<?php

/*
 * This file is part of the Predis package.
 *
 * (c) Daniele Alessandri <suppakilla@gmail.com>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Predis\Connection\Aggregate;

use Predis\ClientException;
use Predis\Command\CommandInterface;
use Predis\Connection\ConnectionException;
use Predis\Connection\NodeConnectionInterface;
use Predis\Replication\ReplicationStrategy;

/**
 * Aggregate connection handling replication of Redis nodes configured in a
 * single master / multiple slaves setup.
 *
 * @author Daniele Alessandri <suppakilla@gmail.com>
 */
class MasterSlaveReplication implements ReplicationInterface
{
    /**
     * @var ReplicationStrategy
     */
    protected $strategy;

    /**
     * @var NodeConnectionInterface
     */
    protected $master;

    /**
     * @var NodeConnectionInterface[]
     */
    protected $slaves = array();

    /**
     * @var NodeConnectionInterface
     */
    protected $current;

    /**
     * {@inheritdoc}
     */
    public function __construct(ReplicationStrategy $strategy = null)
    {
        $this->strategy = $strategy ?: new ReplicationStrategy();
    }

    /**
     * Resets the connection state.
     */
    protected function reset()
    {
        $this->current = null;
    }

    /**
     * {@inheritdoc}
     */
    public function add(NodeConnectionInterface $connection)
    {
        $alias = $connection->getParameters()->alias;

        if ($alias === 'master') {
            $this->master = $connection;
        } else {
            $this->slaves[$alias ?: "slave-$connection"] = $connection;
        }

        $this->reset();
    }

    /**
     * {@inheritdoc}
     */
    public function remove(NodeConnectionInterface $connection)
    {
        if ($connection->getParameters()->alias === 'master') {
            $this->master = null;
            $this->reset();

            return true;
        } else {
            if (($id = array_search($connection, $this->slaves, true)) !== false) {
                unset($this->slaves[$id]);
                $this->reset();

                return true;
            }
        }

        return false;
    }

    /**
     * {@inheritdoc}
     */
    public function getConnection(CommandInterface $command)
    {
        if (!$this->current) {
            if ($this->strategy->isReadOperation($command) && $slave = $this->pickSlave()) {
                $this->current = $slave;
            } else {
                $this->current = $this->getMasterOrDie();
            }

            return $this->current;
        }

        if ($this->current === $master = $this->getMasterOrDie()) {
            return $master;
        }

        if (!$this->strategy->isReadOperation($command) || !$this->slaves) {
            $this->current = $master;
        }

        return $this->current;
    }

    /**
     * {@inheritdoc}
     */
    public function getConnectionById($connectionId)
    {
        if ($connectionId === 'master') {
            return $this->master;
        }

        if (isset($this->slaves[$connectionId])) {
            return $this->slaves[$connectionId];
        }

        return;
    }

    /**
     * {@inheritdoc}
     */
    public function switchTo($connection)
    {
        if (!$connection instanceof NodeConnectionInterface) {
            $connection = $this->getConnectionById($connection);
        }

        if (!$connection) {
            throw new \InvalidArgumentException('Invalid connection or connection not found.');
        }

        if ($connection !== $this->master && !in_array($connection, $this->slaves, true)) {
            throw new \InvalidArgumentException('Invalid connection or connection not found.');
        }

        $this->current = $connection;
    }

    /**
     * Switches to the master server.
     */
    public function switchToMaster()
    {
        $this->switchTo('master');
    }

    /**
     * Switches to a random slave server.
     */
    public function switchToSlave()
    {
        $connection = $this->pickSlave();
        $this->switchTo($connection);
    }

    /**
     * {@inheritdoc}
     */
    public function getCurrent()
    {
        return $this->current;
    }

    /**
     * {@inheritdoc}
     */
    public function getMaster()
    {
        return $this->master;
    }

    /**
     * Returns the connection associated to the master server.
     *
     * @return NodeConnectionInterface
     */
    private function getMasterOrDie()
    {
        if (!$connection = $this->getMaster()) {
            throw new ClientException('No master server available for replication');
        }

        return $connection;
    }

    /**
     * {@inheritdoc}
     */
    public function getSlaves()
    {
        return array_values($this->slaves);
    }

    /**
     * Returns the underlying replication strategy.
     *
     * @return ReplicationStrategy
     */
    public function getReplicationStrategy()
    {
        return $this->strategy;
    }

    /**
     * Returns a random slave.
     *
     * @return NodeConnectionInterface
     */
    protected function pickSlave()
    {
        if ($this->slaves) {
            return $this->slaves[array_rand($this->slaves)];
        }
    }

    /**
     * {@inheritdoc}
     */
    public function isConnected()
    {
        return $this->current ? $this->current->isConnected() : false;
    }

    /**
     * {@inheritdoc}
     */
    public function connect()
    {
        if (!$this->current) {
            if (!$this->current = $this->pickSlave()) {
                if (!$this->current = $this->getMaster()) {
                    throw new ClientException("No available connection for replication");
                }
            }
        }

        $this->current->connect();
    }

    /**
     * {@inheritdoc}
     */
    public function disconnect()
    {
        if ($this->master) {
            $this->master->disconnect();
        }

        foreach ($this->slaves as $connection) {
            $connection->disconnect();
        }
    }

    /**
     * Retries the execution of a command upon slave failure.
     *
     * @param CommandInterface $command Command instance.
     * @param string           $method  Actual method.
     *
     * @return mixed
     */
    private function retryCommandOnFailure(CommandInterface $command, $method)
    {
        RETRY_COMMAND: {
            try {
                $response = $this->getConnection($command)->$method($command);
            } catch (ConnectionException $exception) {
                $connection = $exception->getConnection();
                $connection->disconnect();

                if ($connection === $this->master) {
                    // Throw immediatly if the client was connected to master,
                    // even when the command represents a read-only operation.
                    throw $exception;
                } else {
                    // Otherwise remove the failing slave and attempt to execute
                    // the command again on one of the remaining slaves...
                    $this->remove($connection);
                }

                // ... that is, unless we have no more connections to use.
                if (!$this->slaves && !$this->master) {
                    throw $exception;
                }

                goto RETRY_COMMAND;
            }
        }

        return $response;
    }

    /**
     * {@inheritdoc}
     */
    public function writeRequest(CommandInterface $command)
    {
        $this->retryCommandOnFailure($command, __FUNCTION__);
    }

    /**
     * {@inheritdoc}
     */
    public function readResponse(CommandInterface $command)
    {
        return $this->retryCommandOnFailure($command, __FUNCTION__);
    }

    /**
     * {@inheritdoc}
     */
    public function executeCommand(CommandInterface $command)
    {
        return $this->retryCommandOnFailure($command, __FUNCTION__);
    }

    /**
     * {@inheritdoc}
     */
    public function __sleep()
    {
        return array('master', 'slaves', 'strategy');
    }
}