[PHASE-8] Gather metrics in tcp server

internal/server/tcp.go

@@ -11,6 +11,7 @@ import (
 
 	"hash-of-wisdom/internal/application"
 	"hash-of-wisdom/internal/lib/sl"
+	"hash-of-wisdom/internal/metrics"
 	"hash-of-wisdom/internal/protocol"
 	"hash-of-wisdom/internal/service"
 )
@@ -130,6 +131,10 @@ func (s *TCPServer) acceptLoop(ctx context.Context) {
 func (s *TCPServer) handleConnection(ctx context.Context, rawConn net.Conn) {
 	defer rawConn.Close()
 
+	// Track active connections
+	metrics.ActiveConnections.Inc()
+	defer metrics.ActiveConnections.Dec()
+
 	connLogger := s.logger.With("remote_addr", rawConn.RemoteAddr().String())
 	connLogger.Info("connection accepted")
 
@@ -187,19 +192,38 @@ func (s *TCPServer) processConnection(ctx context.Context, conn net.Conn, logger
 			logger.Debug("client closed connection gracefully")
 			return nil
 		}
+		metrics.RequestErrors.WithLabelValues("decode_error").Inc()
 		logger.Error("failed to decode message", sl.Err(err))
 		return fmt.Errorf("decode error: %w", err)
 	}
 
 	logger.Debug("message decoded", "type", msg.Type, "payload_length", msg.PayloadLength)
 
-	// Process message through application layer
+	// Track all requests
+	metrics.RequestsTotal.Inc()
+
+	// Process message through application layer with timing
+	start := time.Now()
 	response, err := s.wisdomApplication.HandleMessage(ctx, msg)
+	duration := time.Since(start)
+	metrics.RequestDuration.Observe(duration.Seconds())
+
 	if err != nil {
+		metrics.RequestErrors.WithLabelValues("internal_error").Inc()
 		logger.Error("application error", sl.Err(err))
 		return fmt.Errorf("application error: %w", err)
 	}
 
+	// Check if response is an error response
+	if errorResp, isError := response.(*protocol.ErrorResponse); isError {
+		metrics.RequestErrors.WithLabelValues(string(errorResp.Code)).Inc()
+	} else {
+		// Track quotes served for successful solution requests
+		if msg.Type == protocol.SolutionRequestType {
+			metrics.QuotesServed.Inc()
+		}
+	}
+
 	logger.Debug("sending response to client")
 	// Send response using the response's own Encode method
 	if err := response.Encode(dc); err != nil {