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CsvMultipleColumnSorter_Span.cs
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CsvMultipleColumnSorter_Span.cs
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using System;
using System.Collections.Generic;
namespace JOS.Files.Implementations.Sorting;
public class CsvMultipleColumnSorter_Span : IComparer<string>
{
private readonly IReadOnlyCollection<int> _columns;
private readonly char _separator;
public CsvMultipleColumnSorter_Span(
IReadOnlyCollection<int> columns,
char separator = ',')
{
_columns = columns ?? throw new ArgumentNullException(nameof(columns));
_separator = separator;
}
public int Compare(string? x, string? y)
{
if (x == null && y != null)
{
return -1;
}
if (y == null && x != null)
{
return 1;
}
if (x == null || y == null)
{
return 0;
}
var xSpan = x.AsSpan();
var ySpan = y.AsSpan();
var result = 0;
foreach (var column in _columns)
{
var xValue = GetColumnValue(xSpan, column);
var yValue = GetColumnValue(ySpan, column);
result = xValue.CompareTo(yValue, StringComparison.OrdinalIgnoreCase);
if (result != 0)
{
return result;
}
}
return result;
}
/// <summary>
/// Really naive implementation, just used as a POC.
/// </summary>
/// <param name="span"></param>
/// <param name="column"></param>
/// <returns></returns>
private ReadOnlySpan<char> GetColumnValue(ReadOnlySpan<char> span, int column)
{
var columnCounter = 1;
var columnStartIndex = 0;
for (var i = 0; i < span.Length; i++)
{
if (span[i].Equals(_separator))
{
columnCounter++;
continue;
}
if (columnCounter != column)
{
continue;
}
columnStartIndex = i;
break;
}
var columnLength = 0;
var slice = span[columnStartIndex..];
for (var i = 0; i < slice.Length; i++)
{
if (slice[i] != _separator)
{
columnLength++;
}
else
{
break;
}
}
return span.Slice(columnStartIndex, columnLength);
}
}