using System.Collections.Generic;

internal class SLIP {
    private const byte SLIP_EOF = 0xC0;
    private const byte SLIP_ESC = 0xDB;
    private const byte SLIP_ESC_EOF = 0xDC;
    private const byte SLIP_ESC_ESC = 0xDD;

    internal class Frame {
        public byte[] Data { get; private set; }

        public Frame(byte[] data)
        {
            Data = data;
        }
    }

    private List<byte> _pending = new List<byte>();
    private bool _escaped = false;
    private bool _valid = true;
    private readonly object _sync = new object();

    public List<Frame> Consume(byte[] data)
    {
        lock (_sync) {
            var frames = new List<Frame>();

            foreach (var value in data) {
                if (_escaped) {
                    switch (value) {
                        case SLIP_ESC_EOF: {
                                _pending.Add(SLIP_EOF);
                                break;
                            }
                        case SLIP_ESC_ESC: {
                                _pending.Add(SLIP_ESC);
                                break;
                            }
                        default: {
                                _valid = false;
                                _pending.Clear();
                                break;
                            }
                    }

                    _escaped = false;
                } else {
                    switch (value) {
                        case SLIP_EOF: {
                                if (_valid) {
                                    var frame = _pending;
                                    frames.Add(new Frame(frame.ToArray()));
                                }
                                _pending = new List<byte>();
                                _valid = true;
                                break;
                            }
                        case SLIP_ESC: {
                                _escaped = true;
                                break;
                            }
                        default: {
                                if (_valid) {
                                    _pending.Add(value);
                                }
                                break;
                            }
                    }
                }
            }

            return frames;
        }
    }
}