aether/examples/retry_patterns.go

package examples

import (
	"errors"
	"fmt"
	"log"
	"math"
	"math/rand"
	"time"

	"git.flowmade.one/flowmade-one/aether"
)

// SimpleRetryPattern demonstrates a basic retry loop using VersionConflictError.
//
// This pattern is suitable for scenarios where you want to automatically retry
// with exponential backoff when version conflicts occur.
func SimpleRetryPattern(store aether.EventStore, actorID string, eventType string) error {
	const maxRetries = 3
	const initialBackoff = 100 * time.Millisecond

	var event *aether.Event

	for attempt := 0; attempt < maxRetries; attempt++ {
		if attempt > 0 {
			backoff := time.Duration(math.Pow(2, float64(attempt-1))) * initialBackoff
			log.Printf("Retry attempt %d after %v", attempt, backoff)
			time.Sleep(backoff)
		}

		// Get the current version for the actor
		currentVersion, err := store.GetLatestVersion(actorID)
		if err != nil {
			return fmt.Errorf("failed to get latest version: %w", err)
		}

		// Create event with next version
		event = &aether.Event{
			ID:        fmt.Sprintf("evt-%d-%d", time.Now().UnixNano(), attempt),
			EventType: eventType,
			ActorID:   actorID,
			Version:   currentVersion + 1,
			Data:      map[string]interface{}{"attempt": attempt},
			Timestamp: time.Now(),
		}

		// Attempt to save
		if err := store.SaveEvent(event); err == nil {
			log.Printf("Successfully saved event for actor %s at version %d", actorID, event.Version)
			return nil
		} else if !errors.Is(err, aether.ErrVersionConflict) {
			// Some other error occurred
			return fmt.Errorf("save event failed: %w", err)
		}
		// If it's a version conflict, loop will retry
	}

	return fmt.Errorf("failed to save event after %d retries", maxRetries)
}

// ConflictDetailedRetryPattern demonstrates how to extract detailed information
// from VersionConflictError to make intelligent retry decisions.
//
// This pattern shows how to log detailed context and potentially implement
// circuit-breaker logic based on the conflict information.
func ConflictDetailedRetryPattern(store aether.EventStore, actorID string, eventType string) error {
	const maxRetries = 5
	var lastConflictVersion int64

	for attempt := 0; attempt < maxRetries; attempt++ {
		// Get current version
		currentVersion, err := store.GetLatestVersion(actorID)
		if err != nil {
			return err
		}

		// Create event
		event := &aether.Event{
			ID:        fmt.Sprintf("evt-%s-%d", actorID, time.Now().UnixNano()),
			EventType: eventType,
			ActorID:   actorID,
			Version:   currentVersion + 1,
			Data:      map[string]interface{}{"timestamp": time.Now()},
			Timestamp: time.Now(),
		}

		// Attempt to save
		err = store.SaveEvent(event)
		if err == nil {
			return nil // Success
		}

		// Check if it's a version conflict
		var versionErr *aether.VersionConflictError
		if !errors.As(err, &versionErr) {
			// Not a version conflict, fail immediately
			return err
		}

		// Extract detailed context from the conflict error
		log.Printf(
			"Version conflict for actor %q: attempted version %d, current version %d",
			versionErr.ActorID,
			versionErr.AttemptedVersion,
			versionErr.CurrentVersion,
		)

		// Check for thrashing (multiple conflicts with same version)
		if lastConflictVersion == versionErr.CurrentVersion && attempt > 0 {
			log.Printf("Detected version thrashing - circuit breaker would trigger here")
			return fmt.Errorf("circuit breaker: too many conflicts at version %d", versionErr.CurrentVersion)
		}
		lastConflictVersion = versionErr.CurrentVersion

		// Exponential backoff
		backoff := time.Duration(math.Pow(2, float64(attempt))) * 100 * time.Millisecond
		time.Sleep(backoff)
	}

	return fmt.Errorf("failed after %d retries", maxRetries)
}

// JitterRetryPattern implements exponential backoff with jitter to prevent
// thundering herd when multiple writers retry simultaneously.
func JitterRetryPattern(store aether.EventStore, actorID string, eventType string) error {
	const maxRetries = 3
	const baseBackoff = 100 * time.Millisecond
	const maxJitter = 0.1 // 10% jitter

	for attempt := 0; attempt < maxRetries; attempt++ {
		currentVersion, err := store.GetLatestVersion(actorID)
		if err != nil {
			return err
		}

		event := &aether.Event{
			ID:        fmt.Sprintf("evt-%s-%d", actorID, time.Now().UnixNano()),
			EventType: eventType,
			ActorID:   actorID,
			Version:   currentVersion + 1,
			Data:      map[string]interface{}{},
			Timestamp: time.Now(),
		}

		err = store.SaveEvent(event)
		if err == nil {
			return nil
		}

		if !errors.Is(err, aether.ErrVersionConflict) {
			return err
		}

		// Exponential backoff with jitter
		exponentialBackoff := time.Duration(math.Pow(2, float64(attempt))) * baseBackoff
		jitter := time.Duration(rand.Float64() * float64(exponentialBackoff) * maxJitter)
		totalBackoff := exponentialBackoff + jitter

		log.Printf("Retrying in %v (attempt %d/%d)", totalBackoff, attempt+1, maxRetries)
		time.Sleep(totalBackoff)
	}

	return fmt.Errorf("failed after %d retries", maxRetries)
}

// AdaptiveRetryPattern adjusts retry strategy based on version conflict patterns.
//
// This pattern demonstrates how application logic can use CurrentVersion to
// decide whether to retry, give up, or escalate to a higher-level handler.
func AdaptiveRetryPattern(store aether.EventStore, actorID string, eventType string) error {
	const maxRetries = 3

	for attempt := 0; attempt < maxRetries; attempt++ {
		currentVersion, err := store.GetLatestVersion(actorID)
		if err != nil {
			return err
		}

		event := &aether.Event{
			ID:        fmt.Sprintf("evt-%s-%d", actorID, time.Now().UnixNano()),
			EventType: eventType,
			ActorID:   actorID,
			Version:   currentVersion + 1,
			Data:      map[string]interface{}{},
			Timestamp: time.Now(),
		}

		err = store.SaveEvent(event)
		if err == nil {
			return nil
		}

		var versionErr *aether.VersionConflictError
		if !errors.As(err, &versionErr) {
			return err
		}

		// Adaptive backoff based on version distance
		versionDistance := versionErr.CurrentVersion - versionErr.AttemptedVersion
		if versionDistance > 10 {
			// Many concurrent writers - back off more aggressively
			log.Printf("High contention detected (gap: %d), aggressive backoff", versionDistance)
			time.Sleep(time.Duration(versionDistance*10) * time.Millisecond)
		} else if versionDistance > 3 {
			// Moderate contention - normal backoff
			log.Printf("Moderate contention detected (gap: %d)", versionDistance)
			time.Sleep(time.Duration(versionDistance) * time.Millisecond)
		} else {
			// Light contention - minimal backoff
			log.Printf("Light contention detected")
			time.Sleep(50 * time.Millisecond)
		}
	}

	return fmt.Errorf("failed after %d retries", maxRetries)
}

// EventualConsistencyPattern demonstrates how to handle version conflicts
// in an eventually consistent manner by publishing to a retry queue.
//
// This is useful when immediate retry is not feasible, and you want to
// defer the operation to a background worker.
type RetryQueueItem struct {
	Event              *aether.Event
	ConflictVersion    int64
	ConflictAttempted  int64
	NextRetryTime      time.Time
	FailureCount       int
}

func EventualConsistencyPattern(store aether.EventStore, retryQueue chan<- RetryQueueItem, event *aether.Event) {
	err := store.SaveEvent(event)
	if err == nil {
		return
	}

	var versionErr *aether.VersionConflictError
	if !errors.As(err, &versionErr) {
		log.Printf("Non-retryable error: %v", err)
		return
	}

	// Queue for retry - background worker will process this
	retryItem := RetryQueueItem{
		Event:             event,
		ConflictVersion:   versionErr.CurrentVersion,
		ConflictAttempted: versionErr.AttemptedVersion,
		NextRetryTime:     time.Now().Add(1 * time.Second),
		FailureCount:      0,
	}

	select {
	case retryQueue <- retryItem:
		log.Printf("Queued event for retry: actor=%s", event.ActorID)
	case <-time.After(5 * time.Second):
		log.Printf("Failed to queue event for retry (queue full)")
	}
}

// CircuitBreakerPattern implements a simple circuit breaker for version conflicts.
//
// The circuit breaker tracks failure rates and temporarily stops retrying
// when the failure rate gets too high, allowing the system to recover.
type CircuitBreaker struct {
	failureCount      int
	successCount      int
	state             string // "closed", "open", "half-open"
	lastFailureTime   time.Time
	openDuration      time.Duration
	failureThreshold  int
	successThreshold  int
}

func NewCircuitBreaker() *CircuitBreaker {
	return &CircuitBreaker{
		state:            "closed",
		openDuration:     30 * time.Second,
		failureThreshold: 5,
		successThreshold: 3,
	}
}

func (cb *CircuitBreaker) RecordSuccess() {
	if cb.state == "half-open" {
		cb.successCount++
		if cb.successCount >= cb.successThreshold {
			cb.state = "closed"
			cb.failureCount = 0
			cb.successCount = 0
			log.Printf("Circuit breaker closed")
		}
	}
}

func (cb *CircuitBreaker) RecordFailure() {
	cb.lastFailureTime = time.Now()
	cb.failureCount++
	if cb.failureCount >= cb.failureThreshold {
		cb.state = "open"
		log.Printf("Circuit breaker opened")
	}
}

func (cb *CircuitBreaker) CanRetry() bool {
	if cb.state == "closed" {
		return true
	}
	if cb.state == "open" {
		if time.Since(cb.lastFailureTime) > cb.openDuration {
			cb.state = "half-open"
			cb.failureCount = 0
			cb.successCount = 0
			log.Printf("Circuit breaker half-open")
			return true
		}
		return false
	}
	// half-open state allows retries
	return true
}

func CircuitBreakerRetryPattern(store aether.EventStore, cb *CircuitBreaker, actorID string, eventType string) error {
	if !cb.CanRetry() {
		return fmt.Errorf("circuit breaker open - not retrying")
	}

	currentVersion, err := store.GetLatestVersion(actorID)
	if err != nil {
		return err
	}

	event := &aether.Event{
		ID:        fmt.Sprintf("evt-%s-%d", actorID, time.Now().UnixNano()),
		EventType: eventType,
		ActorID:   actorID,
		Version:   currentVersion + 1,
		Data:      map[string]interface{}{},
		Timestamp: time.Now(),
	}

	err = store.SaveEvent(event)
	if err == nil {
		cb.RecordSuccess()
		return nil
	}

	if !errors.Is(err, aether.ErrVersionConflict) {
		return err
	}

	cb.RecordFailure()
	return fmt.Errorf("save failed with version conflict, circuit breaker status: %s", cb.state)
}