anno 0.8.0

//! Ensemble NER - Multi-backend extraction with unsupervised weighted voting.
//!
//! # Method
//!
//! This is an **unsupervised heuristic** approach (no training data required).
//! Conflict resolution uses hand-tuned weights based on expected backend reliability.
//! For supervised weight learning from labeled data, see `WeightLearner`.
//!
//! # The Core Idea
//!
//! Instead of simple priority-based stacking, `EnsembleNER`:
//! 1. Runs ALL available backends opportunistically (in parallel conceptually)
//! 2. Collects candidate entities with provenance
//! 3. Groups overlapping spans into conflict clusters
//! 4. Resolves conflicts using weighted voting with agreement bonus
//!
//! ```text
//! ┌─────────────────────────────────────────────────────────────────────────┐
//! │                    ENSEMBLE NER ARCHITECTURE                            │
//! ├─────────────────────────────────────────────────────────────────────────┤
//! │                                                                         │
//! │  Input: "Tim Cook, CEO of Apple, met with Sundar Pichai"                │
//! │                                                                         │
//! │  ┌──────────────────────────────────────────────────────────────────┐   │
//! │  │ PHASE 1: OPPORTUNISTIC EXTRACTION (parallel)                     │   │
//! │  │                                                                  │   │
//! │  │  Pattern ──────► [no entities]                                   │   │
//! │  │  Heuristic ────► Tim Cook (PER, 0.75), Apple (ORG, 0.80), ...    │   │
//! │  │  GLiNER ────────► Tim Cook (PER, 0.95), Apple (ORG, 0.87), ...   │   │
//! │  │  Candle ────────► [unavailable, skip]                            │   │
//! │  └──────────────────────────────────────────────────────────────────┘   │
//! │                            │                                            │
//! │                            ▼                                            │
//! │  ┌──────────────────────────────────────────────────────────────────┐   │
//! │  │ PHASE 2: CANDIDATE AGGREGATION                                   │   │
//! │  │                                                                  │   │
//! │  │  Span [0:8] "Tim Cook":                                          │   │
//! │  │    • Heuristic: PER (0.75)                                       │   │
//! │  │    • GLiNER: PER (0.95)                                          │   │
//! │  │    Agreement: 2/2 → HIGH confidence                              │   │
//! │  │                                                                  │   │
//! │  │  Span [17:22] "Apple":                                           │   │
//! │  │    • Heuristic: ORG (0.80)                                       │   │
//! │  │    • GLiNER: ORG (0.87)                                          │   │
//! │  │    Agreement: 2/2 → HIGH confidence                              │   │
//! │  └──────────────────────────────────────────────────────────────────┘   │
//! │                            │                                            │
//! │                            ▼                                            │
//! │  ┌──────────────────────────────────────────────────────────────────┐   │
//! │  │ PHASE 3: CONFLICT RESOLUTION (weighted voting)                   │   │
//! │  │                                                                  │   │
//! │  │  Backend weights (learned or configured):                        │   │
//! │  │    Pattern: 0.99 (when fires, almost always right)               │   │
//! │  │    GLiNER:  0.85 (ML-based, good accuracy)                       │   │
//! │  │    Heuristic: 0.65 (reasonable but noisy)                        │   │
//! │  │                                                                  │   │
//! │  │  For span [0:8]:                                                 │   │
//! │  │    Weighted vote = (0.65 * 0.75) + (0.85 * 0.95) = 1.29          │   │
//! │  │    Normalized confidence = 0.91                                  │   │
//! │  └──────────────────────────────────────────────────────────────────┘   │
//! │                            │                                            │
//! │                            ▼                                            │
//! │  ┌──────────────────────────────────────────────────────────────────┐   │
//! │  │ OUTPUT                                                           │   │
//! │  │                                                                  │   │
//! │  │  Entity { text: "Tim Cook", type: PER, conf: 0.91,               │   │
//! │  │           sources: ["heuristic", "gliner"], agreement: 1.0 }     │   │
//! │  └──────────────────────────────────────────────────────────────────┘   │
//! │                                                                         │
//! └─────────────────────────────────────────────────────────────────────────┘
//! ```
//!
//! # Conflict Resolution Strategies
//!
//! ## Weighted Voting (Unsupervised)
//!
//! Each backend has a weight based on its expected reliability:
//! - Pattern backends: high weight (0.95+) when they fire
//! - ML backends: medium-high weight (0.80-0.90)
//! - Heuristic backends: lower weight (0.60-0.70)
//!
//! ## Type-Conditioned Voting
//!
//! Some backends are better at certain types:
//! - Pattern: DATE, MONEY, EMAIL, URL (near-perfect)
//! - GLiNER: PER, ORG (good), LOC (decent)
//! - Heuristic: ORG (good with "Inc", "Corp"), PER (title+name patterns)
//!
//! ## Agreement Bonus
//!
//! When multiple backends agree on type AND span, boost confidence:
//! - 2 backends agree: +0.10 bonus
//! - 3+ backends agree: +0.15 bonus
//!
//! # Example
//!
//! ```rust
//! use anno::{Model, EnsembleNER};
//!
//! let ner = EnsembleNER::new();
//! let entities = ner.extract_entities("Tim Cook leads Apple Inc.", None).unwrap();
//!
//! // Each entity includes provenance and agreement info
//! for e in &entities {
//!     println!("{}: {} (conf: {:.2}, sources: {:?})",
//!              e.entity_type.as_label(), e.text, e.confidence,
//!              e.provenance.as_ref().map(|p| &p.source));
//! }
//! ```

use std::borrow::Cow;
use std::collections::HashMap;
use std::sync::Arc;

use crate::Language;

use crate::backends::method_for_backend_name;
use crate::{Confidence, Entity, EntityType, Error, Model, Result};

pub mod weights;
pub use weights::*;

/// Weighted ensemble of NER backends.
pub struct EnsembleNER {
    backends: Vec<Arc<dyn Model + Send + Sync>>,
    /// Stable backend IDs used for weighting and source tracking.
    ///
    /// This is intentionally decoupled from `backend.name()`, which is a
    /// human-facing label and may vary across implementations (e.g. "GLiNER-ONNX").
    backend_ids: Vec<String>,
    weights: HashMap<String, BackendWeight>,
    agreement_bonus: f64,
    min_confidence: f64,
    /// Transparent name showing constituent backends (e.g., "ensemble(regex|gliner|heuristic)")
    name: String,
    /// Cached static name (avoids Box::leak on every name() call)
    name_static: std::sync::OnceLock<&'static str>,
}

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

impl EnsembleNER {
    /// Create ensemble with all available backends.
    #[must_use]
    pub fn new() -> Self {
        let mut backends: Vec<Arc<dyn Model + Send + Sync>> = Vec::new();
        let mut backend_ids: Vec<&'static str> = Vec::new();

        // Always add pattern (high precision for structured data)
        backends.push(Arc::new(crate::RegexNER::new()));
        backend_ids.push("regex");

        // Add GLiNER if available
        #[cfg(feature = "onnx")]
        {
            use super::GLiNEROnnx;
            use crate::DEFAULT_GLINER_MODEL;
            if let Ok(gliner) = GLiNEROnnx::new(DEFAULT_GLINER_MODEL) {
                backends.push(Arc::new(gliner));
                backend_ids.push("gliner");
            }
        }

        // Add Candle GLiNER if available
        #[cfg(feature = "candle")]
        {
            use super::GLiNERCandle;
            use crate::DEFAULT_GLINER_MODEL;
            if let Ok(candle) = GLiNERCandle::from_pretrained(DEFAULT_GLINER_MODEL) {
                backends.push(Arc::new(candle));
                backend_ids.push("gliner-candle");
            }
        }

        // Always add heuristic as fallback
        backends.push(Arc::new(crate::HeuristicNER::new()));
        backend_ids.push("heuristic");

        // Build transparent name showing constituents
        // Use '|' for parallel weighted voting (no priority ordering)
        let name = format!("ensemble({})", backend_ids.join("|"));

        // Convert default weights to owned strings
        let weights: HashMap<String, BackendWeight> = default_backend_weights()
            .into_iter()
            .map(|(k, v)| (k.to_string(), v))
            .collect();

        Self {
            backends,
            backend_ids: backend_ids.into_iter().map(str::to_string).collect(),
            weights,
            agreement_bonus: 0.10,
            min_confidence: 0.30,
            name,
            name_static: std::sync::OnceLock::new(),
        }
    }

    /// Create with custom backends.
    #[must_use]
    pub fn with_backends(backends: Vec<Box<dyn Model + Send + Sync>>) -> Self {
        // For custom backends, use the backend's reported name as both ID and display string.
        let backend_ids: Vec<String> = backends.iter().map(|b| b.name().to_string()).collect();
        let name = format!("ensemble({})", backend_ids.join("|"));

        let backends: Vec<Arc<dyn Model + Send + Sync>> =
            backends.into_iter().map(Arc::from).collect();

        let weights: HashMap<String, BackendWeight> = default_backend_weights()
            .into_iter()
            .map(|(k, v)| (k.to_string(), v))
            .collect();

        Self {
            backends,
            backend_ids,
            weights,
            agreement_bonus: 0.10,
            min_confidence: 0.30,
            name,
            name_static: std::sync::OnceLock::new(),
        }
    }

    /// Set custom backend weights.
    #[must_use]
    pub fn with_weights(mut self, weights: HashMap<String, BackendWeight>) -> Self {
        self.weights = weights;
        self
    }

    /// Set the agreement bonus (added when multiple backends agree).
    #[must_use]
    pub fn with_agreement_bonus(mut self, bonus: f64) -> Self {
        self.agreement_bonus = bonus;
        self
    }

    /// Set minimum confidence threshold.
    #[must_use]
    pub fn with_min_confidence(mut self, min: f64) -> Self {
        self.min_confidence = min;
        self
    }

    /// Get the weight for a backend and entity type.
    fn get_weight(&self, backend_name: &str, entity_type: &EntityType) -> f64 {
        if let Some(weight) = self.weights.get(backend_name) {
            if let Some(ref type_weights) = weight.per_type {
                type_weights.get(entity_type)
            } else {
                weight.overall
            }
        } else {
            // Unknown backend - use conservative default
            0.50
        }
    }

    /// Resolve overlapping candidates using weighted voting.
    fn resolve_candidates(&self, candidates: Vec<Candidate>) -> Option<Entity> {
        if candidates.is_empty() {
            return None;
        }

        if candidates.len() == 1 {
            // Single candidate - use its confidence directly
            let candidate = candidates
                .into_iter()
                .next()
                .expect("candidates.len() == 1 guarantees next() is Some");
            let mut entity = candidate.entity;
            let original_prov = entity.provenance.clone();
            let original_confidence = entity.confidence;
            // Slight penalty for single-source
            entity.confidence *= 0.95;
            // Set provenance for single-source entities
            entity.provenance = Some(anno_core::Provenance {
                source: std::borrow::Cow::Owned(format!("ensemble({})", candidate.source)),
                // Preserve underlying method/pattern when possible (important for nested ensembles).
                method: original_prov
                    .as_ref()
                    .map(|p| p.method)
                    .unwrap_or_else(|| method_for_backend_name(&candidate.source)),
                pattern: original_prov.as_ref().and_then(|p| p.pattern.clone()),
                raw_confidence: original_prov
                    .as_ref()
                    .and_then(|p| p.raw_confidence)
                    .or(Some(original_confidence)),
                model_version: None,
                timestamp: None,
            });
            return Some(entity);
        }

        // Group by entity type
        let mut type_votes: HashMap<String, Vec<&Candidate>> = HashMap::new();
        for c in &candidates {
            let type_key = c.entity.entity_type.as_label().to_string();
            type_votes.entry(type_key).or_default().push(c);
        }

        // Find the type with highest weighted vote (deterministic tie-breaking).
        //
        // HashMap iteration order can vary across process runs. If two types tie on
        // weighted_sum, we still need a stable selection.
        //
        // Ordering:
        // 1) Higher weighted_sum wins
        // 2) If tied, more candidates (more votes) wins
        // 3) If tied, lexicographically smaller type key wins
        let mut best_type: Option<(String, f64, usize, Vec<&Candidate>)> = None;
        for (type_key, type_candidates) in &type_votes {
            let weighted_sum: f64 = type_candidates
                .iter()
                .map(|c| c.backend_weight * c.entity.confidence)
                .sum();
            let count = type_candidates.len();

            let should_replace = match &best_type {
                None => true,
                Some((best_key, best_sum, best_count, _)) => {
                    if weighted_sum > *best_sum {
                        true
                    } else if weighted_sum < *best_sum {
                        false
                    } else if count > *best_count {
                        true
                    } else if count < *best_count {
                        false
                    } else {
                        type_key < best_key
                    }
                }
            };

            if should_replace {
                best_type = Some((
                    type_key.clone(),
                    weighted_sum,
                    count,
                    type_candidates.clone(),
                ));
            }
        }

        let (_type_key, weighted_sum, _count, winning_candidates) = best_type?;

        // Calculate ensemble confidence
        let num_sources = winning_candidates.len();
        let total_weight: f64 = winning_candidates.iter().map(|c| c.backend_weight).sum();

        let base_confidence = if total_weight > 0.0 {
            weighted_sum / total_weight
        } else {
            0.5
        };

        // Agreement bonus
        let agreement_bonus = if num_sources >= 3 {
            self.agreement_bonus * 1.5
        } else if num_sources >= 2 {
            self.agreement_bonus
        } else {
            0.0
        };

        let final_confidence = (base_confidence + agreement_bonus).min(1.0);

        // Build merged entity
        // Use the candidate with highest individual confidence as base
        let best_candidate = winning_candidates.iter().max_by(|a, b| {
            a.entity
                .confidence
                .partial_cmp(&b.entity.confidence)
                .unwrap_or(std::cmp::Ordering::Equal)
        })?;

        let sources: Vec<String> = winning_candidates
            .iter()
            .map(|c| c.source.clone())
            .collect();

        // Calculate hierarchical confidence scores
        // - linkage: How many backends detected an entity here (normalized)
        // - type_score: Agreement on type classification
        // - boundary: Agreement on exact span boundaries
        let total_candidates = candidates.len() as f32;
        let num_winners = winning_candidates.len() as f32;

        // Linkage: ratio of candidates in winning type
        let linkage = if total_candidates > 0.0 {
            (num_winners / total_candidates).min(1.0)
        } else {
            0.5
        };

        // Type score: confidence in the winning type (weighted)
        let type_score = final_confidence as f32;

        // Boundary: agreement on span boundaries
        // Check if all winning candidates have the same start/end
        let reference_span = (best_candidate.entity.start(), best_candidate.entity.end());
        let span_agreement_count = winning_candidates
            .iter()
            .filter(|c| c.entity.start() == reference_span.0 && c.entity.end() == reference_span.1)
            .count();
        let boundary = if num_winners > 0.0 {
            (span_agreement_count as f32 / num_winners).min(1.0)
        } else {
            1.0
        };

        let mut entity = best_candidate.entity.clone();
        entity.confidence = Confidence::new(final_confidence);
        entity.hierarchical_confidence = Some(anno_core::HierarchicalConfidence::new(
            linkage, type_score, boundary,
        ));
        entity.provenance = Some(anno_core::Provenance {
            source: Cow::Owned(format!("ensemble({})", sources.join("+"))),
            method: anno_core::ExtractionMethod::Consensus,
            pattern: None,
            raw_confidence: Some(Confidence::new(base_confidence)),
            model_version: None,
            timestamp: None,
        });

        Some(entity)
    }
}

impl Model for EnsembleNER {
    fn extract_entities(&self, text: &str, language: Option<Language>) -> Result<Vec<Entity>> {
        if self.backends.is_empty() {
            return Ok(Vec::new());
        }

        // Phase 1: Collect candidates from all backends (parallel)
        let backend_results: Vec<(String, Result<Vec<Entity>>)> = std::thread::scope(|s| {
            let handles: Vec<_> = self
                .backends
                .iter()
                .enumerate()
                .map(|(i, backend)| {
                    let backend_id = self
                        .backend_ids
                        .get(i)
                        .cloned()
                        .unwrap_or_else(|| backend.name().to_string());
                    s.spawn(move || {
                        let result = backend.extract_entities(text, language);
                        (backend_id, result)
                    })
                })
                .collect();

            handles
                .into_iter()
                .map(|h| match h.join() {
                    Ok(pair) => Ok(pair),
                    Err(_) => Err(Error::inference("ensemble backend thread panicked")),
                })
                .collect::<Result<Vec<_>>>()
        })?;

        let mut all_candidates: Vec<Candidate> = Vec::new();
        for (backend_id, result) in backend_results {
            match result {
                Ok(entities) => {
                    for entity in entities {
                        let weight = self.get_weight(&backend_id, &entity.entity_type);
                        all_candidates.push(Candidate {
                            entity,
                            source: backend_id.clone(),
                            backend_weight: weight,
                        });
                    }
                }
                Err(e) => {
                    log::debug!("EnsembleNER: Backend id={} failed: {}", backend_id, e);
                }
            }
        }

        if all_candidates.is_empty() {
            return Ok(Vec::new());
        }

        // Phase 2: Group candidates by overlapping spans
        let mut span_groups: Vec<Vec<Candidate>> = Vec::new();

        for candidate in all_candidates {
            let span = SpanKey::from_entity(&candidate.entity);

            // Find existing group with overlapping span
            let mut found_group = false;
            for group in &mut span_groups {
                if let Some(first) = group.first() {
                    let existing_span = SpanKey::from_entity(&first.entity);
                    if span.overlaps(&existing_span) {
                        group.push(candidate.clone());
                        found_group = true;
                        break;
                    }
                }
            }

            if !found_group {
                span_groups.push(vec![candidate]);
            }
        }

        // Phase 3: Resolve each group
        let mut results: Vec<Entity> = Vec::new();

        for group in span_groups {
            if let Some(entity) = self.resolve_candidates(group) {
                if entity.confidence >= self.min_confidence {
                    results.push(entity);
                }
            }
        }

        // Sort by position
        results.sort_by_key(|e| (e.start(), e.end()));

        Ok(results)
    }

    fn supported_types(&self) -> Vec<EntityType> {
        // Union of all backend types
        let mut types: Vec<EntityType> = Vec::new();
        for backend in &self.backends {
            for t in backend.supported_types() {
                if !types.contains(&t) {
                    types.push(t);
                }
            }
        }
        types
    }

    fn is_available(&self) -> bool {
        // Available if at least one backend is available
        self.backends.iter().any(|b| b.is_available())
    }

    fn name(&self) -> &'static str {
        // Use OnceLock to cache the static string, avoiding repeated memory leaks
        self.name_static
            .get_or_init(|| Box::leak(self.name.clone().into_boxed_str()))
    }

    fn description(&self) -> &'static str {
        "Ensemble NER: weighted voting across multiple backends"
    }

    fn capabilities(&self) -> crate::ModelCapabilities {
        crate::ModelCapabilities::default()
    }
}

// =============================================================================
// Weight Learning
// =============================================================================

/// Training example for weight learning.
#[derive(Debug, Clone)]
pub struct WeightTrainingExample {
    /// Text of the entity
    pub text: String,
    /// True entity type (gold label)
    pub gold_type: EntityType,
    /// Span start
    pub start: usize,
    /// Span end
    pub end: usize,
    /// Predictions from each backend: (backend_name, predicted_type, confidence)
    pub predictions: Vec<(String, EntityType, Confidence)>,
}

/// Statistics for weight learning.
#[derive(Debug, Clone, Default)]
pub struct BackendStats {
    /// Total correct predictions
    pub correct: usize,
    /// Total predictions made
    pub total: usize,
    /// Per-type statistics: (type, correct, total)
    pub per_type: HashMap<String, (usize, usize)>,
}

impl BackendStats {
    /// Calculate overall precision.
    pub fn precision(&self) -> f64 {
        if self.total == 0 {
            0.0
        } else {
            self.correct as f64 / self.total as f64
        }
    }

    /// Calculate per-type precision.
    pub fn type_precision(&self, entity_type: &str) -> f64 {
        if let Some((correct, total)) = self.per_type.get(entity_type) {
            if *total == 0 {
                0.0
            } else {
                *correct as f64 / *total as f64
            }
        } else {
            0.0
        }
    }
}

/// Weight learner for EnsembleNER.
///
/// Learns optimal backend weights from evaluation data.
///
/// # Example
///
/// ```rust,ignore
/// use anno::backends::ensemble::{EnsembleNER, WeightLearner};
///
/// let mut learner = WeightLearner::new();
///
/// // Add training examples from gold data
/// for (text, gold_entities) in gold_data {
///     learner.add_examples(&text, &gold_entities, &backends);
/// }
///
/// // Learn weights
/// let learned_weights = learner.learn_weights();
///
/// // Create ensemble with learned weights
/// let ensemble = EnsembleNER::new().with_weights(learned_weights);
/// ```
pub struct WeightLearner {
    /// Per-backend statistics
    backend_stats: HashMap<String, BackendStats>,
    /// Smoothing factor for precision (avoid division by zero / overfitting)
    smoothing: f64,
}

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

impl WeightLearner {
    /// Create a new weight learner.
    #[must_use]
    pub fn new() -> Self {
        Self {
            backend_stats: HashMap::new(),
            smoothing: 1.0, // Laplace smoothing
        }
    }

    /// Set smoothing factor.
    #[must_use]
    pub fn with_smoothing(mut self, smoothing: f64) -> Self {
        self.smoothing = smoothing;
        self
    }

    /// Add a training example.
    pub fn add_example(&mut self, example: &WeightTrainingExample) {
        for (backend_name, predicted_type, _confidence) in &example.predictions {
            let stats = self.backend_stats.entry(backend_name.clone()).or_default();

            stats.total += 1;
            let correct = *predicted_type == example.gold_type;
            if correct {
                stats.correct += 1;
            }

            // Per-type stats
            let type_key = example.gold_type.as_label().to_string();
            let type_stats = stats.per_type.entry(type_key).or_insert((0, 0));
            type_stats.1 += 1;
            if correct {
                type_stats.0 += 1;
            }
        }
    }

    /// Add examples from gold entities and backend predictions.
    ///
    /// Runs each backend on the text and compares to gold entities.
    pub fn add_from_backends(
        &mut self,
        text: &str,
        gold_entities: &[Entity],
        backends: &[(&str, &dyn Model)],
    ) {
        // Get predictions from each backend
        let mut backend_preds: HashMap<String, Vec<Entity>> = HashMap::new();
        for (name, backend) in backends {
            if let Ok(entities) = backend.extract_entities(text, None) {
                backend_preds.insert(name.to_string(), entities);
            }
        }

        // Match predictions to gold entities
        for gold in gold_entities {
            let mut example = WeightTrainingExample {
                text: gold.text.clone(),
                gold_type: gold.entity_type.clone(),
                start: gold.start(),
                end: gold.end(),
                predictions: Vec::new(),
            };

            for (backend_name, entities) in &backend_preds {
                // Find matching prediction (same span)
                for pred in entities {
                    if pred.start() == gold.start() && pred.end() == gold.end() {
                        example.predictions.push((
                            backend_name.clone(),
                            pred.entity_type.clone(),
                            pred.confidence,
                        ));
                        break;
                    }
                }
            }

            if !example.predictions.is_empty() {
                self.add_example(&example);
            }
        }
    }

    /// Learn optimal weights from accumulated statistics.
    ///
    /// Uses precision-based weighting with Laplace smoothing.
    pub fn learn_weights(&self) -> HashMap<String, BackendWeight> {
        let mut weights = HashMap::new();

        for (backend_name, stats) in &self.backend_stats {
            // Smoothed precision: (correct + smoothing) / (total + 2*smoothing)
            let smoothed_precision = (stats.correct as f64 + self.smoothing)
                / (stats.total as f64 + 2.0 * self.smoothing);

            // Per-type weights
            let mut type_weights = TypeWeights::default();
            for (type_key, (correct, total)) in &stats.per_type {
                let type_precision =
                    (*correct as f64 + self.smoothing) / (*total as f64 + 2.0 * self.smoothing);

                match type_key.as_str() {
                    "PER" | "PERSON" => type_weights.person = type_precision,
                    "ORG" | "ORGANIZATION" => type_weights.organization = type_precision,
                    "LOC" | "LOCATION" | "GPE" => type_weights.location = type_precision,
                    "DATE" => type_weights.date = type_precision,
                    "MONEY" => type_weights.money = type_precision,
                    _ => type_weights.other = type_precision,
                }
            }

            weights.insert(
                backend_name.clone(),
                BackendWeight {
                    overall: smoothed_precision,
                    per_type: Some(type_weights),
                },
            );
        }

        weights
    }

    /// Get statistics for a backend.
    pub fn get_stats(&self, backend_name: &str) -> Option<&BackendStats> {
        self.backend_stats.get(backend_name)
    }

    /// Get all backend names.
    pub fn backend_names(&self) -> Vec<&String> {
        self.backend_stats.keys().collect()
    }
}

// =============================================================================
// Tests
// =============================================================================

#[cfg(test)]
mod tests;