// Copyright 2012-2026 The NATS Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Adapted from server/server_test.go in the NATS server Go source.
// Session 09: standalone unit tests for NatsServer helpers.

using System.Text.RegularExpressions;
using Shouldly;
using Xunit;

namespace ZB.MOM.NatsNet.Server.Tests;

/// <summary>
/// Standalone unit tests for <see cref="NatsServer"/> helpers.
/// Tests that require a running server (listener, TLS, cluster) are marked n/a
/// and will be ported in sessions 10–23.
/// </summary>
public sealed class ServerTests
{
    // =========================================================================
    // TestSemanticVersion — Test ID 2866
    // Validates that ServerConstants.Version matches semver format.
    // Mirrors Go TestSemanticVersion in server/server_test.go.
    // =========================================================================

    [Fact]
    public void Version_IsValidSemVer()
    {
        // SemVer regex: major.minor.patch with optional pre-release / build meta.
        var semVerRe = new Regex(@"^\d+\.\d+\.\d+(-\S+)?(\+\S+)?$", RegexOptions.Compiled);
        semVerRe.IsMatch(ServerConstants.Version).ShouldBeTrue(
            $"Version ({ServerConstants.Version}) is not a valid SemVer string");
    }

    // =========================================================================
    // TestProcessCommandLineArgs — Test ID 2882
    // Tests the ProcessCommandLineArgs helper.
    // The Go version uses flag.FlagSet; our C# port takes string[].
    // Mirrors Go TestProcessCommandLineArgs in server/server_test.go.
    // =========================================================================

    [Fact]
    public void ProcessCommandLineArgs_NoArgs_ReturnsFalse()
    {
        var (showVersion, showHelp, err) = NatsServer.ProcessCommandLineArgs([]);
        err.ShouldBeNull();
        showVersion.ShouldBeFalse();
        showHelp.ShouldBeFalse();
    }

    [Theory]
    [InlineData("version", true,  false)]
    [InlineData("VERSION", true,  false)]
    [InlineData("help",    false, true)]
    [InlineData("HELP",    false, true)]
    public void ProcessCommandLineArgs_KnownSubcommand_ReturnsCorrectFlags(
        string arg, bool wantVersion, bool wantHelp)
    {
        var (showVersion, showHelp, err) = NatsServer.ProcessCommandLineArgs([arg]);
        err.ShouldBeNull();
        showVersion.ShouldBe(wantVersion);
        showHelp.ShouldBe(wantHelp);
    }

    [Fact]
    public void ProcessCommandLineArgs_UnknownSubcommand_ReturnsError()
    {
        var (_, _, err) = NatsServer.ProcessCommandLineArgs(["foo"]);
        err.ShouldNotBeNull();
    }

    // =========================================================================
    // CompressionMode helpers — standalone tests for features 2976–2982
    // =========================================================================

    [Theory]
    [InlineData("off",    CompressionMode.Off)]
    [InlineData("false",  CompressionMode.Off)]
    [InlineData("accept", CompressionMode.Accept)]
    [InlineData("s2_fast", CompressionMode.S2Fast)]
    [InlineData("fast",   CompressionMode.S2Fast)]
    [InlineData("better", CompressionMode.S2Better)]
    [InlineData("best",   CompressionMode.S2Best)]
    public void ValidateAndNormalizeCompressionOption_KnownModes_NormalizesCorrectly(
        string input, string expected)
    {
        var co = new CompressionOpts { Mode = input };
        NatsServer.ValidateAndNormalizeCompressionOption(co, CompressionMode.S2Fast);
        co.Mode.ShouldBe(expected);
    }

    [Fact]
    public void ValidateAndNormalizeCompressionOption_OnAlias_MapsToChosenMode()
    {
        var co = new CompressionOpts { Mode = "on" };
        NatsServer.ValidateAndNormalizeCompressionOption(co, CompressionMode.S2Better);
        co.Mode.ShouldBe(CompressionMode.S2Better);
    }

    [Fact]
    public void ValidateAndNormalizeCompressionOption_S2Auto_UsesDefaults_WhenNoThresholds()
    {
        var co = new CompressionOpts { Mode = "s2_auto" };
        NatsServer.ValidateAndNormalizeCompressionOption(co, CompressionMode.S2Fast);
        co.Mode.ShouldBe(CompressionMode.S2Auto);
        co.RttThresholds.ShouldBe(NatsServer.DefaultCompressionS2AutoRttThresholds.ToList());
    }

    [Fact]
    public void ValidateAndNormalizeCompressionOption_UnsupportedMode_Throws()
    {
        var co = new CompressionOpts { Mode = "bogus" };
        Should.Throw<InvalidOperationException>(
            () => NatsServer.ValidateAndNormalizeCompressionOption(co, CompressionMode.S2Fast));
    }

    [Theory]
    [InlineData(5,   CompressionMode.S2Uncompressed)]  // <= 10 ms threshold
    [InlineData(25,  CompressionMode.S2Fast)]           // 10 < rtt <= 50 ms
    [InlineData(75,  CompressionMode.S2Better)]         // 50 < rtt <= 100 ms
    [InlineData(150, CompressionMode.S2Best)]           // > 100 ms
    public void SelectS2AutoModeBasedOnRtt_DefaultThresholds_CorrectMode(int rttMs, string expected)
    {
        var result = NatsServer.SelectS2AutoModeBasedOnRtt(
            TimeSpan.FromMilliseconds(rttMs),
            NatsServer.DefaultCompressionS2AutoRttThresholds);
        result.ShouldBe(expected);
    }

    [Theory]
    [InlineData(CompressionMode.Off,  CompressionMode.S2Fast, CompressionMode.Off)]
    [InlineData(CompressionMode.Accept, CompressionMode.Accept, CompressionMode.Off)]
    [InlineData(CompressionMode.S2Fast, CompressionMode.Accept, CompressionMode.S2Fast)]
    [InlineData(CompressionMode.Accept, CompressionMode.S2Fast, CompressionMode.S2Fast)]
    [InlineData(CompressionMode.Accept, CompressionMode.S2Auto, CompressionMode.S2Fast)]
    public void SelectCompressionMode_TableDriven(string local, string remote, string expected)
    {
        NatsServer.SelectCompressionMode(local, remote).ShouldBe(expected);
    }

    [Fact]
    public void SelectCompressionMode_RemoteNotSupported_ReturnsNotSupported()
    {
        NatsServer.SelectCompressionMode(CompressionMode.S2Fast, CompressionMode.NotSupported)
            .ShouldBe(CompressionMode.NotSupported);
    }

    [Fact]
    public void CompressOptsEqual_SameMode_ReturnsTrue()
    {
        var c1 = new CompressionOpts { Mode = CompressionMode.S2Fast };
        var c2 = new CompressionOpts { Mode = CompressionMode.S2Fast };
        NatsServer.CompressOptsEqual(c1, c2).ShouldBeTrue();
    }

    [Fact]
    public void CompressOptsEqual_DifferentModes_ReturnsFalse()
    {
        var c1 = new CompressionOpts { Mode = CompressionMode.S2Fast };
        var c2 = new CompressionOpts { Mode = CompressionMode.S2Best };
        NatsServer.CompressOptsEqual(c1, c2).ShouldBeFalse();
    }

    // =========================================================================
    // Validation helpers
    // =========================================================================

    [Fact]
    public void ValidateCluster_ClusterNameWithSpaces_ReturnsError()
    {
        var opts = new ServerOptions();
        opts.Cluster.Name = "bad name";
        var err = NatsServer.ValidateCluster(opts);
        err.ShouldNotBeNull();
        err.ShouldBeSameAs(ServerErrors.ErrClusterNameHasSpaces);
    }

    [Fact]
    public void ValidatePinnedCerts_ValidSha256_ReturnsNull()
    {
        var pinned = new PinnedCertSet(
            [new string('a', 64)]); // 64 hex chars
        var err = NatsServer.ValidatePinnedCerts(pinned);
        err.ShouldBeNull();
    }

    [Fact]
    public void ValidatePinnedCerts_InvalidSha256_ReturnsError()
    {
        var pinned = new PinnedCertSet(["not_a_sha256"]);
        var err = NatsServer.ValidatePinnedCerts(pinned);
        err.ShouldNotBeNull();
    }

    // =========================================================================
    // GetServerProto
    // =========================================================================

    [Fact]
    public void GetServerProto_DefaultOpts_ReturnsMsgTraceProto()
    {
        var opts = new ServerOptions();
        // SetBaselineOptions so OverrideProto gets default 0.
        opts.SetBaselineOptions();
        var (s, err) = NatsServer.NewServer(opts);
        err.ShouldBeNull();
        s.ShouldNotBeNull();
        s!.GetServerProto().ShouldBe(ServerProtocol.MsgTraceProto);
    }

    // =========================================================================
    // Account helpers
    // =========================================================================

    [Fact]
    public void ComputeRoutePoolIdx_PoolSizeOne_AlwaysReturnsZero()
    {
        NatsServer.ComputeRoutePoolIdx(1, "any-account").ShouldBe(0);
        NatsServer.ComputeRoutePoolIdx(0, "any-account").ShouldBe(0);
    }

    [Fact]
    public void ComputeRoutePoolIdx_PoolSizeN_ReturnsIndexInRange()
    {
        const int poolSize = 5;
        var idx = NatsServer.ComputeRoutePoolIdx(poolSize, "my-account");
        idx.ShouldBeInRange(0, poolSize - 1);
    }

    [Fact]
    public void NeedsCompression_Empty_ReturnsFalse()
        => NatsServer.NeedsCompression(string.Empty).ShouldBeFalse();

    [Fact]
    public void NeedsCompression_Off_ReturnsFalse()
        => NatsServer.NeedsCompression(CompressionMode.Off).ShouldBeFalse();

    [Fact]
    public void NeedsCompression_S2Fast_ReturnsTrue()
        => NatsServer.NeedsCompression(CompressionMode.S2Fast).ShouldBeTrue();
}