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

namespace SocketHttpListener
{
    internal class WebSocketFrame : IEnumerable<byte>
    {
        #region Private Fields

        private byte[] _extPayloadLength;
        private Fin _fin;
        private Mask _mask;
        private byte[] _maskingKey;
        private Opcode _opcode;
        private PayloadData _payloadData;
        private byte _payloadLength;
        private Rsv _rsv1;
        private Rsv _rsv2;
        private Rsv _rsv3;

        #endregion

        #region Internal Fields

        internal static readonly byte[] EmptyUnmaskPingData;

        #endregion

        #region Static Constructor

        static WebSocketFrame()
        {
            EmptyUnmaskPingData = CreatePingFrame(Mask.Unmask).ToByteArray();
        }

        #endregion

        #region Private Constructors

        private WebSocketFrame()
        {
        }

        #endregion

        #region Internal Constructors

        internal WebSocketFrame(Opcode opcode, PayloadData payload)
            : this(Fin.Final, opcode, Mask.Mask, payload, false)
        {
        }

        internal WebSocketFrame(Opcode opcode, Mask mask, PayloadData payload)
            : this(Fin.Final, opcode, mask, payload, false)
        {
        }

        internal WebSocketFrame(Fin fin, Opcode opcode, Mask mask, PayloadData payload)
            : this(fin, opcode, mask, payload, false)
        {
        }

        internal WebSocketFrame(
          Fin fin, Opcode opcode, Mask mask, PayloadData payload, bool compressed)
        {
            _fin = fin;
            _rsv1 = isData(opcode) && compressed ? Rsv.On : Rsv.Off;
            _rsv2 = Rsv.Off;
            _rsv3 = Rsv.Off;
            _opcode = opcode;
            _mask = mask;

            var len = payload.Length;
            if (len < 126)
            {
                _payloadLength = (byte)len;
                _extPayloadLength = new byte[0];
            }
            else if (len < 0x010000)
            {
                _payloadLength = (byte)126;
                _extPayloadLength = ((ushort)len).ToByteArrayInternally(ByteOrder.Big);
            }
            else
            {
                _payloadLength = (byte)127;
                _extPayloadLength = len.ToByteArrayInternally(ByteOrder.Big);
            }

            if (mask == Mask.Mask)
            {
                _maskingKey = createMaskingKey();
                payload.Mask(_maskingKey);
            }
            else
            {
                _maskingKey = new byte[0];
            }

            _payloadData = payload;
        }

        #endregion

        #region Public Properties

        public byte[] ExtendedPayloadLength => _extPayloadLength;

        public Fin Fin => _fin;

        public bool IsBinary => _opcode == Opcode.Binary;

        public bool IsClose => _opcode == Opcode.Close;

        public bool IsCompressed => _rsv1 == Rsv.On;

        public bool IsContinuation => _opcode == Opcode.Cont;

        public bool IsControl => _opcode == Opcode.Close || _opcode == Opcode.Ping || _opcode == Opcode.Pong;

        public bool IsData => _opcode == Opcode.Binary || _opcode == Opcode.Text;

        public bool IsFinal => _fin == Fin.Final;

        public bool IsFragmented => _fin == Fin.More || _opcode == Opcode.Cont;

        public bool IsMasked => _mask == Mask.Mask;

        public bool IsPerMessageCompressed => (_opcode == Opcode.Binary || _opcode == Opcode.Text) && _rsv1 == Rsv.On;

        public bool IsPing => _opcode == Opcode.Ping;

        public bool IsPong => _opcode == Opcode.Pong;

        public bool IsText => _opcode == Opcode.Text;

        public ulong Length => 2 + (ulong)(_extPayloadLength.Length + _maskingKey.Length) + _payloadData.Length;

        public Mask Mask => _mask;

        public byte[] MaskingKey => _maskingKey;

        public Opcode Opcode => _opcode;

        public PayloadData PayloadData => _payloadData;

        public byte PayloadLength => _payloadLength;

        public Rsv Rsv1 => _rsv1;

        public Rsv Rsv2 => _rsv2;

        public Rsv Rsv3 => _rsv3;

        #endregion

        #region Private Methods

        private byte[] createMaskingKey()
        {
            var key = new byte[4];
            var rand = new Random();
            rand.NextBytes(key);

            return key;
        }

        private static bool isControl(Opcode opcode)
        {
            return opcode == Opcode.Close || opcode == Opcode.Ping || opcode == Opcode.Pong;
        }

        private static bool isData(Opcode opcode)
        {
            return opcode == Opcode.Text || opcode == Opcode.Binary;
        }

        private static async Task<WebSocketFrame> ReadAsync(byte[] header, Stream stream, bool unmask)
        {
            /* Header */

            // FIN
            var fin = (header[0] & 0x80) == 0x80 ? Fin.Final : Fin.More;
            // RSV1
            var rsv1 = (header[0] & 0x40) == 0x40 ? Rsv.On : Rsv.Off;
            // RSV2
            var rsv2 = (header[0] & 0x20) == 0x20 ? Rsv.On : Rsv.Off;
            // RSV3
            var rsv3 = (header[0] & 0x10) == 0x10 ? Rsv.On : Rsv.Off;
            // Opcode
            var opcode = (Opcode)(header[0] & 0x0f);
            // MASK
            var mask = (header[1] & 0x80) == 0x80 ? Mask.Mask : Mask.Unmask;
            // Payload Length
            var payloadLen = (byte)(header[1] & 0x7f);

            // Check if correct frame.
            var incorrect = isControl(opcode) && fin == Fin.More
                            ? "A control frame is fragmented."
                            : !isData(opcode) && rsv1 == Rsv.On
                              ? "A non data frame is compressed."
                              : null;

            if (incorrect != null)
                throw new WebSocketException(CloseStatusCode.IncorrectData, incorrect);

            // Check if consistent frame.
            if (isControl(opcode) && payloadLen > 125)
                throw new WebSocketException(
                  CloseStatusCode.InconsistentData,
                  "The length of payload data of a control frame is greater than 125 bytes.");

            var frame = new WebSocketFrame();
            frame._fin = fin;
            frame._rsv1 = rsv1;
            frame._rsv2 = rsv2;
            frame._rsv3 = rsv3;
            frame._opcode = opcode;
            frame._mask = mask;
            frame._payloadLength = payloadLen;

            /* Extended Payload Length */

            var size = payloadLen < 126
                       ? 0
                       : payloadLen == 126
                         ? 2
                         : 8;

            var extPayloadLen = size > 0 ? await stream.ReadBytesAsync(size).ConfigureAwait(false) : Array.Empty<byte>();
            if (size > 0 && extPayloadLen.Length != size)
                throw new WebSocketException(
                  "The 'Extended Payload Length' of a frame cannot be read from the data source.");

            frame._extPayloadLength = extPayloadLen;

            /* Masking Key */

            var masked = mask == Mask.Mask;
            var maskingKey = masked ? await stream.ReadBytesAsync(4).ConfigureAwait(false) : Array.Empty<byte>();
            if (masked && maskingKey.Length != 4)
                throw new WebSocketException(
                  "The 'Masking Key' of a frame cannot be read from the data source.");

            frame._maskingKey = maskingKey;

            /* Payload Data */

            ulong len = payloadLen < 126
                        ? payloadLen
                        : payloadLen == 126
                          ? extPayloadLen.ToUInt16(ByteOrder.Big)
                          : extPayloadLen.ToUInt64(ByteOrder.Big);

            byte[] data = null;
            if (len > 0)
            {
                // Check if allowable payload data length.
                if (payloadLen > 126 && len > PayloadData.MaxLength)
                    throw new WebSocketException(
                      CloseStatusCode.TooBig,
                      "The length of 'Payload Data' of a frame is greater than the allowable length.");

                data = payloadLen > 126
                       ? await stream.ReadBytesAsync((long)len, 1024).ConfigureAwait(false)
                       : await stream.ReadBytesAsync((int)len).ConfigureAwait(false);

                //if (data.LongLength != (long)len)
                //    throw new WebSocketException(
                //      "The 'Payload Data' of a frame cannot be read from the data source.");
            }
            else
            {
                data = Array.Empty<byte>();
            }

            var payload = new PayloadData(data, masked);
            if (masked && unmask)
            {
                payload.Mask(maskingKey);
                frame._mask = Mask.Unmask;
                frame._maskingKey = Array.Empty<byte>();
            }

            frame._payloadData = payload;
            return frame;
        }

        #endregion

        #region Internal Methods

        internal static WebSocketFrame CreateCloseFrame(Mask mask, byte[] data)
        {
            return new WebSocketFrame(Opcode.Close, mask, new PayloadData(data));
        }

        internal static WebSocketFrame CreateCloseFrame(Mask mask, PayloadData payload)
        {
            return new WebSocketFrame(Opcode.Close, mask, payload);
        }

        internal static WebSocketFrame CreateCloseFrame(Mask mask, CloseStatusCode code, string reason)
        {
            return new WebSocketFrame(
              Opcode.Close, mask, new PayloadData(((ushort)code).Append(reason)));
        }

        internal static WebSocketFrame CreatePingFrame(Mask mask)
        {
            return new WebSocketFrame(Opcode.Ping, mask, new PayloadData());
        }

        internal static WebSocketFrame CreatePingFrame(Mask mask, byte[] data)
        {
            return new WebSocketFrame(Opcode.Ping, mask, new PayloadData(data));
        }

        internal static WebSocketFrame CreatePongFrame(Mask mask, PayloadData payload)
        {
            return new WebSocketFrame(Opcode.Pong, mask, payload);
        }

        internal static WebSocketFrame CreateWebSocketFrame(
          Fin fin, Opcode opcode, Mask mask, byte[] data, bool compressed)
        {
            return new WebSocketFrame(fin, opcode, mask, new PayloadData(data), compressed);
        }

        internal static Task<WebSocketFrame> ReadAsync(Stream stream)
            => ReadAsync(stream, true);

        internal static async Task<WebSocketFrame> ReadAsync(Stream stream, bool unmask)
        {
            var header = await stream.ReadBytesAsync(2).ConfigureAwait(false);
            if (header.Length != 2)
            {
                throw new WebSocketException(
                  "The header part of a frame cannot be read from the data source.");
            }

            return await ReadAsync(header, stream, unmask).ConfigureAwait(false);
        }

        internal static async Task ReadAsync(
          Stream stream, bool unmask, Action<WebSocketFrame> completed, Action<Exception> error)
        {
            try
            {
                var header = await stream.ReadBytesAsync(2).ConfigureAwait(false);
                if (header.Length != 2)
                {
                    throw new WebSocketException(
                      "The header part of a frame cannot be read from the data source.");
                }

                var frame = await ReadAsync(header, stream, unmask).ConfigureAwait(false);
                completed?.Invoke(frame);
            }
            catch (Exception ex)
            {
                error.Invoke(ex);
            }
        }

        #endregion

        #region Public Methods

        public IEnumerator<byte> GetEnumerator()
        {
            foreach (var b in ToByteArray())
                yield return b;
        }

        public void Print(bool dumped)
        {
            //Console.WriteLine(dumped ? dump(this) : print(this));
        }

        public byte[] ToByteArray()
        {
            using (var buff = new MemoryStream())
            {
                var header = (int)_fin;
                header = (header << 1) + (int)_rsv1;
                header = (header << 1) + (int)_rsv2;
                header = (header << 1) + (int)_rsv3;
                header = (header << 4) + (int)_opcode;
                header = (header << 1) + (int)_mask;
                header = (header << 7) + (int)_payloadLength;
                buff.Write(((ushort)header).ToByteArrayInternally(ByteOrder.Big), 0, 2);

                if (_payloadLength > 125)
                    buff.Write(_extPayloadLength, 0, _extPayloadLength.Length);

                if (_mask == Mask.Mask)
                    buff.Write(_maskingKey, 0, _maskingKey.Length);

                if (_payloadLength > 0)
                {
                    var payload = _payloadData.ToByteArray();
                    if (_payloadLength < 127)
                        buff.Write(payload, 0, payload.Length);
                    else
                        buff.WriteBytes(payload);
                }

                return buff.ToArray();
            }
        }

        public override string ToString()
        {
            return BitConverter.ToString(ToByteArray());
        }

        #endregion

        #region Explicitly Implemented Interface Members

        IEnumerator IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }

        #endregion
    }
}