using System;
using System.IO;
using System.Text;
using MQTTnet.Protocol;

namespace MQTTnet.Serializer
{
    public static class MqttPacketWriter
    {
        public static byte BuildFixedHeader(MqttControlPacketType packetType, byte flags = 0)
        {
            var fixedHeader = (int)packetType << 4;
            fixedHeader |= flags;
            return (byte)fixedHeader;
        }

        public static void Write(this Stream stream, ushort value)
        {
            var buffer = BitConverter.GetBytes(value);
            stream.WriteByte(buffer[1]);
            stream.WriteByte(buffer[0]);
        }

        public static void Write(this Stream stream, ByteWriter value)
        {
            if (value == null) throw new ArgumentNullException(nameof(value));

            stream.Write(value.Value);
        }

        public static void WriteWithLengthPrefix(this Stream stream, string value)
        {
            stream.WriteWithLengthPrefix(Encoding.UTF8.GetBytes(value ?? string.Empty));
        }

        public static void WriteWithLengthPrefix(this Stream stream, byte[] value)
        {
            var length = (ushort)value.Length;

            stream.Write(length);
            stream.Write(value, 0, length);
        }

        public static int EncodeRemainingLength(int length, MemoryStream stream)
        {
            // write the encoded remaining length right aligned on the 4 byte buffer

            if (length <= 0)
            {
                stream.Seek(3, SeekOrigin.Current);
                stream.WriteByte(0);
                return 1;
            }

            var buffer = new byte[4];
            var offset = 0;

            // Alorithm taken from http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html.
            var x = length;
            do
            {
                var encodedByte = x % 128;
                x = x / 128;
                if (x > 0)
                {
                    encodedByte = encodedByte | 128;
                }

                buffer[offset] = (byte)encodedByte;

                offset++;
            } while (x > 0);

            stream.Seek(4 - offset, SeekOrigin.Current);
            stream.Write(buffer, 0, offset);

            return offset;
        }
    }
}