using System;
using Svrnty.CQRS.Events.Abstractions.Delivery;
using Svrnty.CQRS.Events.Abstractions.Subscriptions;
using Svrnty.CQRS.Events.Abstractions.EventStore;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Svrnty.CQRS.Events.Abstractions;
using Svrnty.CQRS.Events.Abstractions.Models;

namespace Svrnty.CQRS.Events.Delivery;

/// <summary>
/// Default implementation of IEventDeliveryService.
/// Handles event filtering and subscription completion logic.
/// Actual delivery to clients is handled by the transport layer (gRPC/SignalR).
/// </summary>
public sealed class EventDeliveryService : IEventDeliveryService
{
    private readonly ISubscriptionStore _subscriptionStore;

    public EventDeliveryService(ISubscriptionStore subscriptionStore)
    {
        _subscriptionStore = subscriptionStore;
    }

    public async Task DeliverEventAsync(ICorrelatedEvent @event, long sequence, CancellationToken cancellationToken = default)
    {
        // Find all subscriptions interested in this correlation
        var subscriptions = await _subscriptionStore.FindByCorrelationIdAsync(@event.CorrelationId, cancellationToken);

        var eventTypeName = @event.GetType().Name;

        foreach (var subscription in subscriptions)
        {
            // Skip if subscription is not active or expired
            if (subscription.Status != SubscriptionStatus.Active || subscription.IsExpired)
                continue;

            // Filter: Only process if subscriber requested this event type
            if (!subscription.ShouldReceive(eventTypeName))
                continue;

            // Check if this is a terminal event
            if (subscription.IsTerminalEvent(eventTypeName))
            {
                subscription.Status = SubscriptionStatus.Completed;
                subscription.CompletedAt = DateTimeOffset.UtcNow;
                await _subscriptionStore.UpdateAsync(subscription, cancellationToken);
            }

            // Note: Actual delivery to the client happens in the gRPC stream handler
            // The handler will query for events where sequence > LastDeliveredSequence
        }
    }
}