// NAC CBPP L0 - Block Propagation Optimization
// 区块传播优化模块 (QUIC + 0-RTT + FEC)

use std::sync::Arc;
use tokio::sync::RwLock;
use std::collections::HashMap;
use nac_udm::primitives::{Hash, Address};
use thiserror::Error;
use serde::{Serialize, Deserialize};

#[derive(Error, Debug)]
pub enum PropagationError {
    #[error("Connection failed: {0}")]
    ConnectionFailed(String),
    
    #[error("Block announce failed: {0}")]
    AnnounceFailed(String),
    
    #[error("Network error: {0}")]
    NetworkError(String),
    
    #[error("Peer not found: {0}")]
    PeerNotFound(Address),
}

/// Block Announce Message
/// 
/// Sent before full block to allow peers to request missing blocks
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct BlockAnnounce {
    /// Block hash
    pub block_hash: Hash,
    
    /// Block height
    pub height: u64,
    
    /// Producer address
    pub producer: Address,
    
    /// Timestamp
    pub timestamp: u64,
    
    /// Number of transactions
    pub tx_count: u32,
}

/// CBP Backbone Network Connection
/// 
/// Represents a connection to another CBP node in the backbone network
#[derive(Debug, Clone)]
pub struct BackboneConnection {
    /// Peer address
    pub peer_address: Address,
    
    /// Connection quality score (0-100)
    pub quality_score: u8,
    
    /// Round-trip time (milliseconds)
    pub rtt_ms: u64,
    
    /// Last seen timestamp
    pub last_seen: u64,
    
    /// Is this a direct connection?
    pub is_direct: bool,
}

/// Block Propagation Manager
/// 
/// Manages the CBP backbone network and optimizes block propagation
pub struct PropagationManager {
    /// CBP backbone connections
    connections: Arc<RwLock<HashMap<Address, BackboneConnection>>>,
    
    /// Pending block announces
    pending_announces: Arc<RwLock<HashMap<Hash, BlockAnnounce>>>,
    
    /// Configuration
    config: PropagationConfig,
}

#[derive(Debug, Clone)]
pub struct PropagationConfig {
    /// Minimum number of CBP connections
    pub min_cbp_connections: usize,
    
    /// Target number of CBP connections
    pub target_cbp_connections: usize,
    
    /// Maximum RTT for backbone connection (ms)
    pub max_rtt_ms: u64,
    
    /// Connection timeout (ms)
    pub connection_timeout_ms: u64,
}

impl Default for PropagationConfig {
    fn default() -> Self {
        Self {
            min_cbp_connections: 12,  // From constitutional clause NET_CONN_MIN_CBP
            target_cbp_connections: 24,
            max_rtt_ms: 500,
            connection_timeout_ms: 5000,
        }
    }
}

impl PropagationManager {
    /// Create a new propagation manager
    pub fn new(config: PropagationConfig) -> Self {
        Self {
            connections: Arc::new(RwLock::new(HashMap::new())),
            pending_announces: Arc::new(RwLock::new(HashMap::new())),
            config,
        }
    }
    
    /// Create with default configuration
    pub fn with_default_config() -> Self {
        Self::new(PropagationConfig::default())
    }
    
    /// Add a CBP backbone connection
    pub async fn add_connection(&self, connection: BackboneConnection) -> Result<(), PropagationError> {
        let mut connections = self.connections.write().await;
        connections.insert(connection.peer_address, connection);
        Ok(())
    }
    
    /// Remove a CBP backbone connection
    pub async fn remove_connection(&self, peer: &Address) -> Result<(), PropagationError> {
        let mut connections = self.connections.write().await;
        connections.remove(peer)
            .ok_or_else(|| PropagationError::PeerNotFound(*peer))?;
        Ok(())
    }
    
    /// Get all active CBP connections
    pub async fn get_connections(&self) -> Vec<BackboneConnection> {
        let connections = self.connections.read().await;
        connections.values().cloned().collect()
    }
    
    /// Check if we have enough CBP connections
    pub async fn has_sufficient_connections(&self) -> bool {
        let connections = self.connections.read().await;
        connections.len() >= self.config.min_cbp_connections
    }
    
    /// Broadcast block announce to all CBP peers
    pub async fn broadcast_block_announce(&self, announce: BlockAnnounce) -> Result<(), PropagationError> {
        // Store pending announce
        {
            let mut pending = self.pending_announces.write().await;
            pending.insert(announce.block_hash, announce.clone());
        }
        
        // Get all connections
        let connections = self.connections.read().await;
        
        if connections.is_empty() {
            return Err(PropagationError::AnnounceFailed(
                "No CBP connections available".to_string()
            ));
        }
        
        // In real implementation, this would send via QUIC
        // For now, we just log the intent
        log::info!(
            "Broadcasting block announce: hash={:?}, height={}, to {} peers",
            announce.block_hash,
            announce.height,
            connections.len()
        );
        
        Ok(())
    }
    
    /// Request full block from peer
    pub async fn request_block(&self, block_hash: Hash, from_peer: Address) -> Result<(), PropagationError> {
        let connections = self.connections.read().await;
        
        if !connections.contains_key(&from_peer) {
            return Err(PropagationError::PeerNotFound(from_peer));
        }
        
        // In real implementation, this would send request via QUIC
        log::info!(
            "Requesting block {:?} from peer {:?}",
            block_hash,
            from_peer
        );
        
        Ok(())
    }
    
    /// Update connection quality score
    pub async fn update_connection_quality(&self, peer: Address, new_score: u8, rtt_ms: u64) -> Result<(), PropagationError> {
        let mut connections = self.connections.write().await;
        
        if let Some(conn) = connections.get_mut(&peer) {
            conn.quality_score = new_score;
            conn.rtt_ms = rtt_ms;
            conn.last_seen = std::time::SystemTime::now()
                .duration_since(std::time::UNIX_EPOCH)
                .unwrap()
                .as_secs();
            Ok(())
        } else {
            Err(PropagationError::PeerNotFound(peer))
        }
    }
    
    /// Get best peers for block propagation (sorted by quality)
    pub async fn get_best_peers(&self, count: usize) -> Vec<BackboneConnection> {
        let connections = self.connections.read().await;
        
        let mut peers: Vec<BackboneConnection> = connections.values().cloned().collect();
        
        // Sort by quality score (descending) and RTT (ascending)
        peers.sort_by(|a, b| {
            b.quality_score.cmp(&a.quality_score)
                .then(a.rtt_ms.cmp(&b.rtt_ms))
        });
        
        peers.into_iter().take(count).collect()
    }
    
    /// Cleanup stale connections
    pub async fn cleanup_stale_connections(&self, max_age_secs: u64) {
        let mut connections = self.connections.write().await;
        let now = std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .unwrap()
            .as_secs();
        
        connections.retain(|_, conn| {
            now - conn.last_seen < max_age_secs
        });
    }
    
    /// Get propagation statistics
    pub async fn get_stats(&self) -> PropagationStats {
        let connections = self.connections.read().await;
        let pending = self.pending_announces.read().await;
        
        let avg_rtt = if !connections.is_empty() {
            connections.values().map(|c| c.rtt_ms).sum::<u64>() / connections.len() as u64
        } else {
            0
        };
        
        let avg_quality = if !connections.is_empty() {
            connections.values().map(|c| c.quality_score as u64).sum::<u64>() / connections.len() as u64
        } else {
            0
        };
        
        PropagationStats {
            total_connections: connections.len(),
            pending_announces: pending.len(),
            avg_rtt_ms: avg_rtt,
            avg_quality_score: avg_quality as u8,
        }
    }
}

/// Propagation statistics
#[derive(Debug, Clone)]
pub struct PropagationStats {
    pub total_connections: usize,
    pub pending_announces: usize,
    pub avg_rtt_ms: u64,
    pub avg_quality_score: u8,
}

#[cfg(test)]
mod tests {
    use super::*;
    
    fn create_test_connection(peer: u64, quality: u8, rtt: u64) -> BackboneConnection {
        BackboneConnection {
            peer_address: Address::from_low_u64_be(peer),
            quality_score: quality,
            rtt_ms: rtt,
            last_seen: std::time::SystemTime::now()
                .duration_since(std::time::UNIX_EPOCH)
                .unwrap()
                .as_secs(),
            is_direct: true,
        }
    }
    
    #[tokio::test]
    async fn test_add_remove_connection() {
        let manager = PropagationManager::with_default_config();
        let conn = create_test_connection(1, 90, 100);
        
        manager.add_connection(conn.clone()).await.unwrap();
        
        let connections = manager.get_connections().await;
        assert_eq!(connections.len(), 1);
        
        manager.remove_connection(&conn.peer_address).await.unwrap();
        
        let connections = manager.get_connections().await;
        assert_eq!(connections.len(), 0);
    }
    
    #[tokio::test]
    async fn test_get_best_peers() {
        let manager = PropagationManager::with_default_config();
        
        // Add peers with different quality scores
        manager.add_connection(create_test_connection(1, 90, 100)).await.unwrap();
        manager.add_connection(create_test_connection(2, 80, 150)).await.unwrap();
        manager.add_connection(create_test_connection(3, 95, 120)).await.unwrap();
        
        let best = manager.get_best_peers(2).await;
        
        assert_eq!(best.len(), 2);
        assert_eq!(best[0].quality_score, 95);  // Best quality
        assert_eq!(best[1].quality_score, 90);  // Second best
    }
    
    #[tokio::test]
    async fn test_broadcast_block_announce() {
        let manager = PropagationManager::with_default_config();
        
        // Add some connections
        manager.add_connection(create_test_connection(1, 90, 100)).await.unwrap();
        manager.add_connection(create_test_connection(2, 85, 120)).await.unwrap();
        
        let announce = BlockAnnounce {
            block_hash: Hash::zero(),
            height: 1000,
            producer: Address::zero(),
            timestamp: 1000,
            tx_count: 10,
        };
        
        let result = manager.broadcast_block_announce(announce).await;
        assert!(result.is_ok());
    }
    
    #[tokio::test]
    async fn test_has_sufficient_connections() {
        let manager = PropagationManager::with_default_config();
        
        assert!(!manager.has_sufficient_connections().await);
        
        // Add minimum required connections (12)
        for i in 0..12 {
            manager.add_connection(create_test_connection(i, 80, 100)).await.unwrap();
        }
        
        assert!(manager.has_sufficient_connections().await);
    }
}