SafelyYouCodingChallenge/dotnet/SafelyYouTests/DeviceHeartBeatHistoryTests.cs

using SafelyYou.Data;

namespace SafelyYouTests;

public class DeviceHeartBeatHistoryTests
{
    private static readonly DateTimeOffset T0 = new(2024, 1, 1, 12, 0, 0, TimeSpan.Zero);
    private static readonly DateTimeOffset T1 = T0.AddMinutes(1);
    private static readonly DateTimeOffset T2 = T0.AddMinutes(2);

    [Test]
    public void Add_FirstHeartbeat_SetsFirstLastAndCount()
    {
        var history = new DeviceHeartBeatHistory();

        var result = history.Add(T0);

        Assert.Multiple(() =>
        {
            Assert.That(result, Is.EqualTo(DeviceHeartBeatHistory.AddResult.Added));
            Assert.That(history.NumberOfHeartBeats, Is.EqualTo(1));
            Assert.That(history.FirstHeartBeat, Is.EqualTo(T0));
            Assert.That(history.LastHeartBeat, Is.EqualTo(T0));
        });
    }

    [Test]
    public void Add_LaterHeartbeat_UpdatesLastAndIncrementsCount()
    {
        var history = new DeviceHeartBeatHistory();
        history.Add(T0);

        var result = history.Add(T1);

        Assert.Multiple(() =>
        {
            Assert.That(result, Is.EqualTo(DeviceHeartBeatHistory.AddResult.Added));
            Assert.That(history.NumberOfHeartBeats, Is.EqualTo(2));
            Assert.That(history.FirstHeartBeat, Is.EqualTo(T0));
            Assert.That(history.LastHeartBeat, Is.EqualTo(T1));
        });
    }

    [Test]
    public void Add_SameTimestampAsLast_IsAccepted()
    {
        var history = new DeviceHeartBeatHistory();
        history.Add(T0);

        var result = history.Add(T0);

        Assert.Multiple(() =>
        {
            Assert.That(result, Is.EqualTo(DeviceHeartBeatHistory.AddResult.Added));
            Assert.That(history.NumberOfHeartBeats, Is.EqualTo(2));
            Assert.That(history.FirstHeartBeat, Is.EqualTo(T0));
            Assert.That(history.LastHeartBeat, Is.EqualTo(T0));
        });
    }

    [Test]
    public void Add_EarlierThanLast_ReturnsOutOfSequenceAndDoesNotMutate()
    {
        var history = new DeviceHeartBeatHistory();
        history.Add(T1);

        var result = history.Add(T0);

        Assert.Multiple(() =>
        {
            Assert.That(result, Is.EqualTo(DeviceHeartBeatHistory.AddResult.OutOfSequence));
            Assert.That(history.NumberOfHeartBeats, Is.EqualTo(1));
            Assert.That(history.FirstHeartBeat, Is.EqualTo(T1));
            Assert.That(history.LastHeartBeat, Is.EqualTo(T1));
        });
    }

    [Test]
    public void Add_MultipleInOrder_KeepsFirstAndAdvancesLast()
    {
        var history = new DeviceHeartBeatHistory();

        Assert.That(history.Add(T0), Is.EqualTo(DeviceHeartBeatHistory.AddResult.Added));
        Assert.That(history.Add(T1), Is.EqualTo(DeviceHeartBeatHistory.AddResult.Added));
        Assert.That(history.Add(T2), Is.EqualTo(DeviceHeartBeatHistory.AddResult.Added));

        Assert.Multiple(() =>
        {
            Assert.That(history.NumberOfHeartBeats, Is.EqualTo(3));
            Assert.That(history.FirstHeartBeat, Is.EqualTo(T0));
            Assert.That(history.LastHeartBeat, Is.EqualTo(T2));
        });
    }

    [Test]
    public void Add_WithGap_StillCountsHeartbeat()
    {
        var history = new DeviceHeartBeatHistory();
        history.Add(T0);

        var muchLater = T0.AddHours(1);
        var result = history.Add(muchLater);

        Assert.Multiple(() =>
        {
            Assert.That(result, Is.EqualTo(DeviceHeartBeatHistory.AddResult.Added));
            Assert.That(history.NumberOfHeartBeats, Is.EqualTo(2));
            Assert.That(history.LastHeartBeat, Is.EqualTo(muchLater));
        });
    }
}