StringInfo.cs

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using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Text.Unicode;
 
namespace System.Globalization;
 
public class StringInfo
{
    private string _str;
 
    private int[] _indexes;
 
    private int[]? Indexes
    {
        get
        {
            if (_indexes == null && String.Length > 0)
            {
                _indexes = ParseCombiningCharacters(String);
            }
            return _indexes;
        }
    }
 
    public string String
    {
        get
        {
            return _str;
        }
        [MemberNotNull("_str")]
        set
        {
            _str = value ?? throw new ArgumentNullException("value");
            _indexes = null;
        }
    }
 
    public int LengthInTextElements
    {
        get
        {
            int[]? indexes = Indexes;
            if (indexes == null)
            {
                return 0;
            }
            return indexes.Length;
        }
    }
 
    public StringInfo()
        : this(string.Empty)
    {
    }
 
    public StringInfo(string value)
    {
        String = value;
    }
 
    public override bool Equals([NotNullWhen(true)] object? value)
    {
        if (value is StringInfo stringInfo)
        {
            return _str.Equals(stringInfo._str);
        }
        return false;
    }
 
    public override int GetHashCode()
    {
        return _str.GetHashCode();
    }
 
    public string SubstringByTextElements(int startingTextElement)
    {
        int[]? indexes = Indexes;
        return SubstringByTextElements(startingTextElement, ((indexes != null) ? indexes.Length : 0) - startingTextElement);
    }
 
    public string SubstringByTextElements(int startingTextElement, int lengthInTextElements)
    {
        int[] array = Indexes ?? Array.Empty<int>();
        if ((uint)startingTextElement >= (uint)array.Length)
        {
            throw new ArgumentOutOfRangeException("startingTextElement", startingTextElement, SR.Arg_ArgumentOutOfRangeException);
        }
        if ((uint)lengthInTextElements > (uint)(array.Length - startingTextElement))
        {
            throw new ArgumentOutOfRangeException("lengthInTextElements", lengthInTextElements, SR.Arg_ArgumentOutOfRangeException);
        }
        int num = array[startingTextElement];
        Index end = ^0;
        if ((uint)(startingTextElement + lengthInTextElements) < (uint)array.Length)
        {
            end = array[startingTextElement + lengthInTextElements];
        }
        return String[num..end];
    }
 
    public static string GetNextTextElement(string str)
    {
        return GetNextTextElement(str, 0);
    }
 
    public static string GetNextTextElement(string str, int index)
    {
        int nextTextElementLength = GetNextTextElementLength(str, index);
        return str.Substring(index, nextTextElementLength);
    }
 
    public static int GetNextTextElementLength(string str)
    {
        return GetNextTextElementLength(str, 0);
    }
 
    public static int GetNextTextElementLength(string str, int index)
    {
        if (str == null)
        {
            ThrowHelper.ThrowArgumentNullException(ExceptionArgument.str);
        }
        if ((uint)index > (uint)str.Length)
        {
            ThrowHelper.ThrowArgumentOutOfRange_IndexException();
        }
        return GetNextTextElementLength(str.AsSpan(index));
    }
 
    public static int GetNextTextElementLength(ReadOnlySpan<char> str)
    {
        return TextSegmentationUtility.GetLengthOfFirstUtf16ExtendedGraphemeCluster(str);
    }
 
    public static TextElementEnumerator GetTextElementEnumerator(string str)
    {
        return GetTextElementEnumerator(str, 0);
    }
 
    public static TextElementEnumerator GetTextElementEnumerator(string str, int index)
    {
        if (str == null)
        {
            ThrowHelper.ThrowArgumentNullException(ExceptionArgument.str);
        }
        if ((uint)index > (uint)str.Length)
        {
            ThrowHelper.ThrowArgumentOutOfRange_IndexException();
        }
        return new TextElementEnumerator(str, index);
    }
 
    public static int[] ParseCombiningCharacters(string str)
    {
        if (str == null)
        {
            ThrowHelper.ThrowArgumentNullException(ExceptionArgument.str);
        }
        Span<int> initialSpan = stackalloc int[64];
        ValueListBuilder<int> valueListBuilder = new ValueListBuilder<int>(initialSpan);
        ReadOnlySpan<char> str2 = str;
        while (!str2.IsEmpty)
        {
            valueListBuilder.Append(str.Length - str2.Length);
            str2 = str2.Slice(GetNextTextElementLength(str2));
        }
        int[] result = valueListBuilder.AsSpan().ToArray();
        valueListBuilder.Dispose();
        return result;
    }
}