Fix SecToTime edge-cases (go-gitea#20610)

- Backport of go-gitea#20610
  - Currently there are edge-cases where the code fails to produce the correct results, this is mainly due to the misusage of the modulo operator. Well this could be fixed, it's better to use a more performant way and simply distract the previous number's cost to calculate the variables.
  - Resolves go-gitea#20589

modules/util/sec_to_time.go

@@ -16,12 +16,24 @@ import (
 // 1563418		-> 2 weeks 4 days
 // 3937125s     -> 1 month 2 weeks
 // 45677465s	-> 1 year 6 months
+//
+// Magic numbers:
+// 3600 = 60 * 60 (amount of seconds in a hour)
+// 86400 = 60 * 60 * 24 (amount of seconds in a day)
 func SecToTime(duration int64) string {
 	formattedTime := ""
-	years := duration / (3600 * 24 * 7 * 4 * 12)
-	months := (duration / (3600 * 24 * 30)) % 12
-	weeks := (duration / (3600 * 24 * 7)) % 4
-	days := (duration / (3600 * 24)) % 7
+	years := (duration / 86400) / 365
+
+	// The following three variables are calculated with taking
+	// into account the previous calculated variables, this avoids
+	// pitfalls when using remainders. As that could lead to incorrect
+	// results when the calculated number equals the quotient number.
+	months := (duration/86400 - years*365) / 30
+	weeks := (duration/86400 - years*365 - months*30) / 7
+	days := duration/86400 - years*365 - months*30 - weeks*7
+
+	// The following three variables are calculated without depending
+	// on the previous calculated variables.
 	hours := (duration / 3600) % 24
 	minutes := (duration / 60) % 60
 	seconds := duration % 60

modules/util/sec_to_time_test.go

@@ -11,10 +11,15 @@ import (
 )
 
 func TestSecToTime(t *testing.T) {
-	assert.Equal(t, SecToTime(66), "1 minute 6 seconds")
-	assert.Equal(t, SecToTime(52410), "14 hours 33 minutes")
-	assert.Equal(t, SecToTime(563418), "6 days 12 hours")
-	assert.Equal(t, SecToTime(1563418), "2 weeks 4 days")
-	assert.Equal(t, SecToTime(3937125), "1 month 2 weeks")
-	assert.Equal(t, SecToTime(45677465), "1 year 5 months")
+	assert.Equal(t, "1 minute 6 seconds", SecToTime(66))
+	assert.Equal(t, "1 hour", SecToTime(3600))
+	assert.Equal(t, "1 hour", SecToTime(3601))
+	assert.Equal(t, "14 hours 33 minutes", SecToTime(52410))
+	assert.Equal(t, "6 days 12 hours", SecToTime(563418))
+	assert.Equal(t, "2 weeks 4 days", SecToTime(1563418))
+	assert.Equal(t, "4 weeks", SecToTime(2419200))
+	assert.Equal(t, "4 weeks 1 day", SecToTime(2505600))
+	assert.Equal(t, "1 month 2 weeks", SecToTime(3937125))
+	assert.Equal(t, "11 months 1 week", SecToTime(29376000))
+	assert.Equal(t, "1 year 5 months", SecToTime(45677465))
 }