each user can define their cadence

sm2.go

@@ -4,12 +4,12 @@ import (
 	"time"
 )
 
-func Next(ts time.Time, history []int) time.Time {
+func SM2Next(ts time.Time, history []int, unit time.Duration) time.Time {
 	n, ef, i := 0, 2.5, 1
 	for j := range history {
 		n, ef, i = sm2Next(history[j], n, ef, i)
 	}
-	return ts.Add(time.Duration(i) * time.Hour * 24)
+	return ts.Add(time.Duration(i) * unit)
 }
 
 // After all scheduled reviews are complete, SuperMemo asks the user to re-review any cards they marked with a grade less than 4 repeatedly until they give a grade ≥ 4.

sm2_test.go

@@ -44,7 +44,7 @@ func TestSM2(t *testing.T) {
 	for name, d := range cases {
 		c := d
 		t.Run(name, func(t *testing.T) {
-			got := Next(ts, c.history)
+			got := SM2Next(ts, c.history, time.Hour*24)
 			t.Logf("Next(\n\t%s, \n\t%+v) = \n\t%s", ts, c.history, got)
 			if got != ts.Add(time.Duration(c.want)*time.Hour*24) {
 				t.Error(c.want, got)

yamldb.go

@@ -20,7 +20,8 @@ type (
 		Answers   map[IDA]Answer
 	}
 	user struct {
-		Tags tags
+		Tags    tags
+		Cadence duration
 	}
 	tags struct {
 		Assignments []IDT
@@ -94,7 +95,15 @@ func (db yamlDB) Next(user IDU, q IDQ) time.Time {
 		}
 		log = append(log, v)
 	}
-	return Next(last, log)
+	return SM2Next(last, log, db.cadence(user))
+}
+
+func (db yamlDB) cadence(user IDU) time.Duration {
+	u := db.Users[user]
+	if u.Cadence == 0 {
+		return time.Hour * 24
+	}
+	return time.Duration(u.Cadence)
 }
 
 func (db yamlDB) Question(q IDQ) Question {