<?php
/**
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 */

namespace MediaWiki\Logger\Monolog;

use Kafka\MetaDataFromKafka;
use Kafka\Produce;
use MediaWiki\Logger\LoggerFactory;
use Monolog\Handler\AbstractProcessingHandler;
use Monolog\Logger;
use Psr\Log\LoggerInterface;

/**
 * Log handler sends log events to a kafka server.
 *
 * Constructor options array arguments:
 * * alias: map from monolog channel to kafka topic name. When no
 *	  alias exists the topic "monolog_$channel" will be used.
 * * swallowExceptions: Swallow exceptions that occur while talking to
 *    kafka. Defaults to false.
 * * logExceptions: Log exceptions talking to kafka here. Either null,
 *    the name of a channel to log to, or an object implementing
 *    FormatterInterface. Defaults to null.
 *
 * Requires the nmred/kafka-php library, version >= 1.3.0
 *
 * @since 1.26
 * @author Erik Bernhardson <ebernhardson@wikimedia.org>
 * @copyright © 2015 Erik Bernhardson and Wikimedia Foundation.
 */
class KafkaHandler extends AbstractProcessingHandler {
	/**
	 * @var Produce Sends requests to kafka
	 */
	protected $produce;

	/**
	 * @var array Optional handler configuration
	 */
	protected $options;

	/**
	 * @var array Map from topic name to partition this request produces to
	 */
	protected $partitions = array();

	/**
	 * @var array defaults for constructor options
	 */
	private static $defaultOptions = array(
		'alias' => array(), // map from monolog channel to kafka topic
		'swallowExceptions' => false, // swallow exceptions sending records
		'logExceptions' => null, // A PSR3 logger to inform about errors
	);

	/**
	 * @param Produce $produce Kafka instance to produce through
	 * @param array $options optional handler configuration
	 * @param int $level The minimum logging level at which this handler will be triggered
	 * @param bool $bubble Whether the messages that are handled can bubble up the stack or not
	 */
	public function __construct( Produce $produce, array $options, $level = Logger::DEBUG, $bubble = true ) {
		parent::__construct( $level, $bubble );
		$this->produce = $produce;
		$this->options = array_merge( self::$defaultOptions, $options );
	}

	/**
	 * Constructs the necessary support objects and returns a KafkaHandler
	 * instance.
	 *
	 * @param string[] $kafkaServers
	 * @param array $options
	 * @param int $level The minimum logging level at which this handle will be triggered
	 * @param bool $bubble Whether the messages that are handled can bubble the stack or not
	 * @return KafkaHandler
	 */
	public static function factory( $kafkaServers, array $options = array(), $level = Logger::DEBUG, $bubble = true ) {
		$metadata = new MetaDataFromKafka( $kafkaServers );
		$produce = new Produce( $metadata );
		if ( isset( $options['logExceptions'] ) && is_string( $options['logExceptions'] ) ) {
			$options['logExceptions'] = LoggerFactory::getInstance( $options['logExceptions'] );
		}
		return new self( $produce, $options, $level, $bubble );
	}

	/**
	 * {@inheritDoc}
	 */
	protected function write( array $record ) {
		if ( $record['formatted'] !== null ) {
			$this->addMessages( $record['channel'], array( $record['formatted'] ) );
			$this->send();
		}
	}

	/**
	 * {@inheritDoc}
	 */
	public function handleBatch( array $batch ) {
		$channels = array();
		foreach ( $batch as $record ) {
			if ( $record['level'] < $this->level ) {
				continue;
			}
			$channels[$record['channel']][] = $this->processRecord( $record );
		}

		$formatter = $this->getFormatter();
		foreach ( $channels as $channel => $records ) {
			$messages = array();
			foreach ( $records as $idx => $record ) {
				$message = $formatter->format( $record );
				if ( $message !== null ) {
					$messages[] = $message;
				}
			}
			if ( $messages ) {
				$this->addMessages($channel, $messages);
			}
		}

		$this->send();
	}

	/**
	 * Send any records in the kafka client internal queue.
	 */
	protected function send() {
		try {
			$this->produce->send();
		} catch ( \Kafka\Exception $e ) {
			$ignore = $this->warning(
				'Error sending records to kafka: {exception}',
				array( 'exception' => $e ) );
			if ( !$ignore ) {
				throw $e;
			}
		}
	}

	/**
	 * @param string $topic Name of topic to get partition for
	 * @return int|null The random partition to produce to for this request,
	 *  or null if a partition could not be determined.
	 */
	protected function getRandomPartition( $topic ) {
		if ( !array_key_exists( $topic, $this->partitions ) ) {
			try {
				$partitions = $this->produce->getAvailablePartitions( $topic );
			} catch ( \Kafka\Exception $e ) {
				$ignore = $this->warning(
					'Error getting metadata for kafka topic {topic}: {exception}',
					array( 'topic' => $topic, 'exception' => $e ) );
				if ( $ignore ) {
					return null;
				}
				throw $e;
			}
			if ( $partitions ) {
				$key = array_rand( $partitions );
				$this->partitions[$topic] = $partitions[$key];
			} else {
				$details = $this->produce->getClient()->getTopicDetail( $topic );
				$ignore = $this->warning(
					'No partitions available for kafka topic {topic}',
					array( 'topic' => $topic, 'kafka' => $details )
				);
				if ( !$ignore ) {
					throw new \RuntimeException( "No partitions available for kafka topic $topic" );
				}
				$this->partitions[$topic] = null;
			}
		}
		return $this->partitions[$topic];
	}

	/**
	 * Adds records for a channel to the Kafka client internal queue.
	 *
	 * @param string $channel Name of Monolog channel records belong to
	 * @param array $records List of records to append
	 */
	protected function addMessages( $channel, array $records ) {
		if ( isset( $this->options['alias'][$channel] ) ) {
			$topic = $this->options['alias'][$channel];
		} else {
			$topic = "monolog_$channel";
		}
		$partition = $this->getRandomPartition( $topic );
		if ( $partition !== null ) {
			$this->produce->setMessages( $topic, $partition, $records );
		}
	}

	/**
	 * @param string $message PSR3 compatible message string
	 * @param array $context PSR3 compatible log context
	 * @return bool true if caller should ignore warning
	 */
	protected function warning( $message, array $context = array() ) {
		if ( $this->options['logExceptions'] instanceof LoggerInterface ) {
			$this->options['logExceptions']->warning( $message, $context );
		}
		return $this->options['swallowExceptions'];
	}
}
