SmallestCSVParser/SmallestCSVParser.cs

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// SmallestCSVParser version 1.1.1 - Copyright (C) 2024 Karl Pickett
using System.Text;

namespace SmallestCSV;


public class SmallestCSVParser
{
    /// <summary>
    /// This is thrown if the CSV has invalid syntax.
    /// </summary>
    public class Error: Exception {
        public Error(string message): base(message) { }
    }

    /// <summary>
    /// This class does not Close/Dispose the `stream`.
    /// </summary>
    public SmallestCSVParser(StreamReader stream) {
        _stream = stream;
        _sb = new();
    }

    /// <summary>
    /// Read all columns for the next row/line.
    /// If we are at end of file, this returns null.
    ///
    /// By default, columns that were quoted (") have their enclosing quotes
    /// removed.  Set `removeEnclosingQuotes` to false if you want to preserve
    /// the quotes, for example to distinguish between an empty quoted vs
    /// unquoted column.
    /// </summary>
    public List<string>? ReadNextRow(bool removeEnclosingQuotes=true) {
        List<string> ret = new();
        while (true) {
            var (column, hasMore) = ReadNextColumn(removeEnclosingQuotes);
            if (column != null) {
                ret.Add(column);
            }
            if (!hasMore) {
                return ret.Any() ? ret : null;
            }
        }
    }

    private (string? Column, bool RowHasMoreColumns) ReadNextColumn(bool removeEnclosingQuotes) {
        _sb.Clear();
        switch (_stream.Peek()) {
            case -1:
                return (null, false);
            case '"':
                ReadQuotedColumn(removeEnclosingQuotes);
                return (_sb.ToString(), !TryFinishLine());
            default:
                ReadNonQuotedColumn();
                return (_sb.ToString(), !TryFinishLine());
        }
    }

    private void ReadQuotedColumn(bool removeEnclosingQuotes) {