// SPDX-FileCopyrightText: Copyright (c) 2024-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
// SPDX-License-Identifier: Apache-2.0

//! Metrics registry trait and implementation for Prometheus metrics
//!
//! This module provides a trait-based interface for creating and managing Prometheus metrics
//! with automatic label injection and hierarchical naming support.

pub mod prometheus_names;

use parking_lot::Mutex;
use std::collections::HashSet;
use std::sync::Arc;

use crate::component::ComponentBuilder;
use anyhow;
use once_cell::sync::Lazy;
use regex::Regex;
use std::any::Any;
use std::collections::HashMap;

// Import commonly used items to avoid verbose prefixes
use prometheus_names::{
    build_component_metric_name, labels, name_prefix, sanitize_prometheus_label,
    sanitize_prometheus_name, work_handler,
};

// Pipeline imports for endpoint creation
use crate::pipeline::{
    AsyncEngine, AsyncEngineContextProvider, Error, ManyOut, ResponseStream, SingleIn, async_trait,
    network::Ingress,
};
use crate::protocols::annotated::Annotated;
use crate::stream;
use crate::stream::StreamExt;

// Prometheus imports
use prometheus::Encoder;

/// Validate that a label slice has no duplicate keys.
/// Returns Ok(()) when all keys are unique; otherwise returns an error naming the duplicate key.
fn validate_no_duplicate_label_keys(labels: &[(&str, &str)]) -> anyhow::Result<()> {
    let mut seen_keys = std::collections::HashSet::new();
    for (key, _) in labels {
        if !seen_keys.insert(*key) {
            return Err(anyhow::anyhow!(
                "Duplicate label key '{}' found in labels",
                key
            ));
        }
    }
    Ok(())
}

/// ==============================
/// Prometheus section
/// ==============================
/// Trait that defines common behavior for Prometheus metric types
pub trait PrometheusMetric: prometheus::core::Collector + Clone + Send + Sync + 'static {
    /// Create a new metric with the given options
    fn with_opts(opts: prometheus::Opts) -> Result<Self, prometheus::Error>
    where
        Self: Sized;

    /// Create a new metric with histogram options and custom buckets
    /// This is a default implementation that will panic for non-histogram metrics
    fn with_histogram_opts_and_buckets(
        _opts: prometheus::HistogramOpts,
        _buckets: Option<Vec<f64>>,
    ) -> Result<Self, prometheus::Error>
    where
        Self: Sized,
    {
        panic!("with_histogram_opts_and_buckets is not implemented for this metric type");
    }

    /// Create a new metric with counter options and label names (for CounterVec)
    /// This is a default implementation that will panic for non-countervec metrics
    fn with_opts_and_label_names(
        _opts: prometheus::Opts,
        _label_names: &[&str],
    ) -> Result<Self, prometheus::Error>
    where
        Self: Sized,
    {
        panic!("with_opts_and_label_names is not implemented for this metric type");
    }
}

// Implement the trait for Counter, IntCounter, and Gauge
impl PrometheusMetric for prometheus::Counter {
    fn with_opts(opts: prometheus::Opts) -> Result<Self, prometheus::Error> {
        prometheus::Counter::with_opts(opts)
    }
}

impl PrometheusMetric for prometheus::IntCounter {
    fn with_opts(opts: prometheus::Opts) -> Result<Self, prometheus::Error> {
        prometheus::IntCounter::with_opts(opts)
    }
}

impl PrometheusMetric for prometheus::Gauge {
    fn with_opts(opts: prometheus::Opts) -> Result<Self, prometheus::Error> {
        prometheus::Gauge::with_opts(opts)
    }
}

impl PrometheusMetric for prometheus::IntGauge {
    fn with_opts(opts: prometheus::Opts) -> Result<Self, prometheus::Error> {
        prometheus::IntGauge::with_opts(opts)
    }
}

impl PrometheusMetric for prometheus::GaugeVec {
    fn with_opts(_opts: prometheus::Opts) -> Result<Self, prometheus::Error> {
        Err(prometheus::Error::Msg(
            "GaugeVec requires label names, use with_opts_and_label_names instead".to_string(),
        ))
    }

    fn with_opts_and_label_names(
        opts: prometheus::Opts,
        label_names: &[&str],
    ) -> Result<Self, prometheus::Error> {
        prometheus::GaugeVec::new(opts, label_names)
    }
}

impl PrometheusMetric for prometheus::IntGaugeVec {
    fn with_opts(_opts: prometheus::Opts) -> Result<Self, prometheus::Error> {
        Err(prometheus::Error::Msg(
            "IntGaugeVec requires label names, use with_opts_and_label_names instead".to_string(),
        ))
    }

    fn with_opts_and_label_names(
        opts: prometheus::Opts,
        label_names: &[&str],
    ) -> Result<Self, prometheus::Error> {
        prometheus::IntGaugeVec::new(opts, label_names)
    }
}

impl PrometheusMetric for prometheus::IntCounterVec {
    fn with_opts(_opts: prometheus::Opts) -> Result<Self, prometheus::Error> {
        Err(prometheus::Error::Msg(
            "IntCounterVec requires label names, use with_opts_and_label_names instead".to_string(),
        ))
    }

    fn with_opts_and_label_names(
        opts: prometheus::Opts,
        label_names: &[&str],
    ) -> Result<Self, prometheus::Error> {
        prometheus::IntCounterVec::new(opts, label_names)
    }
}

// Implement the trait for Histogram
impl PrometheusMetric for prometheus::Histogram {
    fn with_opts(opts: prometheus::Opts) -> Result<Self, prometheus::Error> {
        // Convert Opts to HistogramOpts
        let histogram_opts = prometheus::HistogramOpts::new(opts.name, opts.help);
        prometheus::Histogram::with_opts(histogram_opts)
    }

    fn with_histogram_opts_and_buckets(
        mut opts: prometheus::HistogramOpts,
        buckets: Option<Vec<f64>>,
    ) -> Result<Self, prometheus::Error> {
        if let Some(custom_buckets) = buckets {
            opts = opts.buckets(custom_buckets);
        }
        prometheus::Histogram::with_opts(opts)
    }
}

// Implement the trait for CounterVec
impl PrometheusMetric for prometheus::CounterVec {
    fn with_opts(_opts: prometheus::Opts) -> Result<Self, prometheus::Error> {
        // This will panic - CounterVec needs label names
        panic!("CounterVec requires label names, use with_opts_and_label_names instead");
    }

    fn with_opts_and_label_names(
        opts: prometheus::Opts,
        label_names: &[&str],
    ) -> Result<Self, prometheus::Error> {
        prometheus::CounterVec::new(opts, label_names)
    }
}

/// ==============================
/// Metrics section
/// ==============================
/// Public helper function to create metrics - accessible for Python bindings
pub fn create_metric<T: PrometheusMetric, H: MetricsHierarchy + ?Sized>(
    hierarchy: &H,
    metric_name: &str,
    metric_desc: &str,
    labels: &[(&str, &str)],
    buckets: Option<Vec<f64>>,
    const_labels: Option<&[&str]>,
) -> anyhow::Result<T> {
    // Validate that user-provided labels don't have duplicate keys
    validate_no_duplicate_label_keys(labels)?;
    // Note: stored labels functionality has been removed

    let basename = hierarchy.basename();
    let parent_hierarchies = hierarchy.parent_hierarchies();

    // Build hierarchy path as vector of strings: parent names + [basename]
    let mut hierarchy_names: Vec<String> =
        parent_hierarchies.iter().map(|p| p.basename()).collect();
    hierarchy_names.push(basename.clone());

    let metric_name = build_component_metric_name(metric_name);

    // Build updated_labels: auto-labels first, then `labels` + stored labels
    let mut updated_labels: Vec<(String, String)> = Vec::new();

    // Auto-label injection: Always add dynamo_namespace, dynamo_component, dynamo_endpoint labels
    // based on the hierarchy. Label constants defined in prometheus_names.rs labels module.
    //
    // Python counterpart: components/src/dynamo/common/utils/prometheus.py register_engine_metrics_callback()

    // Validate that user-provided labels don't conflict with auto-generated labels
    for (key, _) in labels {
        if *key == labels::NAMESPACE || *key == labels::COMPONENT || *key == labels::ENDPOINT {
            return Err(anyhow::anyhow!(
                "Label '{}' is automatically added by auto-label injection and cannot be manually set",
                key
            ));
        }
    }

    // Add auto-generated labels with sanitized values
    // Hierarchy: [drt, namespace, component, endpoint]
    if hierarchy_names.len() > 1 {
        let namespace = &hierarchy_names[1];
        if !namespace.is_empty() {
            let valid_namespace = sanitize_prometheus_label(namespace)?;
            if !valid_namespace.is_empty() {
                updated_labels.push((labels::NAMESPACE.to_string(), valid_namespace));
            }
        }
    }
    if hierarchy_names.len() > 2 {
        let component = &hierarchy_names[2];
        if !component.is_empty() {
            let valid_component = sanitize_prometheus_label(component)?;
            if !valid_component.is_empty() {
                updated_labels.push((labels::COMPONENT.to_string(), valid_component));
            }
        }
    }
    if hierarchy_names.len() > 3 {
        let endpoint = &hierarchy_names[3];
        if !endpoint.is_empty() {
            let valid_endpoint = sanitize_prometheus_label(endpoint)?;
            if !valid_endpoint.is_empty() {
                updated_labels.push((labels::ENDPOINT.to_string(), valid_endpoint));
            }
        }
    }

    // Add user labels
    updated_labels.extend(
        labels
            .iter()
            .map(|(k, v)| ((*k).to_string(), (*v).to_string())),
    );
    // Note: stored labels functionality has been removed

    // Handle different metric types
    let prometheus_metric = if std::any::TypeId::of::<T>()
        == std::any::TypeId::of::<prometheus::CounterVec>()
    {
        // Special handling for CounterVec with label names
        // const_labels parameter is required for CounterVec
        if buckets.is_some() {
            return Err(anyhow::anyhow!(
                "buckets parameter is not valid for CounterVec"
            ));
        }
        let mut opts = prometheus::Opts::new(&metric_name, metric_desc);
        for (key, value) in &updated_labels {
            opts = opts.const_label(key.clone(), value.clone());
        }
        let label_names = const_labels
            .ok_or_else(|| anyhow::anyhow!("CounterVec requires const_labels parameter"))?;
        T::with_opts_and_label_names(opts, label_names)?
    } else if std::any::TypeId::of::<T>() == std::any::TypeId::of::<prometheus::GaugeVec>() {
        // Special handling for GaugeVec with label names
        // const_labels parameter is required for GaugeVec
        if buckets.is_some() {
            return Err(anyhow::anyhow!(
                "buckets parameter is not valid for GaugeVec"
            ));
        }
        let mut opts = prometheus::Opts::new(&metric_name, metric_desc);
        for (key, value) in &updated_labels {
            opts = opts.const_label(key.clone(), value.clone());
        }
        let label_names = const_labels
            .ok_or_else(|| anyhow::anyhow!("GaugeVec requires const_labels parameter"))?;
        T::with_opts_and_label_names(opts, label_names)?
    } else if std::any::TypeId::of::<T>() == std::any::TypeId::of::<prometheus::Histogram>() {
        // Special handling for Histogram with custom buckets
        // buckets parameter is valid for Histogram, const_labels is not used
        if const_labels.is_some() {
            return Err(anyhow::anyhow!(
                "const_labels parameter is not valid for Histogram"
            ));
        }
        let mut opts = prometheus::HistogramOpts::new(&metric_name, metric_desc);
        for (key, value) in &updated_labels {
            opts = opts.const_label(key.clone(), value.clone());
        }
        T::with_histogram_opts_and_buckets(opts, buckets)?
    } else if std::any::TypeId::of::<T>() == std::any::TypeId::of::<prometheus::IntCounterVec>() {
        // Special handling for IntCounterVec with label names
        // const_labels parameter is required for IntCounterVec
        if buckets.is_some() {
            return Err(anyhow::anyhow!(
                "buckets parameter is not valid for IntCounterVec"
            ));
        }
        let mut opts = prometheus::Opts::new(&metric_name, metric_desc);
        for (key, value) in &updated_labels {
            opts = opts.const_label(key.clone(), value.clone());
        }
        let label_names = const_labels
            .ok_or_else(|| anyhow::anyhow!("IntCounterVec requires const_labels parameter"))?;
        T::with_opts_and_label_names(opts, label_names)?
    } else if std::any::TypeId::of::<T>() == std::any::TypeId::of::<prometheus::IntGaugeVec>() {
        // Special handling for IntGaugeVec with label names
        // const_labels parameter is required for IntGaugeVec
        if buckets.is_some() {
            return Err(anyhow::anyhow!(
                "buckets parameter is not valid for IntGaugeVec"
            ));
        }
        let mut opts = prometheus::Opts::new(&metric_name, metric_desc);
        for (key, value) in &updated_labels {
            opts = opts.const_label(key.clone(), value.clone());
        }
        let label_names = const_labels
            .ok_or_else(|| anyhow::anyhow!("IntGaugeVec requires const_labels parameter"))?;
        T::with_opts_and_label_names(opts, label_names)?
    } else {
        // Standard handling for Counter, IntCounter, Gauge, IntGauge
        // buckets and const_labels parameters are not valid for these types
        if buckets.is_some() {
            return Err(anyhow::anyhow!(
                "buckets parameter is not valid for Counter, IntCounter, Gauge, or IntGauge"
            ));
        }
        if const_labels.is_some() {
            return Err(anyhow::anyhow!(
                "const_labels parameter is not valid for Counter, IntCounter, Gauge, or IntGauge"
            ));
        }
        let mut opts = prometheus::Opts::new(&metric_name, metric_desc);
        for (key, value) in &updated_labels {
            opts = opts.const_label(key.clone(), value.clone());
        }
        T::with_opts(opts)?
    };

    let collector: Box<dyn prometheus::core::Collector> = Box::new(prometheus_metric.clone());
    hierarchy.get_metrics_registry().add_metric(collector)?;

    Ok(prometheus_metric)
}

/// Wrapper struct that provides access to metrics functionality
/// This struct is accessed via the `.metrics()` method on DistributedRuntime, Namespace, Component, and Endpoint
pub struct Metrics<H: MetricsHierarchy> {
    hierarchy: H,
}

impl<H: MetricsHierarchy> Metrics<H> {
    pub fn new(hierarchy: H) -> Self {
        Self { hierarchy }
    }

    // TODO: Add support for additional Prometheus metric types:
    // - Counter: ✅ IMPLEMENTED - create_counter()
    // - CounterVec: ✅ IMPLEMENTED - create_countervec()
    // - Gauge: ✅ IMPLEMENTED - create_gauge()
    // - GaugeVec: ✅ IMPLEMENTED - create_gaugevec()
    // - GaugeHistogram: create_gauge_histogram() - for gauge histograms
    // - Histogram: ✅ IMPLEMENTED - create_histogram()
    // - HistogramVec with custom buckets: create_histogram_with_buckets()
    // - Info: create_info() - for info metrics with labels
    // - IntCounter: ✅ IMPLEMENTED - create_intcounter()
    // - IntCounterVec: ✅ IMPLEMENTED - create_intcountervec()
    // - IntGauge: ✅ IMPLEMENTED - create_intgauge()
    // - IntGaugeVec: ✅ IMPLEMENTED - create_intgaugevec()
    // - Stateset: create_stateset() - for state-based metrics
    // - Summary: create_summary() - for quantiles and sum/count metrics
    // - SummaryVec: create_summary_vec() - for labeled summaries
    // - Untyped: create_untyped() - for untyped metrics
    //
    // NOTE: The order of create_* methods below is mirrored in lib/bindings/python/rust/lib.rs::Metrics
    // Keep them synchronized when adding new metric types

    /// Create a Counter metric
    pub fn create_counter(
        &self,
        name: &str,
        description: &str,
        labels: &[(&str, &str)],
    ) -> anyhow::Result<prometheus::Counter> {
        create_metric(&self.hierarchy, name, description, labels, None, None)
    }

    /// Create a CounterVec metric with label names (for dynamic labels)
    pub fn create_countervec(
        &self,
        name: &str,
        description: &str,
        const_labels: &[&str],
        const_label_values: &[(&str, &str)],
    ) -> anyhow::Result<prometheus::CounterVec> {
        create_metric(
            &self.hierarchy,
            name,
            description,
            const_label_values,
            None,
            Some(const_labels),
        )
    }

    /// Create a Gauge metric
    pub fn create_gauge(
        &self,
        name: &str,
        description: &str,
        labels: &[(&str, &str)],
    ) -> anyhow::Result<prometheus::Gauge> {
        create_metric(&self.hierarchy, name, description, labels, None, None)
    }

    /// Create a GaugeVec metric with label names (for dynamic labels)
    pub fn create_gaugevec(
        &self,
        name: &str,
        description: &str,
        const_labels: &[&str],
        const_label_values: &[(&str, &str)],
    ) -> anyhow::Result<prometheus::GaugeVec> {
        create_metric(
            &self.hierarchy,
            name,
            description,
            const_label_values,
            None,
            Some(const_labels),
        )
    }

    /// Create a Histogram metric with custom buckets
    pub fn create_histogram(
        &self,
        name: &str,
        description: &str,
        labels: &[(&str, &str)],
        buckets: Option<Vec<f64>>,
    ) -> anyhow::Result<prometheus::Histogram> {
        create_metric(&self.hierarchy, name, description, labels, buckets, None)
    }

    /// Create an IntCounter metric
    pub fn create_intcounter(
        &self,
        name: &str,
        description: &str,
        labels: &[(&str, &str)],
    ) -> anyhow::Result<prometheus::IntCounter> {
        create_metric(&self.hierarchy, name, description, labels, None, None)
    }

    /// Create an IntCounterVec metric with label names (for dynamic labels)
    pub fn create_intcountervec(
        &self,
        name: &str,
        description: &str,
        const_labels: &[&str],
        const_label_values: &[(&str, &str)],
    ) -> anyhow::Result<prometheus::IntCounterVec> {
        create_metric(
            &self.hierarchy,
            name,
            description,
            const_label_values,
            None,
            Some(const_labels),
        )
    }

    /// Create an IntGauge metric
    pub fn create_intgauge(
        &self,
        name: &str,
        description: &str,
        labels: &[(&str, &str)],
    ) -> anyhow::Result<prometheus::IntGauge> {
        create_metric(&self.hierarchy, name, description, labels, None, None)
    }

    /// Create an IntGaugeVec metric with label names (for dynamic labels)
    pub fn create_intgaugevec(
        &self,
        name: &str,
        description: &str,
        const_labels: &[&str],
        const_label_values: &[(&str, &str)],
    ) -> anyhow::Result<prometheus::IntGaugeVec> {
        create_metric(
            &self.hierarchy,
            name,
            description,
            const_label_values,
            None,
            Some(const_labels),
        )
    }

    /// Get metrics in Prometheus text format
    pub fn prometheus_expfmt(&self) -> anyhow::Result<String> {
        self.hierarchy
            .get_metrics_registry()
            .prometheus_expfmt_combined()
    }
}

/// This trait should be implemented by all metric registries, including Prometheus, Envy, OpenTelemetry, and others.
/// It offers a unified interface for creating and managing metrics, organizing sub-registries, and
/// generating output in Prometheus text format.
use crate::traits::DistributedRuntimeProvider;

pub trait MetricsHierarchy: Send + Sync {
    // ========================================================================
    // Required methods - must be implemented by all types
    // ========================================================================

    /// Get the name of this hierarchy (without any hierarchy prefix)
    fn basename(&self) -> String;

    /// Get the parent hierarchies as actual objects (not strings)
    /// Returns a vector of hierarchy references, ordered from root to immediate parent.
    /// For example, an Endpoint would return [DRT, Namespace, Component].
    fn parent_hierarchies(&self) -> Vec<&dyn MetricsHierarchy>;

    /// Get a reference to this hierarchy's metrics registry
    fn get_metrics_registry(&self) -> &MetricsRegistry;

    // ========================================================================
    // Provided methods - have default implementations
    // ========================================================================

    /// Access the metrics interface for this hierarchy
    /// This is a provided method that works for any type implementing MetricsHierarchy
    fn metrics(&self) -> Metrics<&Self>
    where
        Self: Sized,
    {
        Metrics::new(self)
    }
}

// Blanket implementation for references to types that implement MetricsHierarchy
impl<T: MetricsHierarchy + ?Sized> MetricsHierarchy for &T {
    fn basename(&self) -> String {
        (**self).basename()
    }

    fn parent_hierarchies(&self) -> Vec<&dyn MetricsHierarchy> {
        (**self).parent_hierarchies()
    }

    fn get_metrics_registry(&self) -> &MetricsRegistry {
        (**self).get_metrics_registry()
    }
}

/// Type alias for runtime callback functions to reduce complexity
///
/// This type represents an Arc-wrapped callback function that can be:
/// - Shared efficiently across multiple threads and contexts
/// - Cloned without duplicating the underlying closure
/// - Used in generic contexts requiring 'static lifetime
///
/// The Arc wrapper is included in the type to make sharing explicit.
pub type PrometheusUpdateCallback = Arc<dyn Fn() -> anyhow::Result<()> + Send + Sync + 'static>;

/// Type alias for exposition text callback functions that return Prometheus text
pub type PrometheusExpositionFormatCallback =
    Arc<dyn Fn() -> anyhow::Result<String> + Send + Sync + 'static>;

/// Structure to hold Prometheus registries and associated callbacks for a given hierarchy.
///
/// All fields are Arc-wrapped, so cloning shares state. This ensures metrics registered
/// on cloned instances (e.g., cloned Client/Endpoint) are visible to the original.
#[derive(Clone)]
pub struct MetricsRegistry {
    /// The Prometheus registry for this hierarchy.
    /// Arc-wrapped so clones share the same registry (metrics registered on clones are visible everywhere).
    pub prometheus_registry: Arc<std::sync::RwLock<prometheus::Registry>>,

    /// Child registries included when emitting combined `/metrics` output.
    ///
    /// Why this exists:
    /// - Previously, `create_metric()` registered every collector into *all* parent registries
    ///   (Endpoint → Component → Namespace → DRT) so scraping the root registry included everything.
    /// - That fan-out caused Prometheus collisions when different endpoints tried to register the
    ///   same metric name with different const-labels (descriptor mismatch).
    ///
    /// We now register metrics only into the local hierarchy registry to avoid collisions.
    /// `child_registries` rebuilds “what to scrape” as a tree of registries so `/metrics` can:
    /// - traverse registries recursively,
    /// - merge metric families into one exposition payload,
    /// - warn/drop exact duplicate series, while allowing same metric name with different labels.
    child_registries: Arc<std::sync::RwLock<Vec<MetricsRegistry>>>,

    /// Update callbacks invoked before metrics are scraped.
    /// Wrapped in Arc to preserve callbacks across clones (prevents callback loss when MetricsRegistry is cloned).
    pub prometheus_update_callbacks: Arc<std::sync::RwLock<Vec<PrometheusUpdateCallback>>>,

    /// Callbacks that return Prometheus exposition text appended to metrics output.
    /// Wrapped in Arc to preserve callbacks across clones (e.g., vLLM callbacks registered at Endpoint remain accessible at DRT).
    pub prometheus_expfmt_callbacks:
        Arc<std::sync::RwLock<Vec<PrometheusExpositionFormatCallback>>>,
}

impl std::fmt::Debug for MetricsRegistry {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("MetricsRegistry")
            .field("prometheus_registry", &"<RwLock<Registry>>")
            .field(
                "prometheus_update_callbacks",
                &format!(
                    "<RwLock<Vec<Callback>>> with {} callbacks",
                    self.prometheus_update_callbacks.read().unwrap().len()
                ),
            )
            .field(
                "prometheus_expfmt_callbacks",
                &format!(
                    "<RwLock<Vec<Callback>>> with {} callbacks",
                    self.prometheus_expfmt_callbacks.read().unwrap().len()
                ),
            )
            .finish()
    }
}

impl MetricsRegistry {
    /// Create a new metrics registry with an empty Prometheus registry and callback lists
    pub fn new() -> Self {
        Self {
            prometheus_registry: Arc::new(std::sync::RwLock::new(prometheus::Registry::new())),
            child_registries: Arc::new(std::sync::RwLock::new(Vec::new())),
            prometheus_update_callbacks: Arc::new(std::sync::RwLock::new(Vec::new())),
            prometheus_expfmt_callbacks: Arc::new(std::sync::RwLock::new(Vec::new())),
        }
    }

    /// Add a child registry to be included in combined /metrics output.
    ///
    /// Dedup is by underlying Prometheus registry pointer, so repeated registration via clones is safe.
    pub fn add_child_registry(&self, child: &MetricsRegistry) {
        let child_ptr = Arc::as_ptr(&child.prometheus_registry);
        let mut guard = self.child_registries.write().unwrap();
        if guard
            .iter()
            .any(|r| Arc::as_ptr(&r.prometheus_registry) == child_ptr)
        {
            return;
        }
        guard.push(child.clone());
    }

    fn registries_for_combined_scrape(&self) -> Vec<MetricsRegistry> {
        // Traverse child registries recursively so `prometheus_expfmt()` on any hierarchy
        // (DRT/namespace/component/endpoint) includes metrics from its descendants.
        //
        // Dedup by underlying Prometheus registry pointer so multiple paths (e.g. also registering
        // directly on the root) won't duplicate output.
        fn visit(
            registry: &MetricsRegistry,
            out: &mut Vec<MetricsRegistry>,
            seen: &mut HashSet<*const std::sync::RwLock<prometheus::Registry>>,
        ) {
            let ptr = Arc::as_ptr(&registry.prometheus_registry);
            if !seen.insert(ptr) {
                return;
            }

            out.push(registry.clone());

            let children: Vec<MetricsRegistry> = registry
                .child_registries
                .read()
                .unwrap()
                .iter()
                .cloned()
                .collect();
            for child in children {
                visit(&child, out, seen);
            }
        }

        let mut out = Vec::new();
        let mut seen: HashSet<*const std::sync::RwLock<prometheus::Registry>> = HashSet::new();
        visit(self, &mut out, &mut seen);
        out
    }

    /// Combine metrics across this registry and all registered children into one Prometheus exposition output.
    ///
    /// - Families are merged by name; HELP and TYPE must match.
    /// - Multiple series for the same name are allowed if labels differ.
    /// - Exact duplicate series (same name + identical label pairs) are warned and dropped.
    pub fn prometheus_expfmt_combined(&self) -> anyhow::Result<String> {
        let registries = self.registries_for_combined_scrape();

        // Run per-registry update callbacks first.
        for registry in &registries {
            for result in registry.execute_update_callbacks() {
                if let Err(e) = result {
                    tracing::error!("Error executing metrics callback: {}", e);
                }
            }
        }

        // Merge metric families.
        let mut by_name: HashMap<String, prometheus::proto::MetricFamily> = HashMap::new();
        let mut seen_series: HashSet<String> = HashSet::new();

        for (registry_idx, registry) in registries.iter().enumerate() {
            let families = registry.get_prometheus_registry().gather();
            for mut family in families {
                let name = family.name().to_string();

                let entry = by_name.entry(name.clone()).or_insert_with(|| {
                    let mut out = prometheus::proto::MetricFamily::new();
                    out.set_name(name.clone());
                    out.set_help(family.help().to_string());
                    out.set_field_type(family.get_field_type());
                    out
                });

                if entry.help() != family.help()
                    || entry.get_field_type() != family.get_field_type()
                {
                    return Err(anyhow::anyhow!(
                        "Metric family '{}' has inconsistent help/type across registries (idx={})",
                        name,
                        registry_idx
                    ));
                }

                let mut metrics = family.take_metric();
                for metric in metrics.drain(..) {
                    let mut labels: Vec<(String, String)> = metric
                        .get_label()
                        .iter()
                        .map(|lp| (lp.name().to_string(), lp.value().to_string()))
                        .collect();
                    labels.sort_by(|(ka, va), (kb, vb)| (ka, va).cmp(&(kb, vb)));

                    let key = format!(
                        "{}|{}",
                        name,
                        labels
                            .iter()
                            .map(|(k, v)| format!("{}={}", k, v))
                            .collect::<Vec<_>>()
                            .join(",")
                    );

                    if !seen_series.insert(key) {
                        tracing::warn!(
                            metric_name = %name,
                            labels = ?labels,
                            registry_idx,
                            "Duplicate Prometheus series while merging registries; dropping later sample"
                        );
                        continue;
                    }

                    entry.mut_metric().push(metric);
                }
            }
        }

        let mut merged: Vec<prometheus::proto::MetricFamily> = by_name.into_values().collect();
        merged.sort_by(|a, b| a.name().cmp(b.name()));

        let encoder = prometheus::TextEncoder::new();
        let mut buffer = Vec::new();
        encoder.encode(&merged, &mut buffer)?;
        let mut result = String::from_utf8(buffer)?;

        // Append expfmt callbacks deterministically in registry order.
        let mut expfmt = String::new();
        for registry in registries {
            let text = registry.execute_expfmt_callbacks();
            if !text.is_empty() {
                if !expfmt.is_empty() && !expfmt.ends_with('\n') {
                    expfmt.push('\n');
                }
                expfmt.push_str(&text);
            }
        }

        if !expfmt.is_empty() {
            if !result.ends_with('\n') {
                result.push('\n');
            }
            result.push_str(&expfmt);
        }

        Ok(result)
    }

    /// Add a callback function that receives a reference to any MetricsHierarchy
    pub fn add_update_callback(&self, callback: PrometheusUpdateCallback) {
        self.prometheus_update_callbacks
            .write()
            .unwrap()
            .push(callback);
    }

    /// Add an exposition text callback that returns Prometheus text
    pub fn add_expfmt_callback(&self, callback: PrometheusExpositionFormatCallback) {
        self.prometheus_expfmt_callbacks
            .write()
            .unwrap()
            .push(callback);
    }

    /// Execute all update callbacks and return their results
    pub fn execute_update_callbacks(&self) -> Vec<anyhow::Result<()>> {
        self.prometheus_update_callbacks
            .read()
            .unwrap()
            .iter()
            .map(|callback| callback())
            .collect()
    }

    /// Execute all exposition text callbacks and return their concatenated text
    pub fn execute_expfmt_callbacks(&self) -> String {
        let callbacks = self.prometheus_expfmt_callbacks.read().unwrap();
        let mut result = String::new();
        for callback in callbacks.iter() {
            match callback() {
                Ok(text) => {
                    if !text.is_empty() {
                        if !result.is_empty() && !result.ends_with('\n') {
                            result.push('\n');
                        }
                        result.push_str(&text);
                    }
                }
                Err(e) => {
                    tracing::error!("Error executing exposition text callback: {}", e);
                }
            }
        }
        result
    }

    /// Add a Prometheus metric collector to this registry
    pub fn add_metric(
        &self,
        collector: Box<dyn prometheus::core::Collector>,
    ) -> anyhow::Result<()> {
        self.prometheus_registry
            .write()
            .unwrap()
            .register(collector)
            .map_err(|e| anyhow::anyhow!("Failed to register metric: {}", e))
    }

    /// Get a read guard to the Prometheus registry for scraping
    pub fn get_prometheus_registry(&self) -> std::sync::RwLockReadGuard<'_, prometheus::Registry> {
        self.prometheus_registry.read().unwrap()
    }

    /// Returns true if a metric with the given name already exists in the Prometheus registry
    pub fn has_metric_named(&self, metric_name: &str) -> bool {
        self.prometheus_registry
            .read()
            .unwrap()
            .gather()
            .iter()
            .any(|mf| mf.name() == metric_name)
    }
}

impl Default for MetricsRegistry {
    fn default() -> Self {
        Self::new()
    }
}

#[cfg(test)]
mod test_helpers {
    use super::prometheus_names::name_prefix;
    use super::*;

    /// Base function to filter Prometheus output lines based on a predicate.
    /// Returns lines that match the predicate, converted to String.
    fn filter_prometheus_lines<F>(input: &str, mut predicate: F) -> Vec<String>
    where
        F: FnMut(&str) -> bool,
    {
        input
            .lines()
            .filter(|line| predicate(line))
            .map(|line| line.to_string())
            .collect::<Vec<_>>()
    }

    /// Extracts all component metrics (excluding help text and type definitions).
    /// Returns only the actual metric lines with values.
    pub fn extract_metrics(input: &str) -> Vec<String> {
        filter_prometheus_lines(input, |line| {
            line.starts_with(&format!("{}_", name_prefix::COMPONENT))
                && !line.starts_with("#")
                && !line.trim().is_empty()
        })
    }

    /// Parses a Prometheus metric line and extracts the name, labels, and value.
    /// Used instead of fetching metrics directly to test end-to-end results, not intermediate state.
    ///
    /// # Example
    /// ```
    /// let line = "http_requests_total{method=\"GET\"} 1234";
    /// let (name, labels, value) = parse_prometheus_metric(line).unwrap();
    /// assert_eq!(name, "http_requests_total");
    /// assert_eq!(labels.get("method"), Some(&"GET".to_string()));
    /// assert_eq!(value, 1234.0);
    /// ```
    pub fn parse_prometheus_metric(
        line: &str,
    ) -> Option<(String, std::collections::HashMap<String, String>, f64)> {
        if line.trim().is_empty() || line.starts_with('#') {
            return None;
        }

        let parts: Vec<&str> = line.split_whitespace().collect();
        if parts.len() < 2 {
            return None;
        }

        let metric_part = parts[0];
        let value: f64 = parts[1].parse().ok()?;

        let (name, labels) = if metric_part.contains('{') {
            let brace_start = metric_part.find('{').unwrap();
            let brace_end = metric_part.rfind('}').unwrap_or(metric_part.len());
            let name = &metric_part[..brace_start];
            let labels_str = &metric_part[brace_start + 1..brace_end];

            let mut labels = std::collections::HashMap::new();
            for pair in labels_str.split(',') {
                if let Some((k, v)) = pair.split_once('=') {
                    let v = v.trim_matches('"');
                    labels.insert(k.trim().to_string(), v.to_string());
                }
            }
            (name.to_string(), labels)
        } else {
            (metric_part.to_string(), std::collections::HashMap::new())
        };

        Some((name, labels, value))
    }
}

#[cfg(test)]
mod test_metricsregistry_units {
    use super::*;

    #[test]
    fn test_build_component_metric_name_with_prefix() {
        // Test that build_component_metric_name correctly prepends the dynamo_component prefix
        let result = build_component_metric_name("requests");
        assert_eq!(result, "dynamo_component_requests");

        let result = build_component_metric_name("counter");
        assert_eq!(result, "dynamo_component_counter");
    }

    #[test]
    fn test_parse_prometheus_metric() {
        use super::test_helpers::parse_prometheus_metric;
        use std::collections::HashMap;

        // Test parsing a metric with labels
        let line = "http_requests_total{method=\"GET\",status=\"200\"} 1234";
        let parsed = parse_prometheus_metric(line);
        assert!(parsed.is_some());

        let (name, labels, value) = parsed.unwrap();
        assert_eq!(name, "http_requests_total");

        let mut expected_labels = HashMap::new();
        expected_labels.insert("method".to_string(), "GET".to_string());
        expected_labels.insert("status".to_string(), "200".to_string());
        assert_eq!(labels, expected_labels);

        assert_eq!(value, 1234.0);

        // Test parsing a metric without labels
        let line = "cpu_usage 98.5";
        let parsed = parse_prometheus_metric(line);
        assert!(parsed.is_some());

        let (name, labels, value) = parsed.unwrap();
        assert_eq!(name, "cpu_usage");
        assert!(labels.is_empty());
        assert_eq!(value, 98.5);

        // Test parsing a metric with float value
        let line = "response_time{service=\"api\"} 0.123";
        let parsed = parse_prometheus_metric(line);
        assert!(parsed.is_some());

        let (name, labels, value) = parsed.unwrap();
        assert_eq!(name, "response_time");

        let mut expected_labels = HashMap::new();
        expected_labels.insert("service".to_string(), "api".to_string());
        assert_eq!(labels, expected_labels);

        assert_eq!(value, 0.123);

        // Test parsing invalid lines
        assert!(parse_prometheus_metric("").is_none()); // Empty line
        assert!(parse_prometheus_metric("# HELP metric description").is_none()); // Help text
        assert!(parse_prometheus_metric("# TYPE metric counter").is_none()); // Type definition
        assert!(parse_prometheus_metric("metric_name").is_none()); // No value

        println!("✓ Prometheus metric parsing works correctly!");
    }

    #[test]
    fn test_metrics_registry_entry_callbacks() {
        use crate::MetricsRegistry;
        use std::sync::atomic::{AtomicUsize, Ordering};

        // Test 1: Basic callback execution with counter increments
        {
            let registry = MetricsRegistry::new();
            let counter = Arc::new(AtomicUsize::new(0));

            // Add callbacks with different increment values
            for increment in [1, 10, 100] {
                let counter_clone = counter.clone();
                registry.add_update_callback(Arc::new(move || {
                    counter_clone.fetch_add(increment, Ordering::SeqCst);
                    Ok(())
                }));
            }

            // Verify counter starts at 0
            assert_eq!(counter.load(Ordering::SeqCst), 0);

            // First execution
            let results = registry.execute_update_callbacks();
            assert_eq!(results.len(), 3);
            assert!(results.iter().all(|r| r.is_ok()));
            assert_eq!(counter.load(Ordering::SeqCst), 111); // 1 + 10 + 100

            // Second execution - callbacks should be reusable
            let results = registry.execute_update_callbacks();
            assert_eq!(results.len(), 3);
            assert_eq!(counter.load(Ordering::SeqCst), 222); // 111 + 111

            // Test cloning - cloned entry shares callbacks (callbacks are Arc-wrapped)
            let cloned = registry.clone();
            assert_eq!(cloned.execute_update_callbacks().len(), 3);
            assert_eq!(counter.load(Ordering::SeqCst), 333); // 222 + 111

            // Original still has callbacks and shares the same Arc
            registry.execute_update_callbacks();
            assert_eq!(counter.load(Ordering::SeqCst), 444); // 333 + 111
        }

        // Test 2: Mixed success and error callbacks
        {
            let registry = MetricsRegistry::new();
            let counter = Arc::new(AtomicUsize::new(0));

            // Successful callback
            let counter_clone = counter.clone();
            registry.add_update_callback(Arc::new(move || {
                counter_clone.fetch_add(1, Ordering::SeqCst);
                Ok(())
            }));

            // Error callback
            registry.add_update_callback(Arc::new(|| Err(anyhow::anyhow!("Simulated error"))));

            // Another successful callback
            let counter_clone = counter.clone();
            registry.add_update_callback(Arc::new(move || {
                counter_clone.fetch_add(10, Ordering::SeqCst);
                Ok(())
            }));

            // Execute and verify mixed results
            let results = registry.execute_update_callbacks();
            assert_eq!(results.len(), 3);
            assert!(results[0].is_ok());
            assert!(results[1].is_err());
            assert!(results[2].is_ok());

            // Verify error message
            assert_eq!(
                results[1].as_ref().unwrap_err().to_string(),
                "Simulated error"
            );

            // Verify successful callbacks still executed
            assert_eq!(counter.load(Ordering::SeqCst), 11); // 1 + 10

            // Execute again - errors should be consistent
            let results = registry.execute_update_callbacks();
            assert!(results[1].is_err());
            assert_eq!(counter.load(Ordering::SeqCst), 22); // 11 + 11
        }

        // Test 3: Empty registry
        {
            let registry = MetricsRegistry::new();
            let results = registry.execute_update_callbacks();
            assert_eq!(results.len(), 0);
        }
    }
}

#[cfg(feature = "integration")]
#[cfg(test)]
mod test_metricsregistry_prefixes {
    use super::*;
    use crate::distributed::distributed_test_utils::create_test_drt_async;
    use prometheus::core::Collector;

    #[tokio::test]
    async fn test_hierarchical_prefixes_and_parent_hierarchies() {
        let drt = create_test_drt_async().await;

        const DRT_NAME: &str = "";
        const NAMESPACE_NAME: &str = "ns901";
        const COMPONENT_NAME: &str = "comp901";
        const ENDPOINT_NAME: &str = "ep901";
        let namespace = drt.namespace(NAMESPACE_NAME).unwrap();
        let component = namespace.component(COMPONENT_NAME).unwrap();
        let endpoint = component.endpoint(ENDPOINT_NAME);

        // DRT
        assert_eq!(drt.basename(), DRT_NAME);
        assert_eq!(drt.parent_hierarchies().len(), 0);
        // DRT hierarchy is just its basename (empty string)

        // Namespace
        assert_eq!(namespace.basename(), NAMESPACE_NAME);
        assert_eq!(namespace.parent_hierarchies().len(), 1);
        assert_eq!(namespace.parent_hierarchies()[0].basename(), DRT_NAME);
        // Namespace hierarchy is just its basename since parent is empty

        // Component
        assert_eq!(component.basename(), COMPONENT_NAME);
        assert_eq!(component.parent_hierarchies().len(), 2);
        assert_eq!(component.parent_hierarchies()[0].basename(), DRT_NAME);
        assert_eq!(component.parent_hierarchies()[1].basename(), NAMESPACE_NAME);
        // Component hierarchy structure is validated by the individual assertions above

        // Endpoint
        assert_eq!(endpoint.basename(), ENDPOINT_NAME);
        assert_eq!(endpoint.parent_hierarchies().len(), 3);
        assert_eq!(endpoint.parent_hierarchies()[0].basename(), DRT_NAME);
        assert_eq!(endpoint.parent_hierarchies()[1].basename(), NAMESPACE_NAME);
        assert_eq!(endpoint.parent_hierarchies()[2].basename(), COMPONENT_NAME);
        // Endpoint hierarchy structure is validated by the individual assertions above

        // Relationships
        assert!(
            namespace
                .parent_hierarchies()
                .iter()
                .any(|h| h.basename() == drt.basename())
        );
        assert!(
            component
                .parent_hierarchies()
                .iter()
                .any(|h| h.basename() == namespace.basename())
        );
        assert!(
            endpoint
                .parent_hierarchies()
                .iter()
                .any(|h| h.basename() == component.basename())
        );

        // Depth
        assert_eq!(drt.parent_hierarchies().len(), 0);
        assert_eq!(namespace.parent_hierarchies().len(), 1);
        assert_eq!(component.parent_hierarchies().len(), 2);
        assert_eq!(endpoint.parent_hierarchies().len(), 3);

        // Invalid namespace behavior - sanitizes to "_123" and succeeds
        // @ryanolson intended to enable validation (see TODO comment in component.rs) but didn't turn it on,
        // so invalid characters are sanitized in MetricsRegistry rather than rejected.
        let invalid_namespace = drt.namespace("@@123").unwrap();
        let result =
            invalid_namespace
                .metrics()
                .create_counter("test_counter", "A test counter", &[]);
        assert!(result.is_ok());
        if let Ok(counter) = &result {
            // Verify the namespace was sanitized to "_123" in the label
            let desc = counter.desc();
            let namespace_label = desc[0]
                .const_label_pairs
                .iter()
                .find(|l| l.name() == "dynamo_namespace")
                .expect("Should have dynamo_namespace label");
            assert_eq!(namespace_label.value(), "_123");
        }

        // Valid namespace works
        let valid_namespace = drt.namespace("ns567").unwrap();
        assert!(
            valid_namespace
                .metrics()
                .create_counter("test_counter", "A test counter", &[])
                .is_ok()
        );
    }

    #[tokio::test]
    async fn test_expfmt_callback_only_registered_on_endpoint_is_included_once() {
        // Sanity test: if an expfmt callback is registered only on the endpoint registry,
        // scraping from the root (DRT) should still include it exactly once via the
        // child-registry traversal.
        let drt = create_test_drt_async().await;
        let namespace = drt.namespace("ns_expfmt_ep_only").unwrap();
        let component = namespace.component("comp_expfmt_ep_only").unwrap();
        let endpoint = component.endpoint("ep_expfmt_ep_only");

        let metric_line = "dynamo_component_active_decode_blocks{dp_rank=\"0\"} 0\n";
        let callback: PrometheusExpositionFormatCallback =
            Arc::new(move || Ok(metric_line.to_string()));

        endpoint
            .get_metrics_registry()
            .add_expfmt_callback(callback);

        let output = drt.metrics().prometheus_expfmt().unwrap();
        let occurrences = output
            .lines()
            .filter(|line| line == &metric_line.trim_end_matches('\n'))
            .count();

        assert_eq!(
            occurrences, 1,
            "endpoint-registered exposition callback should appear once, got {} occurrences\n\n{}",
            occurrences, output
        );
    }

    #[tokio::test]
    async fn test_recursive_namespace() {
        // Create a distributed runtime for testing
        let drt = create_test_drt_async().await;

        // Create a deeply chained namespace: ns1.ns2.ns3
        let ns1 = drt.namespace("ns1").unwrap();
        let ns2 = ns1.namespace("ns2").unwrap();
        let ns3 = ns2.namespace("ns3").unwrap();

        // Create a component in the deepest namespace
        let component = ns3.component("test-component").unwrap();

        // Verify the hierarchy structure
        assert_eq!(ns1.basename(), "ns1");
        assert_eq!(ns1.parent_hierarchies().len(), 1);
        assert_eq!(ns1.parent_hierarchies()[0].basename(), "");
        // ns1 hierarchy is just its basename since parent is empty

        assert_eq!(ns2.basename(), "ns2");
        assert_eq!(ns2.parent_hierarchies().len(), 2);
        assert_eq!(ns2.parent_hierarchies()[0].basename(), "");
        assert_eq!(ns2.parent_hierarchies()[1].basename(), "ns1");
        // ns2 hierarchy structure validated by parent assertions above

        assert_eq!(ns3.basename(), "ns3");
        assert_eq!(ns3.parent_hierarchies().len(), 3);
        assert_eq!(ns3.parent_hierarchies()[0].basename(), "");
        assert_eq!(ns3.parent_hierarchies()[1].basename(), "ns1");
        assert_eq!(ns3.parent_hierarchies()[2].basename(), "ns2");
        // ns3 hierarchy structure validated by parent assertions above

        assert_eq!(component.basename(), "test-component");
        assert_eq!(component.parent_hierarchies().len(), 4);
        assert_eq!(component.parent_hierarchies()[0].basename(), "");
        assert_eq!(component.parent_hierarchies()[1].basename(), "ns1");
        assert_eq!(component.parent_hierarchies()[2].basename(), "ns2");
        assert_eq!(component.parent_hierarchies()[3].basename(), "ns3");
        // component hierarchy structure validated by parent assertions above

        println!("✓ Chained namespace test passed - all prefixes correct");
    }
}

#[cfg(feature = "integration")]
#[cfg(test)]
mod test_metricsregistry_prometheus_fmt_outputs {
    use super::prometheus_names::name_prefix;
    use super::*;
    use crate::distributed::distributed_test_utils::create_test_drt_async;
    use prometheus::Counter;
    use std::sync::Arc;

    #[tokio::test]
    async fn test_prometheusfactory_using_metrics_registry_trait() {
        // Setup real DRT and registry using the test-friendly constructor
        let drt = create_test_drt_async().await;

        // Use a simple constant namespace name
        let namespace_name = "ns345";

        let namespace = drt.namespace(namespace_name).unwrap();
        let component = namespace.component("comp345").unwrap();
        let endpoint = component.endpoint("ep345");

        // Test Counter creation
        let counter = endpoint
            .metrics()
            .create_counter("testcounter", "A test counter", &[])
            .unwrap();
        counter.inc_by(123.456789);
        let epsilon = 0.01;
        assert!((counter.get() - 123.456789).abs() < epsilon);

        let endpoint_output_raw = endpoint.metrics().prometheus_expfmt().unwrap();
        println!("Endpoint output:");
        println!("{}", endpoint_output_raw);

        let expected_endpoint_output = r#"# HELP dynamo_component_testcounter A test counter
# TYPE dynamo_component_testcounter counter
dynamo_component_testcounter{dynamo_component="comp345",dynamo_endpoint="ep345",dynamo_namespace="ns345"} 123.456789"#.to_string();

        assert_eq!(
            endpoint_output_raw.trim_end_matches('\n'),
            expected_endpoint_output.trim_end_matches('\n'),
            "\n=== ENDPOINT COMPARISON FAILED ===\n\
             Actual:\n{}\n\
             Expected:\n{}\n\
             ==============================",
            endpoint_output_raw,
            expected_endpoint_output
        );

        // Test Gauge creation
        let gauge = component
            .metrics()
            .create_gauge("testgauge", "A test gauge", &[])
            .unwrap();
        gauge.set(50000.0);
        assert_eq!(gauge.get(), 50000.0);

        // Test Prometheus format output for Component (gauge + histogram)
        let component_output_raw = component.metrics().prometheus_expfmt().unwrap();
        println!("Component output:");
        println!("{}", component_output_raw);

        let expected_component_output = r#"# HELP dynamo_component_testcounter A test counter
# TYPE dynamo_component_testcounter counter
dynamo_component_testcounter{dynamo_component="comp345",dynamo_endpoint="ep345",dynamo_namespace="ns345"} 123.456789
# HELP dynamo_component_testgauge A test gauge
# TYPE dynamo_component_testgauge gauge
dynamo_component_testgauge{dynamo_component="comp345",dynamo_namespace="ns345"} 50000"#.to_string();

        assert_eq!(
            component_output_raw.trim_end_matches('\n'),
            expected_component_output.trim_end_matches('\n'),
            "\n=== COMPONENT COMPARISON FAILED ===\n\
             Actual:\n{}\n\
             Expected:\n{}\n\
             ==============================",
            component_output_raw,
            expected_component_output
        );

        let intcounter = namespace
            .metrics()
            .create_intcounter("testintcounter", "A test int counter", &[])
            .unwrap();
        intcounter.inc_by(12345);
        assert_eq!(intcounter.get(), 12345);

        // Test Prometheus format output for Namespace (int_counter + gauge + histogram)
        let namespace_output_raw = namespace.metrics().prometheus_expfmt().unwrap();
        println!("Namespace output:");
        println!("{}", namespace_output_raw);

        let expected_namespace_output = r#"# HELP dynamo_component_testcounter A test counter
# TYPE dynamo_component_testcounter counter
dynamo_component_testcounter{dynamo_component="comp345",dynamo_endpoint="ep345",dynamo_namespace="ns345"} 123.456789
# HELP dynamo_component_testgauge A test gauge
# TYPE dynamo_component_testgauge gauge
dynamo_component_testgauge{dynamo_component="comp345",dynamo_namespace="ns345"} 50000
# HELP dynamo_component_testintcounter A test int counter
# TYPE dynamo_component_testintcounter counter
dynamo_component_testintcounter{dynamo_namespace="ns345"} 12345"#.to_string();

        assert_eq!(
            namespace_output_raw.trim_end_matches('\n'),
            expected_namespace_output.trim_end_matches('\n'),
            "\n=== NAMESPACE COMPARISON FAILED ===\n\
             Actual:\n{}\n\
             Expected:\n{}\n\
             ==============================",
            namespace_output_raw,
            expected_namespace_output
        );

        // Test IntGauge creation
        let intgauge = namespace
            .metrics()
            .create_intgauge("testintgauge", "A test int gauge", &[])
            .unwrap();
        intgauge.set(42);
        assert_eq!(intgauge.get(), 42);

        // Test IntGaugeVec creation
        let intgaugevec = namespace
            .metrics()
            .create_intgaugevec(
                "testintgaugevec",
                "A test int gauge vector",
                &["instance", "status"],
                &[("service", "api")],
            )
            .unwrap();
        intgaugevec
            .with_label_values(&["server1", "active"])
            .set(10);
        intgaugevec
            .with_label_values(&["server2", "inactive"])
            .set(0);

        // Test CounterVec creation
        let countervec = endpoint
            .metrics()
            .create_countervec(
                "testcountervec",
                "A test counter vector",
                &["method", "status"],
                &[("service", "api")],
            )
            .unwrap();
        countervec.with_label_values(&["GET", "200"]).inc_by(10.0);
        countervec.with_label_values(&["POST", "201"]).inc_by(5.0);

        // Test Histogram creation
        let histogram = component
            .metrics()
            .create_histogram("testhistogram", "A test histogram", &[], None)
            .unwrap();
        histogram.observe(1.0);
        histogram.observe(2.5);
        histogram.observe(4.0);

        // Test Prometheus format output for DRT (all metrics combined)
        let drt_output_raw = drt.metrics().prometheus_expfmt().unwrap();
        println!("DRT output:");
        println!("{}", drt_output_raw);

        let expected_drt_output = r#"# HELP dynamo_component_testcounter A test counter
# TYPE dynamo_component_testcounter counter
dynamo_component_testcounter{dynamo_component="comp345",dynamo_endpoint="ep345",dynamo_namespace="ns345"} 123.456789
# HELP dynamo_component_testcountervec A test counter vector
# TYPE dynamo_component_testcountervec counter
dynamo_component_testcountervec{dynamo_component="comp345",dynamo_endpoint="ep345",dynamo_namespace="ns345",method="GET",service="api",status="200"} 10
dynamo_component_testcountervec{dynamo_component="comp345",dynamo_endpoint="ep345",dynamo_namespace="ns345",method="POST",service="api",status="201"} 5
# HELP dynamo_component_testgauge A test gauge
# TYPE dynamo_component_testgauge gauge
dynamo_component_testgauge{dynamo_component="comp345",dynamo_namespace="ns345"} 50000
# HELP dynamo_component_testhistogram A test histogram
# TYPE dynamo_component_testhistogram histogram
dynamo_component_testhistogram_bucket{dynamo_component="comp345",dynamo_namespace="ns345",le="0.005"} 0
dynamo_component_testhistogram_bucket{dynamo_component="comp345",dynamo_namespace="ns345",le="0.01"} 0
dynamo_component_testhistogram_bucket{dynamo_component="comp345",dynamo_namespace="ns345",le="0.025"} 0
dynamo_component_testhistogram_bucket{dynamo_component="comp345",dynamo_namespace="ns345",le="0.05"} 0
dynamo_component_testhistogram_bucket{dynamo_component="comp345",dynamo_namespace="ns345",le="0.1"} 0
dynamo_component_testhistogram_bucket{dynamo_component="comp345",dynamo_namespace="ns345",le="0.25"} 0
dynamo_component_testhistogram_bucket{dynamo_component="comp345",dynamo_namespace="ns345",le="0.5"} 0
dynamo_component_testhistogram_bucket{dynamo_component="comp345",dynamo_namespace="ns345",le="1"} 1
dynamo_component_testhistogram_bucket{dynamo_component="comp345",dynamo_namespace="ns345",le="2.5"} 2
dynamo_component_testhistogram_bucket{dynamo_component="comp345",dynamo_namespace="ns345",le="5"} 3
dynamo_component_testhistogram_bucket{dynamo_component="comp345",dynamo_namespace="ns345",le="10"} 3
dynamo_component_testhistogram_bucket{dynamo_component="comp345",dynamo_namespace="ns345",le="+Inf"} 3
dynamo_component_testhistogram_sum{dynamo_component="comp345",dynamo_namespace="ns345"} 7.5
dynamo_component_testhistogram_count{dynamo_component="comp345",dynamo_namespace="ns345"} 3
# HELP dynamo_component_testintcounter A test int counter
# TYPE dynamo_component_testintcounter counter
dynamo_component_testintcounter{dynamo_namespace="ns345"} 12345
# HELP dynamo_component_testintgauge A test int gauge
# TYPE dynamo_component_testintgauge gauge
dynamo_component_testintgauge{dynamo_namespace="ns345"} 42
# HELP dynamo_component_testintgaugevec A test int gauge vector
# TYPE dynamo_component_testintgaugevec gauge
dynamo_component_testintgaugevec{dynamo_namespace="ns345",instance="server1",service="api",status="active"} 10
dynamo_component_testintgaugevec{dynamo_namespace="ns345",instance="server2",service="api",status="inactive"} 0
# HELP dynamo_component_uptime_seconds Total uptime of the DistributedRuntime in seconds
# TYPE dynamo_component_uptime_seconds gauge
dynamo_component_uptime_seconds 0"#.to_string();

        assert_eq!(
            drt_output_raw.trim_end_matches('\n'),
            expected_drt_output.trim_end_matches('\n'),
            "\n=== DRT COMPARISON FAILED ===\n\
             Expected:\n{}\n\
             Actual (filtered):\n{}\n\
             ==============================",
            expected_drt_output,
            drt_output_raw
        );

        println!("✓ All Prometheus format outputs verified successfully!");
    }

    #[test]
    fn test_refactored_filter_functions() {
        // Test data with component metrics
        let test_input = r#"# HELP dynamo_component_requests Total requests
# TYPE dynamo_component_requests counter
dynamo_component_requests 42
# HELP dynamo_component_latency Response latency
# TYPE dynamo_component_latency histogram
dynamo_component_latency_bucket{le="0.1"} 10
dynamo_component_latency_bucket{le="0.5"} 25
dynamo_component_errors_total 5"#;

        // Test extract_metrics (only actual metric lines, excluding help/type)
        let metrics_only = super::test_helpers::extract_metrics(test_input);
        assert_eq!(metrics_only.len(), 4); // 4 actual metric lines (excluding help/type)
        assert!(
            metrics_only
                .iter()
                .all(|line| line.starts_with("dynamo_component") && !line.starts_with("#"))
        );

        println!("✓ All refactored filter functions work correctly!");
    }

    #[tokio::test]
    async fn test_same_metric_name_different_endpoints() {
        // Test that the same metric name can exist in different endpoints without collision.
        // This validates the multi-registry approach: each endpoint has its own registry,
        // and metrics are merged at scrape time with distinct labels.
        let drt = create_test_drt_async().await;
        let namespace = drt.namespace("ns_test").unwrap();
        let component = namespace.component("comp_test").unwrap();

        // Create two endpoints with the same metric name
        let ep1 = component.endpoint("ep1");
        let ep2 = component.endpoint("ep2");

        let counter1 = ep1
            .metrics()
            .create_counter("requests_total", "Total requests", &[])
            .unwrap();
        counter1.inc_by(100.0);

        let counter2 = ep2
            .metrics()
            .create_counter("requests_total", "Total requests", &[])
            .unwrap();
        counter2.inc_by(200.0);

        // Get merged Prometheus output from component level
        let output = component.metrics().prometheus_expfmt().unwrap();

        let expected_output = r#"# HELP dynamo_component_requests_total Total requests
# TYPE dynamo_component_requests_total counter
dynamo_component_requests_total{dynamo_component="comp_test",dynamo_endpoint="ep1",dynamo_namespace="ns_test"} 100
dynamo_component_requests_total{dynamo_component="comp_test",dynamo_endpoint="ep2",dynamo_namespace="ns_test"} 200"#;

        assert_eq!(
            output.trim_end_matches('\n'),
            expected_output.trim_end_matches('\n'),
            "\n=== MULTI-REGISTRY COMPARISON FAILED ===\n\
             Actual:\n{}\n\
             Expected:\n{}\n\
             ==============================",
            output,
            expected_output
        );

        println!("✓ Multi-registry prevents Prometheus collisions!");
    }

    #[tokio::test]
    async fn test_duplicate_series_warning() {
        // Test that duplicate series (same metric name + same labels) are detected and deduplicated.
        // This should log a warning and keep only one of the duplicate series.
        let drt = create_test_drt_async().await;
        let namespace = drt.namespace("ns_dup").unwrap();
        let component = namespace.component("comp_dup").unwrap();

        // Create two endpoints with counters that will have identical labels when scraped
        let ep1 = component.endpoint("ep_same");
        let ep2 = component.endpoint("ep_same"); // Same endpoint name = duplicate labels

        let counter1 = ep1
            .metrics()
            .create_counter("dup_metric", "Duplicate metric test", &[])
            .unwrap();
        counter1.inc_by(50.0);

        let counter2 = ep2
            .metrics()
            .create_counter("dup_metric", "Duplicate metric test", &[])
            .unwrap();
        counter2.inc_by(75.0);

        // Get merged output - duplicates should be deduplicated
        let output = component.metrics().prometheus_expfmt().unwrap();

        let expected_output = r#"# HELP dynamo_component_dup_metric Duplicate metric test
# TYPE dynamo_component_dup_metric counter
dynamo_component_dup_metric{dynamo_component="comp_dup",dynamo_endpoint="ep_same",dynamo_namespace="ns_dup"} 50"#;

        assert_eq!(
            output.trim_end_matches('\n'),
            expected_output.trim_end_matches('\n'),
            "\n=== DEDUPLICATION COMPARISON FAILED ===\n\
             Actual:\n{}\n\
             Expected:\n{}\n\
             ==============================",
            output,
            expected_output
        );

        println!("✓ Duplicate series detection and deduplication works!");
    }
}