/*
 * License: CPOL
 * Source: https://www.codeproject.com/Tips/823670/Csharp-Light-and-Fast-CSV-Parser
 * Author: Yuriy Magurdumov
 */

using System;
using System.Collections.Generic;
using System.Text;

namespace HeuristicLab.BenchmarkSuite {
  using System.IO;

  public static class CsvParser {
    private static Tuple<T, IEnumerable<T>> HeadAndTail<T>(this IEnumerable<T> source) {
      if (source == null)
        throw new ArgumentNullException("source");
      var en = source.GetEnumerator();
      en.MoveNext();
      return Tuple.Create(en.Current, EnumerateTail(en));
    }

    private static IEnumerable<T> EnumerateTail<T>(IEnumerator<T> en) {
      while (en.MoveNext()) yield return en.Current;
    }

    public static IEnumerable<IList<string>> Parse(string content, char delimiter, char qualifier) {
      using (var reader = new StringReader(content))
        return Parse(reader, delimiter, qualifier);
    }

    public static Tuple<IList<string>, IEnumerable<IList<string>>> ParseHeadAndTail(TextReader reader, char delimiter, char qualifier) {
      return HeadAndTail(Parse(reader, delimiter, qualifier));
    }

    public static IEnumerable<IList<string>> Parse(TextReader reader, char delimiter, char qualifier) {
      var inQuote = false;
      var record = new List<string>();
      var sb = new StringBuilder();

      while (reader.Peek() != -1) {
        var readChar = (char)reader.Read();

        if (readChar == '\n' || (readChar == '\r' && (char)reader.Peek() == '\n')) {
          // If it's a \r\n combo consume the \n part and throw it away.
          if (readChar == '\r')
            reader.Read();

          if (inQuote) {
            if (readChar == '\r')
              sb.Append('\r');
            sb.Append('\n');
          } else {
            if (record.Count > 0 || sb.Length > 0) {
              record.Add(sb.ToString());
              sb.Clear();
            }

            if (record.Count > 0)
              yield return record;

            record = new List<string>(record.Count);
          }
        } else if (sb.Length == 0 && !inQuote) {
          if (readChar == qualifier)
            inQuote = true;
          else if (readChar == delimiter) {
            record.Add(sb.ToString());
            sb.Clear();
          //} else if (char.IsWhiteSpace(readChar)) { // Ignore leading whitespace
          } else
            sb.Append(readChar);
        } else if (readChar == delimiter) {
          if (inQuote)
            sb.Append(delimiter);
          else {
            record.Add(sb.ToString());
            sb.Clear();
          }
        } else if (readChar == qualifier) {
          if (inQuote) {
            if ((char)reader.Peek() == qualifier) {
              reader.Read();
              sb.Append(qualifier);
            } else
              inQuote = false;
          } else
            sb.Append(readChar);
        } else
          sb.Append(readChar);
      }

      if (record.Count > 0 || sb.Length > 0)
        record.Add(sb.ToString());

      if (record.Count > 0)
        yield return record;
    }
  }
}