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 * OPC Foundation MIT License 1.00
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using System;
using System.Collections.Generic;
using System.Threading;
using NUnit.Framework;
using Opc.Ua.Client.Subscriptions.Fakes;

#pragma warning disable CA2007, CA2000

namespace Opc.Ua.Client.Subscriptions.MonitoredItems
{
    /// <summary>
    /// Tests for the reactive-fallback path on
    /// <see cref="CompositeMonitoredItemCollection"/>: when a
    /// partition's
    /// <see cref="Subscription.OnPartitionCapReached"/>
    /// hook signals
    /// <see cref="StatusCodes.BadTooManyMonitoredItems"/>, the
    /// placement policy must mark the partition no-grow so
    /// subsequent <see cref="CompositeMonitoredItemCollection.TryAdd"/>
    /// calls fan out instead of re-targeting the same partition.
    /// </summary>
    [TestFixture]
    [Category("Client")]
    [Category("SubscriptionManager")]
    [Category("LogicalSubscription")]
    [SetCulture("en-us")]
    [SetUICulture("en-us")]
    public sealed class ReactiveFallbackTests
    {
        [Test]
        public void OnPartitionCapReachedMarksPartitionNoGrow()
        {
            FakeManagedSubscription primary = NewFake(1);
            FakeManagedSubscription secondary = NewFake(2);
            var policy = new PartitionPlacementPolicy(uint.MaxValue);
            int factoryCalls = 0;
            var partitions = new List<IManagedSubscription> { primary };
            Lock lockObj = new();
            var composite = new CompositeMonitoredItemCollection(
                partitions, lockObj, policy,
                () =>
                {
                    factoryCalls++;
                    return secondary;
                });

            // Until the reactive fallback fires the policy sees an
            // unbounded cap on the primary, so any TryAdd targets it.
            Assert.That(policy.IsNoGrow(primary), Is.False);

            // Simulate the server returning Bad_TooManyMonitoredItems
            // on the primary partition.
            composite.OnPartitionCapReached(primary);

            Assert.That(policy.IsNoGrow(primary), Is.True,
                "primary must be flagged no-grow after the reactive fallback");

            // Next placement decision must skip the primary and mint
            // a new partition via the factory.
            PlacementDecision decision = policy.Decide(
                new MonitoredItemOptions(),
                partitions);
            Assert.That(decision.RequiresNewPartition, Is.True,
                "primary is no-grow and is the only registered partition — " +
                "the policy must request a new partition");
        }

        [Test]
        public void OnPartitionCapReachedIsNoopForSinglePartitionFastPath()
        {
            // Fast path: composite has no policy / no factory. The
            // reactive fallback hook degrades to a no-op so callers
            // can wire it unconditionally.
            FakeManagedSubscription primary = NewFake(1);
            var composite = new CompositeMonitoredItemCollection(
                [primary],
                new Lock());

            Assert.DoesNotThrow(() => composite.OnPartitionCapReached(primary));
        }

        [Test]
        public void OnPartitionCapReachedThrowsOnNull()
        {
            FakeManagedSubscription primary = NewFake(1);
            var policy = new PartitionPlacementPolicy(uint.MaxValue);
            var composite = new CompositeMonitoredItemCollection(
                [primary],
                new Lock(),
                policy,
                () => NewFake(2));

            Assert.That(() => composite.OnPartitionCapReached(null!),
                Throws.TypeOf<ArgumentNullException>());
        }

        private static FakeManagedSubscription NewFake(uint id)
        {
            return new FakeManagedSubscription
            {
                Id = id,
                Created = true
            };
        }
    }
}