ln.parse/ln.parse/tokenizer/SourceBuffer.cs

using ln.collections;
using System;
using System.IO;

namespace ln.parse.tokenizer
{
    public struct TextPosition
    {
        public int LineNo;
        public int CursorPosition;

        public TextPosition(int line,int cursor)
        {
            LineNo = line;
            CursorPosition = cursor;
        }

        public static TextPosition First => new TextPosition(1, 1);

        public override string ToString() => string.Format("{0}:{1}", LineNo, CursorPosition);
    }

    public class SourceBuffer
    {
        readonly string _buffer;
        BTree<int, TextPosition> statTextPositions = new BTree<int, TextPosition>();

        int linearPosition;
        public int LinearPosition { get => linearPosition; set => linearPosition = value; }
        public TextPosition TextPosition => GetTextPosition(linearPosition);

        public string Text => _buffer;

        public int Length => _buffer.Length;

        public SourceBuffer(char[] buffer) : this(new StringReader(new String(buffer)))
        { }
        public SourceBuffer(TextReader reader) : this(reader.ReadToEnd())
        { }
        public SourceBuffer(string source)
        {
            _buffer = source;
            doStatistics();
        }

        private void doStatistics()
        {
            TextPosition textPosition = new TextPosition();

            for (int n=0;n<(_buffer.Length-1);n++)
            {
                textPosition.CursorPosition++;

                if (_buffer[n] == '\n')
                {
                    textPosition.LineNo++;
                    textPosition.CursorPosition = 0;
                } else if (textPosition.CursorPosition == 1)
                    statTextPositions.Add(n, textPosition);
            }
        }

        public TextPosition GetTextPosition(int linearPosition)
        {
            statTextPositions.TryGetPreviousOrCurrentValue(linearPosition, out TextPosition textPosition);
            return textPosition;
        }

        public string GetText() => _buffer;
        public string GetText(int linearStart) => _buffer.Substring(linearStart);
        public string GetText(int linearStart, int length) => _buffer.Substring(linearStart, length);

        public string GetCurrentText() => _buffer.Substring(linearPosition);


    }
}