var MongoClient = require('mongodb').MongoClient

MongoClient.connect('mongodb://localhost:27017/school', function (err, db) {
  panicIf(err)

  var collection = db.collection('rodents')

  var students = collection.find({})
  students.each(function (err, student) {
    panicIf(err)
    if (student) {
      var max = (student.scores[2].score > student.scores[3].score)? 2 : 3
      var scores = [student.scores[0], student.scores[1], student.scores[max]]

      var query = {"_id" : student._id}
      var change = { $set: {"scores" : scores} }

      collection.update(query, change, function(err, doc) {
        panicIf(err)
      })

    } else {
      db.close()
    }
  })
})

function panicIf(err) {
  if (err) {
    throw err
  }
}