using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DotnetStreams
{
	public class ListTextSource : ITextSource
	{
		private bool isEof;
		private readonly IEnumerable<string> source;
		private IEnumerator<string>? enumerator;
		//private string lastValue;
		private bool firstIsRead;
		private string nextLine;
		public ListTextSource(IEnumerable<string> source)
		{
			this.source = source;
			enumerator = null;
			firstIsRead = false;
			nextLine = string.Empty;
		}

		public virtual void Open()
		{
		}

		public virtual IEnumerable<string> ReadAll()
		{
			return source.AsEnumerable();
		}

		public virtual string Read()
		{
			if (enumerator == null)
				enumerator = source.GetEnumerator();

			string thisLine;
			if (!firstIsRead)
			{
				// Read the first, put it in the "last" buffer.
				isEof = !enumerator.MoveNext();
				nextLine = enumerator.Current;
				firstIsRead = true;
			}

			thisLine = nextLine;

			if (!isEof)
			{
				isEof = !enumerator.MoveNext();
				if (!isEof)
					nextLine = enumerator.Current;
				else
					nextLine = string.Empty;

			}

			return thisLine;
		}

		public virtual bool Eof() => isEof;

		public virtual void Close()
		{
			enumerator = null;
			isEof = false;
		}
	}
}