using StellaOps.Determinism;

namespace StellaOps.Provcache.Events;

/// <summary>
/// Event published when an advisory feed advances to a new epoch.
/// Provcache subscribers use this to invalidate cache entries
/// that were computed against older feed epochs.
/// </summary>
/// <remarks>
/// Stream name: <c>stellaops:events:feed-epoch-advanced</c>
/// </remarks>
public sealed record FeedEpochAdvancedEvent
{
    /// <summary>
    /// Stream name for feed epoch events.
    /// </summary>
    public const string StreamName = "stellaops:events:feed-epoch-advanced";

    /// <summary>
    /// Event type identifier for serialization.
    /// </summary>
    public const string EventType = "feed.epoch.advanced.v1";

    /// <summary>
    /// Unique identifier for this event instance.
    /// </summary>
    public required Guid EventId { get; init; }

    /// <summary>
    /// Timestamp when the event occurred (UTC).
    /// </summary>
    public required DateTimeOffset Timestamp { get; init; }

    /// <summary>
    /// The feed identifier (e.g., "cve", "ghsa", "osv", "redhat-oval").
    /// </summary>
    public required string FeedId { get; init; }

    /// <summary>
    /// The previous epoch identifier.
    /// Format varies by feed (e.g., "2024-12-24T12:00:00Z", "v2024.52").
    /// </summary>
    public required string PreviousEpoch { get; init; }

    /// <summary>
    /// The new epoch identifier.
    /// </summary>
    public required string NewEpoch { get; init; }

    /// <summary>
    /// When the new epoch became effective.
    /// Cache entries with feed_epoch older than this should be invalidated.
    /// </summary>
    public required DateTimeOffset EffectiveAt { get; init; }

    /// <summary>
    /// Number of advisories added in this epoch (for metrics).
    /// </summary>
    public int? AdvisoriesAdded { get; init; }

    /// <summary>
    /// Number of advisories modified in this epoch (for metrics).
    /// </summary>
    public int? AdvisoriesModified { get; init; }

    /// <summary>
    /// Number of advisories withdrawn in this epoch (for metrics).
    /// </summary>
    public int? AdvisoriesWithdrawn { get; init; }

    /// <summary>
    /// Tenant ID if multi-tenant (null for global feeds).
    /// </summary>
    public string? TenantId { get; init; }

    /// <summary>
    /// Correlation ID for distributed tracing.
    /// </summary>
    public string? CorrelationId { get; init; }

    /// <summary>
    /// Creates a new FeedEpochAdvancedEvent.
    /// </summary>
    /// <param name="feedId">The feed identifier.</param>
    /// <param name="previousEpoch">The previous epoch identifier.</param>
    /// <param name="newEpoch">The new epoch identifier.</param>
    /// <param name="effectiveAt">When the new epoch became effective.</param>
    /// <param name="advisoriesAdded">Number of advisories added (for metrics).</param>
    /// <param name="advisoriesModified">Number of advisories modified (for metrics).</param>
    /// <param name="advisoriesWithdrawn">Number of advisories withdrawn (for metrics).</param>
    /// <param name="tenantId">Tenant ID if multi-tenant.</param>
    /// <param name="correlationId">Correlation ID for tracing.</param>
    /// <param name="eventId">Optional event ID (defaults to new GUID).</param>
    /// <param name="timestamp">Optional timestamp (defaults to current UTC time).</param>
    /// <param name="guidProvider">Optional GUID provider for deterministic IDs.</param>
    /// <param name="timeProvider">Optional time provider for deterministic timestamps.</param>
    public static FeedEpochAdvancedEvent Create(
        string feedId,
        string previousEpoch,
        string newEpoch,
        DateTimeOffset effectiveAt,
        int? advisoriesAdded = null,
        int? advisoriesModified = null,
        int? advisoriesWithdrawn = null,
        string? tenantId = null,
        string? correlationId = null,
        Guid? eventId = null,
        DateTimeOffset? timestamp = null,
        IGuidProvider? guidProvider = null,
        TimeProvider? timeProvider = null)
    {
        var guidSource = guidProvider ?? SystemGuidProvider.Instance;
        var timeSource = timeProvider ?? TimeProvider.System;

        return new FeedEpochAdvancedEvent
        {
            EventId = eventId ?? guidSource.NewGuid(),
            Timestamp = timestamp ?? timeSource.GetUtcNow(),
            FeedId = feedId,
            PreviousEpoch = previousEpoch,
            NewEpoch = newEpoch,
            EffectiveAt = effectiveAt,
            AdvisoriesAdded = advisoriesAdded,
            AdvisoriesModified = advisoriesModified,
            AdvisoriesWithdrawn = advisoriesWithdrawn,
            TenantId = tenantId,
            CorrelationId = correlationId
        };
    }
}