/// Abstraction for runtime metrics so the runtime crate does not depend on
/// `prometheus` directly. The CLI (or any other consumer) provides a concrete
/// implementation backed by Prometheus, OpenTelemetry, or whatever it prefers.
pub trait MetricsHook: Send + Sync {
    /// A JSON line failed to parse.
    fn on_parse_error(&self);
    /// `count` events were successfully evaluated.
    fn on_events_processed(&self, count: u64);
    /// `count` detection rule matches were produced.
    fn on_detection_matches(&self, count: u64);
    /// `count` correlation rule matches were produced.
    fn on_correlation_matches(&self, count: u64);
    /// Observe per-event processing latency in seconds.
    fn observe_processing_latency(&self, seconds: f64);
    /// The input queue depth changed by `delta` (positive = enqueue, negative = dequeue).
    fn on_input_queue_depth_change(&self, delta: i64);
    /// Back-pressure event: a source tried to send but the channel was full.
    fn on_back_pressure(&self);
    /// Observe the batch size used for a single engine lock acquisition.
    fn observe_batch_size(&self, size: u64);
    /// The output queue depth changed by `delta`.
    fn on_output_queue_depth_change(&self, delta: i64);
    /// Observe end-to-end pipeline latency (dequeue → sink) in seconds.
    fn observe_pipeline_latency(&self, seconds: f64);
    /// Report current correlation state entry count.
    fn set_correlation_state_entries(&self, count: u64);

    /// A single detection rule matched. Labels enable per-rule Prometheus counters.
    fn on_detection_match_detail(&self, _rule_title: &str, _level: &str) {}
    /// A single correlation rule matched. Labels enable per-rule Prometheus counters.
    fn on_correlation_match_detail(
        &self,
        _rule_title: &str,
        _level: &str,
        _correlation_type: &str,
    ) {
    }

    /// One enrichment call completed (success, skip, error, timeout, drop).
    /// `kind` is the enricher's declared kind (`detection` / `correlation`).
    /// `status` is one of `success` / `skip` / `error` / `timeout` / `drop`.
    fn on_enrichment_completed(
        &self,
        _enricher_id: &str,
        _kind: &str,
        _status: &str,
        _duration_seconds: f64,
    ) {
    }
    /// The enrichment queue depth changed (positive = a result entered the
    /// pipeline, negative = a result completed). Sum across both kinds.
    fn on_enrichment_queue_depth_change(&self, _delta: i64) {}
    /// HTTP enrichment cache lookup hit a live entry.
    fn on_enrichment_http_cache_hit(&self, _enricher_id: &str) {}
    /// HTTP enrichment cache lookup missed (no entry).
    fn on_enrichment_http_cache_miss(&self, _enricher_id: &str) {}
    /// HTTP enrichment cache lookup found an expired entry and evicted it.
    fn on_enrichment_http_cache_expiration(&self, _enricher_id: &str) {}

    /// Pre-register an enricher's `enricher_id` + `kind` label set so
    /// `rsigma_enrichment_total{...}` and
    /// `rsigma_enrichment_duration_seconds{...}` are emitted with their
    /// `# HELP` and `# TYPE` lines from the very first `/metrics`
    /// scrape, even before the enricher has run. Called once per
    /// configured enricher at pipeline construction.
    fn register_enricher(&self, _enricher_id: &str, _kind: &str) {}
    /// Pre-register the three HTTP-cache counter label sets for an
    /// `HttpEnricher` instance so the cache counters are visible on
    /// `/metrics` from startup, even before any cache event fires.
    fn register_http_enricher_cache(&self, _enricher_id: &str) {}
}

/// No-op implementation for use when metrics are disabled (e.g., `rsigma run`).
pub struct NoopMetrics;

impl MetricsHook for NoopMetrics {
    fn on_parse_error(&self) {}
    fn on_events_processed(&self, _count: u64) {}
    fn on_detection_matches(&self, _count: u64) {}
    fn on_correlation_matches(&self, _count: u64) {}
    fn observe_processing_latency(&self, _seconds: f64) {}
    fn on_input_queue_depth_change(&self, _delta: i64) {}
    fn on_back_pressure(&self) {}
    fn observe_batch_size(&self, _size: u64) {}
    fn on_output_queue_depth_change(&self, _delta: i64) {}
    fn observe_pipeline_latency(&self, _seconds: f64) {}
    fn set_correlation_state_entries(&self, _count: u64) {}
}
