using System.Text.Json;
using Akka.Actor;
using Akka.TestKit.Xunit2;
using ScadaLink.Commons.Messages.Notification;
using ScadaLink.Commons.Types.Enums;

namespace ScadaLink.StoreAndForward.Tests;

/// <summary>
/// Notification Outbox: tests for the site Store-and-Forward notification delivery
/// handler. "Delivering" a buffered notification means forwarding it to the central
/// cluster (via the site communication actor) and treating central's
/// <see cref="NotificationSubmitAck"/> as the delivery outcome.
/// </summary>
public class NotificationForwarderTests : TestKit
{
    private static readonly TimeSpan ForwardTimeout = TimeSpan.FromSeconds(2);

    /// <summary>
    /// Builds a buffered notification S&amp;F message whose payload matches the shape
    /// produced by the site <c>Notify.Send</c> enqueue path (Task 19): a serialized
    /// <see cref="NotificationSubmit"/> carrying a script-generated
    /// <see cref="NotificationSubmit.NotificationId"/>. The S&amp;F message
    /// <see cref="StoreAndForwardMessage.Id"/> equals that same id.
    /// </summary>
    private static StoreAndForwardMessage BufferedNotification(
        string id = "msg-1", string listName = "Operators",
        string subject = "Pump alarm", string message = "Pump 3 tripped",
        string? originInstance = "Plant.Pump3", string? sourceScript = "alarmScript")
    {
        var payload = JsonSerializer.Serialize(new NotificationSubmit(
            NotificationId: id,
            ListName: listName,
            Subject: subject,
            Body: message,
            // SourceSiteId is re-stamped by the forwarder; the enqueue side leaves it blank.
            SourceSiteId: string.Empty,
            SourceInstanceId: originInstance,
            SourceScript: sourceScript,
            SiteEnqueuedAt: DateTimeOffset.UtcNow));
        return new StoreAndForwardMessage
        {
            Id = id,
            Category = StoreAndForwardCategory.Notification,
            Target = listName,
            PayloadJson = payload,
            OriginInstanceName = originInstance,
        };
    }

    [Fact]
    public async Task Deliver_ForwardsNotificationSubmitToCentralTarget_AndReturnsTrueOnAccept()
    {
        var centralProbe = CreateTestProbe();
        var forwarder = new NotificationForwarder(
            centralProbe.Ref, "site-7", ForwardTimeout);

        var msg = BufferedNotification(
            id: "msg-1", listName: "Operators", subject: "Pump alarm",
            message: "Pump 3 tripped", originInstance: "Plant.Pump3");

        var deliverTask = forwarder.DeliverAsync(msg);

        // The central target receives a NotificationSubmit whose fields map from the
        // buffered payload; reply Accepted so the handler completes as delivered.
        var submit = centralProbe.ExpectMsg<NotificationSubmit>();
        Assert.Equal("msg-1", submit.NotificationId);
        Assert.Equal("Operators", submit.ListName);
        Assert.Equal("Pump alarm", submit.Subject);
        Assert.Equal("Pump 3 tripped", submit.Body);
        // SourceSiteId is re-stamped by the forwarder from its own site id.
        Assert.Equal("site-7", submit.SourceSiteId);
        Assert.Equal("Plant.Pump3", submit.SourceInstanceId);
        // The originating script travels through from the buffered payload.
        Assert.Equal("alarmScript", submit.SourceScript);
        centralProbe.Reply(new NotificationSubmitAck(submit.NotificationId, Accepted: true, Error: null));

        Assert.True(await deliverTask);
    }

    [Fact]
    public async Task Deliver_FallsBackToTarget_WhenPayloadListNameIsEmpty()
    {
        var centralProbe = CreateTestProbe();
        var forwarder = new NotificationForwarder(
            centralProbe.Ref, "site-7", ForwardTimeout);

        // A buffered payload carrying an empty-string ListName: the empty value must not
        // be forwarded — the forwarder falls back to the S&F message Target instead.
        var payload = JsonSerializer.Serialize(new NotificationSubmit(
            NotificationId: "msg-empty-list",
            ListName: "",
            Subject: "Pump alarm",
            Body: "Pump 3 tripped",
            SourceSiteId: string.Empty,
            SourceInstanceId: "Plant.Pump3",
            SourceScript: null,
            SiteEnqueuedAt: DateTimeOffset.UtcNow));
        var msg = new StoreAndForwardMessage
        {
            Id = "msg-empty-list",
            Category = StoreAndForwardCategory.Notification,
            Target = "Operators",
            PayloadJson = payload,
            OriginInstanceName = "Plant.Pump3",
        };

        var deliverTask = forwarder.DeliverAsync(msg);

        var submit = centralProbe.ExpectMsg<NotificationSubmit>();
        Assert.Equal("Operators", submit.ListName);
        centralProbe.Reply(new NotificationSubmitAck(submit.NotificationId, Accepted: true, Error: null));

        Assert.True(await deliverTask);
    }

    [Fact]
    public async Task Deliver_ThrowsTransient_WhenAckIsNotAccepted()
    {
        var centralProbe = CreateTestProbe();
        var forwarder = new NotificationForwarder(
            centralProbe.Ref, "site-7", ForwardTimeout);

        var deliverTask = forwarder.DeliverAsync(BufferedNotification());

        var submit = centralProbe.ExpectMsg<NotificationSubmit>();
        centralProbe.Reply(new NotificationSubmitAck(
            submit.NotificationId, Accepted: false, Error: "central rejected"));

        // A non-accepted ack is a transient failure — the handler throws so the S&F
        // engine keeps the message buffered and retries the forward.
        await Assert.ThrowsAnyAsync<Exception>(() => deliverTask);
    }

    [Fact]
    public async Task Deliver_ThrowsTransient_WhenNoReplyWithinTimeout()
    {
        // A probe that never replies stands in for central being unreachable.
        var centralProbe = CreateTestProbe();
        var forwarder = new NotificationForwarder(
            centralProbe.Ref, "site-7", TimeSpan.FromMilliseconds(300));

        // No reply within the timeout → transient failure → throw.
        await Assert.ThrowsAnyAsync<Exception>(() => forwarder.DeliverAsync(BufferedNotification()));
    }

    [Fact]
    public async Task Deliver_UsesStableNotificationId_AcrossRetriesOfSameMessage()
    {
        var centralProbe = CreateTestProbe();
        var forwarder = new NotificationForwarder(
            centralProbe.Ref, "site-7", ForwardTimeout);

        var buffered = BufferedNotification(id: "stable-msg-id");

        var first = forwarder.DeliverAsync(buffered);
        var submit1 = centralProbe.ExpectMsg<NotificationSubmit>();
        centralProbe.Reply(new NotificationSubmitAck(submit1.NotificationId, true, null));
        await first;

        var second = forwarder.DeliverAsync(buffered);
        var submit2 = centralProbe.ExpectMsg<NotificationSubmit>();
        centralProbe.Reply(new NotificationSubmitAck(submit2.NotificationId, true, null));
        await second;

        // The NotificationId is the central idempotency key — it must be identical for
        // every forward attempt of the same buffered S&F message.
        Assert.Equal(submit1.NotificationId, submit2.NotificationId);
        Assert.Equal("stable-msg-id", submit1.NotificationId);
    }
}
