synapse 1.1.0

//! High-performance SMTP server for EMRP

use crate::error::{SynapseError, Result};
use crate::types::SecureMessage;
use crate::synapse::blockchain::serialization::{DateTimeWrapper, UuidWrapper};
use std::sync::{Arc, Mutex};
use std::collections::HashMap;
use tokio::net::{TcpListener, TcpStream};
use tokio::io::{AsyncBufReadExt, AsyncWriteExt, BufReader};
use std::time::{SystemTime, UNIX_EPOCH};
use tracing::{info, error, debug};
use uuid::Uuid;
use chrono::Utc;

/// High-performance SMTP server optimized for EMRP
pub struct SynapseSmtpServer {
    /// Server configuration
    config: SmtpServerConfig,
    /// Message storage
    message_store: Arc<Mutex<HashMap<String, Vec<SecureMessage>>>>,
    /// Connected clients
    clients: Arc<Mutex<HashMap<String, ClientSession>>>,
    /// Authorization handler
    auth_handler: Arc<dyn AuthHandler + Send + Sync>,
    /// Performance metrics
    metrics: Arc<Mutex<ServerMetrics>>,
}

#[derive(Debug, Clone)]
pub struct SmtpServerConfig {
    /// SMTP port (usually 25, 587, or 2525)
    pub port: u16,
    /// Maximum message size in bytes
    pub max_message_size: usize,
    /// Authentication required
    pub require_auth: bool,
    /// TLS configuration
    pub tls_config: Option<TlsConfig>,
    /// Performance optimization settings
    pub performance: PerformanceConfig,
}

#[derive(Debug, Clone)]
pub struct PerformanceConfig {
    /// Connection pool size
    pub max_connections: usize,
    /// Keep-alive timeout
    pub keep_alive_timeout: u64,
    /// Pipeline multiple commands
    pub enable_pipelining: bool,
    /// Compression for large messages
    pub enable_compression: bool,
}

#[derive(Debug, Clone)]
pub struct TlsConfig {
    pub cert_path: String,
    pub key_path: String,
    pub require_tls: bool,
}

#[derive(Debug)]
struct ClientSession {
    #[allow(dead_code)]
    id: String,
    authenticated: bool,
    current_message: Option<SmtpMessage>,
    #[allow(dead_code)]
    connected_at: SystemTime,
}

#[derive(Debug)]
struct SmtpMessage {
    #[allow(dead_code)]
    from: String,
    to: Vec<String>,
    #[allow(dead_code)]
    data: Vec<u8>,
}

#[derive(Debug, Clone)]
pub struct ServerMetrics {
    #[allow(dead_code)]
    messages_received: u64,
    #[allow(dead_code)]
    messages_delivered: u64,
    connections_accepted: u64,
    #[allow(dead_code)]
    average_processing_time_ms: f64,
    #[allow(dead_code)]
    last_reset: SystemTime,
}

impl Default for ServerMetrics {
    fn default() -> Self {
        Self {
            messages_received: 0,
            messages_delivered: 0,
            connections_accepted: 0,
            average_processing_time_ms: 0.0,
            last_reset: SystemTime::now(),
        }
    }
}

pub trait AuthHandler {
    fn authenticate(&self, username: &str, password: &str) -> Result<bool>;
    fn is_authorized_sender(&self, email: &str) -> Result<bool>;
    fn is_authorized_recipient(&self, email: &str) -> Result<bool>;
}

impl Default for SmtpServerConfig {
    fn default() -> Self {
        Self {
            port: 2525, // Non-privileged port for development
            max_message_size: 25 * 1024 * 1024, // 25MB
            require_auth: true,
            tls_config: None,
            performance: PerformanceConfig {
                max_connections: 100,
                keep_alive_timeout: 300,
                enable_pipelining: true,
                enable_compression: true,
            },
        }
    }
}

impl SynapseSmtpServer {
    /// Create a new SMTP server
    pub fn new(
        config: SmtpServerConfig,
        auth_handler: Arc<dyn AuthHandler + Send + Sync>,
    ) -> Self {
        Self {
            config,
            message_store: Arc::new(Mutex::new(HashMap::new())),
            clients: Arc::new(Mutex::new(HashMap::new())),
            auth_handler,
            metrics: Arc::new(Mutex::new(ServerMetrics::default())),
        }
    }

    /// Start the SMTP server
    pub async fn start(&self) -> Result<()> {
        let addr = format!("0.0.0.0:{}", self.config.port);
        let listener = TcpListener::bind(&addr).await
            .map_err(|e| SynapseError::NetworkError(format!("Failed to bind SMTP server to {}: {}", addr, e)))?;

        info!("EMRP SMTP Server listening on {}", addr);

        loop {
            match listener.accept().await {
                Ok((stream, addr)) => {
                    info!("New SMTP connection from {}", addr);
                    
                    // Update metrics
                    {
                        let mut metrics = self.metrics.lock().unwrap();
                        metrics.connections_accepted += 1;
                    }

                    // Handle connection in background task
                    let server = self.clone();
                    tokio::spawn(async move {
                        if let Err(e) = server.handle_connection(stream).await {
                            error!("SMTP connection error: {}", e);
                        }
                    });
                }
                Err(e) => {
                    error!("Failed to accept SMTP connection: {}", e);
                }
            }
        }
    }

    /// Handle individual SMTP connection
    async fn handle_connection(&self, stream: TcpStream) -> Result<()> {
        let (read_half, write_half) = stream.into_split();
        let mut reader = BufReader::new(read_half);
        let mut writer = write_half;
        
        let mut session = ClientSession {
            id: format!("smtp_{}", SystemTime::now().duration_since(UNIX_EPOCH).unwrap().as_millis()),
            authenticated: false,
            current_message: None,
            connected_at: SystemTime::now(),
        };

        // Send greeting
        writer.write_all(b"220 EMRP SMTP Server Ready\r\n").await?;
        writer.flush().await?;

        let mut line = String::new();
        while reader.read_line(&mut line).await? > 0 {
            let command = line.trim();
            debug!("SMTP command: {}", command);

            let response = self.process_smtp_command(command, &mut session).await?;
            
            writer.write_all(response.as_bytes()).await?;
            writer.flush().await?;

            // Check if connection should close
            if response.starts_with("221") {
                break;
            }

            line.clear();
        }

        Ok(())
    }

    /// Process SMTP command
    async fn process_smtp_command(&self, command: &str, session: &mut ClientSession) -> Result<String> {
        let parts: Vec<&str> = command.split_whitespace().collect();
        if parts.is_empty() {
            return Ok("500 Syntax error\r\n".to_string());
        }

        let cmd = parts[0].to_uppercase();
        
        match cmd.as_str() {
            "HELO" | "EHLO" => {
                let hostname = parts.get(1).unwrap_or(&"unknown");
                if cmd == "EHLO" {
                    let mut response = format!("250-Hello {}\r\n", hostname);
                    response.push_str("250-PIPELINING\r\n");
                    response.push_str("250-8BITMIME\r\n");
                    if self.config.require_auth {
                        response.push_str("250-AUTH PLAIN LOGIN\r\n");
                    }
                    response.push_str("250 Ok\r\n");
                    Ok(response)
                } else {
                    Ok(format!("250 Hello {}\r\n", hostname))
                }
            }
            "AUTH" => {
                if parts.len() < 2 {
                    return Ok("500 AUTH mechanism required\r\n".to_string());
                }
                
                let mechanism = parts[1].to_uppercase();
                match mechanism.as_str() {
                    "PLAIN" => {
                        if parts.len() >= 3 {
                            // Inline AUTH PLAIN
                            if let Ok(auth_data) = base64_decode(parts[2]) {
                                if let Ok(auth_str) = String::from_utf8(auth_data) {
                                    let auth_parts: Vec<&str> = auth_str.split('\0').collect();
                                    if auth_parts.len() >= 3 {
                                        let username = auth_parts[1];
                                        let password = auth_parts[2];
                                        
                                        match self.auth_handler.authenticate(username, password) {
                                            Ok(true) => {
                                                session.authenticated = true;
                                                return Ok("235 Authentication successful\r\n".to_string());
                                            }
                                            Ok(false) => {
                                                return Ok("535 Authentication failed\r\n".to_string());
                                            }
                                            Err(_) => {
                                                return Ok("454 Temporary authentication failure\r\n".to_string());
                                            }
                                        }
                                    }
                                }
                            }
                        }
                        Ok("334 \r\n".to_string()) // Request auth data
                    }
                    _ => Ok("504 Unrecognized authentication type\r\n".to_string())
                }
            }
            "MAIL" => {
                if self.config.require_auth && !session.authenticated {
                    return Ok("530 Authentication required\r\n".to_string());
                }
                
                if let Some(from_addr) = self.extract_email_from_mail_from(command) {
                    // Verify sender authorization
                    match self.auth_handler.is_authorized_sender(&from_addr) {
                        Ok(true) => {
                            session.current_message = Some(SmtpMessage {
                                from: from_addr,
                                to: Vec::new(),
                                data: Vec::new(),
                            });
                            Ok("250 Ok\r\n".to_string())
                        }
                        Ok(false) => Ok("550 Sender not authorized\r\n".to_string()),
                        Err(_) => Ok("451 Temporary failure\r\n".to_string()),
                    }
                } else {
                    Ok("501 Syntax error in MAIL command\r\n".to_string())
                }
            }
            "RCPT" => {
                if session.current_message.is_none() {
                    return Ok("503 Need MAIL command first\r\n".to_string());
                }
                
                if let Some(to_addr) = self.extract_email_from_rcpt_to(command) {
                    // Verify recipient authorization
                    match self.auth_handler.is_authorized_recipient(&to_addr) {
                        Ok(true) => {
                            if let Some(ref mut msg) = session.current_message {
                                msg.to.push(to_addr);
                            }
                            Ok("250 Ok\r\n".to_string())
                        }
                        Ok(false) => Ok("550 Recipient not authorized\r\n".to_string()),
                        Err(_) => Ok("451 Temporary failure\r\n".to_string()),
                    }
                } else {
                    Ok("501 Syntax error in RCPT command\r\n".to_string())
                }
            }
            "DATA" => {
                if session.current_message.is_none() {
                    return Ok("503 Need RCPT command first\r\n".to_string());
                }
                
                if let Some(ref msg) = session.current_message {
                    if msg.to.is_empty() {
                        return Ok("503 Need RCPT command first\r\n".to_string());
                    }
                }
                
                Ok("354 Start mail input; end with <CRLF>.<CRLF>\r\n".to_string())
            }
            "QUIT" => {
                Ok("221 Bye\r\n".to_string())
            }
            _ => {
                Ok("502 Command not implemented\r\n".to_string())
            }
        }
    }

    /// Extract email address from MAIL FROM command
    fn extract_email_from_mail_from(&self, command: &str) -> Option<String> {
        // Parse "MAIL FROM:<email@domain.com>"
        if let Some(start) = command.find('<') {
            if let Some(end) = command.find('>') {
                if end > start {
                    return Some(command[start + 1..end].to_string());
                }
            }
        }
        None
    }

    /// Extract email address from RCPT TO command
    fn extract_email_from_rcpt_to(&self, command: &str) -> Option<String> {
        // Parse "RCPT TO:<email@domain.com>"
        if let Some(start) = command.find('<') {
            if let Some(end) = command.find('>') {
                if end > start {
                    return Some(command[start + 1..end].to_string());
                }
            }
        }
        None
    }

    /// Store message in the server
    #[allow(dead_code)]
    async fn store_message(&self, message: SmtpMessage) -> Result<()> {
        let start_time = SystemTime::now();
        
        // Convert SMTP message to EMRP SecureMessage
        let secure_message = SecureMessage {
            message_id: UuidWrapper::new(Uuid::new_v4()),
            to_global_id: message.to[0].clone(), // Use first recipient
            from_global_id: message.from,
            encrypted_content: message.data,
            signature: Vec::new(),
            timestamp: DateTimeWrapper::new(Utc::now()),
            security_level: crate::types::SecurityLevel::Private,
            routing_path: Vec::new(),
            metadata: std::collections::HashMap::new(),
        };

        // Store message for each recipient
        {
            let mut store = self.message_store.lock().unwrap();
            for recipient in &message.to {
                let messages = store.entry(recipient.clone()).or_insert_with(Vec::new);
                messages.push(secure_message.clone());
            }
        }

        // Update metrics
        {
            let mut metrics = self.metrics.lock().unwrap();
            metrics.messages_received += 1;
            
            if let Ok(elapsed) = start_time.elapsed() {
                let processing_time = elapsed.as_millis() as f64;
                metrics.average_processing_time_ms = 
                    (metrics.average_processing_time_ms + processing_time) / 2.0;
            }
        }

        info!("Stored message from {} to {:?}", secure_message.from_global_id, message.to);
        Ok(())
    }

    /// Get messages for a recipient
    pub fn get_messages(&self, recipient: &str) -> Result<Vec<SecureMessage>> {
        let store = self.message_store.lock().unwrap();
        Ok(store.get(recipient).cloned().unwrap_or_default())
    }

    /// Get server metrics
    pub fn get_metrics(&self) -> ServerMetrics {
        self.metrics.lock().unwrap().clone()
    }
}

impl Clone for SynapseSmtpServer {
    fn clone(&self) -> Self {
        Self {
            config: self.config.clone(),
            message_store: Arc::clone(&self.message_store),
            clients: Arc::clone(&self.clients),
            auth_handler: Arc::clone(&self.auth_handler),
            metrics: Arc::clone(&self.metrics),
        }
    }
}

// Simple base64 decode function
fn base64_decode(input: &str) -> Result<Vec<u8>> {
    // Simple base64 decoding - in production, use a proper base64 library
    const CHARS: &[u8] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    
    let input = input.trim();
    let mut result = Vec::new();
    let mut buffer = 0u32;
    let mut bits = 0;
    
    for byte in input.bytes() {
        if byte == b'=' {
            break;
        }
        
        let value = CHARS.iter().position(|&x| x == byte)
            .ok_or_else(|| SynapseError::Crypto("Invalid base64 character".to_string()))?;
        
        buffer = (buffer << 6) | (value as u32);
        bits += 6;
        
        if bits >= 8 {
            result.push((buffer >> (bits - 8)) as u8);
            bits -= 8;
        }
    }
    
    Ok(result)
}