Upsilon/Upsilon/Text/SourceText.cs

using System;

namespace Upsilon.Text
{
    public class SourceText
    {
        private readonly string _text;
        private readonly SourceTextLine[] _lines;

        public SourceText(string text)
        {
            _text = text;
            var lines = text.Split('\n');
            _lines = new SourceTextLine[lines.Length];
            var linePos = 0;
            for (var index = 0; index < lines.Length; index++)
            {
                var line = lines[index];
                _lines[index] = new SourceTextLine(linePos, line.Length);
                linePos += line.Length;
            }
        }

        public string GetSpan(int start, int length)
        {
            if (start < 0)
            {
                length += start;
                start = 0;
            };
            if (start >= _text.Length)
                return string.Empty;
            if (start + length >= _text.Length) length = _text.Length - start;
            return _text.Substring(start, length);
        }

        public (int Line, int Pos) GetLinePosition(int spanPos)
        {
            var min = 0;
            var max = _lines.Length - 1;
            while (min <= max)
            {
                var mid = (min + max) / 2 ;
                var midLine = _lines[mid];
                if (midLine.Start <= spanPos && midLine.End > spanPos)
                {
                    var pos = spanPos - midLine.Start;
                    return (mid, pos);
                }
                if (spanPos >= midLine.End)
                {
                    min = mid + 1;
                }
                else if (spanPos < midLine.Start)
                {
                    max = mid - 1;
                }
            }
            var newPos = spanPos - _lines[min].Start;
            return (min, newPos);
        }

        public string GetSpan(TextSpan span)
        {
            return GetSpan(span.Start, span.Length);
        }
    }
}