var MongoClient = require('mongodb').MongoClient

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

    var collection = db.collection('students')

    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 newscores = [student.scores[0], student.scores[1], student.scores[max]]
            student.scores = newscores

            var query = {"_id" : student._id}

            collection.update(query, student, function(err, doc) {
                panicIf(err)
                console.log('Updated')
                console.dir(doc)
                console.log('\n\n')
            })

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

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