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

namespace Svrnty.CQRS.Events.Abstractions.EventStore;

/// <summary>
/// Storage abstraction for persisting and retrieving events.
/// Implementations can use any storage mechanism (SQL, NoSQL, in-memory, etc.).
/// </summary>
public interface IEventStore
{
    /// <summary>
    /// Append an event to the store and assign it a sequence number.
    /// </summary>
    /// <param name="event">The event to store.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>The sequence number assigned to this event.</returns>
    Task<long> AppendAsync(ICorrelatedEvent @event, CancellationToken cancellationToken = default);

    /// <summary>
    /// Append multiple events in a batch.
    /// </summary>
    /// <param name="events">The events to store.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>Dictionary mapping event IDs to their sequence numbers.</returns>
    Task<Dictionary<string, long>> AppendBatchAsync(IEnumerable<ICorrelatedEvent> events, CancellationToken cancellationToken = default);

    /// <summary>
    /// Get events for a specific correlation ID.
    /// </summary>
    /// <param name="correlationId">The correlation ID to query.</param>
    /// <param name="afterSequence">Only return events after this sequence number (for catch-up).</param>
    /// <param name="eventTypes">Optional filter for specific event types.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>List of stored events ordered by sequence.</returns>
    Task<List<StoredEvent>> GetEventsAsync(
        string correlationId,
        long afterSequence = 0,
        HashSet<string>? eventTypes = null,
        CancellationToken cancellationToken = default);

    /// <summary>
    /// Get a specific event by its ID.
    /// </summary>
    /// <param name="eventId">The event ID.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>The stored event, or null if not found.</returns>
    Task<StoredEvent?> GetEventByIdAsync(string eventId, CancellationToken cancellationToken = default);

    /// <summary>
    /// Delete events older than the specified date (for cleanup/retention policies).
    /// </summary>
    /// <param name="olderThan">Delete events older than this date.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>Number of events deleted.</returns>
    Task<int> DeleteOldEventsAsync(DateTimeOffset olderThan, CancellationToken cancellationToken = default);
}