using Akka.Actor;
using Akka.TestKit;
using Akka.TestKit.Xunit2;
using Microsoft.Extensions.Logging.Abstractions;
using ScadaLink.Commons.Messages.Streaming;
using ScadaLink.Commons.Types.Flattening;
using ScadaLink.SiteRuntime.Actors;
using ScadaLink.SiteRuntime.Persistence;
using ScadaLink.SiteRuntime.Scripts;
using System.Reflection;
using System.Text.Json;

namespace ScadaLink.SiteRuntime.Tests.Actors;

/// <summary>
/// Regression coverage for SiteRuntime-017 — the Instance Actor must not hand its
/// own live mutable <c>_attributes</c> dictionary by reference into the
/// <see cref="ScriptActor"/> / <see cref="AlarmActor"/> constructors.
///
/// Each child constructor runs on the child's own mailbox thread and seeds itself
/// by enumerating the dictionary it was given. The Instance Actor concurrently
/// mutates <c>_attributes</c> in <c>HandleAttributeValueChanged</c> /
/// <c>HandleTagValueUpdate</c>. <see cref="Dictionary{TKey,TValue}"/> is not safe
/// for concurrent read/write: if a child enumerates the shared live dictionary
/// while the Instance Actor inserts into it, the child constructor throws
/// <see cref="InvalidOperationException"/> ("collection was modified") — surfacing
/// as <c>ActorInitializationException</c> and stopping the child.
///
/// The fix: <c>CreateChildActors</c> snapshots <c>_attributes</c> once on the
/// Instance Actor thread (<c>new Dictionary&lt;,&gt;(_attributes)</c>) and hands
/// each child that private copy. This test asserts the isolation contract
/// directly and deterministically: every child's seed dictionary must be a
/// distinct object from the Instance Actor's live <c>_attributes</c>, while still
/// carrying the same point-in-time contents.
/// </summary>
public class InstanceActorChildAttributeRaceTests : TestKit, IDisposable
{
    private readonly SiteStorageService _storage;
    private readonly ScriptCompilationService _compilationService;
    private readonly SharedScriptLibrary _sharedScriptLibrary;
    private readonly SiteRuntimeOptions _options;
    private readonly string _dbFile;

    public InstanceActorChildAttributeRaceTests()
    {
        _dbFile = Path.Combine(Path.GetTempPath(), $"instance-race-test-{Guid.NewGuid():N}.db");
        _storage = new SiteStorageService(
            $"Data Source={_dbFile}",
            NullLogger<SiteStorageService>.Instance);
        _storage.InitializeAsync().GetAwaiter().GetResult();
        _compilationService = new ScriptCompilationService(
            NullLogger<ScriptCompilationService>.Instance);
        _sharedScriptLibrary = new SharedScriptLibrary(
            _compilationService, NullLogger<SharedScriptLibrary>.Instance);
        _options = new SiteRuntimeOptions
        {
            MaxScriptCallDepth = 10,
            ScriptExecutionTimeoutSeconds = 30
        };
    }

    void IDisposable.Dispose()
    {
        Shutdown();
        try { File.Delete(_dbFile); } catch { /* cleanup */ }
    }

    private static FlattenedConfiguration BuildConfig(string instanceName)
        => new()
        {
            InstanceUniqueName = instanceName,
            Attributes =
            [
                new ResolvedAttribute { CanonicalName = "Temperature", Value = "98.6", DataType = "Double" },
                new ResolvedAttribute { CanonicalName = "Pressure", Value = "12", DataType = "Int32" },
                new ResolvedAttribute { CanonicalName = "Label", Value = "Main Pump", DataType = "String" }
            ],
            Scripts =
            [
                new ResolvedScript
                {
                    CanonicalName = "WorkerA", Code = "return 1;",
                    TriggerType = "ValueChange",
                    TriggerConfiguration = "{\"AttributeName\":\"Temperature\"}"
                },
                new ResolvedScript
                {
                    CanonicalName = "WorkerB", Code = "return 2;",
                    TriggerType = "ValueChange",
                    TriggerConfiguration = "{\"AttributeName\":\"Pressure\"}"
                }
            ],
            Alarms =
            [
                new ResolvedAlarm
                {
                    CanonicalName = "HighTemp",
                    TriggerType = "ValueMatch",
                    TriggerConfiguration = "{}",
                    PriorityLevel = 1
                }
            ]
        };

    /// <summary>Resolves the live actor instance behind a local <see cref="IActorRef"/>.</summary>
    private static object GetActorInstance(IActorRef actorRef)
    {
        var cell = ((ActorRefWithCell)actorRef).Underlying;
        // ActorCell exposes the actor instance via its internal Actor property.
        var actorProp = cell.GetType().GetProperty(
            "Actor", BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public);
        var instance = actorProp!.GetValue(cell);
        Assert.NotNull(instance);
        return instance!;
    }

    private static Dictionary<string, object?> GetPrivateAttributes(InstanceActor instance)
    {
        var field = typeof(InstanceActor).GetField(
            "_attributes", BindingFlags.Instance | BindingFlags.NonPublic);
        return (Dictionary<string, object?>)field!.GetValue(instance)!;
    }

    [Fact]
    public async Task ChildActors_AreSeededFromAnIsolatedCopy_NotTheLiveAttributesDictionary()
    {
        const string instanceName = "RacePump";
        var config = BuildConfig(instanceName);

        var testRef = ActorOfAsTestActorRef<InstanceActor>(
            Props.Create(() => new InstanceActor(
                instanceName,
                JsonSerializer.Serialize(config),
                _storage,
                _compilationService,
                _sharedScriptLibrary,
                null,
                _options,
                NullLogger<InstanceActor>.Instance)),
            "instance");

        var instanceActor = testRef.UnderlyingActor;
        var liveAttributes = GetPrivateAttributes(instanceActor);

        // Sanity: the children were created.
        Assert.Equal(2, instanceActor.ScriptActorCount);
        Assert.Equal(1, instanceActor.AlarmActorCount);

        // Every child Script Actor must have been seeded from a dictionary that
        // is NOT the Instance Actor's live _attributes field — otherwise the
        // child constructor would enumerate a dictionary the Instance Actor
        // mutates on another thread (SiteRuntime-017).
        foreach (var name in new[] { "WorkerA", "WorkerB" })
        {
            var child = await Sys.ActorSelection(testRef.Path / $"script-{name}")
                .ResolveOne(TimeSpan.FromSeconds(5));
            var scriptActor = (ScriptActor)GetActorInstance(child);

            Assert.NotNull(scriptActor.SeedAttributesReference);
            Assert.False(
                ReferenceEquals(scriptActor.SeedAttributesReference, liveAttributes),
                $"Script Actor '{name}' was seeded from the Instance Actor's live " +
                "_attributes dictionary by reference (SiteRuntime-017). It must be " +
                "given a private snapshot copy.");

            // The snapshot must still carry the same point-in-time contents.
            Assert.Equal(liveAttributes.Count, scriptActor.SeedAttributesReference!.Count);
            foreach (var kvp in liveAttributes)
            {
                Assert.True(scriptActor.SeedAttributesReference.ContainsKey(kvp.Key));
            }
        }

        // The Alarm Actor must likewise be seeded from an isolated copy.
        var alarmChild = await Sys.ActorSelection(testRef.Path / "alarm-HighTemp")
            .ResolveOne(TimeSpan.FromSeconds(5));
        var alarmActor = (AlarmActor)GetActorInstance(alarmChild);

        Assert.NotNull(alarmActor.SeedAttributesReference);
        Assert.False(
            ReferenceEquals(alarmActor.SeedAttributesReference, liveAttributes),
            "Alarm Actor 'HighTemp' was seeded from the Instance Actor's live " +
            "_attributes dictionary by reference (SiteRuntime-017). It must be " +
            "given a private snapshot copy.");
        Assert.Equal(liveAttributes.Count, alarmActor.SeedAttributesReference!.Count);
    }
}