namespace StellaOps.Provcache;

/// <summary>
/// High-level service interface for Provcache operations.
/// Orchestrates cache store and repository with metrics and invalidation logic.
/// </summary>
public interface IProvcacheService
{
    /// <summary>
    /// Gets a cached decision by VeriKey.
    /// </summary>
    /// <param name="veriKey">The cache key.</param>
    /// <param name="bypassCache">If true, skip cache and force re-evaluation.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>The cache result with decision if found.</returns>
    Task<ProvcacheServiceResult> GetAsync(
        string veriKey,
        bool bypassCache = false,
        CancellationToken cancellationToken = default);

    /// <summary>
    /// Stores a decision in the cache.
    /// </summary>
    /// <param name="entry">The cache entry to store.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>True if the entry was stored successfully.</returns>
    Task<bool> SetAsync(ProvcacheEntry entry, CancellationToken cancellationToken = default);

    /// <summary>
    /// Gets or computes a decision using a factory function for cache misses.
    /// </summary>
    /// <param name="veriKey">The cache key.</param>
    /// <param name="factory">Factory function to create the entry on cache miss.</param>
    /// <param name="bypassCache">If true, skip cache and force re-computation.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>The cached or newly computed entry.</returns>
    Task<ProvcacheEntry> GetOrComputeAsync(
        string veriKey,
        Func<CancellationToken, Task<ProvcacheEntry>> factory,
        bool bypassCache = false,
        CancellationToken cancellationToken = default);

    /// <summary>
    /// Invalidates a cache entry by VeriKey.
    /// </summary>
    /// <param name="veriKey">The cache key.</param>
    /// <param name="reason">Reason for invalidation (for audit log).</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>True if the entry existed and was invalidated.</returns>
    Task<bool> InvalidateAsync(
        string veriKey,
        string? reason = null,
        CancellationToken cancellationToken = default);

    /// <summary>
    /// Invalidates entries by invalidation criteria.
    /// </summary>
    /// <param name="request">The invalidation request.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>Invalidation result with count of affected entries.</returns>
    Task<InvalidationResult> InvalidateByAsync(
        InvalidationRequest request,
        CancellationToken cancellationToken = default);

    /// <summary>
    /// Gets cache metrics for monitoring.
    /// </summary>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>Cache metrics.</returns>
    Task<ProvcacheMetrics> GetMetricsAsync(CancellationToken cancellationToken = default);

    /// <summary>
    /// Prunes expired entries from the cache.
    /// </summary>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>Number of entries pruned.</returns>
    Task<long> PruneExpiredAsync(CancellationToken cancellationToken = default);
}

/// <summary>
/// Result of a cache service lookup.
/// </summary>
public sealed record ProvcacheServiceResult
{
    /// <summary>
    /// The cache result status.
    /// </summary>
    public required ProvcacheResultStatus Status { get; init; }

    /// <summary>
    /// The cache entry if found.
    /// </summary>
    public ProvcacheEntry? Entry { get; init; }

    /// <summary>
    /// Whether the result came from cache (true) or needs computation (false).
    /// </summary>
    public bool WasCached => Status == ProvcacheResultStatus.CacheHit;

    /// <summary>
    /// Source of the cache hit for diagnostics.
    /// </summary>
    public string? Source { get; init; }

    /// <summary>
    /// Time taken for the lookup in milliseconds.
    /// </summary>
    public double ElapsedMs { get; init; }

    /// <summary>
    /// Creates a cache hit result.
    /// </summary>
    public static ProvcacheServiceResult Hit(ProvcacheEntry entry, string source, double elapsedMs) => new()
    {
        Status = ProvcacheResultStatus.CacheHit,
        Entry = entry,
        Source = source,
        ElapsedMs = elapsedMs
    };

    /// <summary>
    /// Creates a cache miss result.
    /// </summary>
    public static ProvcacheServiceResult Miss(double elapsedMs) => new()
    {
        Status = ProvcacheResultStatus.CacheMiss,
        Entry = null,
        Source = null,
        ElapsedMs = elapsedMs
    };

    /// <summary>
    /// Creates a bypassed result (cache was skipped).
    /// </summary>
    public static ProvcacheServiceResult Bypassed() => new()
    {
        Status = ProvcacheResultStatus.Bypassed,
        Entry = null,
        Source = null,
        ElapsedMs = 0
    };

    /// <summary>
    /// Creates an expired result.
    /// </summary>
    public static ProvcacheServiceResult Expired(ProvcacheEntry entry, double elapsedMs) => new()
    {
        Status = ProvcacheResultStatus.Expired,
        Entry = entry,
        Source = "expired",
        ElapsedMs = elapsedMs
    };
}

/// <summary>
/// Cache result status.
/// </summary>
public enum ProvcacheResultStatus
{
    /// <summary>
    /// Entry was found in cache and is valid.
    /// </summary>
    CacheHit,

    /// <summary>
    /// Entry was not found in cache.
    /// </summary>
    CacheMiss,

    /// <summary>
    /// Cache was bypassed (force re-computation).
    /// </summary>
    Bypassed,

    /// <summary>
    /// Entry was found but has expired.
    /// </summary>
    Expired
}

/// <summary>
/// Request for cache invalidation by criteria.
/// </summary>
public sealed record InvalidationRequest
{
    /// <summary>
    /// The invalidation type.
    /// </summary>
    public required InvalidationType Type { get; init; }

    /// <summary>
    /// The value to match for invalidation.
    /// </summary>
    public required string Value { get; init; }

    /// <summary>
    /// Reason for invalidation (for audit log).
    /// </summary>
    public string? Reason { get; init; }

    /// <summary>
    /// Actor who initiated the invalidation.
    /// </summary>
    public string? Actor { get; init; }

    /// <summary>
    /// Creates an invalidation request by policy hash.
    /// </summary>
    public static InvalidationRequest ByPolicyHash(string policyHash, string? reason = null) => new()
    {
        Type = InvalidationType.PolicyHash,
        Value = policyHash,
        Reason = reason ?? "policy-update"
    };

    /// <summary>
    /// Creates an invalidation request by signer set hash.
    /// </summary>
    public static InvalidationRequest BySignerSetHash(string signerSetHash, string? reason = null) => new()
    {
        Type = InvalidationType.SignerSetHash,
        Value = signerSetHash,
        Reason = reason ?? "signer-revocation"
    };

    /// <summary>
    /// Creates an invalidation request by feed epoch.
    /// </summary>
    public static InvalidationRequest ByFeedEpochOlderThan(string feedEpoch, string? reason = null) => new()
    {
        Type = InvalidationType.FeedEpochOlderThan,
        Value = feedEpoch,
        Reason = reason ?? "feed-update"
    };

    /// <summary>
    /// Creates an invalidation request by key pattern.
    /// </summary>
    public static InvalidationRequest ByPattern(string pattern, string? reason = null) => new()
    {
        Type = InvalidationType.Pattern,
        Value = pattern,
        Reason = reason ?? "pattern-invalidation"
    };
}

/// <summary>
/// Type of invalidation criteria.
/// </summary>
public enum InvalidationType
{
    /// <summary>
    /// Invalidate by policy hash.
    /// </summary>
    PolicyHash,

    /// <summary>
    /// Invalidate by signer set hash.
    /// </summary>
    SignerSetHash,

    /// <summary>
    /// Invalidate entries with feed epoch older than specified.
    /// </summary>
    FeedEpochOlderThan,

    /// <summary>
    /// Invalidate by key pattern.
    /// </summary>
    Pattern,

    /// <summary>
    /// Invalidate expired entries.
    /// </summary>
    Expired
}

/// <summary>
/// Result of an invalidation operation.
/// </summary>
public sealed record InvalidationResult
{
    /// <summary>
    /// Number of entries invalidated.
    /// </summary>
    public required long EntriesAffected { get; init; }

    /// <summary>
    /// The invalidation request that was executed.
    /// </summary>
    public required InvalidationRequest Request { get; init; }

    /// <summary>
    /// Timestamp of the invalidation.
    /// </summary>
    public required DateTimeOffset Timestamp { get; init; }

    /// <summary>
    /// Whether the invalidation was logged for audit.
    /// </summary>
    public bool WasLogged { get; init; }
}

/// <summary>
/// Cache metrics for monitoring and observability.
/// </summary>
public sealed record ProvcacheMetrics
{
    /// <summary>
    /// Total cache requests since startup.
    /// </summary>
    public long TotalRequests { get; init; }

    /// <summary>
    /// Total cache hits since startup.
    /// </summary>
    public long TotalHits { get; init; }

    /// <summary>
    /// Total cache misses since startup.
    /// </summary>
    public long TotalMisses { get; init; }

    /// <summary>
    /// Cache hit rate (0.0 - 1.0).
    /// </summary>
    public double HitRate => TotalRequests == 0 ? 0.0 : (double)TotalHits / TotalRequests;

    /// <summary>
    /// Average lookup latency in milliseconds.
    /// </summary>
    public double AvgLatencyMs { get; init; }

    /// <summary>
    /// P99 lookup latency in milliseconds.
    /// </summary>
    public double P99LatencyMs { get; init; }

    /// <summary>
    /// Current number of entries in cache.
    /// </summary>
    public long CurrentEntryCount { get; init; }

    /// <summary>
    /// Total invalidations since startup.
    /// </summary>
    public long TotalInvalidations { get; init; }

    /// <summary>
    /// Valkey cache health status.
    /// </summary>
    public bool ValkeyCacheHealthy { get; init; }

    /// <summary>
    /// Postgres repository health status.
    /// </summary>
    public bool PostgresRepositoryHealthy { get; init; }

    /// <summary>
    /// Timestamp when metrics were collected.
    /// </summary>
    public DateTimeOffset CollectedAt { get; init; }
}