﻿/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

namespace DotPulsar.Internal
{
    using PulsarApi;
    using System;
    using System.Buffers;
    using System.IO;

    public static class Serializer
    {
        public static T Deserialize<T>(ReadOnlySequence<byte> sequence)
        {
            //TODO Fix this when protobuf-net start supporting sequences or .NET supports creating a stream from a sequence
            using var ms = new MemoryStream(sequence.ToArray());
            return ProtoBuf.Serializer.Deserialize<T>(ms);
        }

        public static ReadOnlySequence<byte> Serialize(BaseCommand command)
        {
            var commandBytes = Serialize<BaseCommand>(command);
            var commandSizeBytes = ToBigEndianBytes((uint) commandBytes.Length);
            var totalSizeBytes = ToBigEndianBytes((uint) commandBytes.Length + 4);

            return new SequenceBuilder<byte>()
                .Append(totalSizeBytes)
                .Append(commandSizeBytes)
                .Append(commandBytes)
                .Build();
        }

        public static ReadOnlySequence<byte> Serialize(BaseCommand command, MessageMetadata metadata, ReadOnlySequence<byte> payload)
        {
            var commandBytes = Serialize<BaseCommand>(command);
            var commandSizeBytes = ToBigEndianBytes((uint) commandBytes.Length);

            var metadataBytes = Serialize(metadata);
            var metadataSizeBytes = ToBigEndianBytes((uint) metadataBytes.Length);

            var sb = new SequenceBuilder<byte>().Append(metadataSizeBytes).Append(metadataBytes).Append(payload);
            var checksum = Crc32C.Calculate(sb.Build());

            return sb.Prepend(ToBigEndianBytes(checksum))
                .Prepend(Constants.MagicNumber)
                .Prepend(commandBytes)
                .Prepend(commandSizeBytes)
                .Prepend(ToBigEndianBytes((uint) sb.Length))
                .Build();
        }

        public static byte[] ToBigEndianBytes(uint integer)
        {
            var union = new UIntUnion(integer);

            return BitConverter.IsLittleEndian
                ? new[] { union.B3, union.B2, union.B1, union.B0 }
                : new[] { union.B0, union.B1, union.B2, union.B3 };
        }

        private static byte[] Serialize<T>(T item)
        {
            using var ms = new MemoryStream();
            ProtoBuf.Serializer.Serialize(ms, item);
            return ms.ToArray();
        }
    }
}