<?php
class mysqlFailOver {
    private $numServers = 0;
    private $servers = array();
    private $currentServer = array();
    private $iCurrentServer = 0;
    private $newReplicationChain = array();
    function __construct($svrs) {
        if ($newChain)
            $this->BuildChain($svrs);
        if (!is_array($svrs)) {
            die("Failover Failure: Non array object passed to constructor.");
        }
        $this->numServers = count($svrs);
        $this->servers    = $svrs;
        if ($this->queryTest()) {
            $this->rebuildReplicationChain();
        }
        return $this->link;
    }
    private function queryTest() {
        $this->link = @mysqli_connect($this->servers[$this->iCurrentServer]['hostname'], $this->servers[$this->iCurrentServer]['username'], $this->servers[$this->iCurrentServer]['password'], $this->servers[$this->iCurrentServer]['database']);
        $result     = @mysqli_query("SELECT 1 FROM DUAL", $this->link);
        if (!$result) {
            switch (mysqli_errno($this->link)) {
                case 2002:
                case 2003:
                case 2005:
                    $this->servers[$this->iCurrentServer]['connection_error'] = true;
                    if ($this->iCurrentServer == 0)
                        $this->servers[$this->iCurrentServer]['was_master'] = true;
                    $this->iCurrentServer++;
                    if ($this->iCurrentServer < $this->numServers) {
                        $this->queryTest();
                    }
                    break;
                default:
                    die("Failover Failure: " . mysqli_error($this->link) . " is not a failover event.");
            }
        } else {
            return true;
        }
    }
    private function rebuildReplicationChain() {
        $lastReplicationChain = $this->getLastReplicationChain();
        $offlineNodes         = array();
        $onlineNodes          = array();
        foreach ($this->servers as $s) {
            if ($s['connection_error']) {
                $offlineNodes[$s['hostname']] = $s;
            } else {
                $onlineNodes[$s['hostname']] = $s;
            }
        }
        foreach ($lastReplicationChain as $node) {
            foreach ($onlineNodes as $replacement) {
                if ($replacement['hostname'] == $node['hostname']) {
                    $newReplicationChain[] = $replacement;
                }
            }
        }
        foreach ($lastReplicationChain as $node) {
            foreach ($offlineNodes as $downedNode) {
                if ($downedNode['hostname'] == $node['hostname']) {
                    $newReplicationChain[] = $downedNode;
                }
            }
        }
        $this->newReplicationChain = $newReplicationChain;
        $this->updateChainRole();
    }
    private function getLastReplicationChain() {
        $lastReplicationChainQuery = mysqli_query("SELECT * FROM `mysql_replication_chain` ORDER BY `position` ASC", $this->link);
        while ($chainData = mysqli_fetch_assoc($lastReplicationChainQuery)) {
            $lastReplicationChain[] = $chainData;
        }
        return $lastReplicationChain;
    }
    private function updateChainRole($host, $position) {
        $this->syncSlaves();
        foreach ($this->newReplicationChain as $position => $node) {
            mysqli_query("UPDATE `mysql_replication_chain` SET `position` = '" . $position . "' WHERE `hostname` = '" . $node['hostname'] . "'", $this->link);
        }
    }
    private function syncSlaves() {
        foreach ($this->newReplicationChain as $node) {
            $nodeLink = @mysqli_connect($node['hostname'], $node['username'], $node['password'], $node['database']);
            if ($nodeLink) {
                mysqli_query("STOP SLAVE IO_THREAD");
                $synced = false;
                while ($synced == false) {
                    $result = mysqli_query("SHOW PROCESSLIST", $nodeLink);
                    while ($process == mysqli_fetch_assoc($result)) {
                        if (strstr($process['State'], 'Slave has read all relay log')) {
                            $synced = true;
                            break;
                        }
                    }
                }
            } else {
                // TODO: Add more logic to rebuild chain recursivly if there are multiple failures.
            }
        }
        //Set the next slave in line to master STOP SLAVE
        $master   = $this->newReplicationChain[0];
        $nodeLink = @mysqli_connect($master['hostname'], $master['username'], $master['password'], $master['database']);
        mysqli_query("STOP SLAVE", $nodeLink);
        mysqli_query("RESET MASTER", $nodeLink);
        mysqli_close($nodeLink);
        $changeMasterSQL = "CHANGE MASTER TO MASTER_HOST='" . $master['hostname'] . "',    MASTER_USER='" . $master['username'] . "', MASTER_PASSWORD='" . $master['password'] . "'";
        for ($i = 0; $i < count($this->newReplicationChain); $i++) {
            if (!isset($this->newReplicationChain[$i]['connection_error'])) {
                $slave     = $this->newReplicationChain[$i];
                $slaveLink = @mysqli_connect($slave['hostname'], $slave['username'], $slave['password'], $slave['database']);
                mysqli_query("STOP SLAVE", $slaveLink);
                mysqli_query($changeMasterSQL, $slaveLink);
                mysqli_query("START SLAVE", $slaveLink);
                mysqli_close($slaveLink);
            }
        }
    }
}
?>