DodoSSH/tests/DodoSSH.Client.Domain.Tests/HostSecretMergeTests.cs

using static DodoSSH.Client.Domain.Tests.HostFactory;

namespace DodoSSH.Client.Domain.Tests;

/// <summary>
/// Merging a host field by field.
/// </summary>
/// <remarks>
/// The primitives are covered by <see cref="ThreeWayMergeTests"/>; this is about the wiring — that
/// every field is actually routed through a merge, that the collections use the right strategy, and
/// that a conflict names the field precisely enough for a user to act on it.
/// </remarks>
public sealed class HostSecretMergeTests
{
    [Fact]
    public void NeitherSideChanged_ProducesTheSameHostAndNoConflicts()
    {
        var host = Host();

        var result = HostSecretMerge.Merge(host, host, host);

        result.Merged.ShouldBe(host);
        result.HasConflicts.ShouldBeFalse();
    }

    [Fact]
    public void EachSideChangedADifferentField_BothSurvive()
    {
        // The reason a field-level merge is worth writing at all.
        var ancestor = Host();
        var local = ancestor with { Notes = "rotate quarterly" };
        var remote = ancestor with { Username = "postgres" };

        var result = HostSecretMerge.Merge(ancestor, local, remote);

        result.Merged.Notes.ShouldBe("rotate quarterly");
        result.Merged.Username.ShouldBe("postgres");
        result.HasConflicts.ShouldBeFalse();
    }

    [Fact]
    public void EveryScalarField_IsRoutedThroughAMerge()
    {
        // A field added to HostSecret but forgotten in the merge would silently revert to the remote
        // value forever. Changing each one only locally proves each is actually consulted.
        var ancestor = Host();

        var local = ancestor with
        {
            Label = "prod-db-1",
            Hostname = "db1.internal",
            Port = 2222,
            Username = "admin",
            Notes = "primary",
            JumpHostIds = JumpChain.Create([Bastion]),
            Options = HostOptions.Create([new HostOption("Compression", "yes")]),
            RelayEnabled = true,
        };

        var result = HostSecretMerge.Merge(ancestor, local, ancestor);

        result.Merged.ShouldBe(local);
        result.HasConflicts.ShouldBeFalse();
    }

    [Fact]
    public void AClashingScalar_TakesRemoteAndNamesTheFieldItDiscarded()
    {
        var ancestor = Host();
        var local = ancestor with { Hostname = "db-mine.internal" };
        var remote = ancestor with { Hostname = "db-theirs.internal" };

        var result = HostSecretMerge.Merge(ancestor, local, remote);

        result.Merged.Hostname.ShouldBe("db-theirs.internal");

        var conflict = result.Conflicts.ShouldHaveSingleItem();
        conflict.Field.ShouldBe(nameof(HostSecret.Hostname));
        conflict.Kept.ShouldBe("db-theirs.internal");
        conflict.Discarded.ShouldBe("db-mine.internal");
        conflict.DiscardedSide.ShouldBe(MergeSide.Local);
    }

    [Fact]
    public void AClashingPort_IsReportedAsANumberNotAsBlank()
    {
        // Rendering the losing value is the entire point of the conflict record; a non-string field
        // that formatted to nothing would leave the user unable to restore it.
        var ancestor = Host(port: 22);
        var result = HostSecretMerge.Merge(ancestor, ancestor with { Port = 2222 }, ancestor with { Port = 2200 });

        var conflict = result.Conflicts.ShouldHaveSingleItem();
        conflict.Field.ShouldBe(nameof(HostSecret.Port));
        conflict.Kept.ShouldBe("2200");
        conflict.Discarded.ShouldBe("2222");
    }

    [Fact]
    public void AJumpChain_MergesAsAWholeRouteRatherThanAsASet()
    {
        // Deliberate, and the opposite of how the directives merge. Unioning two chains would
        // produce a route neither user configured and would silently change which machine is
        // reached through which — so this conflicts instead, and reports the discarded route.
        var ancestor = Host();
        var local = ancestor with { JumpHostIds = JumpChain.Create([Bastion]) };
        var remote = ancestor with { JumpHostIds = JumpChain.Create([Relay]) };

        var result = HostSecretMerge.Merge(ancestor, local, remote);

        result.Merged.JumpHostIds.Equals(JumpChain.Create([Relay])).ShouldBeTrue();
        result.Merged.JumpHostIds.Count.ShouldBe(1);

        var conflict = result.Conflicts.ShouldHaveSingleItem();
        conflict.Field.ShouldBe(nameof(HostSecret.JumpHostIds));
        conflict.Discarded.ShouldNotBeNull();
        conflict.Discarded.ShouldContain(Bastion.ToString());
    }

    [Fact]
    public void AReorderedJumpChain_IsAChange()
    {
        var ancestor = Host(jumps: [Bastion, Relay]);
        var local = ancestor with { JumpHostIds = JumpChain.Create([Relay, Bastion]) };

        var result = HostSecretMerge.Merge(ancestor, local, ancestor);

        result.Merged.JumpHostIds.Equals(JumpChain.Create([Relay, Bastion])).ShouldBeTrue();
    }

    [Fact]
    public void Directives_MergePerNameSoBothAdditionsSurvive()
    {
        var ancestor = Host();
        var local = ancestor with { Options = HostOptions.Create([new HostOption("Compression", "yes")]) };
        var remote = ancestor with
        {
            Options = HostOptions.Create([new HostOption("ServerAliveInterval", "30")]),
        };

        var result = HostSecretMerge.Merge(ancestor, local, remote);

        result.Merged.Options.Count.ShouldBe(2);
        result.Merged.Options.TryGetValue("Compression", out var compression).ShouldBeTrue();
        compression.ShouldBe("yes");
        result.Merged.Options.TryGetValue("ServerAliveInterval", out var keepAlive).ShouldBeTrue();
        keepAlive.ShouldBe("30");
        result.HasConflicts.ShouldBeFalse();
    }

    [Fact]
    public void AClashingDirective_NamesTheDirectiveNotJustTheField()
    {
        // "Options changed" would be useless. The user needs to know which one.
        var ancestor = Host(options: [("Compression", "yes")]);
        var local = ancestor with { Options = HostOptions.Create([new HostOption("Compression", "no")]) };
        var remote = ancestor with
        {
            Options = HostOptions.Create([new HostOption("Compression", "delayed")]),
        };

        var result = HostSecretMerge.Merge(ancestor, local, remote);

        var conflict = result.Conflicts.ShouldHaveSingleItem();
        conflict.Field.ShouldBe("Options[Compression]");
        conflict.Kept.ShouldBe("delayed");
        conflict.Discarded.ShouldBe("no");
    }

    [Fact]
    public void ARemovedDirectiveTheOtherSideEdited_KeepsTheValue()
    {
        var ancestor = Host(options: [("Compression", "yes")]);
        var local = ancestor with { Options = HostOptions.Empty };
        var remote = ancestor with { Options = HostOptions.Create([new HostOption("Compression", "no")]) };

        var result = HostSecretMerge.Merge(ancestor, local, remote);

        result.Merged.Options.TryGetValue("Compression", out var value).ShouldBeTrue();
        value.ShouldBe("no");
        result.Conflicts.ShouldHaveSingleItem().DiscardedWasRemoval.ShouldBeTrue();
    }

    [Fact]
    public void TheMergedHost_IsAlwaysValidWhenBothInputsWere()
    {
        // A merge that produced an unstorable host would strand the item: it could never be pushed
        // and the conflict could never clear.
        var ancestor = Host();
        var local = ancestor with { Label = "mine", Port = 2222 };
        var remote = ancestor with { Label = "theirs", Hostname = "other.internal" };

        var result = HostSecretMerge.Merge(ancestor, local, remote);

        result.Merged.TryValidate(out var error).ShouldBeTrue(error);
    }

    [Fact]
    public void ResolvingAConflictConverges()
    {
        // Two clients, both merging, must reach the same host and then stop. Re-merging the result
        // against the remote produces no further conflict — which is what stops an endless
        // push-conflict-merge-push loop between two machines.
        var ancestor = Host();
        var local = ancestor with { Notes = "mine", Username = "a" };
        var remote = ancestor with { Notes = "theirs", Hostname = "other.internal" };

        var first = HostSecretMerge.Merge(ancestor, local, remote);
        first.HasConflicts.ShouldBeTrue();

        var second = HostSecretMerge.Merge(remote, first.Merged, remote);

        second.HasConflicts.ShouldBeFalse();
        second.Merged.ShouldBe(first.Merged);
    }
}