public static void AddAttempt(Guid cardId, bool result)
{
// scoring
double score = 0d;
DateTime now = DateTime.Now;
Attempt lastAttempt = new Attempt();
using (CitizenEntities db = new CitizenEntities())
{
if (db.Attempts.Where(a => a.Card.CardId == cardId).Count() > 0)
{
lastAttempt = db.Attempts.Where(a => a.Card.CardId == cardId).OrderByDescending(a => a.CreateDate).First();
}
else lastAttempt = null;
if (lastAttempt != null)
{
double minSinceLast = (now - lastAttempt.CreateDate).TotalMinutes;
if (minSinceLast <= 0) throw new Exception("New attempt CreateDate happened before last attempt. Impossible!!");
if (result)
score = 1d - (1d / (Math.Log(minSinceLast + 9d, 10d)));
else score = -(1d / (Math.Log(minSinceLast + 9d, 10d)));
}
// update card, and insert new attempt.
Card card = db.Cards.Where(c => c.CardId == cardId).First();
if (score > 0d) card.Score = Math.Max(card.Score, score);
if (score < 0d) card.Score = Math.Min(card.Score, score);
else card.Score = 0d;
card.Attempts.Add(new Attempt() { AttemptId = Guid.NewGuid(), Card = card, CreateDate = now, Result = result });
db.SaveChanges();
}
}
public static Card GetNextCard()
{
// first fetch:
// - have attempt(s), but less than 3; and
// - no attempt in last 1 min; and
// - not in last 5 attempts
using (CitizenEntities db = new CitizenEntities())
{
List<Guid> temp1 = (from a in db.Attempts
group a by a.Card.CardId into g
where g.Count() > 0 && g.Count() < 4
select g.Key).ToList();
if (temp1.Count != 0)
{
DateTime oneMinBack = DateTime.Now.AddMinutes(-1);
List<Guid> temp2 = (from a in db.Attempts
where a.CreateDate > oneMinBack
select a.Card.CardId).ToList();
List<Guid> temp3 = (from a in db.Attempts
orderby a.CreateDate descending
select a.Card.CardId).Take(5).ToList();
List<Guid> temp4 = (from t in temp1
where !temp2.Contains(t) && !temp3.Contains(t)
select t).ToList();
if (temp4.Count != 0)
{
Random ran = new Random();
Guid picked = temp4[ran.Next(temp4.Count)];
return db.Cards.Where(c => c.CardId == picked).First();
}
}
// second fetch:
// - no attempt in last 5 mins
// - no frequent correct ones
// - has 2+ correct attempts in the past 1 day; or
// - has 5+ correct attempts in the past 1 week
// - if last attempt correct, pick from score<=0; otherwise, pick from score>0.
// - if no last attempt, do not pay attention to score.
// - if found, pick the one has min(|score|)
DateTime now = DateTime.Now;
DateTime fiveMinBack = now.AddMinutes(-5);
DateTime oneDayBack = now.AddDays(-1);
DateTime oneWeekBack = now.AddDays(-7);
List<Card> temp5 = (from c in db.Cards
where c.Attempts.Where(a => a.CreateDate > fiveMinBack).Count() == 0
select c).ToList();
if (temp5.Count == 0) return null;
List<Guid> frequentCorrectDay = (from a in db.Attempts
where a.CreateDate > oneDayBack && a.Result == true
group a by a.Card.CardId into g
where g.Count() >= 2
select g.Key).ToList();
List<Guid> frequentCorrectWeek = (from a in db.Attempts
where a.CreateDate > oneWeekBack && a.Result == true
group a by a.Card.CardId into g
where g.Count() >= 5
select g.Key).ToList();
temp5 = temp5.Where(c => !frequentCorrectDay.Contains(c.CardId) && !frequentCorrectWeek.Contains(c.CardId)).ToList();
Attempt lastAttempt = new Attempt();
if (db.Attempts.Count() != 0) lastAttempt = db.Attempts.OrderByDescending(a => a.CreateDate).First();
else lastAttempt = null;
List<Card> temp6 = new List<Card>();
if (lastAttempt != null)
{
if (lastAttempt.Result) temp6 = temp5.Where(c => c.Score <= 0).ToList();
else temp6 = temp5.Where(c => c.Score > 0).ToList();
}
if (temp6.Count == 0) temp6 = temp5;
return (from t in temp6
orderby Math.Abs(t.Score)
select t).First();
}
}
