package routing

import (
	"sync"
	"time"
)

// CircuitBreaker tracks provider failures with tiered cooldowns.
// Thread-safe for concurrent use. Implements CooldownTracker.
//
// The circuit breaker applies different cooldown durations based on error type:
//   - Rate limits (429) and quota errors: DefaultCooldownPeriod (1 hour)
//   - Transient server errors (5xx): TransientCooldownPeriod (30 seconds)
//
// This allows quick fallback to backup providers while still giving
// the primary provider time to recover from transient issues.
//
// Note: Exempt providers (ExemptProviders map) never enter cooldown.
// This is enforced by the executor, not the circuit breaker itself.
type CircuitBreaker struct {
	mu                      sync.RWMutex
	failedUntil             map[string]time.Time // provider name -> time when cooldown ends
	cooldownPeriod          time.Duration        // for rate limits/quota
	transientCooldownPeriod time.Duration        // for server errors
}

// NewCircuitBreaker creates a circuit breaker with default tiered cooldowns.
// If cooldown is 0, DefaultCooldownPeriod (1 hour) is used for rate limits.
func NewCircuitBreaker(cooldown time.Duration) *CircuitBreaker {
	if cooldown == 0 {
		cooldown = DefaultCooldownPeriod
	}
	return &CircuitBreaker{
		failedUntil:             make(map[string]time.Time),
		cooldownPeriod:          cooldown,
		transientCooldownPeriod: TransientCooldownPeriod,
	}
}

// NewCircuitBreakerWithTransientCooldown creates a circuit breaker with
// custom cooldown periods for rate limits and transient errors.
func NewCircuitBreakerWithTransientCooldown(rateLimitCooldown, transientCooldown time.Duration) *CircuitBreaker {
	if rateLimitCooldown == 0 {
		rateLimitCooldown = DefaultCooldownPeriod
	}
	if transientCooldown == 0 {
		transientCooldown = TransientCooldownPeriod
	}
	return &CircuitBreaker{
		failedUntil:             make(map[string]time.Time),
		cooldownPeriod:          rateLimitCooldown,
		transientCooldownPeriod: transientCooldown,
	}
}

// RecordFailure applies tiered cooldowns based on error classification.
// Returns true if the provider entered cooldown.
//
// The cooldown duration depends on the error type:
//   - Rate limit (429) or quota errors: long cooldown
//   - Transient server errors (5xx): short cooldown
//   - Other errors: no cooldown
func (cb *CircuitBreaker) RecordFailure(providerName string, err error) bool {
	failureType := ClassifyError(err)
	if failureType == FailureTypeNone {
		return false
	}

	cb.mu.Lock()
	defer cb.mu.Unlock()

	var cooldown time.Duration
	switch failureType {
	case FailureTypeRateLimit:
		cooldown = cb.cooldownPeriod
	case FailureTypeTransient:
		cooldown = cb.transientCooldownPeriod
	default:
		return false
	}

	cb.failedUntil[providerName] = time.Now().Add(cooldown)
	return true
}

// IsAvailable returns true if the provider is not in cooldown.
func (cb *CircuitBreaker) IsAvailable(providerName string) bool {
	cb.mu.RLock()
	defer cb.mu.RUnlock()

	until, exists := cb.failedUntil[providerName]
	if !exists {
		return true
	}
	return time.Now().After(until)
}

// CooldownRemaining returns how long until a provider's cooldown expires.
// Returns 0 if the provider is not in cooldown.
func (cb *CircuitBreaker) CooldownRemaining(providerName string) time.Duration {
	cb.mu.RLock()
	defer cb.mu.RUnlock()

	until, exists := cb.failedUntil[providerName]
	if !exists {
		return 0
	}

	remaining := time.Until(until)
	if remaining < 0 {
		return 0
	}
	return remaining
}

// Reset removes a provider from cooldown, making it available immediately.
func (cb *CircuitBreaker) Reset(providerName string) {
	cb.mu.Lock()
	defer cb.mu.Unlock()

	delete(cb.failedUntil, providerName)
}

// ResetAll clears all cooldowns.
func (cb *CircuitBreaker) ResetAll() {
	cb.mu.Lock()
	defer cb.mu.Unlock()

	cb.failedUntil = make(map[string]time.Time)
}

// Compile-time interface check
var _ CooldownTracker = (*CircuitBreaker)(nil)