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

namespace Svrnty.CQRS.Events.Abstractions.Streaming;

/// <summary>
/// Performs health checks on event streams and subscriptions.
/// </summary>
public interface IStreamHealthCheck
{
    /// <summary>
    /// Checks the health of a specific stream.
    /// </summary>
    /// <param name="streamName">Name of the stream to check.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>Health check result for the stream.</returns>
    Task<HealthCheckResult> CheckStreamHealthAsync(string streamName, CancellationToken cancellationToken = default);

    /// <summary>
    /// Checks the health of a specific subscription.
    /// </summary>
    /// <param name="streamName">Name of the stream.</param>
    /// <param name="subscriptionName">Name of the subscription to check.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>Health check result for the subscription.</returns>
    Task<HealthCheckResult> CheckSubscriptionHealthAsync(string streamName, string subscriptionName, CancellationToken cancellationToken = default);

    /// <summary>
    /// Checks the health of all configured streams.
    /// </summary>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>Dictionary of stream names to health check results.</returns>
    Task<IReadOnlyDictionary<string, HealthCheckResult>> CheckAllStreamsAsync(CancellationToken cancellationToken = default);

    /// <summary>
    /// Checks the health of all subscriptions across all streams.
    /// </summary>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>Dictionary of subscription keys (streamName:subscriptionName) to health check results.</returns>
    Task<IReadOnlyDictionary<string, HealthCheckResult>> CheckAllSubscriptionsAsync(CancellationToken cancellationToken = default);
}

/// <summary>
/// Configuration for stream health checks.
/// </summary>
public sealed class StreamHealthCheckOptions
{
    /// <summary>
    /// Maximum consumer lag (in events) before marking as degraded.
    /// Default: 1000 events.
    /// </summary>
    public long DegradedConsumerLagThreshold { get; set; } = 1000;

    /// <summary>
    /// Maximum consumer lag (in events) before marking as unhealthy.
    /// Default: 10000 events.
    /// </summary>
    public long UnhealthyConsumerLagThreshold { get; set; } = 10000;

    /// <summary>
    /// Maximum time without progress before marking consumer as stalled (degraded).
    /// Default: 5 minutes.
    /// </summary>
    public TimeSpan DegradedStalledThreshold { get; set; } = TimeSpan.FromMinutes(5);

    /// <summary>
    /// Maximum time without progress before marking consumer as stalled (unhealthy).
    /// Default: 15 minutes.
    /// </summary>
    public TimeSpan UnhealthyStalledThreshold { get; set; } = TimeSpan.FromMinutes(15);

    /// <summary>
    /// Timeout for health check operations.
    /// Default: 5 seconds.
    /// </summary>
    public TimeSpan HealthCheckTimeout { get; set; } = TimeSpan.FromSeconds(5);
}