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

namespace DotnetStreams
{
	public class FileTextSource : ITextSource
	{
		protected FileStream? file;
		protected StreamReader? reader;
		protected string filename;

		public FileTextSource(string filename)
		{
			this.filename = filename;
			file = null;
			reader = null;
		}

		public virtual void Open()
		{
			file = new FileStream(filename, FileMode.Open, FileAccess.Read, FileShare.Read);
			reader = new StreamReader(file);
		}

		public virtual IEnumerable<string> ReadAll()
		{
			string? line = reader?.ReadLine();
			while (line != null)
			{
				yield return line;
				line = reader?.ReadLine();
			}
		}

		public virtual string Read()
		{
			if (!Eof())
				return reader?.ReadLine() ?? string.Empty;
			else
				return string.Empty;
		}

		public virtual bool Eof()
		{
			return reader?.EndOfStream ?? true;
		}

		public virtual void Close()
		{
			try
			{
				file?.Flush();
			}
			finally
			{
				try
				{
					file?.Close();
				}
				finally
				{
					file?.Dispose();
				}
			}
		}
	}
}