feat: Add circuit breaker pattern implementation to API server with configurable thresholds and timeout

- Add State enum with Closed, Open, and HalfOpen states and String method
- Add CircuitBreaker struct with mutex, state tracking, failure/success counters, and timeout
- Add Config struct with FailureThreshold, SuccessThreshold, and Timeout fields
- Add NewCircuitBreaker constructor with Config parameter
- Add DefaultConfig with 5 failure threshold, 2 success threshold, and 60 second timeout

apps/api-server/internal/circuitbreaker/circuitbreaker.go

@@ -0,0 +1,142 @@
+package circuitbreaker
+
+import (
+	"errors"
+	"sync"
+	"time"
+)
+
+// State represents the state of the circuit breaker
+type State int
+
+const (
+	StateClosed State = iota
+	StateOpen
+	StateHalfOpen
+)
+
+func (s State) String() string {
+	switch s {
+	case StateClosed:
+		return "Closed"
+	case StateOpen:
+		return "Open"
+	case StateHalfOpen:
+		return "HalfOpen"
+	default:
+		return "Unknown"
+	}
+}
+
+// CircuitBreaker implements the circuit breaker pattern
+type CircuitBreaker struct {
+	mu                sync.Mutex
+	state             State
+	failureCount      uint
+	failureThreshold  uint
+	successThreshold  uint
+	timeout           time.Duration
+	lastFailureTime   time.Time
+	halfOpenSuccesses uint
+}
+
+// Config holds the configuration for the circuit breaker
+type Config struct {
+	FailureThreshold uint
+	SuccessThreshold uint
+	Timeout          time.Duration
+}
+
+// NewCircuitBreaker creates a new circuit breaker with the given configuration
+func NewCircuitBreaker(config Config) *CircuitBreaker {
+	return &CircuitBreaker{
+		state:            StateClosed,
+		failureThreshold: config.FailureThreshold,
+		successThreshold: config.SuccessThreshold,
+		timeout:          config.Timeout,
+	}
+}
+
+// DefaultConfig returns a default configuration for the circuit breaker
+func DefaultConfig() Config {
+	return Config{
+		FailureThreshold: 5,
+		SuccessThreshold: 2,
+		Timeout:          60 * time.Second,
+	}
+}
+
+// Execute runs the given function with circuit breaker protection
+func (cb *CircuitBreaker) Execute(fn func() error) error {
+	cb.mu.Lock()
+	
+	// Check if we should attempt to transition from Open to HalfOpen
+	if cb.state == StateOpen && time.Since(cb.lastFailureTime) > cb.timeout {
+		cb.state = StateHalfOpen
+		cb.halfOpenSuccesses = 0
+	}
+	
+	// If circuit is open, reject the request
+	if cb.state == StateOpen {
+		cb.mu.Unlock()
+		return errors.New("circuit breaker is open")
+	}
+	
+	cb.mu.Unlock()
+	
+	// Execute the function
+	err := fn()
+	
+	cb.mu.Lock()
+	defer cb.mu.Unlock()
+	
+	if err != nil {
+		cb.onFailure()
+		return err
+	}
+	
+	cb.onSuccess()
+	return nil
+}
+
+// onFailure handles a failed operation
+func (cb *CircuitBreaker) onFailure() {
+	cb.failureCount++
+	cb.lastFailureTime = time.Now()
+	
+	if cb.failureCount >= cb.failureThreshold {
+		cb.state = StateOpen
+	}
+}
+
+// onSuccess handles a successful operation
+func (cb *CircuitBreaker) onSuccess() {
+	if cb.state == StateClosed {
+		cb.failureCount = 0
+		return
+	}
+	
+	if cb.state == StateHalfOpen {
+		cb.halfOpenSuccesses++
+		if cb.halfOpenSuccesses >= cb.successThreshold {
+			cb.state = StateClosed
+			cb.failureCount = 0
+		}
+	}
+}
+
+// GetState returns the current state of the circuit breaker
+func (cb *CircuitBreaker) GetState() State {
+	cb.mu.Lock()
+	defer cb.mu.Unlock()
+	return cb.state
+}
+
+// Reset resets the circuit breaker to closed state
+func (cb *CircuitBreaker) Reset() {
+	cb.mu.Lock()
+	defer cb.mu.Unlock()
+	cb.state = StateClosed
+	cb.failureCount = 0
+	cb.halfOpenSuccesses = 0
+}