<?php
/**
 * Gestor de colas con Redis para procesamiento asíncrono
 * Implementa pattern Producer-Consumer para mensajes de WhatsApp
 */

namespace WhatsApp\Queue;

use Predis\Client as RedisClient;
use Monolog\Logger;

class RedisQueue {
    private $redis;
    private $logger;
    private $queuePrefix = 'whatsapp:queue:';
    
    // Límites de rate limiting para WhatsApp Business API
    const RATE_LIMIT_WINDOW = 1; // segundos
    const MAX_MESSAGES_PER_SECOND = 80;
    const RATE_LIMIT_KEY = 'whatsapp:ratelimit:';
    
    public function __construct(RedisClient $redis = null, Logger $logger = null) {
        // Conectar a Redis con configuración desde .env
        $this->redis = $redis ?? new RedisClient([
            'scheme' => getenv('REDIS_SCHEME') ?: 'tcp',
            'host'   => getenv('REDIS_HOST') ?: '127.0.0.1',
            'port'   => getenv('REDIS_PORT') ?: 6379,
            'password' => getenv('REDIS_PASSWORD') ?: null,
            'database' => getenv('REDIS_DB') ?: 0,
        ]);
        
        $this->logger = $logger;
    }
    
    /**
     * Agregar mensaje a la cola para procesamiento asíncrono
     * 
     * @param string $queueName Nombre de la cola (ej: 'messages', 'media', 'notifications')
     * @param array $data Datos del mensaje a procesar
     * @param int $priority Prioridad (0=alta, 1=normal, 2=baja)
     * @return bool
     */
    public function push(string $queueName, array $data, int $priority = 1): bool {
        try {
            $payload = json_encode([
                'data' => $data,
                'priority' => $priority,
                'queued_at' => time(),
                'attempts' => 0
            ]);
            
            // Usar LPUSH para agregar al inicio (FIFO con BRPOP)
            $key = $this->queuePrefix . $queueName;
            $result = $this->redis->lpush($key, [$payload]);
            
            if ($this->logger) {
                $this->logger->info("Message pushed to queue", [
                    'queue' => $queueName,
                    'priority' => $priority,
                    'data_keys' => array_keys($data)
                ]);
            }
            
            return $result > 0;
        } catch (\Exception $e) {
            if ($this->logger) {
                $this->logger->error("Failed to push to queue", [
                    'queue' => $queueName,
                    'error' => $e->getMessage()
                ]);
            }
            return false;
        }
    }
    
    /**
     * Obtener mensaje de la cola (bloqueante)
     * 
     * @param string|array $queueName Nombre de cola(s) a escuchar
     * @param int $timeout Timeout en segundos (0 = infinito)
     * @return array|null [queue_name, payload] o null si timeout
     */
    public function pop($queueName, int $timeout = 5): ?array {
        try {
            $queues = is_array($queueName) ? $queueName : [$queueName];
            $keys = array_map(fn($q) => $this->queuePrefix . $q, $queues);
            
            // BRPOP espera hasta que haya un elemento o timeout
            $result = $this->redis->brpop($keys, $timeout);
            
            if (!$result) {
                return null;
            }
            
            // $result = [queue_key, payload_json]
            $queueKey = $result[0];
            $payload = json_decode($result[1], true);
            
            // Extraer nombre de cola sin prefijo
            $queue = str_replace($this->queuePrefix, '', $queueKey);
            
            if ($this->logger) {
                $this->logger->debug("Message popped from queue", [
                    'queue' => $queue,
                    'attempts' => $payload['attempts'] ?? 0
                ]);
            }
            
            return [
                'queue' => $queue,
                'data' => $payload['data'] ?? [],
                'priority' => $payload['priority'] ?? 1,
                'queued_at' => $payload['queued_at'] ?? time(),
                'attempts' => $payload['attempts'] ?? 0
            ];
        } catch (\Exception $e) {
            if ($this->logger) {
                $this->logger->error("Failed to pop from queue", [
                    'queue' => $queueName,
                    'error' => $e->getMessage()
                ]);
            }
            return null;
        }
    }
    
    /**
     * Re-encolar mensaje fallido con backoff exponencial
     * 
     * @param string $queueName
     * @param array $message Mensaje original con metadata
     * @param int $maxAttempts Intentos máximos antes de mover a DLQ
     * @return bool
     */
    public function retry(string $queueName, array $message, int $maxAttempts = 3): bool {
        $attempts = ($message['attempts'] ?? 0) + 1;
        
        if ($attempts >= $maxAttempts) {
            // Mover a Dead Letter Queue
            return $this->moveToDLQ($queueName, $message);
        }
        
        // Incrementar contador de intentos
        $message['attempts'] = $attempts;
        $message['last_attempt'] = time();
        
        // Backoff exponencial: 2^attempts segundos
        $delay = pow(2, $attempts);
        
        try {
            $payload = json_encode($message);
            $delayedKey = $this->queuePrefix . $queueName . ':delayed';
            
            // Usar ZADD con score = timestamp futuro
            $executeAt = time() + $delay;
            $this->redis->zadd($delayedKey, [$payload => $executeAt]);
            
            if ($this->logger) {
                $this->logger->warning("Message scheduled for retry", [
                    'queue' => $queueName,
                    'attempt' => $attempts,
                    'delay' => $delay,
                    'execute_at' => date('Y-m-d H:i:s', $executeAt)
                ]);
            }
            
            return true;
        } catch (\Exception $e) {
            if ($this->logger) {
                $this->logger->error("Failed to schedule retry", [
                    'queue' => $queueName,
                    'error' => $e->getMessage()
                ]);
            }
            return false;
        }
    }
    
    /**
     * Mover mensaje a Dead Letter Queue (mensajes que fallaron definitivamente)
     */
    private function moveToDLQ(string $queueName, array $message): bool {
        try {
            $dlqKey = $this->queuePrefix . 'dlq:' . $queueName;
            $payload = json_encode([
                'original_message' => $message,
                'failed_at' => time(),
                'attempts' => $message['attempts'] ?? 0
            ]);
            
            $this->redis->lpush($dlqKey, [$payload]);
            
            if ($this->logger) {
                $this->logger->error("Message moved to DLQ", [
                    'queue' => $queueName,
                    'attempts' => $message['attempts'] ?? 0
                ]);
            }
            
            return true;
        } catch (\Exception $e) {
            if ($this->logger) {
                $this->logger->critical("Failed to move to DLQ", [
                    'queue' => $queueName,
                    'error' => $e->getMessage()
                ]);
            }
            return false;
        }
    }
    
    /**
     * Procesar mensajes delayed (ejecutar cron cada minuto)
     */
    public function processDelayed(string $queueName): int {
        try {
            $delayedKey = $this->queuePrefix . $queueName . ':delayed';
            $now = time();
            
            // Obtener mensajes cuyo score (timestamp) <= ahora
            $messages = $this->redis->zrangebyscore($delayedKey, '-inf', $now);
            
            $processed = 0;
            foreach ($messages as $payload) {
                $message = json_decode($payload, true);
                
                // Mover de delayed a queue normal
                if ($this->push($queueName, $message['data'], $message['priority'] ?? 1)) {
                    $this->redis->zrem($delayedKey, $payload);
                    $processed++;
                }
            }
            
            if ($processed > 0 && $this->logger) {
                $this->logger->info("Processed delayed messages", [
                    'queue' => $queueName,
                    'count' => $processed
                ]);
            }
            
            return $processed;
        } catch (\Exception $e) {
            if ($this->logger) {
                $this->logger->error("Failed to process delayed", [
                    'queue' => $queueName,
                    'error' => $e->getMessage()
                ]);
            }
            return 0;
        }
    }
    
    /**
     * Verificar rate limit para WhatsApp API
     * 
     * @param string $identifier Identificador único (ej: phone_number_id)
     * @return bool true si puede enviar, false si excede límite
     */
    public function checkRateLimit(string $identifier): bool {
        try {
            $key = self::RATE_LIMIT_KEY . $identifier;
            $count = $this->redis->incr($key);
            
            // Establecer expiración solo en el primer incremento
            if ($count == 1) {
                $this->redis->expire($key, self::RATE_LIMIT_WINDOW);
            }
            
            if ($count > self::MAX_MESSAGES_PER_SECOND) {
                if ($this->logger) {
                    $this->logger->warning("Rate limit exceeded", [
                        'identifier' => $identifier,
                        'count' => $count,
                        'limit' => self::MAX_MESSAGES_PER_SECOND
                    ]);
                }
                return false;
            }
            
            return true;
        } catch (\Exception $e) {
            if ($this->logger) {
                $this->logger->error("Rate limit check failed", [
                    'error' => $e->getMessage()
                ]);
            }
            // En caso de error, permitir para no bloquear
            return true;
        }
    }
    
    /**
     * Obtener estadísticas de las colas
     */
    public function getStats(array $queueNames = ['messages', 'media', 'notifications']): array {
        $stats = [];
        
        foreach ($queueNames as $queueName) {
            $key = $this->queuePrefix . $queueName;
            $delayedKey = $key . ':delayed';
            $dlqKey = $this->queuePrefix . 'dlq:' . $queueName;
            
            $stats[$queueName] = [
                'pending' => $this->redis->llen($key),
                'delayed' => $this->redis->zcard($delayedKey),
                'failed' => $this->redis->llen($dlqKey)
            ];
        }
        
        return $stats;
    }
    
    /**
     * Limpiar colas (para testing/desarrollo)
     */
    public function flush(string $queueName = null): bool {
        try {
            if ($queueName) {
                $keys = [
                    $this->queuePrefix . $queueName,
                    $this->queuePrefix . $queueName . ':delayed',
                    $this->queuePrefix . 'dlq:' . $queueName
                ];
                foreach ($keys as $key) {
                    $this->redis->del([$key]);
                }
            } else {
                // Flush todas las colas con el prefijo
                $pattern = $this->queuePrefix . '*';
                $keys = $this->redis->keys($pattern);
                if (!empty($keys)) {
                    $this->redis->del($keys);
                }
            }
            
            if ($this->logger) {
                $this->logger->info("Queue flushed", ['queue' => $queueName ?? 'all']);
            }
            
            return true;
        } catch (\Exception $e) {
            if ($this->logger) {
                $this->logger->error("Failed to flush queue", [
                    'queue' => $queueName,
                    'error' => $e->getMessage()
                ]);
            }
            return false;
        }
    }
    
    /**
     * Cerrar conexión Redis
     */
    public function disconnect(): void {
        if ($this->redis) {
            $this->redis->disconnect();
        }
    }
}