using System.Net;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Hosting.Server;
using Microsoft.AspNetCore.Hosting.Server.Features;
using Microsoft.AspNetCore.Server.Kestrel.Core;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using ZB.MOM.WW.LocalDb;
using ZB.MOM.WW.LocalDb.Replication;
using ZB.MOM.WW.ScadaBridge.Host;

namespace ZB.MOM.WW.ScadaBridge.IntegrationTests;

/// <summary>
/// Serializes the site-pair convergence tests against each other: each one stands up a real
/// Kestrel listener plus two SQLite files, and running them concurrently under CI
/// contention is a flakiness risk.
/// </summary>
[CollectionDefinition("LocalDbSitePairConvergence")]
public sealed class LocalDbSitePairConvergenceCollection;

/// <summary>
/// Two ScadaBridge site nodes replicating the consolidated site database over a REAL
/// loopback gRPC transport, through the REAL fail-closed auth interceptor.
/// </summary>
/// <remarks>
/// <para>
/// This is the test that answers the question Phase 1 exists to answer: does a site node
/// pair actually stop losing operation-tracking and site-event state? Everything upstream
/// of it — schema helpers, DI wiring, the interceptor — can be individually green while the
/// pair still fails to converge.
/// </para>
/// <para>
/// It uses <see cref="SiteLocalDbSetup.OnReady"/>, not a hand-written schema, so the tables,
/// their primary keys, and the registration ORDER under test are the ones the host actually
/// runs. A separate schema here would prove only that the test agrees with itself.
/// </para>
/// <para>
/// Offline: no docker, no external services. Loopback Kestrel with h2c.
/// </para>
/// </remarks>
[Collection("LocalDbSitePairConvergence")]
public sealed class LocalDbSitePairConvergenceTests : IAsyncLifetime
{
    private const string SharedApiKey = "site-pair-convergence-key";
    private static readonly TimeSpan ConvergeTimeout = TimeSpan.FromSeconds(30);

    private readonly string _pathA = Path.Combine(Path.GetTempPath(), $"sitepairA-{Guid.NewGuid():N}.db");
    private readonly string _pathB = Path.Combine(Path.GetTempPath(), $"sitepairB-{Guid.NewGuid():N}.db");

    // The databases are owned by the fixture, in their own providers, and registered into the
    // hosts as pre-constructed instances. MS.DI does not dispose instances it did not create,
    // so tearing a host down (the offline-peer scenario) leaves the databases intact and
    // writable — which is exactly what lets node A accumulate writes while B is down.
    private ServiceProvider _dbProviderA = null!;
    private ServiceProvider _dbProviderB = null!;

    private IHost? _serverHost;      // node B — passive
    private IHost? _initiatorHost;   // node A — dials the peer

    static LocalDbSitePairConvergenceTests() =>
        // Grpc.Net.Client dials the loopback server over HTTP/2 cleartext.
        AppContext.SetSwitch("System.Net.Http.SocketsHttpHandler.Http2UnencryptedSupport", true);

    private ILocalDb A => _dbProviderA.GetRequiredService<ILocalDb>();
    private ILocalDb B => _dbProviderB.GetRequiredService<ILocalDb>();

    public async Task InitializeAsync()
    {
        _dbProviderA = BuildDatabaseProvider(_pathA, "node-a");
        _dbProviderB = BuildDatabaseProvider(_pathB, "node-b");

        // Force construction (and therefore OnReady) before anything replicates.
        _ = A;
        _ = B;

        await StartPassiveAsync();
        await StartInitiatorAsync();
    }

    public async Task DisposeAsync()
    {
        await StopHostAsync(_initiatorHost);
        await StopHostAsync(_serverHost);
        await _dbProviderA.DisposeAsync();
        await _dbProviderB.DisposeAsync();

        Microsoft.Data.Sqlite.SqliteConnection.ClearAllPools();
        foreach (var path in new[] { _pathA, _pathB })
        {
            foreach (var suffix in new[] { "", "-wal", "-shm" })
            {
                try { File.Delete(path + suffix); } catch { /* best effort */ }
            }
        }
    }

    // ---- fixture internals ------------------------------------------------------------

    /// <summary>
    /// A provider owning one consolidated site database, initialized through the host's own
    /// <see cref="SiteLocalDbSetup.OnReady"/> — same schema, same registration order.
    /// </summary>
    private static ServiceProvider BuildDatabaseProvider(string path, string nodeName)
    {
        var config = new ConfigurationBuilder()
            .AddInMemoryCollection(new Dictionary<string, string?>
            {
                ["LocalDb:Path"] = path,
                ["ScadaBridge:Node:NodeName"] = nodeName,
                // Point the legacy migrator at paths that do not exist, so it no-ops rather
                // than picking up stray files from the test working directory.
                ["ScadaBridge:OperationTracking:ConnectionString"] =
                    $"Data Source={Path.Combine(Path.GetTempPath(), $"absent-{Guid.NewGuid():N}.db")}",
                ["ScadaBridge:SiteEventLog:DatabasePath"] =
                    Path.Combine(Path.GetTempPath(), $"absent-{Guid.NewGuid():N}.db"),
            })
            .Build();

        return new ServiceCollection()
            .AddZbLocalDb(config, db => SiteLocalDbSetup.OnReady(db, config))
            .BuildServiceProvider();
    }

    private static IConfiguration ReplicationConfig(string? peerAddress)
    {
        var values = new Dictionary<string, string?>
        {
            // Tight flush + bounded reconnect backoff so convergence is observable well
            // inside the poll deadline. The 60 s production default would let the doubling
            // backoff overrun it after a peer outage.
            ["LocalDb:Replication:FlushInterval"] = "00:00:00.050",
            ["LocalDb:Replication:ReconnectBackoffMax"] = "00:00:02",
            // Both nodes share one key — the interceptor is fail-closed, so a mismatch here
            // turns every scenario below red (verified by deliberately breaking it).
            ["LocalDb:Replication:ApiKey"] = SharedApiKey,
        };

        if (peerAddress is not null)
            values["LocalDb:Replication:PeerAddress"] = peerAddress;

        return new ConfigurationBuilder().AddInMemoryCollection(values).Build();
    }

    private async Task StartPassiveAsync()
    {
        var config = ReplicationConfig(peerAddress: null);

        _serverHost = await new HostBuilder()
            .ConfigureWebHost(web =>
            {
                web.UseKestrel(o =>
                    o.Listen(IPAddress.Loopback, 0, listen => listen.Protocols = HttpProtocols.Http2));
                web.ConfigureServices(services =>
                {
                    services.AddLogging();
                    services.AddRouting();
                    // The REAL interceptor, not a stand-in. If it rejected legitimate peer
                    // traffic, every scenario below would fail — which is the point.
                    services.AddGrpc(o => o.Interceptors.Add<LocalDbSyncAuthInterceptor>());
                    services.AddSingleton(B);
                    services.AddZbLocalDbReplication(config);
                });
                web.Configure(app =>
                {
                    app.UseRouting();
                    app.UseEndpoints(e => e.MapZbLocalDbSync());
                });
            })
            .StartAsync();
    }

    private async Task StartInitiatorAsync()
    {
        var config = ReplicationConfig(PassiveAddress());

        _initiatorHost = await new HostBuilder()
            .ConfigureServices(services =>
            {
                services.AddLogging();
                services.AddSingleton(A);
                services.AddZbLocalDbReplication(config);
            })
            .StartAsync();
    }

    private string PassiveAddress()
        => _serverHost!.Services.GetRequiredService<IServer>()
            .Features.Get<IServerAddressesFeature>()!.Addresses.Single();

    private static async Task StopHostAsync(IHost? host)
    {
        if (host is null) return;
        try { await host.StopAsync(TimeSpan.FromSeconds(5)); } catch { /* teardown */ }
        host.Dispose();
    }

    // ---- data helpers -----------------------------------------------------------------

    private static Task WriteTrackingAsync(ILocalDb db, string id, string status, string target)
        => db.ExecuteAsync(
            """
            INSERT INTO OperationTracking (
                TrackedOperationId, Kind, TargetSummary, Status, RetryCount,
                CreatedAtUtc, UpdatedAtUtc)
            VALUES (@id, 'ApiCallCached', @target, @status, 0, @now, @now)
            ON CONFLICT(TrackedOperationId) DO UPDATE SET
                Status = excluded.Status,
                TargetSummary = excluded.TargetSummary,
                UpdatedAtUtc = excluded.UpdatedAtUtc;
            """,
            new { id, status, target, now = DateTime.UtcNow.ToString("o") });

    private static Task WriteEventAsync(ILocalDb db, string id, string message)
        => db.ExecuteAsync(
            """
            INSERT INTO site_events (id, timestamp, event_type, severity, source, message)
            VALUES (@id, @ts, 'script', 'Info', 'convergence-test', @message);
            """,
            new { id, ts = DateTimeOffset.UtcNow.ToString("o"), message });

    private static async Task<string?> ReadTrackingStatusAsync(ILocalDb db, string id)
    {
        var rows = await db.QueryAsync(
            "SELECT Status FROM OperationTracking WHERE TrackedOperationId = @id",
            static r => r.GetString(0), new { id });
        return rows.Count == 0 ? null : rows[0];
    }

    private static Task<IReadOnlyList<string>> ReadEventIdsAsync(ILocalDb db)
        => db.QueryAsync("SELECT id FROM site_events ORDER BY id", static r => r.GetString(0));

    /// <summary>Polls <paramref name="condition"/> until true or the deadline passes.</summary>
    private static async Task WaitUntilAsync(Func<Task<bool>> condition, string because)
    {
        var deadline = DateTime.UtcNow + ConvergeTimeout;
        while (DateTime.UtcNow < deadline)
        {
            if (await condition()) return;
            await Task.Delay(50);
        }

        Assert.Fail($"Timed out after {ConvergeTimeout.TotalSeconds:0}s waiting for: {because}");
    }

    // ---- scenarios --------------------------------------------------------------------

    [Fact]
    public async Task TrackingRow_WrittenOnA_BecomesReadableOnB()
    {
        await WriteTrackingAsync(A, "op-a-1", "Submitted", "ERP.GetOrder");

        await WaitUntilAsync(
            async () => await ReadTrackingStatusAsync(B, "op-a-1") == "Submitted",
            "the tracking row written on node A to appear on node B");
    }

    [Fact]
    public async Task TrackingRow_WrittenOnB_BecomesReadableOnA()
    {
        // Replication is bidirectional even though only A dials: proving the passive node's
        // writes flow back is what makes a failover in EITHER direction safe.
        await WriteTrackingAsync(B, "op-b-1", "Submitted", "ERP.GetOrder");

        await WaitUntilAsync(
            async () => await ReadTrackingStatusAsync(A, "op-b-1") == "Submitted",
            "the tracking row written on node B to appear on node A");
    }

    [Fact]
    public async Task SameOperation_UpdatedOnBothNodes_ConvergesToOneWinner()
    {
        // Last-writer-wins on the primary key. The specific winner is not asserted — that is
        // the HLC's business — but the two nodes MUST agree, and must agree on a value one of
        // them actually wrote rather than a merge of both.
        await WriteTrackingAsync(A, "op-conflict", "Submitted", "ERP.GetOrder");
        await WaitUntilAsync(
            async () => await ReadTrackingStatusAsync(B, "op-conflict") is not null,
            "the conflicting row to exist on both nodes before it is updated");

        await WriteTrackingAsync(A, "op-conflict", "Delivered", "ERP.GetOrder");
        await WriteTrackingAsync(B, "op-conflict", "Parked", "ERP.GetOrder");

        await WaitUntilAsync(
            async () =>
            {
                var a = await ReadTrackingStatusAsync(A, "op-conflict");
                var b = await ReadTrackingStatusAsync(B, "op-conflict");
                return a is not null && a == b;
            },
            "both nodes to converge on one status for the contended operation");

        var winner = await ReadTrackingStatusAsync(A, "op-conflict");
        Assert.Contains(winner, new[] { "Delivered", "Parked" });
    }

    [Fact]
    public async Task EventsLoggedOnBothNodes_ConvergeToTheUnion_WithNoIdCollisions()
    {
        // The reason site_events moved to GUID ids. Under the old autoincrement scheme both
        // nodes would independently mint id=1, id=2, ... and last-writer-wins on the primary
        // key would silently DESTROY one node's events instead of merging them. The union
        // count is the assertion that catches that.
        var idsFromA = Enumerable.Range(0, 5).Select(_ => Guid.NewGuid().ToString("N")).ToList();
        var idsFromB = Enumerable.Range(0, 5).Select(_ => Guid.NewGuid().ToString("N")).ToList();

        foreach (var id in idsFromA) await WriteEventAsync(A, id, "from A");
        foreach (var id in idsFromB) await WriteEventAsync(B, id, "from B");

        var expected = idsFromA.Concat(idsFromB).OrderBy(x => x, StringComparer.Ordinal).ToList();

        await WaitUntilAsync(
            async () => (await ReadEventIdsAsync(A)).SequenceEqual(expected)
                        && (await ReadEventIdsAsync(B)).SequenceEqual(expected),
            "both nodes to hold the union of all 10 events");
    }

    [Fact]
    public async Task PeerOffline_ThenRejoins_CatchesUpOnEverythingItMissed()
    {
        // The failover case that motivates Phase 1: one node is down while the other keeps
        // working, and nothing written during the outage may be lost.
        await StopHostAsync(_serverHost);
        _serverHost = null;

        var idsDuringOutage = Enumerable.Range(0, 5).Select(_ => Guid.NewGuid().ToString("N")).ToList();
        foreach (var id in idsDuringOutage) await WriteEventAsync(A, id, "written while B was down");
        await WriteTrackingAsync(A, "op-during-outage", "Delivered", "ERP.GetOrder");

        // Node B's database survived the host teardown (pre-constructed instance), so this is
        // a genuine rejoin rather than a fresh node. It comes back on a NEW loopback port;
        // the initiator's channel factory re-reads the peer address on each reconnect.
        await StartPassiveAsync();
        await StopHostAsync(_initiatorHost);
        await StartInitiatorAsync();

        await WaitUntilAsync(
            async () =>
            {
                var events = await ReadEventIdsAsync(B);
                return idsDuringOutage.All(events.Contains)
                       && await ReadTrackingStatusAsync(B, "op-during-outage") == "Delivered";
            },
            "node B to catch up on everything written while it was offline");
    }
}