using System.Net;
using System.Text;
using ZB.MOM.WW.Overview.Polling;

namespace ZB.MOM.WW.Overview.Tests;

/// <summary>
/// Golden-payload tests for the health client. The fixtures are hand-written to the exact shape
/// <c>ZbHealthWriter</c> emits — including an entry WITH <c>data</c> (0.2.0+) and one WITHOUT
/// (every check that publishes none, and every pre-0.2.0 node), because tolerating both is what
/// lets the dashboard run against a fleet that is only partly bumped.
/// </summary>
public class ZbHealthReportClientTests
{
    private const string ReadyHealthyWithData = """
        {
          "status": "Healthy",
          "totalDurationMs": 12.34,
          "entries": {
            "akka-cluster": {
              "status": "Healthy",
              "description": "Akka cluster member status: Up",
              "durationMs": 1.23,
              "data": {
                "selfAddress": "akka.tcp://scadabridge@site-a-a:8082",
                "selfRoles": ["Site", "site-a"],
                "memberCount": 2,
                "unreachableCount": 0,
                "leader": "akka.tcp://scadabridge@site-a-a:8082"
              }
            },
            "localdb": {
              "status": "Healthy",
              "description": "Site LocalDb reachable.",
              "durationMs": 0.45
            }
          }
        }
        """;

    private const string ReadyUnhealthyNoData = """
        {
          "status": "Unhealthy",
          "totalDurationMs": 3001.5,
          "entries": {
            "database": {
              "status": "Unhealthy",
              "description": null,
              "durationMs": 3000.1
            }
          }
        }
        """;

    private static ZbHealthReportClient ClientReturning(
        HttpStatusCode statusCode,
        string body,
        string contentType = "application/json") =>
        new(new HttpClient(new StubHandler((statusCode, body, contentType))));

    private static readonly TimeSpan ProbeTimeout = TimeSpan.FromSeconds(3);

    [Fact]
    public async Task Probe_HealthyBody_ParsesEnvelopeAndEntries()
    {
        var client = ClientReturning(HttpStatusCode.OK, ReadyHealthyWithData);

        var result = await client.ProbeAsync("http://node/health/ready", ProbeTimeout);

        Assert.True(result.Reachable);
        Assert.Equal(200, result.StatusCode);
        Assert.Equal("Healthy", result.Report!.Status);
        Assert.Equal(12.34, result.Report.TotalDurationMs);
        Assert.Equal(new[] { "akka-cluster", "localdb" }, result.Report.Entries.Keys.OrderBy(k => k, StringComparer.Ordinal));
        Assert.Equal("Site LocalDb reachable.", result.Report.Entries["localdb"].Description);
    }

    [Fact]
    public async Task Probe_EntryWithData_ExposesLeaderAndCounts()
    {
        var client = ClientReturning(HttpStatusCode.OK, ReadyHealthyWithData);

        var result = await client.ProbeAsync("http://node/health/ready", ProbeTimeout);
        var entry = result.Report!.Entries["akka-cluster"];

        Assert.Equal("akka.tcp://scadabridge@site-a-a:8082", entry.DataString("leader"));
        Assert.Equal(2, entry.DataInt("memberCount"));
        Assert.Equal(0, entry.DataInt("unreachableCount"));
    }

    [Fact]
    public async Task Probe_EntryWithoutData_ReadsAsNullNotAsAnError()
    {
        // The 0.1.0-era / no-data case. It must degrade to "no leader shown", never to a parse
        // failure — that tolerance is what keeps the dashboard usable mid-rollout.
        var client = ClientReturning(HttpStatusCode.OK, ReadyHealthyWithData);

        var result = await client.ProbeAsync("http://node/health/ready", ProbeTimeout);
        var entry = result.Report!.Entries["localdb"];

        Assert.True(result.Reachable);
        Assert.Null(entry.Data);
        Assert.Null(entry.DataString("leader"));
        Assert.Null(entry.DataInt("memberCount"));
    }

    [Fact]
    public async Task Probe_503_IsAParseableAnswer_NotAFailedProbe()
    {
        // 503 carries a full body naming the failing check — the single most useful payload the
        // dashboard receives. Treating it as a transport failure would throw that away.
        var client = ClientReturning(HttpStatusCode.ServiceUnavailable, ReadyUnhealthyNoData);

        var result = await client.ProbeAsync("http://node/health/ready", ProbeTimeout);

        Assert.True(result.Reachable);
        Assert.Equal(503, result.StatusCode);
        Assert.Equal("Unhealthy", result.Report!.Status);
        Assert.Null(result.Report.Entries["database"].Description);
    }

    [Theory]
    [InlineData("<html><body>502 Bad Gateway</body></html>")]
    [InlineData("not json at all")]
    public async Task Probe_NonJsonBody_IsUnreachable(string body)
    {
        var client = ClientReturning(HttpStatusCode.OK, body, contentType: "text/html");

        var result = await client.ProbeAsync("http://node/health/ready", ProbeTimeout);

        Assert.False(result.Reachable);
        Assert.Null(result.Report);
        Assert.NotNull(result.Error);
    }

    [Fact]
    public async Task Probe_ConnectionRefused_IsUnreachableAndDoesNotThrow()
    {
        var client = new ZbHealthReportClient(
            new HttpClient(new ThrowingHandler(new HttpRequestException("Connection refused"))));

        var result = await client.ProbeAsync("http://node/health/ready", ProbeTimeout);

        Assert.False(result.Reachable);
        Assert.Contains("refused", result.Error, StringComparison.OrdinalIgnoreCase);
    }

    [Fact]
    public async Task Probe_Timeout_IsUnreachableAndReportsTheTimeout()
    {
        var client = new ZbHealthReportClient(new HttpClient(new HangingHandler()));

        var result = await client.ProbeAsync("http://node/health/ready", TimeSpan.FromMilliseconds(50));

        Assert.False(result.Reachable);
        Assert.Contains("timed out", result.Error, StringComparison.OrdinalIgnoreCase);
    }

    [Fact]
    public async Task Probe_HostShutdown_PropagatesCancellation()
    {
        // A shutdown must NOT be recorded as a timed-out instance — the sweep is being abandoned,
        // and writing "Unreachable" for every node on the way out would be a lie in the snapshot.
        using var shutdown = new CancellationTokenSource();
        await shutdown.CancelAsync();
        var client = new ZbHealthReportClient(new HttpClient(new HangingHandler()));

        await Assert.ThrowsAnyAsync<OperationCanceledException>(
            () => client.ProbeAsync("http://node/health/ready", ProbeTimeout, shutdown.Token));
    }

    [Theory]
    [InlineData(HttpStatusCode.OK, 200)]
    [InlineData(HttpStatusCode.ServiceUnavailable, 503)]
    public async Task ProbeStatus_EmptyBody_IsStillAnAnswer(HttpStatusCode status, int expected)
    {
        // The active tier answers with a status code; the body is not part of that contract. An
        // empty 200/503 is the endpoint telling us the role plainly, and insisting on parseable
        // JSON here reports every such node as "role unknown".
        var client = ClientReturning(status, string.Empty);

        var result = await client.ProbeStatusAsync("http://node/health/active", ProbeTimeout);

        Assert.True(result.Reachable);
        Assert.Equal(expected, result.StatusCode);
        Assert.Null(result.Report);
        Assert.Null(result.Error);
    }

    [Fact]
    public async Task ProbeStatus_StillParsesABodyWhenOneIsThere()
    {
        var client = ClientReturning(HttpStatusCode.OK, ReadyHealthyWithData);

        var result = await client.ProbeStatusAsync("http://node/health/active", ProbeTimeout);

        Assert.Equal("Healthy", result.Report!.Status);
    }

    [Fact]
    public async Task ProbeStatus_TransportFailure_IsStillUnreachable()
    {
        // Relaxing the body requirement must not relax what "reachable" means.
        var client = new ZbHealthReportClient(
            new HttpClient(new ThrowingHandler(new HttpRequestException("Connection refused"))));

        var result = await client.ProbeStatusAsync("http://node/health/active", ProbeTimeout);

        Assert.False(result.Reachable);
        Assert.Null(result.StatusCode);
    }

    [Fact]
    public async Task Probe_ReadyTierStillDemandsAParseableBody()
    {
        // The ready tier's body IS the payload — the per-check list and the leader data come from
        // it. An empty 200 there means something other than a family app is on that port.
        var client = ClientReturning(HttpStatusCode.OK, string.Empty);

        var result = await client.ProbeAsync("http://node/health/ready", ProbeTimeout);

        Assert.False(result.Reachable);
    }

    private sealed class StubHandler((HttpStatusCode Status, string Body, string ContentType) response)
        : HttpMessageHandler
    {
        protected override Task<HttpResponseMessage> SendAsync(
            HttpRequestMessage request, CancellationToken cancellationToken) =>
            Task.FromResult(new HttpResponseMessage(response.Status)
            {
                Content = new StringContent(response.Body, Encoding.UTF8, response.ContentType),
            });
    }

    private sealed class ThrowingHandler(Exception exception) : HttpMessageHandler
    {
        protected override Task<HttpResponseMessage> SendAsync(
            HttpRequestMessage request, CancellationToken cancellationToken) =>
            Task.FromException<HttpResponseMessage>(exception);
    }

    private sealed class HangingHandler : HttpMessageHandler
    {
        protected override async Task<HttpResponseMessage> SendAsync(
            HttpRequestMessage request, CancellationToken cancellationToken)
        {
            await Task.Delay(Timeout.InfiniteTimeSpan, cancellationToken).ConfigureAwait(false);
            return new HttpResponseMessage(HttpStatusCode.OK);
        }
    }
}