Avalonia/tests/Avalonia.Skia.UnitTests/Media/TextFormatting/TextCollapsingBidiTests.cs

#nullable enable

using System.Collections.Generic;
using System.Linq;
using System.Text;
using Avalonia.Media;
using Avalonia.Media.TextFormatting;
using Xunit;

namespace Avalonia.Skia.UnitTests.Media.TextFormatting
{
    /// <summary>
    /// Characterization tests for <see cref="TextCollapsingProperties"/>
    /// implementations, with emphasis on BiDi correctness.
    /// </summary>
    public class TextCollapsingBidiTests
    {
        [Fact]
        public void Ltr_TrailingCharacter_Trims_From_End()
        {
            using (TextFormatterTests.Start())
            {
                var line = BuildLine("Hello world", FlowDirection.LeftToRight);
                var collapsing = TrailingChar(line.Width / 2, FlowDirection.LeftToRight);
                var collapsed = line.Collapse(collapsing);

                AssertCollapsed(collapsed, line);
                var text = LogicalText(collapsed);
                Assert.Contains("…", text);
                Assert.StartsWith("H", text);
            }
        }

        [Fact]
        public void Ltr_TrailingWord_Trims_On_Word_Boundary()
        {
            using (TextFormatterTests.Start())
            {
                var line = BuildLine("Hello world foo", FlowDirection.LeftToRight);
                var collapsing = TrailingWord(line.Width / 2, FlowDirection.LeftToRight);
                var collapsed = line.Collapse(collapsing);

                AssertCollapsed(collapsed, line);
                Assert.Contains("…", LogicalText(collapsed));
            }
        }

        [Fact]
        public void Ltr_PrefixCharacterEllipsis_Preserves_Prefix_And_Suffix()
        {
            using (TextFormatterTests.Start())
            {
                var line = BuildLine("01234 01234 01234", FlowDirection.LeftToRight);
                var collapsing = LeadingPrefix(prefixLength: 8, width: 120.0, FlowDirection.LeftToRight);
                var collapsed = line.Collapse(collapsing);

                AssertCollapsed(collapsed, line);
                var text = LogicalText(collapsed);
                Assert.StartsWith("01234 01", text);
                Assert.Contains("…", text);
                // Suffix must reappear after the symbol.
                Assert.EndsWith("4 01234", text);
            }
        }

        [Fact]
        public void Ltr_PathSegmentEllipsis_Collapses_Middle()
        {
            using (TextFormatterTests.Start())
            {
                var line = BuildLine("verylongdirectory\\file.txt", FlowDirection.LeftToRight);
                var collapsing = new TextPathSegmentEllipsis(
                    "…", line.Width / 2,
                    new GenericTextRunProperties(Typeface.Default),
                    FlowDirection.LeftToRight);
                var collapsed = line.Collapse(collapsing);

                AssertCollapsed(collapsed, line);
                var text = LogicalText(collapsed);
                Assert.Contains("…", text);
                // Last segment ("file.txt") should be preserved on at least
                // some prefix; we don't assert exact width because Width math
                // depends on the font.
                Assert.Contains(".txt", text);
            }
        }

        [Fact]
        public void Width_Greater_Than_Line_Returns_Same_Line()
        {
            using (TextFormatterTests.Start())
            {
                var line = BuildLine("abc", FlowDirection.LeftToRight);
                var collapsing = TrailingChar(line.Width + 100, FlowDirection.LeftToRight);
                var collapsed = line.Collapse(collapsing);

                // Collapse returns null → TextLineImpl.Collapse returns `this`.
                Assert.Same(line, collapsed);
                Assert.False(collapsed.HasCollapsed);
            }
        }

        [Fact]
        public void Width_Less_Than_Symbol_Returns_Empty_Collapsed_Line()
        {
            using (TextFormatterTests.Start())
            {
                var line = BuildLine("abcdef", FlowDirection.LeftToRight);

                // Width below symbol width → implementation returns [] → line
                // gets HasCollapsed = true but no runs.
                var collapsing = TrailingChar(width: 0.001, FlowDirection.LeftToRight);
                var collapsed = line.Collapse(collapsing);

                Assert.True(collapsed.HasCollapsed);
                Assert.Empty(collapsed.TextRuns);
            }
        }

        [Fact]
        public void Rtl_TrailingCharacter_Preserves_Logical_Prefix()
        {
            using (TextFormatterTests.Start())
            {
                const string text = "السلام عليكم ورحمة الله وبركاته";
                var line = BuildLine(text, FlowDirection.RightToLeft);
                var collapsing = TrailingChar(line.Width / 2, FlowDirection.RightToLeft);
                var collapsed = line.Collapse(collapsing);

                AssertCollapsed(collapsed, line);
                var logical = LogicalText(collapsed);
                Assert.Contains("…", logical);
                Assert.StartsWith(text.Substring(0, 1), logical);
            }
        }

        [Fact]
        public void Rtl_TrailingWord_Preserves_Logical_Prefix()
        {
            using (TextFormatterTests.Start())
            {
                const string text = "السلام عليكم ورحمة الله وبركاته";
                var line = BuildLine(text, FlowDirection.RightToLeft);
                var collapsing = TrailingWord(line.Width / 2, FlowDirection.RightToLeft);
                var collapsed = line.Collapse(collapsing);

                AssertCollapsed(collapsed, line);
                Assert.Contains("…", LogicalText(collapsed));
            }
        }

        [Fact]
        public void Rtl_PrefixCharacterEllipsis_Preserves_Logical_Prefix()
        {
            using (TextFormatterTests.Start())
            {
                const string text = "السلام عليكم ورحمة الله وبركاته";
                var line = BuildLine(text, FlowDirection.RightToLeft);
                var collapsing = LeadingPrefix(prefixLength: 4, width: line.Width / 2, FlowDirection.RightToLeft);
                var collapsed = line.Collapse(collapsing);

                AssertCollapsed(collapsed, line);
                var logical = LogicalText(collapsed);
                Assert.StartsWith(text.Substring(0, 4), logical);
                Assert.Contains("…", logical);
            }
        }

        [Fact]
        public void Mixed_TrailingCharacter_Preserves_Logical_Prefix()
        {
            using (TextFormatterTests.Start())
            {
                const string text = "Hello مرحبا world";
                var line = BuildLine(text, FlowDirection.LeftToRight);
                var collapsing = TrailingChar(line.Width * 0.6, FlowDirection.LeftToRight);
                var collapsed = line.Collapse(collapsing);

                AssertCollapsed(collapsed, line);
                Assert.StartsWith("Hello", LogicalText(collapsed));
            }
        }

        [Fact]
        public void Mixed_PrefixCharacterEllipsis_Preserves_Logical_Prefix_And_Suffix()
        {
            using (TextFormatterTests.Start())
            {
                const string text = "Hello مرحبا world";
                var line = BuildLine(text, FlowDirection.LeftToRight);
                var collapsing = LeadingPrefix(prefixLength: 5, width: line.Width * 0.6, FlowDirection.LeftToRight);
                var collapsed = line.Collapse(collapsing);

                AssertCollapsed(collapsed, line);
                var logical = LogicalText(collapsed);
                Assert.StartsWith("Hello", logical);
                Assert.Contains("…", logical);
            }
        }

        [Fact]
        public void Mixed_TrailingWord_Preserves_Logical_Prefix()
        {
            using (TextFormatterTests.Start())
            {
                const string text = "Hello مرحبا world";
                var line = BuildLine(text, FlowDirection.LeftToRight);
                var collapsing = TrailingWord(line.Width * 0.6, FlowDirection.LeftToRight);
                var collapsed = line.Collapse(collapsing);

                AssertCollapsed(collapsed, line);
                var logical = LogicalText(collapsed);
                Assert.Contains("…", logical);
                Assert.StartsWith("Hello", logical);
            }
        }

        [Fact]
        public void Mixed_PathSegmentEllipsis_Preserves_Last_Segment()
        {
            using (TextFormatterTests.Start())
            {
                // Mixed-bidi path: ASCII-only separators with an RTL directory
                // name embedded. Segmentation is separator-driven, so the
                // logical-tail segment ("file.txt") must survive.
                const string text = "C:\\folder\\مجلد\\file.txt";
                var line = BuildLine(text, FlowDirection.LeftToRight);
                var collapsing = new TextPathSegmentEllipsis(
                    "…", line.Width / 2,
                    new GenericTextRunProperties(Typeface.Default),
                    FlowDirection.LeftToRight);
                var collapsed = line.Collapse(collapsing);

                AssertCollapsed(collapsed, line);
                var logical = LogicalText(collapsed);
                Assert.Contains("…", logical);
                Assert.Contains("file.txt", logical);
            }
        }

        [Fact]
        public void Rtl_PathSegmentEllipsis_Preserves_Last_Segment()
        {
            using (TextFormatterTests.Start())
            {
                // Pure-RTL path. Avalonia's font fallback may render Arabic as
                // .notdef glyphs in the test environment, but segmentation is
                // character-driven (separators are ASCII '/' and '\\') so the
                // logical-tail segment "ملف.txt" must still be detected and
                // preserved.
                const string text = "مجلد/مجلد2/ملف.txt";
                var line = BuildLine(text, FlowDirection.RightToLeft);
                var collapsing = new TextPathSegmentEllipsis(
                    "…", line.Width / 2,
                    new GenericTextRunProperties(Typeface.Default),
                    FlowDirection.RightToLeft);
                var collapsed = line.Collapse(collapsing);

                AssertCollapsed(collapsed, line);
                var logical = LogicalText(collapsed);
                Assert.Contains("…", logical);
                Assert.Contains("ملف.txt", logical);
            }
        }

        [Fact]
        public void Ltr_PathSegmentEllipsis_Middle_Collapse_Preserves_First_And_Last_Segments()
        {
            using (TextFormatterTests.Start())
            {
                // 3-segment path; middle is intentionally long so collapsing
                // it alone produces a fitting result.
                const string text = "a/middlemiddlemiddlemiddlemiddlemiddlemiddlemiddlemiddlemiddle/c.txt";
                var line = BuildLine(text, FlowDirection.LeftToRight);
                var budget = line.Width * 0.3;
                var collapsing = new TextPathSegmentEllipsis(
                    "…", budget,
                    new GenericTextRunProperties(Typeface.Default),
                    FlowDirection.LeftToRight);
                var collapsed = line.Collapse(collapsing);

                AssertCollapsed(collapsed, line);
                var logical = LogicalText(collapsed);
                Assert.Contains("…", logical);
                Assert.Contains("a", logical);
                Assert.Contains("c.txt", logical);
            }
        }

        [Fact]
        public void Rtl_PathSegmentEllipsis_Middle_Collapse_Preserves_First_And_Last_Segments()
        {
            using (TextFormatterTests.Start())
            {
                const string text = "اول/منتصفمنتصفمنتصفمنتصفمنتصفمنتصفمنتصفمنتصف/اخر.txt";
                var line = BuildLine(text, FlowDirection.RightToLeft);
                var budget = line.Width * 0.3;
                var collapsing = new TextPathSegmentEllipsis(
                    "…", budget,
                    new GenericTextRunProperties(Typeface.Default),
                    FlowDirection.RightToLeft);
                var collapsed = line.Collapse(collapsing);

                AssertCollapsed(collapsed, line);
                var logical = LogicalText(collapsed);
                Assert.Contains("…", logical);
                Assert.Contains("اول", logical);
                Assert.Contains("اخر.txt", logical);
            }
        }

        [Theory]
        [InlineData("Hello world abcdef", true)]
        [InlineData("السلام عليكم ورحمة", false)]
        public void TryMeasureCharacters_Returned_Length_Fits_Logical_Leading_In_Budget(string text, bool ltr)
        {
            using (TextFormatterTests.Start())
            {
                var dir = ltr ? FlowDirection.LeftToRight : FlowDirection.RightToLeft;
                var line = BuildLine(text, dir);
                var shapedRun = line.TextRuns.OfType<ShapedTextRun>().FirstOrDefault();
                Assert.NotNull(shapedRun);

                var buffer = shapedRun!.ShapedBuffer;
                var totalWidth = shapedRun.Size.Width;

                // Probe at several budget points; the contract must hold at all of them.
                for (var i = 1; i < 10; i++)
                {
                    var budget = totalWidth * i / 10;
                    if (!shapedRun.TryMeasureCharacters(budget, out var measured) || measured <= 0)
                    {
                        continue;
                    }

                    // The width of the LOGICAL leading `measured` characters must fit
                    // in `budget`. GetCharRangeWidth uses the cluster cache, which is
                    // built in logical order for both directions.
                    var actualLeadingWidth = buffer.GetCharRangeWidth(0, measured);

                    Assert.True(actualLeadingWidth <= budget + 0.5,
                        $"{dir}: budget={budget:F2}, measured={measured}, " +
                        $"actual logical-leading width={actualLeadingWidth:F2}");
                }
            }
        }

        [Theory]
        [InlineData("Hello world abcdef", true)]
        [InlineData("السلام عليكم ورحمة", false)]
        public void TryMeasureCharactersBackwards_Returned_Length_Fits_Logical_Trailing_In_Budget(string text, bool ltr)
        {
            using (TextFormatterTests.Start())
            {
                var dir = ltr ? FlowDirection.LeftToRight : FlowDirection.RightToLeft;
                var line = BuildLine(text, dir);
                var shapedRun = line.TextRuns.OfType<ShapedTextRun>().FirstOrDefault();
                Assert.NotNull(shapedRun);

                var buffer = shapedRun!.ShapedBuffer;
                var totalWidth = shapedRun.Size.Width;
                var textLength = shapedRun.Length;

                for (var i = 1; i < 10; i++)
                {
                    var budget = totalWidth * i / 10;
                    if (!shapedRun.TryMeasureCharactersBackwards(budget, out var measured, out _) || measured <= 0)
                    {
                        continue;
                    }

                    var actualTrailingWidth = buffer.GetCharRangeWidth(textLength - measured, textLength);

                    Assert.True(actualTrailingWidth <= budget + 0.5,
                        $"{dir}: budget={budget:F2}, measured={measured}, " +
                        $"actual logical-trailing width={actualTrailingWidth:F2}");
                }
            }
        }

        [Fact]
        public void LogicalTextRunEnumerator_Without_IndexedRuns_Returns_Distinct_Runs()
        {
            using (TextFormatterTests.Start())
            {
                var props = new GenericTextRunProperties(Typeface.Default);
                var runs = new TextRun[]
                {
                    new TextCharacters("AAA", props),
                    new TextCharacters("BBB", props),
                    new TextCharacters("CCC", props),
                };

                // Construct TextLineImpl directly and SKIP FinalizeLine so that
                // _indexedTextRuns stays null. This is exactly the branch
                // LogicalTextRunEnumerator handles incorrectly today.
                var paragraphProps = new GenericTextParagraphProperties(props);
                var line = new TextLineImpl(runs, 0, 9, double.PositiveInfinity, paragraphProps);

                var enumerator = new LogicalTextRunEnumerator(line);
                var seen = new List<TextRun>();
                while (enumerator.MoveNext(out var run))
                {
                    seen.Add(run!);
                }

                Assert.Equal(3, seen.Count);
                Assert.Same(runs[0], seen[0]);
                Assert.Same(runs[1], seen[1]);
                Assert.Same(runs[2], seen[2]);
            }
        }

        [Fact]
        public void LeadingPrefix_Negative_PrefixLength_Throws()
        {
            using (TextFormatterTests.Start())
            {
                var props = new GenericTextRunProperties(Typeface.Default);
                Assert.Throws<System.ArgumentOutOfRangeException>(
                    () => new TextLeadingPrefixCharacterEllipsis(
                        "…", prefixLength: -1, width: 100, props, FlowDirection.LeftToRight));
            }
        }

        [Fact]
        public void LeadingPrefix_Honours_FlowDirection_For_Symbol()
        {
            using (TextFormatterTests.Start())
            {
                const string text = "السلام عليكم ورحمة";
                var line = BuildLine(text, FlowDirection.RightToLeft);
                var collapsing = LeadingPrefix(prefixLength: 4, width: line.Width / 2, FlowDirection.RightToLeft);
                var collapsed = line.Collapse(collapsing);

                AssertCollapsed(collapsed, line);

                // The ellipsis symbol's run should pick up the RTL bidi level
                // from the FlowDirection passed to the constructor. Today the
                // ctor in Collapse() hardcodes LeftToRight, so the symbol run
                // has IsLeftToRight == true.
                var ellipsisRun = collapsed.TextRuns
                    .OfType<ShapedTextRun>()
                    .FirstOrDefault(r => r.Text.ToString().Contains("…"));
                Assert.NotNull(ellipsisRun);
                Assert.False(ellipsisRun!.ShapedBuffer.IsLeftToRight);
            }
        }

        [Fact]
        public void Collapse_With_Multiple_Shaped_Runs_Preserves_Ellipsis()
        {
            // Three independent runs via FixedRunsTextSource. Trim point lands
            // somewhere in the middle — collapse must not silently drop a run
            // or duplicate one (covers the SplitTextRuns interaction).
            using (TextFormatterTests.Start())
            {
                var props = new GenericTextRunProperties(Typeface.Default);
                var sourceRuns = new TextRun[]
                {
                    new TextCharacters("AAAA", props),
                    new TextCharacters("BBBB", props),
                    new TextCharacters("CCCC", props),
                };
                var src = new FixedRunsTextSource(sourceRuns);
                var formatter = new TextFormatterImpl();
                var line = formatter.FormatLine(src, 0, double.PositiveInfinity,
                    new GenericTextParagraphProperties(props));
                Assert.NotNull(line);

                var collapsing = TrailingChar(line!.Width / 2, FlowDirection.LeftToRight);
                var collapsed = line.Collapse(collapsing);

                AssertCollapsed(collapsed, line);
                var text = LogicalText(collapsed);
                Assert.Contains("…", text);
                // Every preserved character must come from the original source
                // text in original order — no garbage.
                var preserved = text.Replace("…", string.Empty);
                Assert.StartsWith(preserved, "AAAABBBBCCCC");
            }
        }

        [Fact]
        public void LeadingPrefix_With_Fully_Fitting_Tail_Run_Does_Not_Throw()
        {
            // Regression: on a multi-run line a logical-tail run can fit entirely
            // within the remaining suffix budget. TryMeasureCharactersBackwards then
            // returns suffixCount == run.Length, and the old code called
            // ShapedTextRun.Split(0), which throws ArgumentOutOfRangeException. The
            // long leading run forces the collapse; the short trailing run wholly
            // fits the suffix budget and exercises that boundary.
            using (TextFormatterTests.Start())
            {
                var props = new GenericTextRunProperties(Typeface.Default);
                var sourceRuns = new TextRun[]
                {
                    new TextCharacters("AAAAAAAAAAAA", props), // long: forces the collapse
                    new TextCharacters("B", props),            // short: wholly fits the suffix budget
                };
                var src = new FixedRunsTextSource(sourceRuns);
                var formatter = new TextFormatterImpl();
                var line = formatter.FormatLine(src, 0, double.PositiveInfinity,
                    new GenericTextParagraphProperties(props));
                Assert.NotNull(line);

                var collapsing = LeadingPrefix(prefixLength: 2, width: line!.Width * 0.7, FlowDirection.LeftToRight);

                // Previously threw ArgumentOutOfRangeException from Split(0).
                var collapsed = line.Collapse(collapsing);

                AssertCollapsed(collapsed, line);
                var text = LogicalText(collapsed);
                Assert.Contains("…", text);
                // The fully-fitting trailing run must survive in the logical-tail suffix.
                Assert.Contains("B", text);
            }
        }

        private static TextLine BuildLine(string text, FlowDirection flow)
        {
            var props = new GenericTextRunProperties(Typeface.Default, 12, foregroundBrush: Brushes.Black);
            var paragraphProps = new GenericTextParagraphProperties(
                flow, TextAlignment.Left, true, true, props, TextWrapping.NoWrap, 0, 0, 0);
            var source = new SingleBufferTextSource(text, props);
            var formatter = new TextFormatterImpl();
            var line = formatter.FormatLine(source, 0, double.PositiveInfinity, paragraphProps);
            Assert.NotNull(line);
            return line!;
        }

        private static TextTrailingCharacterEllipsis TrailingChar(double width, FlowDirection flow)
            => new("…", width, new GenericTextRunProperties(Typeface.Default), flow);

        private static TextTrailingWordEllipsis TrailingWord(double width, FlowDirection flow)
            => new("…", width, new GenericTextRunProperties(Typeface.Default), flow);

        private static TextLeadingPrefixCharacterEllipsis LeadingPrefix(
            int prefixLength, double width, FlowDirection flow)
            => new("…", prefixLength, width,
                new GenericTextRunProperties(Typeface.Default), flow);

        private static void AssertCollapsed(TextLine collapsed, TextLine original)
        {
            Assert.NotSame(original, collapsed);
            Assert.True(collapsed.HasCollapsed,
                "Collapsed line must report HasCollapsed = true.");
        }

        /// <summary>
        /// Concatenates run text in logical order via
        /// <see cref="LogicalTextRunEnumerator"/>. For LTR-only lines this
        /// equals walking <c>TextRuns</c> directly; for RTL/mixed lines it
        /// returns the original-text order (what the collapse contract
        /// requires) instead of the visual post-bidi order.
        /// </summary>
        private static string LogicalText(TextLine line)
        {
            var enumerator = new LogicalTextRunEnumerator(line);
            var sb = new StringBuilder();
            while (enumerator.MoveNext(out var run))
            {
                sb.Append(run!.Text.Span);
            }
            return sb.ToString();
        }

        /// <summary>
        /// Local copy of the FixedRunsTextSource pattern used in
        /// TextLineTests — that class is private, so duplicate here.
        /// </summary>
        private sealed class FixedRunsTextSource : ITextSource
        {
            private readonly IReadOnlyList<TextRun> _textRuns;

            public FixedRunsTextSource(IReadOnlyList<TextRun> textRuns)
            {
                _textRuns = textRuns;
            }

            public TextRun? GetTextRun(int textSourceIndex)
            {
                var pos = 0;
                foreach (var run in _textRuns)
                {
                    if (pos == textSourceIndex)
                    {
                        return run;
                    }
                    pos += run.Length;
                }
                return null;
            }
        }
    }
}