#![warn(missing_docs)]
//! Comprehensive P99 latency tracking for critical HFT operations
//!
//! This module provides high-precision latency measurement and percentile tracking
//! for all critical trading operations in the Foxhunt HFT system.

use hdrhistogram::Histogram;
use std::sync::{Arc, RwLock};
use std::time::Instant;
use std::collections::HashMap;

/// High-precision latency tracker using HDR histogram for accurate percentile calculations
pub struct LatencyTracker {
    histogram: RwLock<Histogram<u64>>,
    operation_name: String,
}

impl LatencyTracker {
    /// Create a new latency tracker for a specific operation
    pub fn new(operation_name: &str) -> Self {
        Self {
            histogram: RwLock::new(
                Histogram::new_with_bounds(1, 60_000_000_000, 3).unwrap() // 1ns to 60s
            ),
            operation_name: operation_name.to_string(),
        }
    }

    /// Record a latency measurement in nanoseconds
    pub fn record(&self, nanos: u64) {
        if let Ok(mut hist) = self.histogram.write() {
            let _ = hist.record(nanos);
        }
    }

    /// Get the 99th percentile latency in nanoseconds
    pub fn get_p99(&self) -> u64 {
        self.histogram
            .read()
            .map(|hist| hist.value_at_percentile(99.0))
            .unwrap_or(0)
    }

    /// Get the 50th percentile (median) latency in nanoseconds
    pub fn get_p50(&self) -> u64 {
        self.histogram
            .read()
            .map(|hist| hist.value_at_percentile(50.0))
            .unwrap_or(0)
    }

    /// Get the 95th percentile latency in nanoseconds
    pub fn get_p95(&self) -> u64 {
        self.histogram
            .read()
            .map(|hist| hist.value_at_percentile(95.0))
            .unwrap_or(0)
    }

    /// Get the 99.9th percentile latency in nanoseconds
    pub fn get_p999(&self) -> u64 {
        self.histogram
            .read()
            .map(|hist| hist.value_at_percentile(99.9))
            .unwrap_or(0)
    }

    /// Get the maximum recorded latency in nanoseconds
    pub fn get_max(&self) -> u64 {
        self.histogram
            .read()
            .map(|hist| hist.max())
            .unwrap_or(0)
    }

    /// Get the minimum recorded latency in nanoseconds
    pub fn get_min(&self) -> u64 {
        self.histogram
            .read()
            .map(|hist| hist.min())
            .unwrap_or(0)
    }

    /// Get the mean latency in nanoseconds
    pub fn get_mean(&self) -> f64 {
        self.histogram
            .read()
            .map(|hist| hist.mean())
            .unwrap_or(0.0)
    }

    /// Get the total number of recorded samples
    pub fn get_count(&self) -> u64 {
        self.histogram
            .read()
            .map(|hist| hist.len())
            .unwrap_or(0)
    }

    /// Reset all recorded latencies
    pub fn reset(&self) {
        if let Ok(mut hist) = self.histogram.write() {
            hist.reset();
        }
    }

    /// Get comprehensive latency statistics
    pub fn get_stats(&self) -> LatencyStats {
        if let Ok(hist) = self.histogram.read() {
            LatencyStats {
                operation: self.operation_name.clone(),
                count: hist.len(),
                min: hist.min(),
                max: hist.max(),
                mean: hist.mean(),
                p50: hist.value_at_percentile(50.0),
                p95: hist.value_at_percentile(95.0),
                p99: hist.value_at_percentile(99.0),
                p999: hist.value_at_percentile(99.9),
            }
        } else {
            LatencyStats::default_for_operation(&self.operation_name)
        }
    }
}

/// Comprehensive latency statistics for an operation
#[derive(Debug, Clone)]
pub struct LatencyStats {
    /// Operation name
    pub operation: String,
    /// Total number of samples
    pub count: u64,
    /// Minimum latency (nanoseconds)
    pub min: u64,
    /// Maximum latency (nanoseconds)
    pub max: u64,
    /// Mean latency (nanoseconds)
    pub mean: f64,
    /// 50th percentile latency (nanoseconds)
    pub p50: u64,
    /// 95th percentile latency (nanoseconds)
    pub p95: u64,
    /// 99th percentile latency (nanoseconds)
    pub p99: u64,
    /// 99.9th percentile latency (nanoseconds)
    pub p999: u64,
}

impl LatencyStats {
    fn default_for_operation(operation: &str) -> Self {
        Self {
            operation: operation.to_string(),
            count: 0,
            min: 0,
            max: 0,
            mean: 0.0,
            p50: 0,
            p95: 0,
            p99: 0,
            p999: 0,
        }
    }

    /// Convert nanoseconds to microseconds
    pub fn p99_micros(&self) -> f64 {
        self.p99 as f64 / 1_000.0
    }

    /// Convert nanoseconds to milliseconds
    pub fn p99_millis(&self) -> f64 {
        self.p99 as f64 / 1_000_000.0
    }

    /// Check if P99 latency exceeds threshold (in nanoseconds)
    pub fn exceeds_p99_threshold(&self, threshold_nanos: u64) -> bool {
        self.p99 > threshold_nanos
    }

    /// Format latency for human-readable output
    pub fn format_p99(&self) -> String {
        if self.p99 < 1_000 {
            format!("{}ns", self.p99)
        } else if self.p99 < 1_000_000 {
            format!("{:.1}μs", self.p99 as f64 / 1_000.0)
        } else if self.p99 < 1_000_000_000 {
            format!("{:.1}ms", self.p99 as f64 / 1_000_000.0)
        } else {
            format!("{:.1}s", self.p99 as f64 / 1_000_000_000.0)
        }
    }
}

/// Global registry for all latency trackers in the system
pub struct LatencyRegistry {
    trackers: RwLock<HashMap<String, Arc<LatencyTracker>>>,
}

impl LatencyRegistry {
    /// Create a new latency registry
    pub fn new() -> Self {
        Self {
            trackers: RwLock::new(HashMap::new()),
        }
    }

    /// Get or create a latency tracker for an operation
    pub fn get_tracker(&self, operation: &str) -> Arc<LatencyTracker> {
        {
            let trackers = self.trackers.read().unwrap();
            if let Some(tracker) = trackers.get(operation) {
                return Arc::clone(tracker);
            }
        }

        let mut trackers = self.trackers.write().unwrap();
        let tracker = Arc::new(LatencyTracker::new(operation));
        trackers.insert(operation.to_string(), Arc::clone(&tracker));
        tracker
    }

    /// Get all registered tracker statistics
    pub fn get_all_stats(&self) -> Vec<LatencyStats> {
        let trackers = self.trackers.read().unwrap();
        trackers
            .values()
            .map(|tracker| tracker.get_stats())
            .collect()
    }

    /// Reset all trackers
    pub fn reset_all(&self) {
        let trackers = self.trackers.read().unwrap();
        for tracker in trackers.values() {
            tracker.reset();
        }
    }
}

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

/// RAII timer for automatic latency measurement
pub struct LatencyTimer {
    tracker: Arc<LatencyTracker>,
    start: Instant,
}

impl LatencyTimer {
    /// Start timing an operation
    pub fn start(tracker: Arc<LatencyTracker>) -> Self {
        Self {
            tracker,
            start: Instant::now(),
        }
    }

    /// Manually record the elapsed time (useful for early recording)
    pub fn record_now(&self) {
        let elapsed = self.start.elapsed().as_nanos() as u64;
        self.tracker.record(elapsed);
    }
}

impl Drop for LatencyTimer {
    fn drop(&mut self) {
        let elapsed = self.start.elapsed().as_nanos() as u64;
        self.tracker.record(elapsed);
    }
}

/// Global latency registry instance
static GLOBAL_REGISTRY: std::sync::OnceLock<LatencyRegistry> = std::sync::OnceLock::new();

/// Get the global latency registry
pub fn global_registry() -> &'static LatencyRegistry {
    GLOBAL_REGISTRY.get_or_init(|| LatencyRegistry::new())
}

/// Convenience macro for timing operations
#[macro_export]
macro_rules! time_operation {
    ($operation:expr, $code:block) => {{
        let tracker = $crate::monitoring::latency_tracker::global_registry()
            .get_tracker($operation);
        let _timer = $crate::monitoring::latency_tracker::LatencyTimer::start(tracker);
        $code
    }};
}

/// Convenience function to record a single latency measurement
pub fn record_latency(operation: &str, nanos: u64) {
    let tracker = global_registry().get_tracker(operation);
    tracker.record(nanos);
}

/// Critical HFT operation names for consistent tracking
pub mod operations {
    /// Order placement latency
    pub const ORDER_PLACEMENT: &str = "order_placement";
    /// Order cancellation latency
    pub const ORDER_CANCELLATION: &str = "order_cancellation";
    /// Market data processing latency
    pub const MARKET_DATA_PROCESSING: &str = "market_data_processing";
    /// Risk check latency
    pub const RISK_CHECK: &str = "risk_check";
    /// Position update latency
    pub const POSITION_UPDATE: &str = "position_update";
    /// Trade execution latency
    pub const TRADE_EXECUTION: &str = "trade_execution";
    /// Signal generation latency
    pub const SIGNAL_GENERATION: &str = "signal_generation";
    /// Portfolio rebalancing latency
    pub const PORTFOLIO_REBALANCING: &str = "portfolio_rebalancing";
    /// Database write latency
    pub const DATABASE_WRITE: &str = "database_write";
    /// Database read latency
    pub const DATABASE_READ: &str = "database_read";
    /// Message queue publish latency
    pub const MESSAGE_PUBLISH: &str = "message_publish";
    /// Message queue consume latency
    pub const MESSAGE_CONSUME: &str = "message_consume";
    /// Broker API call latency
    pub const BROKER_API_CALL: &str = "broker_api_call";
    /// AI model inference latency
    pub const AI_MODEL_INFERENCE: &str = "ai_model_inference";
    /// End-to-end trade latency
    pub const END_TO_END_TRADE: &str = "end_to_end_trade";
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::thread;
    use std::time::Duration;

    #[test]
    fn test_latency_tracker_basic() {
        let tracker = LatencyTracker::new("test_operation");
        
        // Record some test latencies
        tracker.record(1000); // 1μs
        tracker.record(2000); // 2μs
        tracker.record(5000); // 5μs
        tracker.record(10000); // 10μs
        
        assert_eq!(tracker.get_count(), 4);
        assert!(tracker.get_p50() > 0);
        assert!(tracker.get_p99() > 0);
        assert!(tracker.get_max() >= 10000);
        assert!(tracker.get_min() <= 1000);
    }

    #[test]
    fn test_latency_timer() {
        let tracker = Arc::new(LatencyTracker::new("timer_test"));
        let tracker_clone = Arc::clone(&tracker);
        
        {
            let _timer = LatencyTimer::start(tracker_clone);
            thread::sleep(Duration::from_micros(100));
        }
        
        assert_eq!(tracker.get_count(), 1);
        assert!(tracker.get_p99() > 50_000); // Should be > 50μs
    }

    #[test]
    fn test_latency_registry() {
        let registry = LatencyRegistry::new();
        
        let tracker1 = registry.get_tracker("operation1");
        let tracker2 = registry.get_tracker("operation2");
        let tracker1_again = registry.get_tracker("operation1");
        
        // Should return the same tracker for the same operation
        assert!(Arc::ptr_eq(&tracker1, &tracker1_again));
        
        tracker1.record(1000);
        tracker2.record(2000);
        
        let stats = registry.get_all_stats();
        assert_eq!(stats.len(), 2);
    }

    #[test]
    fn test_latency_stats_formatting() {
        let tracker = LatencyTracker::new("format_test");
        
        tracker.record(500); // 500ns
        tracker.record(1500); // 1.5μs
        tracker.record(1_500_000); // 1.5ms
        
        let stats = tracker.get_stats();
        let formatted = stats.format_p99();
        
        // Should format appropriately based on magnitude
        assert!(!formatted.is_empty());
    }

    #[test]
    fn test_time_operation_macro() {
        let result = time_operation!("macro_test", {
            thread::sleep(Duration::from_micros(10));
            42
        });
        
        assert_eq!(result, 42);
        
        let tracker = global_registry().get_tracker("macro_test");
        assert_eq!(tracker.get_count(), 1);
    }
}