using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;
using System.Text.Json;

namespace MusicBridge.Agent.Network;

internal sealed record TrustedDevice(string Id, string Name, string TokenHash, DateTimeOffset CreatedAt);

internal sealed class IdentityStore : IDisposable
{
    private sealed record Identity(int Version, byte[] Certificate, TrustedDevice[] Devices);
    private readonly FileStream owner;
    private readonly string path;
    private Identity identity = null!;
    public X509Certificate2 Certificate { get; private set; } = null!;
    public IReadOnlyList<TrustedDevice> Devices => identity.Devices;
    public static string DefaultDirectory => Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "MusicBridge");

    public IdentityStore(string directory)
    {
        Directory.CreateDirectory(directory);
        path = Path.Combine(directory, "identity.dat");
        // Prevent two agents from racing the certificate or overwriting trusted devices.
        owner = new FileStream(Path.Combine(directory, "identity.lock"), FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.None);
        try
        {
            if (File.Exists(path))
            {
                if (new FileInfo(path).Length > 1024 * 1024) throw new InvalidDataException("Хранилище слишком большое.");
                var clear = UserProtection.Unprotect(File.ReadAllBytes(path));
                try { identity = JsonSerializer.Deserialize<Identity>(clear) ?? throw new InvalidDataException("Пустое хранилище."); }
                finally { CryptographicOperations.ZeroMemory(clear); }
                if (identity.Version != 1 || identity.Certificate is null || identity.Devices is null || identity.Devices.Length > 8
                    || identity.Devices.Any(d => d is null || !Guid.TryParseExact(d.Id, "N", out _) || string.IsNullOrWhiteSpace(d.Name)
                        || d.Name.Length > 64 || d.TokenHash is null || d.TokenHash.Length != 64 || !d.TokenHash.All(Uri.IsHexDigit))
                    || identity.Devices.Select(d => d.Id).Distinct().Count() != identity.Devices.Length)
                    throw new InvalidDataException("Неверный формат хранилища.");
                Certificate = X509CertificateLoader.LoadPkcs12(identity.Certificate, null);
                if (!Certificate.HasPrivateKey || Certificate.NotAfter.ToUniversalTime() <= DateTime.UtcNow)
                    throw new InvalidDataException("Сертификат недоступен или истёк. Хранилище сохранено без изменений.");
            }
            else
            {
                Certificate = AgentCertificate.Create();
                identity = new(1, Certificate.Export(X509ContentType.Pfx), []);
                Save(identity);
            }
        }
        catch
        {
            Certificate?.Dispose();
            if (identity?.Certificate is { } bytes) CryptographicOperations.ZeroMemory(bytes);
            owner.Dispose();
            throw;
        }
    }

    public void SaveDevices(TrustedDevice[] devices)
    {
        var updated = identity with { Devices = devices };
        Save(updated); // Commit to memory only after the protected file is safely replaced.
        identity = updated;
    }

    private void Save(Identity value)
    {
        var clear = JsonSerializer.SerializeToUtf8Bytes(value);
        byte[] encrypted;
        try { encrypted = UserProtection.Protect(clear); }
        finally { CryptographicOperations.ZeroMemory(clear); }
        var temporary = path + ".tmp";
        try
        {
            using (var file = new FileStream(temporary, FileMode.Create, FileAccess.Write, FileShare.None))
            {
                file.Write(encrypted);
                file.Flush(flushToDisk: true);
            }
            File.Move(temporary, path, overwrite: true);
        }
        finally { if (File.Exists(temporary)) File.Delete(temporary); }
    }

    public void Dispose()
    {
        Certificate.Dispose();
        CryptographicOperations.ZeroMemory(identity.Certificate);
        owner.Dispose();
    }
}