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

namespace Ideafixxxer.CsvParser
{
	public class CsvParser
	{
		private const char CommaCharacter = ',';
		private const char QuoteCharacter = '"';

		#region Nested types

		private abstract class ParserState
		{
			public static readonly LineStartState LineStartState = new LineStartState();
			public static readonly ValueStartState ValueStartState = new ValueStartState();
			public static readonly ValueState ValueState = new ValueState();
			public static readonly QuotedValueState QuotedValueState = new QuotedValueState();
			public static readonly QuoteState QuoteState = new QuoteState();

			public abstract ParserState AnyChar(char ch, ParserContext context);
			public abstract ParserState Comma(ParserContext context);
			public abstract ParserState Quote(ParserContext context);
			public abstract ParserState EndOfLine(ParserContext context);
		}

		private class LineStartState : ParserState
		{
			public override ParserState AnyChar(char ch, ParserContext context)
			{
				context.AddChar(ch);
				return ValueState;
			}

			public override ParserState Comma(ParserContext context)
			{
				context.AddValue();
				return ValueStartState;
			}

			public override ParserState Quote(ParserContext context)
			{
				return QuotedValueState;
			}

			public override ParserState EndOfLine(ParserContext context)
			{
				context.AddLine();
				return LineStartState;
			}
		}

		private class ValueStartState : LineStartState
		{
			public override ParserState EndOfLine(ParserContext context)
			{
				context.AddValue();
				context.AddLine();
				return LineStartState;
			}
		}

		private class ValueState : ParserState
		{
			public override ParserState AnyChar(char ch, ParserContext context)
			{
				context.AddChar(ch);
				return ValueState;
			}

			public override ParserState Comma(ParserContext context)
			{
				context.AddValue();
				return ValueStartState;
			}

			public override ParserState Quote(ParserContext context)
			{
				context.AddChar(QuoteCharacter);
				return ValueState;
			}

			public override ParserState EndOfLine(ParserContext context)
			{
				context.AddValue();
				context.AddLine();
				return LineStartState;
			}
		}

		private class QuotedValueState : ParserState
		{
			public override ParserState AnyChar(char ch, ParserContext context)
			{
				context.AddChar(ch);
				return QuotedValueState;
			}

			public override ParserState Comma(ParserContext context)
			{
				context.AddChar(CommaCharacter);
				return QuotedValueState;
			}

			public override ParserState Quote(ParserContext context)
			{
				return QuoteState;
			}

			public override ParserState EndOfLine(ParserContext context)
			{
				context.AddChar('\r');
				context.AddChar('\n');
				return QuotedValueState;
			}
		}

		private class QuoteState : ParserState
		{
			public override ParserState AnyChar(char ch, ParserContext context)
			{
				//undefined, ignore "
				context.AddChar(ch);
				return QuotedValueState;
			}

			public override ParserState Comma(ParserContext context)
			{
				context.AddValue();
				return ValueStartState;
			}

			public override ParserState Quote(ParserContext context)
			{
				context.AddChar(QuoteCharacter);
				return QuotedValueState;
			}

			public override ParserState EndOfLine(ParserContext context)
			{
				context.AddValue();
				context.AddLine();
				return LineStartState;
			}
		}

		private class ParserContext
		{
			private readonly StringBuilder _currentValue = new StringBuilder();
			private readonly List<string[]> _lines = new List<string[]>();
			private readonly List<string> _currentLine = new List<string>();

			public void AddChar(char ch)
			{
				_currentValue.Append(ch);
			}

			public void AddValue()
			{
				_currentLine.Add(_currentValue.ToString());
				_currentValue.Remove(0, _currentValue.Length);
			}

			public void AddLine()
			{
				_lines.Add(_currentLine.ToArray());
				_currentLine.Clear();
			}

			public List<string[]> GetAllLines()
			{
				if (_currentValue.Length > 0)
				{
					AddValue();
				}
				if (_currentLine.Count > 0)
				{
					AddLine();
				}
				return _lines;
			}
		}

		#endregion

		public string[][] Parse(string csvData)
		{
			var context = new ParserContext();

			// Handle both Windows and Mac line endings
			string[] lines = csvData.Split(new string[] { "\r\n", "\n" }, StringSplitOptions.RemoveEmptyEntries);

			ParserState currentState = ParserState.LineStartState;
			foreach (string next in lines)
			{
				foreach (char ch in next)
				{
					switch (ch)
					{
					case CommaCharacter:
						currentState = currentState.Comma(context);
						break;
					case QuoteCharacter:
						currentState = currentState.Quote(context);
						break;
					default:
						currentState = currentState.AnyChar(ch, context);
						break;
					}
				}
				currentState = currentState.EndOfLine(context);
			}
			List<string[]> allLines = context.GetAllLines();
			return allLines.ToArray();
		}
	}
}