#!/usr/bin/env ruby

require 'bundler/setup'
require 'mysql2'
require 'socket'
require 'pp'

Thread.abort_on_exception = false
$old_master, $new_master, $username, $password = *ARGV
unless $old_master && $new_master && $username && $password
  puts "Usage: master_cut OLD_MASTER NEW_MASTER USERNAME PASSWORD"
  exit
end

def open_cx(host)
  host, port = host.split(":")
  port = port.to_i if port
  Mysql2::Client.new(:host => host, :username => $username, :password => $password, :port => port)
end

def set_rw(cx)
  cx.query("SET GLOBAL READ_ONLY=0")  
end

def set_ro(cx)
  cx.query("SET GLOBAL READ_ONLY=1")  
end

$swapped_ok = false

def fail(reason)
  puts "Failed preflight check: #{reason}"
  exit false
end

def preflight_check
  cx = open_cx($old_master)
  rw = cx.query("select @@read_only as read_only").first['read_only']
  fail("old-master #{$old_master} is read-only!") if rw != 0

  slave_cx = open_cx($new_master)
  rw = slave_cx.query("select @@read_only as read_only").first['read_only']
  fail("new-master #{$old_master} is read-write!") if rw != 1

  slave_info = slave_cx.query("show slave status").first
  fail("slave is stopped!") unless slave_info['Slave_IO_Running'] == 'Yes' && slave_info['Slave_SQL_Running'] == 'Yes'
  fail("slave is delayed") if slave_info['Seconds_Behind_Master'].nil? || slave_info['Seconds_Behind_Master'] > 0  
 
  master_ip, slave_master_ip = [$old_master, slave_info['Master_Host']].map do |h|
    h = h.split(':').first
    Socket.gethostbyname(h)[3].unpack("CCCC") 
  end

  if master_ip != slave_master_ip
    fail("slave does not appear to be replicating off master! (master: #{master_ip.join('.')}, slave's master: #{slave_master_ip.join('.')})") 
  end
end

def process_kill_thread
  Thread.new do
    cx = open_cx($old_master)
    sleep 5
    while !$swapped_ok
      my_id = cx.query("SELECT CONNECTION_ID() as id").first['id']
      processlist = cx.query("show processlist")
      processlist.each do |process|
        next if process['Info'] =~ /SET GLOBAL READ_ONLY/
        next if process['Id'].to_i == my_id.to_i
        puts "killing #{process}"
        cx.query("kill #{process['Id']}") 
      end
      sleep 0.1
    end
  end
end

def swap_thread
  Thread.new do 
    master = open_cx($old_master)
    slave = open_cx($new_master)
    set_ro(master)
    slave.query("slave stop")
    new_master_info = slave.query("show master status").first
    set_rw(slave)
    $swapped_ok = true
    puts "Swapped #{$old_master} and #{$new_master}"
    puts "New master information at time of swap: "
    pp new_master_info 
    exit
  end
end

preflight_check

threads = []
threads << process_kill_thread
threads << swap_thread
threads.each(&:join)