using GatewayKeepalive.Core;

namespace GatewayKeepalive.Tests;

internal sealed class CheckFailedException(string message, Exception? inner = null) : Exception(message, inner);

internal static class Check
{
    public static void True(bool condition, string message)
    {
        if (!condition) throw new CheckFailedException(message);
    }

    public static void False(bool condition, string message) => True(!condition, message);

    public static void Equal<T>(T expected, T actual, string message)
    {
        if (!EqualityComparer<T>.Default.Equals(expected, actual))
            throw new CheckFailedException($"{message} (expected: {expected}, actual: {actual})");
    }

    public static void Contains(string expected, string actual, string message)
    {
        if (!actual.Contains(expected, StringComparison.Ordinal))
            throw new CheckFailedException($"{message} (missing: {expected}, actual: {actual})");
    }

    public static void SequenceEqual<T>(IEnumerable<T> expected, IEnumerable<T> actual, string message)
    {
        var left = expected.ToArray();
        var right = actual.ToArray();
        if (!left.SequenceEqual(right))
            throw new CheckFailedException($"{message} (expected: [{string.Join(", ", left)}], actual: [{string.Join(", ", right)}])");
    }

    public static TException Throws<TException>(Action action, string message) where TException : Exception
    {
        try { action(); }
        catch (TException exception) { return exception; }
        catch (Exception exception) { throw new CheckFailedException($"{message}: expected {typeof(TException).Name}, got {exception.GetType().Name}: {exception.Message}", exception); }
        throw new CheckFailedException($"{message}: expected {typeof(TException).Name}, but no exception was thrown");
    }

    public static async Task<TException> ThrowsAsync<TException>(Func<Task> action, string message) where TException : Exception
    {
        try { await action(); }
        catch (TException exception) { return exception; }
        catch (Exception exception) { throw new CheckFailedException($"{message}: expected {typeof(TException).Name}, got {exception.GetType().Name}: {exception.Message}", exception); }
        throw new CheckFailedException($"{message}: expected {typeof(TException).Name}, but no exception was thrown");
    }

    public static async Task<Exception> ThrowsAnyAsync(Func<Task> action, string message)
    {
        try { await action(); }
        catch (Exception exception) { return exception; }
        throw new CheckFailedException($"{message}: expected an exception, but no exception was thrown");
    }
}

internal sealed class ManualTimeProvider : TimeProvider
{
    private DateTimeOffset _utcNow = new(2026, 1, 1, 0, 0, 0, TimeSpan.Zero);
    private long _timestamp;

    public override DateTimeOffset GetUtcNow() => _utcNow;
    public override long GetTimestamp() => _timestamp;
    public override long TimestampFrequency => TimeSpan.TicksPerSecond;

    public void Advance(TimeSpan amount)
    {
        if (amount < TimeSpan.Zero) throw new ArgumentOutOfRangeException(nameof(amount));
        _utcNow += amount;
        _timestamp += amount.Ticks;
    }

    public void AdvanceSeconds(int seconds) => Advance(TimeSpan.FromSeconds(seconds));
}

internal sealed class TempDirectory : IDisposable
{
    public TempDirectory()
    {
        // The test host may not be allowed to create siblings in the system temp root.
        // Keep disposable state beside the test binary; it is still outside the product data paths.
        DirectoryPath = Path.Combine(AppContext.BaseDirectory, "test-temp", Guid.NewGuid().ToString("N"));
        Directory.CreateDirectory(DirectoryPath);
    }

    public string DirectoryPath { get; }

    public void Dispose()
    {
        if (Directory.Exists(DirectoryPath)) Directory.Delete(DirectoryPath, recursive: true);
    }
}

internal sealed record BackendWrite(string Operation, string Target);

internal sealed class FakeBackend(NetworkSnapshot initial) : INetworkBackend
{
    public bool IsAdministrator { get; set; } = true;
    public NetworkSnapshot Current { get; set; } = initial;
    public List<BackendWrite> Writes { get; } = [];
    public int CaptureCount { get; private set; }
    public Func<Guid, CancellationToken, Task<NetworkSnapshot>>? CaptureBehavior { get; set; }
    public Func<NetworkSnapshot, Task>? RouteWriteBehavior { get; set; }
    public Func<DnsConfiguration, Task>? DnsWriteBehavior { get; set; }

    public Task<IReadOnlyList<AdapterInfo>> ListAdaptersAsync(CancellationToken cancellationToken)
    {
        cancellationToken.ThrowIfCancellationRequested();
        return Task.FromResult<IReadOnlyList<AdapterInfo>>([Current.Adapter]);
    }

    public async Task<NetworkSnapshot> CaptureAsync(Guid adapterId, CancellationToken cancellationToken)
    {
        cancellationToken.ThrowIfCancellationRequested();
        CaptureCount++;
        Check.Equal(Current.Adapter.Id, adapterId, "The service captured an unexpected adapter");
        return CaptureBehavior is null
            ? Current
            : await CaptureBehavior(adapterId, cancellationToken);
    }

    public async Task WriteRoutesAsync(NetworkSnapshot desired, CancellationToken cancellationToken)
    {
        cancellationToken.ThrowIfCancellationRequested();
        Writes.Add(new("route", desired.Gateway ?? "<empty>"));
        if (RouteWriteBehavior is not null) await RouteWriteBehavior(desired);
        else ApplyRoutes(desired);
    }

    public async Task WriteDnsAsync(Guid adapterId, DnsConfiguration desired, CancellationToken cancellationToken)
    {
        cancellationToken.ThrowIfCancellationRequested();
        Check.Equal(Current.Adapter.Id, adapterId, "The service wrote DNS for an unexpected adapter");
        var target = desired.Automatic ? "auto" : string.Join(",", desired.Servers);
        Writes.Add(new("dns", target));
        if (DnsWriteBehavior is not null) await DnsWriteBehavior(desired);
        else ApplyDns(desired);
    }

    public void ApplyRoutes(NetworkSnapshot desired) => Current = Current with { Routes = desired.Routes };

    public void ApplyDns(DnsConfiguration desired) => Current = Current with
    {
        Dns = desired,
        EffectiveDns = desired.Automatic ? [] : desired.Servers,
    };
}

internal sealed class FakeProbe : IHealthProbe
{
    public HealthReport Report { get; set; } = new([], ProxyHealthy: true, InternetHealthy: true, DateTimeOffset.UtcNow);
    public bool VerifyResult { get; set; } = true;
    public Exception? VerifyException { get; set; }
    public Func<AppSettings, NetworkSnapshot, CancellationToken, Task<HealthReport>>? CheckBehavior { get; set; }
    public int CheckCount { get; private set; }
    public int VerifyCount { get; private set; }
    public NetworkSnapshot? VerifiedSnapshot { get; private set; }
    public CancellationToken VerifyToken { get; private set; }

    public async Task<HealthReport> CheckAsync(AppSettings settings, NetworkSnapshot snapshot, CancellationToken cancellationToken)
    {
        cancellationToken.ThrowIfCancellationRequested();
        CheckCount++;
        return CheckBehavior is null
            ? Report with { CheckedAt = DateTimeOffset.UtcNow }
            : await CheckBehavior(settings, snapshot, cancellationToken);
    }

    public Task<bool> VerifyInternetAsync(AppSettings settings, NetworkSnapshot snapshot, CancellationToken cancellationToken)
    {
        VerifyCount++;
        VerifiedSnapshot = snapshot;
        VerifyToken = cancellationToken;
        if (VerifyException is not null) throw VerifyException;
        return Task.FromResult(VerifyResult);
    }
}

internal sealed class SwitchHarness : IDisposable
{
    public SwitchHarness(NetworkSnapshot initial, bool administrator = true)
    {
        Backend = new FakeBackend(initial) { IsAdministrator = administrator };
        Probe = new FakeProbe();
        Store = new JsonStore(Temp.DirectoryPath);
        Service = new SwitchService(Backend, Probe, Store, Logs.Add);
    }

    public TempDirectory Temp { get; } = new();
    public FakeBackend Backend { get; }
    public FakeProbe Probe { get; }
    public JsonStore Store { get; }
    public SwitchService Service { get; }
    public List<string> Logs { get; } = [];

    public void Dispose() => Temp.Dispose();
}

internal static class Fixtures
{
    public static readonly Guid AdapterId = Guid.Parse("2C64EAB9-27A7-45CC-8C26-9DC77C54A58B");

    public static AppSettings Settings() => new()
    {
        Configured = true,
        AdapterId = AdapterId,
        DirectGateway = "192.168.6.1",
        ProxyGateway = "192.168.6.2",
        ProxyDns = "192.168.6.2",
        DirectDnsAutomatic = true,
        UseSocks = true,
        SocksPort = 1070,
        TestHosts = ["probe.invalid"],
        RequiredHealthyTargets = 1,
        IntervalSeconds = 5,
        SuccessThreshold = 3,
        FailureThreshold = 3,
        RecoveryCooldownSeconds = 30,
        FailureCooldownSeconds = 5,
        ProbeTimeoutMs = 500,
        RoundTimeoutMs = 1000,
        Policy = ControlPolicy.Auto,
    };

    public static NetworkSnapshot Baseline(string fingerprint = "network-a")
    {
        var adapter = new AdapterInfo(
            AdapterId,
            7,
            "Offline test adapter",
            Up: true,
            Addresses: [new Ipv4Address("192.168.6.10", 24)],
            InterfaceMetric: 25,
            NetworkFingerprint: fingerprint);
        var route = new RouteEntry("192.168.6.1", 10, 0x1000, 7);
        return new NetworkSnapshot(adapter, [route], DnsConfiguration.Auto, ["192.168.6.1"], DateTimeOffset.UtcNow);
    }

    public static HealthReport Health(bool proxyHealthy, bool internetHealthy) =>
        new([], proxyHealthy, internetHealthy, DateTimeOffset.UtcNow);
}