using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging.Abstractions;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Configuration;
using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
using ZB.MOM.WW.OtOpcUa.Server.Hosting;
using ZB.MOM.WW.OtOpcUa.Server.Redundancy;

namespace ZB.MOM.WW.OtOpcUa.Server.Tests;

/// <summary>
///     Unit tests for <see cref="GenerationRefreshHostedService"/>. Exercises the
///     lease-around-refresh semantics via a stub generation-query delegate — the real
///     DB path is exercised end-to-end by the Phase 6.3 compliance script.
/// </summary>
[Trait("Category", "Unit")]
public sealed class GenerationRefreshHostedServiceTests : IDisposable
{
    private readonly OtOpcUaConfigDbContext _db;
    private readonly IDbContextFactory<OtOpcUaConfigDbContext> _dbFactory;

    public GenerationRefreshHostedServiceTests()
    {
        var opts = new DbContextOptionsBuilder<OtOpcUaConfigDbContext>()
            .UseInMemoryDatabase($"gen-refresh-{Guid.NewGuid():N}")
            .Options;
        _db = new OtOpcUaConfigDbContext(opts);
        _dbFactory = new DbContextFactory(opts);
    }

    public void Dispose() => _db.Dispose();

    [Fact]
    public async Task First_tick_applies_current_generation_and_closes_the_lease()
    {
        var coordinator = await SeedCoordinatorAsync();
        var leases = new ApplyLeaseRegistry();
        var service = NewService(coordinator, leases, currentGeneration: () => 42);

        leases.IsApplyInProgress.ShouldBeFalse("no lease before first tick");
        await service.TickAsync(CancellationToken.None);

        service.LastAppliedGenerationId.ShouldBe(42);
        service.TickCount.ShouldBe(1);
        service.RefreshCount.ShouldBe(1);
        leases.IsApplyInProgress.ShouldBeFalse("lease must be disposed after the apply window");
    }

    [Fact]
    public async Task Subsequent_tick_with_same_generation_is_a_no_op()
    {
        var coordinator = await SeedCoordinatorAsync();
        var leases = new ApplyLeaseRegistry();
        var service = NewService(coordinator, leases, currentGeneration: () => 42);

        await service.TickAsync(CancellationToken.None);
        await service.TickAsync(CancellationToken.None);

        service.TickCount.ShouldBe(2);
        service.RefreshCount.ShouldBe(1, "second identical tick must skip the refresh");
        leases.IsApplyInProgress.ShouldBeFalse();
    }

    [Fact]
    public async Task Generation_change_triggers_new_refresh()
    {
        var coordinator = await SeedCoordinatorAsync();
        var leases = new ApplyLeaseRegistry();
        var current = 42L;
        var service = NewService(coordinator, leases, currentGeneration: () => current);

        await service.TickAsync(CancellationToken.None);
        current = 43L;
        await service.TickAsync(CancellationToken.None);

        service.LastAppliedGenerationId.ShouldBe(43);
        service.RefreshCount.ShouldBe(2);
    }

    [Fact]
    public async Task Null_generation_means_no_published_config_yet_and_does_not_apply()
    {
        var coordinator = await SeedCoordinatorAsync();
        var leases = new ApplyLeaseRegistry();
        var service = NewService(coordinator, leases, currentGeneration: () => null);

        await service.TickAsync(CancellationToken.None);

        service.LastAppliedGenerationId.ShouldBeNull();
        service.RefreshCount.ShouldBe(0);
        service.TickCount.ShouldBe(1);
    }

    [Fact]
    public async Task Lease_is_opened_during_the_refresh_window()
    {
        // Drive a query delegate that *also* observes lease state mid-call: the delegate
        // fires before BeginApplyLease, so it sees IsApplyInProgress=false here, not
        // during the lease window. We observe the lease from the outside by checking
        // OpenLeaseCount on completion — if the `await using` mis-disposed we'd see 1
        // dangling. Cleanest assertion in a stub-only world.
        var coordinator = await SeedCoordinatorAsync();
        var leases = new ApplyLeaseRegistry();
        var service = NewService(coordinator, leases, currentGeneration: () => 42);

        await service.TickAsync(CancellationToken.None);

        leases.OpenLeaseCount.ShouldBe(0, "IAsyncDisposable dispose must fire regardless of outcome");
    }

    // Bug #12 fix — verifies the previously-missing wiring: applies and heartbeats both
    // emit sp_RegisterNodeGenerationApplied so Admin UI Fleet status + Redundancy LastSeenAt
    // surface live state.

    [Fact]
    public async Task First_apply_reports_Applied_status_to_central_db()
    {
        var coordinator = await SeedCoordinatorAsync();
        var leases = new ApplyLeaseRegistry();
        var calls = new List<(long Gen, NodeApplyStatus Status, string? Error)>();
        var service = NewService(coordinator, leases, currentGeneration: () => 42, registerCalls: calls);

        await service.TickAsync(CancellationToken.None);

        calls.Count.ShouldBe(1, "exactly one register call per apply window");
        calls[0].Gen.ShouldBe(42);
        calls[0].Status.ShouldBe(NodeApplyStatus.Applied);
        calls[0].Error.ShouldBeNull();
    }

    [Fact]
    public async Task No_change_tick_heartbeats_with_Applied_status()
    {
        var coordinator = await SeedCoordinatorAsync();
        var leases = new ApplyLeaseRegistry();
        var calls = new List<(long Gen, NodeApplyStatus Status, string? Error)>();
        var service = NewService(coordinator, leases, currentGeneration: () => 42, registerCalls: calls);

        await service.TickAsync(CancellationToken.None); // initial apply
        await service.TickAsync(CancellationToken.None); // no-change heartbeat
        await service.TickAsync(CancellationToken.None); // no-change heartbeat

        calls.Count.ShouldBe(3, "one apply call + two heartbeat calls");
        calls.ShouldAllBe(c => c.Gen == 42 && c.Status == NodeApplyStatus.Applied && c.Error == null);
    }

    [Fact]
    public async Task Register_call_failure_does_not_break_apply_or_block_subsequent_ticks()
    {
        var coordinator = await SeedCoordinatorAsync();
        var leases = new ApplyLeaseRegistry();
        var registerCallCount = 0;
        var service = new GenerationRefreshHostedService(
            new NodeOptions { NodeId = "A", ClusterId = "c1", ConfigDbConnectionString = "unused" },
            leases, coordinator, NullLogger<GenerationRefreshHostedService>.Instance,
            tickInterval: TimeSpan.FromSeconds(1),
            currentGenerationQuery: _ => Task.FromResult<long?>(42),
            registerAppliedAsync: (gen, status, err, ct) =>
            {
                registerCallCount++;
                throw new InvalidOperationException("simulated DB outage during register");
            });

        await service.TickAsync(CancellationToken.None); // apply succeeds, register throws
        await service.TickAsync(CancellationToken.None); // heartbeat throws

        registerCallCount.ShouldBe(2, "both register attempts must run");
        service.LastAppliedGenerationId.ShouldBe(42, "register failure must not roll back the cursor");
    }

    // ---- fixture helpers ---------------------------------------------------

    private async Task<RedundancyCoordinator> SeedCoordinatorAsync()
    {
        _db.ServerClusters.Add(new ServerCluster
        {
            ClusterId = "c1", Name = "W", Enterprise = "zb", Site = "w",
            RedundancyMode = RedundancyMode.None, CreatedBy = "test",
        });
        _db.ClusterNodes.Add(new ClusterNode
        {
            NodeId = "A", ClusterId = "c1",
            RedundancyRole = RedundancyRole.Primary, Host = "a",
            ApplicationUri = "urn:A", CreatedBy = "test",
        });
        await _db.SaveChangesAsync();

        var coordinator = new RedundancyCoordinator(
            _dbFactory, NullLogger<RedundancyCoordinator>.Instance, "A", "c1");
        await coordinator.InitializeAsync(CancellationToken.None);
        return coordinator;
    }

    private static GenerationRefreshHostedService NewService(
        RedundancyCoordinator coordinator,
        ApplyLeaseRegistry leases,
        Func<long?> currentGeneration,
        List<(long Gen, NodeApplyStatus Status, string? Error)>? registerCalls = null) =>
        new(new NodeOptions { NodeId = "A", ClusterId = "c1", ConfigDbConnectionString = "unused" },
            leases, coordinator, NullLogger<GenerationRefreshHostedService>.Instance,
            tickInterval: TimeSpan.FromSeconds(1),
            currentGenerationQuery: _ => Task.FromResult(currentGeneration()),
            registerAppliedAsync: registerCalls is null
                ? (_, _, _, _) => Task.CompletedTask
                : (gen, status, err, _) => { registerCalls.Add((gen, status, err)); return Task.CompletedTask; });

    private sealed class DbContextFactory(DbContextOptions<OtOpcUaConfigDbContext> options)
        : IDbContextFactory<OtOpcUaConfigDbContext>
    {
        public OtOpcUaConfigDbContext CreateDbContext() => new(options);
    }
}