using System.Text.Json;
using Akka.Actor;
using Akka.TestKit.Xunit2;
using Microsoft.Extensions.Logging.Abstractions;
using ZB.MOM.WW.ScadaBridge.Commons.Messages.DebugView;
using ZB.MOM.WW.ScadaBridge.Commons.Types.Flattening;
using ZB.MOM.WW.ScadaBridge.SiteRuntime.Actors;
using ZB.MOM.WW.ScadaBridge.SiteRuntime.Persistence;
using ZB.MOM.WW.ScadaBridge.SiteRuntime.Scripts;
using ZB.MOM.WW.ScadaBridge.TestSupport;

namespace ZB.MOM.WW.ScadaBridge.SiteRuntime.Tests.Actors;

/// <summary>
/// Review 2026-10-21 01/SR-P3: boot/failover compile warm was serial within a batch and
/// serialised across batches — batch k+1's compiles did not start until batch k's actors existed
/// AND the stagger delay had elapsed, so recovery time was the sum of every distinct compile plus
/// every delay, on one thread. The next batch is now warmed while the current batch's delay runs,
/// and a batch's distinct compile units are warmed in parallel.
/// </summary>
public class StartupBatchPrewarmTests : TestKit, IDisposable
{
    private readonly SiteStorageService _storage;
    private readonly SiteScriptCompileCache _compileCache = new();
    private readonly ScriptCompilationService _compilationService;
    private readonly SharedScriptLibrary _sharedScriptLibrary;
    private readonly TestLocalDb _localDb;

    /// <summary>Creates a temporary LocalDb-backed site store and an observable compile cache.</summary>
    public StartupBatchPrewarmTests()
    {
        _localDb = TestLocalDb.CreateTemp("startup-prewarm");
        _storage = new SiteStorageService(_localDb.Db, NullLogger<SiteStorageService>.Instance);
        _storage.InitializeAsync().GetAwaiter().GetResult();
        _compilationService = new ScriptCompilationService(
            NullLogger<ScriptCompilationService>.Instance, _compileCache);
        _sharedScriptLibrary = new SharedScriptLibrary(
            _compilationService, NullLogger<SharedScriptLibrary>.Instance);
    }

    /// <inheritdoc />
    void IDisposable.Dispose()
    {
        Shutdown();
        var path = _localDb.Path;
        _localDb.Dispose();
        TestLocalDb.DeleteFiles(path);
    }

    private static string ConfigWithScript(string name, int distinct) => JsonSerializer.Serialize(new FlattenedConfiguration
    {
        InstanceUniqueName = name,
        Attributes = [new ResolvedAttribute { CanonicalName = "A", Value = "1", DataType = "Int32" }],
        Scripts = [new ResolvedScript { CanonicalName = "S", Code = $"return {distinct} * 2;" }]
    });

    private async Task<bool> IsRunningAsync(IActorRef dm, string name)
    {
        var snapshot = await dm.Ask<DebugViewSnapshot>(
            new DebugSnapshotRequest(name, Guid.NewGuid().ToString("N")), TimeSpan.FromSeconds(5));
        return !snapshot.InstanceNotFound;
    }

    /// <summary>
    /// Two one-instance batches with a long stagger delay: batch 2's script is compiled while the
    /// delay after batch 1 is still running, i.e. BEFORE batch 2's Instance Actor exists. Before
    /// the fix its compile only started once the delay had elapsed.
    /// </summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [Fact]
    public async Task NextBatch_IsWarmedDuringTheStaggerDelay()
    {
        await _storage.StoreDeployedConfigAsync("B0", ConfigWithScript("B0", 1001), "d0", "r0", true);
        await _storage.StoreDeployedConfigAsync("B1", ConfigWithScript("B1", 1002), "d1", "r1", true);

        var dm = ActorOf(Props.Create(() => new DeploymentManagerActor(
            _storage, _compilationService, _sharedScriptLibrary, null,
            new SiteRuntimeOptions
            {
                StartupBatchSize = 1, StartupBatchDelayMs = 6000, InstanceSweepIntervalSeconds = 0
            },
            NullLogger<DeploymentManagerActor>.Instance,
            dclManager: null, healthCollector: null, serviceProvider: null,
            loggerFactory: null, configFetcher: null)));

        // Batch 1 is up...
        await AwaitAssertAsync(async () => Assert.True(await IsRunningAsync(dm, "B0") || await IsRunningAsync(dm, "B1")),
            TimeSpan.FromSeconds(20), TimeSpan.FromMilliseconds(50));

        // ...and both scripts are compiled while exactly one instance is running.
        await AwaitAssertAsync(() =>
        {
            Assert.True(_compileCache.Count >= 2, $"compile cache holds {_compileCache.Count} entries");
            return Task.CompletedTask;
        }, TimeSpan.FromSeconds(3), TimeSpan.FromMilliseconds(50));
        Assert.False(await IsRunningAsync(dm, "B0") && await IsRunningAsync(dm, "B1"),
            "the second batch was created early — the stagger delay must be unchanged");

        // The stagger itself is unchanged: batch 2 still starts after the delay.
        await AwaitAssertAsync(async () =>
            Assert.True(await IsRunningAsync(dm, "B0") && await IsRunningAsync(dm, "B1")),
            TimeSpan.FromSeconds(20), TimeSpan.FromMilliseconds(100));
    }
}