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 *
 * OPC Foundation MIT License 1.00
 *
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// IDE0230: byte-array literals below are opaque binary test vectors, not text; a
// UTF-8 "..."u8 literal would misrepresent their intent, so keep the explicit byte arrays.
#pragma warning disable IDE0230 // Use UTF-8 string literal

// CA2007: tests run without a SynchronizationContext; ConfigureAwait(false)
// adds noise without a behavioural benefit. Disabled file-level for the suite.
#pragma warning disable CA2007

using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using NUnit.Framework;
using Opc.Ua.Redundancy;

namespace Opc.Ua.Server.Tests.Redundancy
{
    /// <summary>
    /// Unit tests for <see cref="InMemorySharedKeyValueStore"/>.
    /// </summary>
    [TestFixture]
    [Category("Distributed")]
    [Parallelizable(ParallelScope.All)]
    public class InMemorySharedKeyValueStoreTests
    {
        /// <summary>
        /// Verifies that an in-memory shared-store value can be retrieved after insertion.
        /// </summary>
        [Test]
        public async Task SetAndTryGetReturnsStoredValueAsync()
        {
            using var store = new InMemorySharedKeyValueStore();
            var payload = ByteString.From(new byte[] { 1, 2, 3 });

            await store.SetAsync("k1", payload).ConfigureAwait(false);
            (bool found, ByteString value) = await store.TryGetAsync("k1").ConfigureAwait(false);

            Assert.That(found, Is.True);
            Assert.That(value.ToArray(), Is.EqualTo(payload.ToArray()));
        }

        /// <summary>
        /// Verifies that reading a missing shared-store key returns false.
        /// </summary>
        [Test]
        public async Task TryGetMissingKeyReturnsFalseAsync()
        {
            using var store = new InMemorySharedKeyValueStore();

            (bool found, ByteString value) = await store.TryGetAsync("missing").ConfigureAwait(false);

            Assert.That(found, Is.False);
            Assert.That(value.IsNull, Is.True);
        }

        /// <summary>
        /// Verifies that compare-and-swap creates an entry when the key is absent.
        /// </summary>
        [Test]
        public async Task CompareAndSwapCreatesWhenAbsentAsync()
        {
            using var store = new InMemorySharedKeyValueStore();
            var value = ByteString.From(new byte[] { 9 });

            bool created = await store.CompareAndSwapAsync("k", default, value).ConfigureAwait(false);
            bool createdAgain = await store.CompareAndSwapAsync("k", default, value).ConfigureAwait(false);

            Assert.That(created, Is.True);
            Assert.That(createdAgain, Is.False, "second create-if-absent must fail because the key now exists");
        }

        /// <summary>
        /// Verifies that compare-and-swap replaces an entry when the expected value matches.
        /// </summary>
        [Test]
        public async Task CompareAndSwapSwapsWhenValueMatchesAsync()
        {
            using var store = new InMemorySharedKeyValueStore();
            var first = ByteString.From(new byte[] { 1 });
            var second = ByteString.From(new byte[] { 2 });
            await store.SetAsync("k", first).ConfigureAwait(false);

            bool swapped = await store.CompareAndSwapAsync("k", first, second).ConfigureAwait(false);
            (bool found, ByteString value) = await store.TryGetAsync("k").ConfigureAwait(false);

            Assert.That(swapped, Is.True);
            Assert.That(found, Is.True);
            Assert.That(value.ToArray(), Is.EqualTo(second.ToArray()));
        }

        /// <summary>
        /// Verifies that compare-and-swap deletes a matching entry when the replacement is null.
        /// </summary>
        [Test]
        public async Task CompareAndSwapDeletesWhenReplacementIsNullAsync()
        {
            using var store = new InMemorySharedKeyValueStore();
            var value = ByteString.From(new byte[] { 1 });
            await store.SetAsync("k", value).ConfigureAwait(false);

            bool deleted = await store.CompareAndSwapAsync(
                "k",
                value,
                default).ConfigureAwait(false);
            (bool found, _) = await store.TryGetAsync("k")
                .ConfigureAwait(false);

            Assert.That(deleted, Is.True);
            Assert.That(found, Is.False);
        }

        /// <summary>
        /// Verifies that compare-and-swap fails when the expected value does not match.
        /// </summary>
        [Test]
        public async Task CompareAndSwapFailsWhenValueMismatchAsync()
        {
            using var store = new InMemorySharedKeyValueStore();
            var actual = ByteString.From(new byte[] { 1 });
            var wrongExpected = ByteString.From(new byte[] { 7 });
            var desired = ByteString.From(new byte[] { 2 });
            await store.SetAsync("k", actual).ConfigureAwait(false);

            bool swapped = await store.CompareAndSwapAsync("k", wrongExpected, desired).ConfigureAwait(false);
            (bool found, ByteString value) = await store.TryGetAsync("k").ConfigureAwait(false);

            Assert.That(swapped, Is.False);
            Assert.That(found, Is.True);
            Assert.That(value.ToArray(), Is.EqualTo(actual.ToArray()), "value must be unchanged on a failed CAS");
        }

        /// <summary>
        /// Verifies that deletion removes the shared-store entry.
        /// </summary>
        [Test]
        public async Task DeleteRemovesKeyAsync()
        {
            using var store = new InMemorySharedKeyValueStore();
            await store.SetAsync("k", ByteString.From(new byte[] { 1 })).ConfigureAwait(false);

            bool deleted = await store.DeleteAsync("k").ConfigureAwait(false);
            bool deletedAgain = await store.DeleteAsync("k").ConfigureAwait(false);
            (bool found, _) = await store.TryGetAsync("k").ConfigureAwait(false);

            Assert.That(deleted, Is.True);
            Assert.That(deletedAgain, Is.False);
            Assert.That(found, Is.False);
        }

        /// <summary>
        /// Verifies that scanning returns only shared-store keys matching the requested prefix.
        /// </summary>
        [Test]
        public async Task ScanReturnsMatchingPrefixOnlyAsync()
        {
            using var store = new InMemorySharedKeyValueStore();
            await store.SetAsync("a/1", ByteString.From(new byte[] { 1 })).ConfigureAwait(false);
            await store.SetAsync("a/2", ByteString.From(new byte[] { 2 })).ConfigureAwait(false);
            await store.SetAsync("b/1", ByteString.From(new byte[] { 3 })).ConfigureAwait(false);

            var keys = new List<string>();
            await foreach (KeyValuePair<string, ByteString> entry in store.ScanAsync("a/"))
            {
                keys.Add(entry.Key);
            }

            Assert.That(keys, Is.EquivalentTo(["a/1", "a/2"]));
        }

        /// <summary>
        /// Verifies that a prefix watcher observes set and delete operations.
        /// </summary>
        [Test]
        public async Task WatchObservesSetAndDeleteForPrefixAsync()
        {
            using var store = new InMemorySharedKeyValueStore();
            using var cts = new CancellationTokenSource();

            // Driving the enumerator manually guarantees the watcher is
            // registered (synchronous prefix of the iterator runs on the
            // first MoveNextAsync) before any mutation is published — no
            // delays, no flakiness.
            await using IAsyncEnumerator<KeyValueChange> enumerator =
                store.WatchAsync("a/", cts.Token).GetAsyncEnumerator();

            ValueTask<bool> first = enumerator.MoveNextAsync();
            await store.SetAsync("b/ignored", ByteString.From(new byte[] { 0 })).ConfigureAwait(false);
            await store.SetAsync("a/1", ByteString.From(new byte[] { 1 })).ConfigureAwait(false);

            Assert.That(await first.ConfigureAwait(false), Is.True);
            Assert.That(enumerator.Current.Kind, Is.EqualTo(KeyValueChangeKind.Set));
            Assert.That(enumerator.Current.Key, Is.EqualTo("a/1"));

            ValueTask<bool> second = enumerator.MoveNextAsync();
            await store.DeleteAsync("a/1").ConfigureAwait(false);

            Assert.That(await second.ConfigureAwait(false), Is.True);
            Assert.That(enumerator.Current.Kind, Is.EqualTo(KeyValueChangeKind.Delete));
            Assert.That(enumerator.Current.Key, Is.EqualTo("a/1"));

            cts.Cancel();
        }
    }
}