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 *
 * OPC Foundation MIT License 1.00
 *
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 * obtaining a copy of this software and associated documentation
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#nullable enable

using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

namespace Opc.Ua.Client.Subscriptions.Fakes
{
    /// <summary>
    /// Hand-rolled fake for <see cref="IMessageAckQueue"/>. Records every
    /// invocation and lets tests override return behaviour via callback
    /// fields. Replaces <c>Mock&lt;IMessageAckQueue&gt;</c>.
    /// </summary>
    internal sealed class FakeMessageAckQueue : IMessageAckQueue
    {
        public List<SubscriptionAcknowledgement> QueuedAcks { get; } = [];
        public List<uint> CompletedSubscriptions { get; } = [];
        public int UpdateCalls { get; private set; }

        /// <summary>
        /// Optional override for <see cref="QueueAsync"/>. If null, returns
        /// completed.
        /// </summary>
        public Func<SubscriptionAcknowledgement, CancellationToken, ValueTask>? OnQueueAsync { get; set; }

        /// <summary>
        /// Optional override for <see cref="CompleteAsync"/>. If null,
        /// returns completed.
        /// </summary>
        public Func<uint, CancellationToken, ValueTask>? OnCompleteAsync { get; set; }

        public ValueTask QueueAsync(SubscriptionAcknowledgement ack,
            CancellationToken ct = default)
        {
            QueuedAcks.Add(ack);
            return OnQueueAsync?.Invoke(ack, ct) ?? default;
        }

        public ValueTask CompleteAsync(uint subscriptionId,
            CancellationToken ct = default)
        {
            CompletedSubscriptions.Add(subscriptionId);
            return OnCompleteAsync?.Invoke(subscriptionId, ct) ?? default;
        }

        /// <summary>
        /// Records the subscription ids dropped via
        /// <see cref="DropPendingForSubscription"/> so tests can assert
        /// stale-ack pruning happened during recovery.
        /// </summary>
        public List<uint> DroppedSubscriptions { get; } = [];

        public int DropPendingForSubscription(uint subscriptionId)
        {
            DroppedSubscriptions.Add(subscriptionId);
            return QueuedAcks.RemoveAll(
                ack => ack.SubscriptionId == subscriptionId);
        }

        public void Update()
        {
            UpdateCalls++;
        }

        /// <summary>
        /// Test-controlled value for the
        /// <see cref="IMessageAckQueue.PoolNotifications"/> setter the
        /// subscription dispatcher reads to decide whether to perform the
        /// pooled-notification reuse walk.
        /// </summary>
        public bool PoolNotifications { get; set; }
    }
}