﻿/*
 * 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) => ProtoBuf.Serializer.Deserialize<T>(sequence);

    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();
    }
}