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UnusualDatabaseProgram.cs
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UnusualDatabaseProgram.cs
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using System.Buffers.Binary;
using System.Collections.Concurrent;
using System.Net;
using System.Text;
namespace protohackers;
public class UnusualDatabaseProgram : UdpServerBase
{
private readonly ConcurrentDictionary<byte[], byte[]> _data = new(new ArrayComparer());
private byte[] Version => "version=Ken's Key-Value Store 1.0"u8.ToArray();
private byte[] EmptyKey => "==="u8.ToArray();
protected override async Task ProcessDatagram(byte[] data, IPEndPoint endPoint)
{
if(data.Length > 1000) return;
int pos = 0;
for (int i = 0; i < data.Length; i++)
{
if (data[i] == '=')
{
pos = i;
break;
}
if (i == data.Length - 1)
{
pos = -1;
}
}
if (data.SequenceEqual("version"u8.ToArray()))
{
await SendAsync(Version, endPoint);
}
else if(data.Length == 0)
{
if (_data.TryGetValue(EmptyKey, out var value))
{
await SendAsync(Array.Empty<byte>().Concat(new[] { (byte)'=' }).Concat(value).ToArray(), endPoint);
}
}
else if (pos == -1)
{
if (_data.TryGetValue(data, out var value))
{
await SendAsync(data.Concat(new[] { (byte)'=' }).Concat(value).ToArray(), endPoint);
}
}
else if (pos == 0)
{
if (data.Length == 1)
{
_data.AddOrUpdate(EmptyKey, Array.Empty<byte>(),
(key, oldValue) => Array.Empty<byte>());
}
else
{
_data.AddOrUpdate(EmptyKey, data[1..],
(key, oldValue) => data[1..]);
}
}
else if(pos == data.Length - 1)
{
_data.AddOrUpdate(data[..^1], Array.Empty<byte>(),
(key, oldValue) => Array.Empty<byte>());
}
else
{
_data.AddOrUpdate(data[..pos], data[(pos + 1)..],
(key, oldValue) => data[(pos + 1)..]);
}
}
private class ArrayComparer : IEqualityComparer<byte[]>
{
public bool Equals(byte[]? x, byte[]? y)
{
return y != null && x != null && x.SequenceEqual(y);
}
public int GetHashCode(byte[] obj)
{
var md5 = System.Security.Cryptography.MD5.HashData(obj);
return BinaryPrimitives.ReadInt32LittleEndian(md5);
}
}
}