using System;
using Svrnty.CQRS.Events.Abstractions.Subscriptions;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using Svrnty.CQRS.Events.Abstractions.Models;

namespace Svrnty.CQRS.Events.Abstractions.Subscriptions;

/// <summary>
/// Service for managing event subscriptions.
/// Provides high-level operations for subscribing, unsubscribing, and managing subscriptions.
/// </summary>
public interface IEventSubscriptionService
{
    /// <summary>
    /// Create a new subscription to events for a correlation ID.
    /// </summary>
    /// <param name="request">Subscription request details.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>The created subscription.</returns>
    Task<EventSubscription> SubscribeAsync(SubscriptionRequest request, CancellationToken cancellationToken = default);

    /// <summary>
    /// Unsubscribe from events (marks subscription as cancelled).
    /// </summary>
    /// <param name="subscriptionId">The subscription ID to cancel.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    Task UnsubscribeAsync(string subscriptionId, CancellationToken cancellationToken = default);

    /// <summary>
    /// Get all active subscriptions for a subscriber (for catch-up on reconnect).
    /// </summary>
    /// <param name="subscriberId">The subscriber ID.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>List of active subscriptions.</returns>
    Task<List<EventSubscription>> GetActiveSubscriptionsAsync(string subscriberId, CancellationToken cancellationToken = default);

    /// <summary>
    /// Mark a subscription as completed (terminal event received).
    /// </summary>
    /// <param name="subscriptionId">The subscription ID.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    Task CompleteSubscriptionAsync(string subscriptionId, CancellationToken cancellationToken = default);

    /// <summary>
    /// Update the last delivered sequence for a subscription.
    /// </summary>
    /// <param name="subscriptionId">The subscription ID.</param>
    /// <param name="sequence">The sequence number that was delivered.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    Task UpdateLastDeliveredAsync(string subscriptionId, long sequence, CancellationToken cancellationToken = default);
}

/// <summary>
/// Request to create a new event subscription.
/// </summary>
public sealed class SubscriptionRequest
{
    /// <summary>
    /// ID of the subscriber (typically user ID or client ID).
    /// </summary>
    public required string SubscriberId { get; init; }

    /// <summary>
    /// Correlation ID to subscribe to.
    /// </summary>
    public required string CorrelationId { get; init; }

    /// <summary>
    /// Event types to receive (empty = all types).
    /// </summary>
    public HashSet<string> EventTypes { get; init; } = new();

    /// <summary>
    /// Event types that complete the subscription.
    /// </summary>
    public HashSet<string> TerminalEventTypes { get; init; } = new();

    /// <summary>
    /// How events should be delivered.
    /// </summary>
    public DeliveryMode DeliveryMode { get; init; } = DeliveryMode.Immediate;

    /// <summary>
    /// Optional timeout duration for this subscription.
    /// </summary>
    public TimeSpan? Timeout { get; init; }
}