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

namespace Larkdown.Parser.Lexer
{
	class BlockLexer
	{
		private IList<string> _lines;
		private IEnumerator<string> _enumerator;

		public BlockLexer(string source)
		{
			_lines = source.Split(new[] { "\n" }, 0);
			_enumerator = _lines.GetEnumerator();
		}

		public BlockToken NextToken()
		{
			if (!_enumerator.MoveNext())
			{
				return null;
			}

			var line = _enumerator.Current;
			var indent = 0;
			while (indent < line.Length && IsIndent(line[indent++])) { }

			if (indent > 0)
			{
				line = line.Substring(indent);
			}

			return new BlockToken(BlockTokenType.Line, indent, line);
		}

		private bool IsIndent(char c)
		{
			return c == ' ' || c == '\t';
		}
	}
}