class Redis::Client::Connector::Sentinel

def check(client)
  # Check the instance is really of the role we are looking for.
  # We can't assume the command is supported since it was introduced
  # recently and this client should work with old stuff.
  begin
    role = client.call([:role])[0]
  rescue Redis::CommandError
    # Assume the test is passed if we can't get a reply from ROLE...
    role = @role
  end
  if role != @role
    client.disconnect
    raise ConnectionError, "Instance role mismatch. Expected #{@role}, got #{role}."
  end
end

def initialize(options)
  super(options)
  @options[:db] = DEFAULTS.fetch(:db)
  @sentinels = @options.delete(:sentinels).dup
  @role = (@options[:role] || "master").to_s
  @master = @options[:host]
end

def resolve
  result = case @role
  when "master"
    resolve_master
  when "slave"
    resolve_slave
  else
    raise ArgumentError, "Unknown instance role #{@role}"
  end
  result || (raise ConnectionError, "Unable to fetch #{@role} via Sentinel.")
end

def resolve_master
  sentinel_detect do |client|
    if reply = client.call(["sentinel", "get-master-addr-by-name", @master])
      { host: reply[0], port: reply[1] }
    end
  end
end

def resolve_slave
  sentinel_detect do |client|
    if reply = client.call(["sentinel", "slaves", @master])
      slaves = reply.map { |s| s.each_slice(2).to_h }
      slaves.each { |s| s['flags'] = s.fetch('flags').split(',') }
      slaves.reject! { |s| s.fetch('flags').include?('s_down') }
      if slaves.empty?
        raise CannotConnectError, 'No slaves available.'
      else
        slave = slaves.sample
        {
          host: slave.fetch('ip'),
          port: slave.fetch('port')
        }
      end
    end
  end
end

def sentinel_detect
  @sentinels.each do |sentinel|
    client = Client.new(@options.merge({
                                         host: sentinel[:host] || sentinel["host"],
                                         port: sentinel[:port] || sentinel["port"],
                                         username: sentinel[:username] || sentinel["username"],
                                         password: sentinel[:password] || sentinel["password"],
                                         reconnect_attempts: 0
                                       }))
    begin
      if result = yield(client)
        # This sentinel responded. Make sure we ask it first next time.
        @sentinels.delete(sentinel)
        @sentinels.unshift(sentinel)
        return result
      end
    rescue BaseConnectionError
    ensure
      client.disconnect
    end
  end
  raise CannotConnectError, "No sentinels available."
end