.UnicodeCalculator and our own port of wcwidth. Specifically, the
    ///     UnicodeCalculator is more accurate to spec where null has a width of 0, and our port says it's -1.
    /// </summary>
    /// <param name="expectedColumns"></param>
    /// <param name="scalar"></param>
    [Theory]
    [InlineData (0, 0)]
    [InlineData (-1, 1)]
    [InlineData (-1, 2)]
    [InlineData (-1, 3)]
    [InlineData (-1, 4)]
    [InlineData (-1, 5)]
    [InlineData (-1, 6)]
    [InlineData (-1, 7)]
    [InlineData (-1, 8)]
    [InlineData (-1, 9)]
    [InlineData (-1, 10)]
    [InlineData (-1, 11)]
    [InlineData (-1, 12)]
    [InlineData (-1, 13)]
    [InlineData (-1, 14)]
    [InlineData (-1, 15)]
    [InlineData (-1, 16)]
    [InlineData (-1, 17)]
    [InlineData (-1, 18)]
    [InlineData (-1, 19)]
    [InlineData (-1, 20)]
    [InlineData (-1, 21)]
    [InlineData (-1, 22)]
    [InlineData (-1, 23)]
    [InlineData (-1, 24)]
    [InlineData (-1, 25)]
    [InlineData (-1, 26)]
    [InlineData (-1, 27)]
    [InlineData (-1, 28)]
    [InlineData (-1, 29)]
    [InlineData (-1, 30)]
    [InlineData (-1, 31)]
    public void Rune_GetColumns_Non_Printable (int expectedColumns, int scalar)
    {
        var rune = new Rune (scalar);
        Assert.Equal (expectedColumns, rune.GetColumns ());
        Assert.Equal (0, rune.ToString ().GetColumns ());
    }

    [Fact]
    public void Rune_GetColumns_Versus_String_GetColumns_With_Non_Printable_Characters ()
    {
        var sumRuneWidth = 0;
        var sumConsoleWidth = 0;

        for (uint i = 0; i < 32; i++)
        {
            sumRuneWidth += ((Rune)i).GetColumns ();
            sumConsoleWidth += ((Rune)i).ToString ().GetColumns ();
        }

        Assert.Equal (-31, sumRuneWidth);
        Assert.Equal (0, sumConsoleWidth);
    }

    [Theory]
    [InlineData ('\ud800', true)]
    [InlineData ('\udbff', true)]
    [InlineData ('\udc00', false)]
    [InlineData ('\udfff', false)]
    [InlineData ('\uefff', null)]
    public void Rune_IsHighSurrogate_IsLowSurrogate (char code, bool? isHighSurrogate)
    {
        if (isHighSurrogate == true)
        {
            Assert.True (char.IsHighSurrogate (code));
        }
        else if (isHighSurrogate == false)
        {
            Assert.True (char.IsLowSurrogate (code));
        }
        else
        {
            Assert.False (char.IsHighSurrogate (code));
            Assert.False (char.IsLowSurrogate (code));
        }
    }

    [Theory]
    [InlineData (true, '\u1100')]
    [InlineData (true, '\ud83c', '\udf39')]
    [InlineData (true, '\udbff', '\udfff')]
    [InlineData (false, '\ud801')]
    [InlineData (false, '\ud83e')]
    public void Rune_IsValid (bool valid, params char [] chars)
    {
        Rune rune = default;
        var isValid = true;

        if (chars.Length == 1)
        {
            try
            {
                rune = new Rune (chars [0]);
            }
            catch (Exception)
            {
                isValid = false;
            }
        }
        else
        {
            rune = new Rune (chars [0], chars [1]);
        }

        if (valid)
        {
            Assert.NotEqual (default (Rune), rune);
            Assert.True (Rune.IsValid (rune.Value));
            Assert.True (valid);
        }
        else
        {
            Assert.False (valid);
            Assert.False (isValid);
        }
    }

    [Theory]
    [InlineData ("First line.")]
    [InlineData ("Hello, 𝔹𝕆𝔹")]
    public void Rune_ToRunes (string text)
    {
        Rune [] runes = text.ToRunes ();

        for (var i = 0; i < runes.Length; i++)
        {
            Assert.Equal (text.EnumerateRunes ().ToArray () [i].Value, runes [i].Value);
        }
    }

    [Fact]
    public void Sum_Of_Rune_GetColumns_Is_Not_Always_Equal_To_String_GetColumns ()
    {
        const int start = 0x000000;
        const int end = 0x10ffff;

        for (int i = start; i <= end; i++)
        {
            if (char.IsSurrogate ((char)i))
            {
                continue;
            }

            var r = new Rune ((uint)i);
            var us = r.ToString ();
            var hex = i.ToString ("x6");
            int v = int.Parse (hex, NumberStyles.HexNumber);
            string s = char.ConvertFromUtf32 (v);

            if (!r.IsSurrogatePair ())
            {
                Assert.Equal (r.ToString (), us);
                Assert.Equal (us, s);

                if (r.GetColumns () < 0)
                {
                    Assert.NotEqual (r.GetColumns (), us.GetColumns ());
                    Assert.NotEqual (s.EnumerateRunes ().Sum (c => c.GetColumns ()), us.GetColumns ());
                }
                else
                {
                    Assert.Equal (r.GetColumns (), us.GetColumns ());
                    Assert.Equal (s.EnumerateRunes ().Sum (c => c.GetColumns ()), us.GetColumns ());
                }

                Assert.Equal (us.GetRuneCount (), s.Length);
            }
            else
            {
                Assert.Equal (r.ToString (), us);
                Assert.Equal (us, s);
                Assert.Equal (r.GetColumns (), us.GetColumns ());
                Assert.Equal (s.GetColumns (), us.GetColumns ());

                Assert.Equal (
                              1,
                              us.GetRuneCount ()
                             ); // Here returns 1 because is a valid surrogate pair resulting in only rune >=U+10000..U+10FFFF
                Assert.Equal (2, s.Length); // String always preserves the originals values of each surrogate pair
            }
        }
    }

    [Theory]
    [InlineData ('a', 1, 1)]
    [InlineData (31, 1, 1)]
    [InlineData (123, 1, 1)]
    [InlineData (127, 1, 1)]
    [InlineData ('\u1150', 1, 3)]
    [InlineData ('\u1161', 1, 3)]
    [InlineData (0x16fe0, 2, 4)]
    public void System_Text_Rune_SequenceLength (int code, int utf16Length, int utf8Length)
    {
        var r = new Rune (code);
        Assert.Equal (utf16Length, r.Utf16SequenceLength);
        Assert.Equal (utf8Length, r.Utf8SequenceLength);
    }

    [Fact]
    public void Test_All_Surrogate_Pairs_Range ()
    {
        for (uint h = 0xd800; h <= 0xdbff; h++)
        {
            for (uint l = 0xdc00; l <= 0xdfff; l++)
            {
                var r = new Rune ((char)h, (char)l);
                var us = r.ToString ();
                var hex = r.Value.ToString ("x6");
                int v = int.Parse (hex, NumberStyles.HexNumber);
                string s = char.ConvertFromUtf32 (v);

                Assert.True (v >= 0x10000 && v <= RuneExtensions.MaxUnicodeCodePoint);
                Assert.Equal (r.ToString (), us);
                Assert.Equal (us, s);
                Assert.Equal (r.GetColumns (), us.GetColumns ());
                Assert.Equal (s.GetColumns (), us.GetColumns ());

                Assert.Equal (
                              1,
                              us.GetRuneCount ()
                             ); // Here returns 1 because is a valid surrogate pair resulting in only rune >=U+10000..U+10FFFF
                Assert.Equal (2, s.Length); // String always preserves the originals values of each surrogate pair
            }
        }
    }

    [Theory]
    [InlineData ("<22><><EFBFBD>", false)]
    [InlineData ("Hello, 世界", true)]
    [InlineData (new byte [] { 0xff, 0xfe, 0xfd }, false)]
    [InlineData (new byte [] { 0xf0, 0x9f, 0x8d, 0x95 }, true)]
    public void Test_CanBeEncodedAsRune_Extension (object text, bool canBeEncodedAsRune)
    {
        string str;

        if (text is string)
        {
            str = (string)text;

            if (canBeEncodedAsRune)
            {
                Assert.True (RuneExtensions.CanBeEncodedAsRune (Encoding.Unicode.GetBytes (str.ToCharArray ())));
            }
            else
            {
                Assert.False (RuneExtensions.CanBeEncodedAsRune (Encoding.Unicode.GetBytes (str.ToCharArray ())));
            }
        }
        else if (text is byte [])
        {
            str = StringExtensions.ToString ((byte [])text);

            if (canBeEncodedAsRune)
            {
                Assert.True (RuneExtensions.CanBeEncodedAsRune (Encoding.Unicode.GetBytes (str.ToCharArray ())));
            }
            else
            {
                Assert.False (RuneExtensions.CanBeEncodedAsRune (Encoding.Unicode.GetBytes (str.ToCharArray ())));
            }
        }
    }

    [Theory]
    [InlineData ("Hello, 世界", 13, 11, 9, "界世 ,olleH")] // Without Surrogate Pairs
    [InlineData ("Hello, 𝔹𝕆𝔹", 19, 10, 13, "𝔹𝕆𝔹 ,olleH")] // With Surrogate Pairs
    public void Test_DecodeLastRune_Extension (
        string text,
        int bytesLength,
        int colsLength,
        int textLength,
        string encoded
    )
    {
        List<Rune> runes = new ();
        var tSize = 0;

        for (int i = text.GetRuneCount () - 1; i >= 0; i--)
        {
            (Rune rune, int size) = text.DecodeLastRune (i);
            runes.Add (rune);
            tSize += size;
        }

        var result = StringExtensions.ToString (runes);
        Assert.Equal (encoded, result);
        Assert.Equal (bytesLength, tSize);
        Assert.Equal (colsLength, result.GetColumns ());
        Assert.Equal (textLength, result.Length);
    }

    [Theory]
    [InlineData ("Hello, 世界", 13, 11, 9)] // Without Surrogate Pairs
    [InlineData ("Hello, 𝔹𝕆𝔹", 19, 10, 13)] // With Surrogate Pairs
    public void Test_DecodeRune_Extension (string text, int bytesLength, int colsLength, int textLength)
    {
        List<Rune> runes = new ();
        var tSize = 0;

        for (var i = 0; i < text.GetRuneCount (); i++)
        {
            (Rune rune, int size) = text.DecodeRune (i);
            runes.Add (rune);
            tSize += size;
        }

        var result = StringExtensions.ToString (runes);
        Assert.Equal (text, result);
        Assert.Equal (bytesLength, tSize);
        Assert.Equal (colsLength, result.GetColumns ());
        Assert.Equal (textLength, result.Length);
    }

    [Theory]
    [InlineData ('\uea85', null, "", false)] // Private Use Area
    [InlineData (0x1F356, new [] { '\ud83c', '\udf56' }, "🍖", true)] // 🍖 Meat On Bone
    public void Test_DecodeSurrogatePair (int code, char []? charsValue, string runeString, bool isSurrogatePair)
    {
        var rune = new Rune (code);
        char []? chars;

        if (isSurrogatePair)
        {
            Assert.True (rune.DecodeSurrogatePair (out chars));
            Assert.Equal (2, chars!.Length);
            Assert.Equal (charsValue! [0], chars [0]);
            Assert.Equal (charsValue [1], chars [1]);
            Assert.Equal (runeString, new Rune (chars [0], chars [1]).ToString ());
        }
        else
        {
            Assert.False (rune.DecodeSurrogatePair (out chars));
            Assert.Null (chars);
            Assert.Equal (runeString, rune.ToString ());
        }

        Assert.Equal (chars, charsValue);
    }

    [Theory]
    [InlineData (unchecked ((char)0x40D7C0), (char)0xDC20, 0, "\0", false)]
    [InlineData ((char)0x0065, (char)0x0301, 0, "\0", false)]
    [InlineData ('\ud83c', '\udf56', 0x1F356, "🍖", true)] // 🍖 Meat On Bone
    public void Test_EncodeSurrogatePair (
        char highSurrogate,
        char lowSurrogate,
        int runeValue,
        string runeString,
        bool isSurrogatePair
    )
    {
        Rune rune;

        if (isSurrogatePair)
        {
            Assert.True (RuneExtensions.EncodeSurrogatePair ('\ud83c', '\udf56', out rune));
        }
        else
        {
            Assert.False (RuneExtensions.EncodeSurrogatePair (highSurrogate, lowSurrogate, out rune));
        }

        Assert.Equal (runeValue, rune.Value);
        Assert.Equal (runeString, rune.ToString ());
    }

    [Theory]
    [InlineData ('\ue0fd', false)]
    [InlineData ('\ud800', true)]
    [InlineData ('\udfff', true)]
    public void Test_IsSurrogate (char code, bool isSurrogate)
    {
        if (isSurrogate)
        {
            Assert.True (char.IsSurrogate (code.ToString (), 0));
        }
        else
        {
            Assert.False (char.IsSurrogate (code.ToString (), 0));
        }
    }

    [Theory]
    [InlineData (500000000)]
    [InlineData (0xf801, 0xdfff)]
    public void Test_MaxRune (params int [] codes)
    {
        if (codes.Length == 1)
        {
            Assert.Throws<ArgumentOutOfRangeException> (() => new Rune (codes [0]));
        }
        else
        {
            Assert.Throws<ArgumentOutOfRangeException> (() => new Rune ((char)codes [0], (char)codes [1]));
        }
    }

    [Theory]
    [InlineData (
                    '\u006f',
                    '\u0302',
                    "\u006f\u0302",
                    1,
                    0,
                    2,
                    "o",
                    "̂",
                    "ô",
                    1,
                    2
                )]
    [InlineData (
                    '\u0065',
                    '\u0301',
                    "\u0065\u0301",
                    1,
                    0,
                    2,
                    "e",
                    "́",
                    "é",
                    1,
                    2
                )]
    public void Test_NonSpacingChar (
        int code1,
        int code2,
        string code,
        int rune1Length,
        int rune2Length,
        int codeLength,
        string code1String,
        string code2String,
        string joinString,
        int joinLength,
        int bytesLength
    )
    {
        var rune = new Rune (code1);
        var nsRune = new Rune (code2);
        Assert.Equal (rune1Length, rune.GetColumns ());
        Assert.Equal (rune2Length, nsRune.GetColumns ());
        var ul = rune.ToString ();
        Assert.Equal (code1String, ul);
        var uns = nsRune.ToString ();
        Assert.Equal (code2String, uns);
        string f = $"{rune}{nsRune}".Normalize ();
        Assert.Equal (f, joinString);
        Assert.Equal (f, code.Normalize ());
        Assert.Equal (joinLength, f.GetColumns ());
        Assert.Equal (joinLength, code.EnumerateRunes ().Sum (c => c.GetColumns ()));
        Assert.Equal (codeLength, code.Length);
        (Rune nrune, int size) = f.DecodeRune ();
        Assert.Equal (f.ToRunes () [0], nrune);
        Assert.Equal (bytesLength, size);
    }

    [Theory]
    [InlineData (0x20D0, 0x20EF)]
    [InlineData (0x2310, 0x231F)]
    [InlineData (0x1D800, 0x1D80F)]
    public void Test_Range (int start, int end)
    {
        for (int i = start; i <= end; i++)
        {
            var r = new Rune ((uint)i);
            var us = r.ToString ();
            var hex = i.ToString ("x6");
            int v = int.Parse (hex, NumberStyles.HexNumber);
            string s = char.ConvertFromUtf32 (v);

            if (!r.IsSurrogatePair ())
            {
                Assert.Equal (r.ToString (), us);
                Assert.Equal (us, s);
                Assert.Equal (r.GetColumns (), us.GetColumns ());

                Assert.Equal (
                              us.GetRuneCount (),
                              s.Length
                             ); // For not surrogate pairs string.RuneCount is always equal to String.Length
            }
            else
            {
                Assert.Equal (r.ToString (), us);
                Assert.Equal (us, s);
                Assert.Equal (r.GetColumns (), us.GetColumns ());

                Assert.Equal (
                              1,
                              us.GetRuneCount ()
                             ); // Here returns 1 because is a valid surrogate pair resulting in only rune >=U+10000..U+10FFFF
                Assert.Equal (2, s.Length); // String always preserves the originals values of each surrogate pair
            }

            Assert.Equal (s.GetColumns (), us.GetColumns ());
        }
    }

    [Fact]
    public void Test_SurrogatePair_From_String ()
    {
        Assert.True (ProcessTestStringUseChar ("𐓏𐓘𐓻𐓘𐓻𐓟 𐒻𐓟"));
        Assert.Throws<Exception> (() => ProcessTestStringUseChar ("\ud801"));

        Assert.True (ProcessStringUseRune ("𐓏𐓘𐓻𐓘𐓻𐓟 𐒻𐓟"));
        Assert.Throws<Exception> (() => ProcessStringUseRune ("\ud801"));
    }

    [Fact]
    public void TestRuneIsLetter ()
    {
        Assert.Equal (5, CountLettersInString ("Hello"));
        Assert.Equal (8, CountLettersInString ("𐓏𐓘𐓻𐓘𐓻𐓟 𐒻𐓟"));
    }

    [Fact]
    public void TestSplit ()
    {
        var inputString = "🐂, 🐄, 🐆";
        string [] splitOnSpace = inputString.Split (' ');
        string [] splitOnComma = inputString.Split (',');
        Assert.Equal (3, splitOnSpace.Length);
        Assert.Equal (3, splitOnComma.Length);
    }

    [Theory]
    [InlineData ("a", "utf-8", 1)]
    [InlineData ("a", "utf-16", 1)]
    [InlineData ("a", "utf-32", 3)]
    [InlineData ("𝔹", "utf-8", 4)]
    [InlineData ("𝔹", "utf-16", 4)]
    [InlineData ("𝔹", "utf-32", 3)]
    public void GetEncodingLength_ReturnsLengthBasedOnSelectedEncoding (string runeStr, string encodingName, int expectedLength)
    {
        Rune rune = runeStr.EnumerateRunes ().Single ();
        var encoding = Encoding.GetEncoding (encodingName);

        int actualLength = rune.GetEncodingLength (encoding);

        Assert.Equal (expectedLength, actualLength);
    }

    private int CountLettersInString (string s)
    {
        var letterCount = 0;

        foreach (Rune rune in s.EnumerateRunes ())
        {
            if (Rune.IsLetter (rune))
            {
                letterCount++;
            }
        }

        return letterCount;
    }

    private void PrintTextElementCount (
        string us,
        string s,
        int consoleWidth,
        int runeCount,
        int stringCount,
        int txtElementCount
    )
    {
        Assert.Equal (us.Length, s.Length);
        Assert.Equal (us, s);
        Assert.Equal (consoleWidth, us.GetColumns ());
        Assert.Equal (runeCount, us.GetRuneCount ());
        Assert.Equal (stringCount, s.Length);

        var textElementCount = 0;

        foreach (string _ in GraphemeHelper.GetGraphemes (s))
        {
            textElementCount++; // For versions prior to Net5.0 the StringInfo class might handle some grapheme clusters incorrectly.
        }

        Assert.Equal (txtElementCount, textElementCount);
    }

    private bool ProcessStringUseRune (string s)
    {
        string us = s;
        var rs = "";
        Rune codePoint;
        List<Rune> runes = new ();
        var colWidth = 0;

        for (var i = 0; i < s.Length; i++)
        {
            Rune rune = default;

            if (Rune.IsValid (s [i]))
            {
                rune = new Rune (s [i]);
                Assert.True (Rune.IsValid (rune.Value));
                runes.Add (rune);
                Assert.Equal (s [i], rune.Value);
                Assert.False (rune.IsSurrogatePair ());
            }
            else if (i + 1 < s.Length && RuneExtensions.EncodeSurrogatePair (s [i], s [i + 1], out codePoint))
            {
                Assert.Equal (0, rune.Value);
                Assert.False (Rune.IsValid (s [i]));
                rune = codePoint;
                runes.Add (rune);
                var sp = new string (new [] { s [i], s [i + 1] });
                Assert.Equal (sp, codePoint.ToString ());
                Assert.True (codePoint.IsSurrogatePair ());
                i++; // Increment the iterator by the number of surrogate pair
            }
            else
            {
                Assert.Throws<ArgumentOutOfRangeException> (() => new Rune (s [i]));

                throw new Exception ("String was not well-formed UTF-16.");
            }

            colWidth += rune.GetColumns (); // Increment the column width of this Rune
            rs += rune.ToString ();
        }

        Assert.Equal (us.GetColumns (), colWidth);
        Assert.Equal (s, rs);
        Assert.Equal (s, StringExtensions.ToString (runes));

        return true;
    }

    private bool ProcessTestStringUseChar (string s)
    {
        char surrogateChar = default;

        for (var i = 0; i < s.Length; i++)
        {
            Rune r;

            if (char.IsSurrogate (s [i]))
            {
                if (surrogateChar != default (int) && char.IsSurrogate (surrogateChar))
                {
                    r = new Rune (surrogateChar, s [i]);
                    Assert.True (r.IsSurrogatePair ());
                    int codePoint = char.ConvertToUtf32 (surrogateChar, s [i]);
                    RuneExtensions.EncodeSurrogatePair (surrogateChar, s [i], out Rune rune);
                    Assert.Equal (codePoint, rune.Value);
                    var sp = new string (new [] { surrogateChar, s [i] });
                    r = (Rune)codePoint;
                    Assert.Equal (sp, r.ToString ());
                    Assert.True (r.IsSurrogatePair ());

                    surrogateChar = default (char);
                }
                else if (i < s.Length - 1)
                {
                    surrogateChar = s [i];
                }
                else
                {
                    Assert.Throws<ArgumentOutOfRangeException> (() => new Rune (s [i]));

                    throw new Exception ("String was not well-formed UTF-16.");
                }
            }
            else
            {
                r = new Rune (s [i]);
                var buff = new byte [4];
                ((Rune)s [i]).Encode (buff);
                Assert.Equal ((int)s [i], buff [0]);
                Assert.Equal (s [i], r.Value);
                Assert.True (Rune.IsValid (r.Value));
                Assert.False (r.IsSurrogatePair ());
            }
        }

        return true;
    }

    [Theory]
    [InlineData (0x0041, new byte [] { 0x41 })]                  // 'A', ASCII
    [InlineData (0x00E9, new byte [] { 0xC3, 0xA9 })]            // 'é', 2-byte UTF-8
    [InlineData (0x20AC, new byte [] { 0xE2, 0x82, 0xAC })]      // '€', 3-byte UTF-8
    [InlineData (0x1F600, new byte [] { 0xF0, 0x9F, 0x98, 0x80 })] // 😀 emoji, 4-byte UTF-8
    public void Encode_WritesExpectedBytes (int codePoint, byte [] expectedBytes)
    {
        // Arrange
        Rune rune = new Rune (codePoint);
        byte [] buffer = new byte [10]; // extra space
        for (int i = 0; i < buffer.Length; i++)
        {
            buffer [i] = 0xFF;
        }

        // Act
        int written = rune.Encode (buffer);

        // Assert
        Assert.Equal (expectedBytes.Length, written);
        for (int i = 0; i < written; i++)
        {
            Assert.Equal (expectedBytes [i], buffer [i]);
        }
    }

    [Fact]
    public void Encode_WithStartAndCount_WritesPartialBytes ()
    {
        // Arrange: U+1F600 😀 (4 bytes)
        Rune rune = new Rune (0x1F600);
        byte [] buffer = new byte [10];
        for (int i = 0; i < buffer.Length; i++)
        {
            buffer [i] = 0xFF;
        }

        // Act: write starting at index 2, limit count to 2 bytes
        int written = rune.Encode (buffer, start: 2, count: 2);

        // Assert
        Assert.Equal (2, written);
        // Original UTF-8 bytes: F0 9F 98 80
        Assert.Equal (0xF0, buffer [2]);
        Assert.Equal (0x9F, buffer [3]);
        // Remaining buffer untouched
        Assert.Equal (0xFF, buffer [0]);
        Assert.Equal (0xFF, buffer [1]);
        Assert.Equal (0xFF, buffer [4]);
    }

    [Fact]
    public void Encode_WithCountGreaterThanRuneBytes_WritesAllBytes ()
    {
        // Arrange: é → C3 A9
        Rune rune = new Rune ('é');
        byte [] buffer = new byte [10];
        for (int i = 0; i < buffer.Length; i++)
        {
            buffer [i] = 0xFF;
        }

        // Act: count larger than needed
        int written = rune.Encode (buffer, start: 1, count: 10);

        // Assert
        Assert.Equal (2, written);
        Assert.Equal (0xC3, buffer [1]);
        Assert.Equal (0xA9, buffer [2]);
        Assert.Equal (0xFF, buffer [3]); // next byte untouched
    }

    [Fact]
    public void Encode_ZeroCount_WritesNothing ()
    {
        Rune rune = new Rune ('A');
        byte [] buffer = new byte [5];
        for (int i = 0; i < buffer.Length; i++)
        {
            buffer [i] = 0xFF;
        }

        int written = rune.Encode (buffer, start: 0, count: 0);

        Assert.Equal (0, written);
        foreach (var b in buffer)
        {
            Assert.Equal (0xFF, b); // buffer untouched
        }
    }
}