bzzz/pkg/health/integration_example.go

package health

import (
	"context"
	"fmt"
	"net/http"
	"time"

	"github.com/anthonyrawlins/bzzz/pkg/shutdown"
)

// IntegrationExample demonstrates how to integrate health monitoring and graceful shutdown
func IntegrationExample() {
	// Create logger (in real implementation, use your logging system)
	logger := &defaultLogger{}

	// Create shutdown manager
	shutdownManager := shutdown.NewManager(30*time.Second, logger)

	// Create health manager
	healthManager := NewManager("node-123", "v1.0.0", logger)
	
	// Connect health manager to shutdown manager for critical failures
	healthManager.SetShutdownManager(shutdownManager)

	// Register some example health checks
	setupHealthChecks(healthManager)

	// Create and register components for graceful shutdown
	setupShutdownComponents(shutdownManager, healthManager)

	// Start systems
	if err := healthManager.Start(); err != nil {
		logger.Error("Failed to start health manager: %v", err)
		return
	}

	// Start health HTTP server
	if err := healthManager.StartHTTPServer(8081); err != nil {
		logger.Error("Failed to start health HTTP server: %v", err)
		return
	}

	// Add shutdown hooks
	setupShutdownHooks(shutdownManager, healthManager, logger)

	// Start shutdown manager (begins listening for signals)
	shutdownManager.Start()

	logger.Info("🚀 System started with integrated health monitoring and graceful shutdown")
	logger.Info("📊 Health endpoints available at:")
	logger.Info("  - http://localhost:8081/health (overall health)")
	logger.Info("  - http://localhost:8081/health/ready (readiness)")
	logger.Info("  - http://localhost:8081/health/live (liveness)")
	logger.Info("  - http://localhost:8081/health/checks (detailed checks)")

	// Wait for shutdown
	shutdownManager.Wait()
	logger.Info("✅ System shutdown completed")
}

// setupHealthChecks registers various health checks
func setupHealthChecks(healthManager *Manager) {
	// Database connectivity check (critical)
	databaseCheck := CreateDatabaseCheck("primary-db", func() error {
		// Simulate database ping
		time.Sleep(10 * time.Millisecond)
		// Return nil for healthy, error for unhealthy
		return nil
	})
	healthManager.RegisterCheck(databaseCheck)

	// Memory usage check (warning only)
	memoryCheck := CreateMemoryCheck(0.85) // Alert if > 85%
	healthManager.RegisterCheck(memoryCheck)

	// Disk space check (warning only)
	diskCheck := CreateDiskSpaceCheck("/var/lib/bzzz", 0.90) // Alert if > 90%
	healthManager.RegisterCheck(diskCheck)

	// Custom application-specific health check
	customCheck := &HealthCheck{
		Name:        "p2p-connectivity",
		Description: "P2P network connectivity check",
		Enabled:     true,
		Critical:    true, // This is critical for P2P systems
		Interval:    15 * time.Second,
		Timeout:     10 * time.Second,
		Checker: func(ctx context.Context) CheckResult {
			// Simulate P2P connectivity check
			time.Sleep(50 * time.Millisecond)
			
			// Simulate occasionally failing check
			connected := time.Now().Unix()%10 != 0 // Fail 10% of the time
			
			if !connected {
				return CheckResult{
					Healthy:   false,
					Message:   "No P2P peers connected",
					Details: map[string]interface{}{
						"connected_peers": 0,
						"min_peers":      1,
					},
					Timestamp: time.Now(),
				}
			}
			
			return CheckResult{
				Healthy:   true,
				Message:   "P2P connectivity OK",
				Details: map[string]interface{}{
					"connected_peers": 5,
					"min_peers":      1,
				},
				Timestamp: time.Now(),
			}
		},
	}
	healthManager.RegisterCheck(customCheck)

	// Election system health check
	electionCheck := &HealthCheck{
		Name:        "election-system",
		Description: "Election system health check",
		Enabled:     true,
		Critical:    false, // Elections can be temporarily unhealthy
		Interval:    30 * time.Second,
		Timeout:     5 * time.Second,
		Checker: func(ctx context.Context) CheckResult {
			// Simulate election system check
			healthy := true
			message := "Election system operational"
			
			return CheckResult{
				Healthy:   healthy,
				Message:   message,
				Details: map[string]interface{}{
					"current_admin": "node-456",
					"election_term": 42,
					"last_election": time.Now().Add(-10 * time.Minute),
				},
				Timestamp: time.Now(),
			}
		},
	}
	healthManager.RegisterCheck(electionCheck)
}

// setupShutdownComponents registers components for graceful shutdown
func setupShutdownComponents(shutdownManager *shutdown.Manager, healthManager *Manager) {
	// Register health manager for shutdown (high priority to stop health checks early)
	healthComponent := shutdown.NewGenericComponent("health-manager", 10, true).
		SetShutdownFunc(func(ctx context.Context) error {
			return healthManager.Stop()
		})
	shutdownManager.Register(healthComponent)

	// Simulate HTTP server
	httpServer := &http.Server{Addr: ":8080"}
	httpComponent := shutdown.NewHTTPServerComponent("main-http-server", httpServer, 20)
	shutdownManager.Register(httpComponent)

	// Simulate P2P node
	p2pComponent := shutdown.NewP2PNodeComponent("p2p-node", func() error {
		// Simulate P2P node cleanup
		time.Sleep(2 * time.Second)
		return nil
	}, 30)
	shutdownManager.Register(p2pComponent)

	// Simulate database connections
	dbComponent := shutdown.NewDatabaseComponent("database-pool", func() error {
		// Simulate database connection cleanup
		time.Sleep(1 * time.Second)
		return nil
	}, 40)
	shutdownManager.Register(dbComponent)

	// Simulate worker pool
	workerStopCh := make(chan struct{})
	workerComponent := shutdown.NewWorkerPoolComponent("background-workers", workerStopCh, 5, 50)
	shutdownManager.Register(workerComponent)

	// Simulate monitoring/metrics system
	monitoringComponent := shutdown.NewMonitoringComponent("metrics-system", func() error {
		// Simulate metrics system cleanup
		time.Sleep(500 * time.Millisecond)
		return nil
	}, 60)
	shutdownManager.Register(monitoringComponent)
}

// setupShutdownHooks adds hooks for different shutdown phases
func setupShutdownHooks(shutdownManager *shutdown.Manager, healthManager *Manager, logger shutdown.Logger) {
	// Pre-shutdown hook: Mark system as stopping
	shutdownManager.AddHook(shutdown.PhasePreShutdown, func(ctx context.Context) error {
		logger.Info("🔄 Pre-shutdown: Marking system as stopping")
		
		// Update health status to stopping
		status := healthManager.GetStatus()
		status.Status = StatusStopping
		status.Message = "System is shutting down"
		
		return nil
	})

	// Shutdown hook: Log progress
	shutdownManager.AddHook(shutdown.PhaseShutdown, func(ctx context.Context) error {
		logger.Info("🔄 Shutdown phase: Components are being shut down")
		return nil
	})

	// Post-shutdown hook: Final health status update and cleanup
	shutdownManager.AddHook(shutdown.PhasePostShutdown, func(ctx context.Context) error {
		logger.Info("🔄 Post-shutdown: Performing final cleanup")
		
		// Any final cleanup that needs to happen after components are shut down
		return nil
	})

	// Cleanup hook: Final logging and state persistence
	shutdownManager.AddHook(shutdown.PhaseCleanup, func(ctx context.Context) error {
		logger.Info("🔄 Cleanup: Finalizing shutdown process")
		
		// Save any final state, flush logs, etc.
		return nil
	})
}

// HealthAwareComponent is an example of how to create components that integrate with health monitoring
type HealthAwareComponent struct {
	name           string
	healthManager  *Manager
	checkName      string
	isRunning      bool
	stopCh         chan struct{}
}

// NewHealthAwareComponent creates a component that registers its own health check
func NewHealthAwareComponent(name string, healthManager *Manager) *HealthAwareComponent {
	comp := &HealthAwareComponent{
		name:          name,
		healthManager: healthManager,
		checkName:     fmt.Sprintf("%s-health", name),
		stopCh:        make(chan struct{}),
	}

	// Register health check for this component
	healthCheck := &HealthCheck{
		Name:        comp.checkName,
		Description: fmt.Sprintf("Health check for %s component", name),
		Enabled:     true,
		Critical:    false,
		Interval:    30 * time.Second,
		Timeout:     10 * time.Second,
		Checker: func(ctx context.Context) CheckResult {
			if comp.isRunning {
				return CheckResult{
					Healthy:   true,
					Message:   fmt.Sprintf("%s is running normally", comp.name),
					Timestamp: time.Now(),
				}
			}
			
			return CheckResult{
				Healthy:   false,
				Message:   fmt.Sprintf("%s is not running", comp.name),
				Timestamp: time.Now(),
			}
		},
	}
	
	healthManager.RegisterCheck(healthCheck)
	return comp
}

// Start starts the component
func (c *HealthAwareComponent) Start() error {
	c.isRunning = true
	return nil
}

// Name returns the component name
func (c *HealthAwareComponent) Name() string {
	return c.name
}

// Priority returns the shutdown priority
func (c *HealthAwareComponent) Priority() int {
	return 50
}

// CanForceStop returns whether the component can be force-stopped
func (c *HealthAwareComponent) CanForceStop() bool {
	return true
}

// Shutdown gracefully shuts down the component
func (c *HealthAwareComponent) Shutdown(ctx context.Context) error {
	c.isRunning = false
	close(c.stopCh)
	
	// Unregister health check
	c.healthManager.UnregisterCheck(c.checkName)
	
	return nil
}