lambdust 0.1.1

//! Parallel generational garbage collector coordinator
//!
//! This module implements the main coordinator for the parallel generational 
//! garbage collector, managing collection phases, thread synchronization, and
//! generation-specific collection algorithms.

use crate::eval::value::Value;
use crate::jit::metrics::JitMetrics;
use std::collections::{HashMap, VecDeque};
use std::sync::{Arc, RwLock, Mutex, Condvar, atomic::{AtomicBool, AtomicU64, AtomicUsize, Ordering}};
use std::time::{Duration, Instant};
use std::thread::{self, ThreadId};

/// Configuration for the parallel garbage collector
#[derive(Debug, Clone)]
pub struct ParallelGcConfig {
    /// Maximum number of collector threads
    pub max_collector_threads: usize,
    /// Young generation heap size limit (bytes)
    pub young_generation_size: usize,
    /// Old generation heap size limit (bytes)
    pub old_generation_size: usize,
    /// Large object size threshold (bytes)
    pub large_object_threshold: usize,
    /// Target pause time for minor collections (milliseconds)
    pub target_minor_pause_ms: u64,
    /// Target pause time for major collections (milliseconds)
    pub target_major_pause_ms: u64,
    /// Enable NUMA-aware allocation
    pub numa_aware: bool,
    /// Enable adaptive tuning
    pub adaptive_tuning: bool,
}

impl Default for ParallelGcConfig {
    fn default() -> Self {
        ParallelGcConfig {
            max_collector_threads: num_cpus::get(),
            young_generation_size: 64 * 1024 * 1024, // 64MB
            old_generation_size: 256 * 1024 * 1024,  // 256MB
            large_object_threshold: 32 * 1024,       // 32KB
            target_minor_pause_ms: 10,               // 10ms
            target_major_pause_ms: 50,               // 50ms
            numa_aware: true,
            adaptive_tuning: true,
        }
    }
}

/// Collection phase indicator
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum CollectionPhase {
    /// No collection in progress
    Idle,
    /// Minor collection (young generation)
    MinorCollection,
    /// Major collection (full heap)
    MajorCollection,
    /// Incremental collection in progress
    IncrementalCollection,
    /// Concurrent marking phase
    ConcurrentMarking,
}

/// GC statistics and metrics
#[derive(Debug, Default)]
pub struct GcStatistics {
    /// Total number of minor collections
    pub minor_collections: AtomicU64,
    /// Total number of major collections  
    pub major_collections: AtomicU64,
    /// Total time spent in minor collections
    pub minor_collection_time: AtomicU64,
    /// Total time spent in major collections
    pub major_collection_time: AtomicU64,
    /// Total bytes allocated
    pub total_allocated: AtomicU64,
    /// Total bytes reclaimed
    pub total_reclaimed: AtomicU64,
    /// Average minor collection pause times (nanoseconds)
    pub avg_minor_pause_ns: AtomicU64,
    /// Average major collection pause times (nanoseconds)
    pub avg_major_pause_ns: AtomicU64,
    /// Current heap utilization percentage
    pub heap_utilization: AtomicUsize,
}

impl GcStatistics {
    /// Create new statistics instance
    pub fn new() -> Self {
        Self::default()
    }

    /// Record a minor collection
    pub fn record_minor_collection(&self, pause_time: Duration) {
        self.minor_collections.fetch_add(1, Ordering::Relaxed);
        let pause_ns = pause_time.as_nanos() as u64;
        self.minor_collection_time.fetch_add(pause_ns, Ordering::Relaxed);
        
        // Update running average
        let count = self.minor_collections.load(Ordering::Relaxed);
        let total_time = self.minor_collection_time.load(Ordering::Relaxed);
        self.avg_minor_pause_ns.store(total_time / count, Ordering::Relaxed);
    }

    /// Record a major collection
    pub fn record_major_collection(&self, pause_time: Duration) {
        self.major_collections.fetch_add(1, Ordering::Relaxed);
        let pause_ns = pause_time.as_nanos() as u64;
        self.major_collection_time.fetch_add(pause_ns, Ordering::Relaxed);
        
        // Update running average
        let count = self.major_collections.load(Ordering::Relaxed);
        let total_time = self.major_collection_time.load(Ordering::Relaxed);
        self.avg_major_pause_ns.store(total_time / count, Ordering::Relaxed);
    }

    /// Update allocation statistics
    pub fn record_allocation(&self, size: u64) {
        self.total_allocated.fetch_add(size, Ordering::Relaxed);
    }

    /// Update reclamation statistics
    pub fn record_reclamation(&self, size: u64) {
        self.total_reclaimed.fetch_add(size, Ordering::Relaxed);
    }

    /// Update heap utilization
    pub fn update_heap_utilization(&self, percentage: usize) {
        self.heap_utilization.store(percentage, Ordering::Relaxed);
    }
}

/// Thread-safe safepoint coordination
#[derive(Debug)]
pub struct SafepointCoordinator {
    /// Whether a safepoint is requested
    safepoint_requested: AtomicBool,
    /// Number of threads that have reached the safepoint
    threads_at_safepoint: AtomicUsize,
    /// Total number of mutator threads
    total_threads: AtomicUsize,
    /// Synchronization primitives
    safepoint_lock: Mutex<()>,
    safepoint_reached: Condvar,
    safepoint_released: Condvar,
}

impl SafepointCoordinator {
    /// Create new safepoint coordinator
    pub fn new() -> Self {
        SafepointCoordinator {
            safepoint_requested: AtomicBool::new(false),
            threads_at_safepoint: AtomicUsize::new(0),
            total_threads: AtomicUsize::new(0),
            safepoint_lock: Mutex::new(()),
            safepoint_reached: Condvar::new(),
            safepoint_released: Condvar::new(),
        }
    }

    /// Register a mutator thread
    pub fn register_thread(&self) {
        self.total_threads.fetch_add(1, Ordering::Relaxed);
    }

    /// Unregister a mutator thread
    pub fn unregister_thread(&self) {
        self.total_threads.fetch_sub(1, Ordering::Relaxed);
    }

    /// Request all threads to reach safepoint
    pub fn request_safepoint(&self) -> Result<(), String> {
        self.safepoint_requested.store(true, Ordering::Relaxed);
        
        let mut lock = self.safepoint_lock.lock().map_err(|_| "Failed to acquire safepoint lock")?;
        
        // Wait for all threads to reach safepoint
        let total = self.total_threads.load(Ordering::Relaxed);
        
        loop {
            let threads_reached = self.threads_at_safepoint.load(Ordering::Relaxed);
            if threads_reached >= total {
                break;
            }
            
            match self.safepoint_reached.wait_timeout(lock, Duration::from_millis(100)) {
                Ok((new_lock, timeout_result)) => {
                    lock = new_lock;
                    if timeout_result.timed_out() {
                        // Check if threads are making progress
                        let current_reached = self.threads_at_safepoint.load(Ordering::Relaxed);
                        if current_reached < threads_reached {
                            return Err("Timeout waiting for threads to reach safepoint".to_string());
                        }
                    }
                }
                Err(_) => return Err("Error waiting for safepoint".to_string()),
            }
        }

        Ok(())
    }

    /// Release threads from safepoint
    pub fn release_safepoint(&self) {
        self.safepoint_requested.store(false, Ordering::Relaxed);
        self.threads_at_safepoint.store(0, Ordering::Relaxed);
        self.safepoint_released.notify_all();
    }

    /// Check if safepoint is requested (called by mutator threads)
    pub fn check_safepoint(&self) -> bool {
        if self.safepoint_requested.load(Ordering::Relaxed) {
            self.reach_safepoint();
            true
        } else {
            false
        }
    }

    /// Reach safepoint (called by mutator threads)
    fn reach_safepoint(&self) {
        self.threads_at_safepoint.fetch_add(1, Ordering::Relaxed);
        self.safepoint_reached.notify_all();

        // Wait for release
        let lock = self.safepoint_lock.lock().unwrap();
        let _result = self.safepoint_released.wait_while(lock, |_| {
            self.safepoint_requested.load(Ordering::Relaxed)
        });
    }
}

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

/// Main parallel garbage collector coordinator
#[derive(Debug)]
pub struct ParallelGc {
    /// GC configuration
    config: Arc<ParallelGcConfig>,
    /// Current collection phase
    current_phase: Arc<RwLock<CollectionPhase>>,
    /// GC statistics
    statistics: Arc<GcStatistics>,
    /// Safepoint coordinator
    safepoint: Arc<SafepointCoordinator>,
    /// JIT metrics integration
    jit_metrics: Option<Arc<RwLock<JitMetrics>>>,
    /// Adaptive tuning parameters
    adaptive_params: Arc<RwLock<AdaptiveTuningParams>>,
    /// Collection request queue
    collection_requests: Arc<Mutex<VecDeque<CollectionRequest>>>,
    /// Worker thread pool
    worker_threads: Arc<RwLock<Vec<thread::JoinHandle<()>>>>,
    /// Shutdown flag
    shutdown_requested: Arc<AtomicBool>,
}

/// Adaptive tuning parameters
#[derive(Debug, Clone)]
pub struct AdaptiveTuningParams {
    /// Current allocation rate (bytes per second)
    allocation_rate: f64,
    /// Recent pause time samples
    pause_time_samples: VecDeque<Duration>,
    /// Current heap growth rate
    heap_growth_rate: f64,
    /// Recommended collection frequency adjustment
    collection_frequency_multiplier: f64,
}

impl Default for AdaptiveTuningParams {
    fn default() -> Self {
        AdaptiveTuningParams {
            allocation_rate: 0.0,
            pause_time_samples: VecDeque::with_capacity(100),
            heap_growth_rate: 1.0,
            collection_frequency_multiplier: 1.0,
        }
    }
}

/// Collection request types
#[derive(Debug, Clone)]
pub enum CollectionRequest {
    /// Minor collection requested
    Minor,
    /// Major collection requested  
    Major,
    /// Incremental collection step
    IncrementalStep,
    /// Emergency collection (low memory)
    Emergency,
}

impl ParallelGc {
    /// Create a new parallel garbage collector
    pub fn new(config: ParallelGcConfig) -> Self {
        ParallelGc {
            config: Arc::new(config),
            current_phase: Arc::new(RwLock::new(CollectionPhase::Idle)),
            statistics: Arc::new(GcStatistics::new()),
            safepoint: Arc::new(SafepointCoordinator::new()),
            jit_metrics: None,
            adaptive_params: Arc::new(RwLock::new(AdaptiveTuningParams::default())),
            collection_requests: Arc::new(Mutex::new(VecDeque::new())),
            worker_threads: Arc::new(RwLock::new(Vec::new())),
            shutdown_requested: Arc::new(AtomicBool::new(false)),
        }
    }

    /// Initialize the garbage collector with optional JIT metrics integration
    pub fn initialize(&mut self, jit_metrics: Option<Arc<RwLock<JitMetrics>>>) -> Result<(), String> {
        self.jit_metrics = jit_metrics;
        self.start_worker_threads()?;
        Ok(())
    }

    /// Start worker threads for concurrent collection
    fn start_worker_threads(&self) -> Result<(), String> {
        let num_threads = self.config.max_collector_threads;
        let mut worker_handles = self.worker_threads.write().map_err(|_| "Failed to acquire worker threads lock")?;
        
        for thread_id in 0..num_threads {
            let config = Arc::clone(&self.config);
            let statistics = Arc::clone(&self.statistics);
            let safepoint = Arc::clone(&self.safepoint);
            let collection_requests = Arc::clone(&self.collection_requests);
            let shutdown_requested = Arc::clone(&self.shutdown_requested);
            let current_phase = Arc::clone(&self.current_phase);

            let handle = thread::Builder::new()
                .name(format!("gc-worker-{thread_id}"))
                .spawn(move || {
                    Self::worker_thread_main(
                        thread_id,
                        config,
                        statistics,
                        safepoint,
                        collection_requests,
                        current_phase,
                        shutdown_requested,
                    );
                })
                .map_err(|e| format!("Failed to spawn GC worker thread: {e}"))?;

            worker_handles.push(handle);
        }

        Ok(())
    }

    /// Main worker thread function
    fn worker_thread_main(
        _thread_id: usize,
        _config: Arc<ParallelGcConfig>,
        _statistics: Arc<GcStatistics>,
        _safepoint: Arc<SafepointCoordinator>,
        collection_requests: Arc<Mutex<VecDeque<CollectionRequest>>>,
        _current_phase: Arc<RwLock<CollectionPhase>>,
        shutdown_requested: Arc<AtomicBool>,
    ) {
        while !shutdown_requested.load(Ordering::Relaxed) {
            // Check for collection requests
            let request = {
                let mut requests = collection_requests.lock().unwrap();
                requests.pop_front()
            };

            match request {
                Some(CollectionRequest::Minor) => {
                    // TODO: Implement minor collection
                }
                Some(CollectionRequest::Major) => {
                    // TODO: Implement major collection
                }
                Some(CollectionRequest::IncrementalStep) => {
                    // TODO: Implement incremental step
                }
                Some(CollectionRequest::Emergency) => {
                    // TODO: Implement emergency collection
                }
                None => {
                    // No work available, sleep briefly
                    thread::sleep(Duration::from_millis(1));
                }
            }
        }
    }

    /// Request a minor collection
    pub fn request_minor_collection(&self) -> Result<(), String> {
        let mut requests = self.collection_requests.lock().map_err(|_| "Failed to acquire collection requests lock")?;
        requests.push_back(CollectionRequest::Minor);
        Ok(())
    }

    /// Request a major collection
    pub fn request_major_collection(&self) -> Result<(), String> {
        let mut requests = self.collection_requests.lock().map_err(|_| "Failed to acquire collection requests lock")?;
        requests.push_back(CollectionRequest::Major);
        Ok(())
    }

    /// Get current GC statistics
    pub fn get_statistics(&self) -> &GcStatistics {
        &self.statistics
    }

    /// Get current collection phase
    pub fn get_current_phase(&self) -> CollectionPhase {
        *self.current_phase.read().unwrap()
    }

    /// Update adaptive tuning parameters based on recent performance
    pub fn update_adaptive_tuning(&self, allocation_rate: f64, recent_pause: Duration) {
        if !self.config.adaptive_tuning {
            return;
        }

        if let Ok(mut params) = self.adaptive_params.write() {
            params.allocation_rate = allocation_rate;
            
            // Keep a rolling window of pause time samples
            params.pause_time_samples.push_back(recent_pause);
            if params.pause_time_samples.len() > 100 {
                params.pause_time_samples.pop_front();
            }

            // Calculate average pause time
            let avg_pause = if !params.pause_time_samples.is_empty() {
                let total: Duration = params.pause_time_samples.iter().sum();
                total / params.pause_time_samples.len() as u32
            } else {
                Duration::from_millis(0)
            };

            // Adjust collection frequency based on pause times
            let target_pause = Duration::from_millis(self.config.target_minor_pause_ms);
            if avg_pause > target_pause {
                // Pause times too high, collect more frequently
                params.collection_frequency_multiplier = (params.collection_frequency_multiplier * 1.1).min(3.0);
            } else if avg_pause < target_pause / 2 {
                // Pause times very low, can collect less frequently
                params.collection_frequency_multiplier = (params.collection_frequency_multiplier * 0.9).max(0.5);
            }
        }
    }

    /// Register a mutator thread with the safepoint coordinator
    pub fn register_mutator_thread(&self) {
        self.safepoint.register_thread();
    }

    /// Unregister a mutator thread from the safepoint coordinator
    pub fn unregister_mutator_thread(&self) {
        self.safepoint.unregister_thread();
    }

    /// Check if a safepoint is requested (called by mutator threads)
    pub fn check_safepoint(&self) -> bool {
        self.safepoint.check_safepoint()
    }

    /// Shutdown the garbage collector
    pub fn shutdown(&self) -> Result<(), String> {
        // Signal shutdown
        self.shutdown_requested.store(true, Ordering::Relaxed);

        // Wait for worker threads to finish
        let mut handles = self.worker_threads.write().map_err(|_| "Failed to acquire worker threads lock")?;
        while let Some(handle) = handles.pop() {
            handle.join().map_err(|_| "Failed to join worker thread")?;
        }

        Ok(())
    }
}

impl Drop for ParallelGc {
    fn drop(&mut self) {
        let _ = self.shutdown();
    }
}