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

namespace IrcTokens
{
    public class StatefulDecoder
    {
        private byte[] _buffer;
        private Encoding _encoding;
        private Encoding _fallback;

        public StatefulDecoder()
        {
            Clear();
        }

        public Encoding Encoding
        {
            get => _encoding ?? Encoding.GetEncoding(Encoding.UTF8.CodePage, EncoderFallback.ExceptionFallback,
                DecoderFallback.ExceptionFallback);
            set
            {
                if (value != null)
                    _encoding = Encoding.GetEncoding(value.CodePage, EncoderFallback.ExceptionFallback,
                        DecoderFallback.ReplacementFallback);
            }
        }

        public Encoding Fallback
        {
            get => _fallback ?? Encoding.GetEncoding(Encoding.GetEncoding("iso-8859-1").CodePage,
                EncoderFallback.ExceptionFallback, DecoderFallback.ExceptionFallback);
            set
            {
                if (value != null)
                    _fallback = Encoding.GetEncoding(value.CodePage, EncoderFallback.ReplacementFallback,
                        DecoderFallback.ReplacementFallback);
            }
        }

        public string Pending => Encoding.GetString(_buffer);

        public void Clear()
        {
            _buffer = Array.Empty<byte>();
        }

        public List<Line> Push(string data)
        {
            var bytes = Encoding.GetBytes(data);
            return Push(bytes, bytes.Length);
        }

        public List<Line> Push(byte[] data, int bytesReceived)
        {
            if (data == null) return null;

            _buffer = _buffer == null ? Array.Empty<byte>() : _buffer.Concat(data.Take(bytesReceived)).ToArray();

            var listLines = _buffer.Split((byte) '\n').Select(l => l.Trim((byte) '\r')).ToList();
            _buffer = listLines.LastOrDefault() ?? Array.Empty<byte>();

            var decodeLines = new List<Line>();
            foreach (var line in listLines.SkipLast(1).Select(l => l.ToArray()))
                try
                {
                    decodeLines.Add(new Line(Encoding.GetString(line)));
                }
                catch (DecoderFallbackException)
                {
                    decodeLines.Add(new Line(Fallback.GetString(line)));
                }

            return decodeLines;
        }
    }
}