Alpha version cron 'next' function

src/cron/expression.v

@@ -3,50 +3,117 @@ module cron
 import math
 import time
 
+const days_in_month = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
+
 struct CronExpression {
-	minutes []u32
-	hours   []u32
-	days    []u32
+	minutes []int
+	hours   []int
+	days    []int
+	months  []int
 }
 
 // next calculates the earliest time this cron expression is valid.
-pub fn (ce &CronExpression) next(ref &time.Time) time.Time {
-	res := time.Time{}
+pub fn (ce &CronExpression) next(ref time.Time) ?time.Time {
+	mut minute_index := 0
+	mut hour_index := 0
+	mut day_index := 0
+	mut month_index := 0
 
-	mut day := 0
-	mut hour := 0
-	mut minute := 0
+	for month_index < ce.months.len && ref.month > ce.months[month_index] {
+		month_index++
+	}
 
-	// Find the next minute
-	// If ref.minute is greater than 
-	if ref.minute >= ce.minutes[ce.minutes.len - 1] || ref.minute < ce.minutes[0] {
-		minute = ce.minutes[0]
-	}else{
-		for i in 0..ce.minutes.len {
-			if ce.minutes[i] > ref.minute {
-				minute = ce.minutes[i]
-				break
+	if month_index < ce.months.len {
+		for day_index < ce.days.len && ref.day > ce.days[day_index] {
+			day_index++
+		}
+
+		if day_index < ce.days.len {
+			for hour_index < ce.hours.len && ref.hour > ce.hours[hour_index] {
+				hour_index++
+			}
+
+			if hour_index < ce.hours.len {
+				// For each unit, we calculate what the next value is
+				for minute_index < ce.minutes.len && ref.minute >= ce.minutes[minute_index] {
+					minute_index++
+				}
 			}
 		}
 	}
 
-	return res
+
+	// Sometime we have to shift values one more
+	if minute_index == ce.minutes.len && hour_index < ce.hours.len {
+		hour_index += 1
+	}
+
+	if hour_index == ce.hours.len && day_index < ce.days.len {
+		day_index += 1
+	}
+
+	if day_index == ce.days.len && month_index < ce.months.len {
+		month_index += 1
+	}
+
+	mut minute := ce.minutes[minute_index % ce.minutes.len]
+	mut hour := ce.hours[hour_index % ce.hours.len]
+	mut day := ce.days[day_index % ce.days.len]
+
+	mut reset := false
+
+	// If the day can't be planned in the current month, we go to the next one
+	// and go back to day one
+	if day > days_in_month[ce.months[month_index % ce.months.len] - 1] {
+		month_index += 1
+		day = ce.days[0]
+
+		// Make sure we only plan in a month that the day occurs in
+		for day > days_in_month[ce.months[month_index & ce.months.len] - 1] {
+			month_index += 1
+
+			// Prevent scenario where there are no months that can be scheduled.
+			if month_index == 2 * ce.months.len {
+				return error('No schedulable moment.')
+			}
+		}
+	}
+
+
+	month := ce.months[month_index % ce.months.len]
+	mut year := ref.year
+
+	if month_index >= ce.months.len {
+		year++
+	}
+
+	return time.Time{
+		year: year
+		month: month
+		day: day
+		minute: minute
+		hour: hour
+	}
+}
+
+fn (ce &CronExpression) next_from_now() ?time.Time {
+	return ce.next(time.now())
 }
 
 // parse_range parses a given string into a range of sorted integers, if
 // possible.
-fn parse_range(s string, min u32, max u32) ?[]u32 {
-	mut out := []u32{}
+fn parse_range(s string, min int, max int) ?[]int {
+	mut out := []int{}
 	mut start := min
-	mut interval := u32(1)
+	mut interval := 1
 
 	if s != '*' {
 		exps := s.split('/')
 
-		start = math.min(max, math.max(exps[0].u32(), min))
+		start = math.min(max, math.max(exps[0].int(), min))
 
 		if exps.len > 1 {
-			interval = exps[1].u32()
+			interval = exps[1].int()
 		}
 		// Here, s solely consists of a number, so that's the only value we
 		// should return.
@@ -69,15 +136,22 @@ fn parse_range(s string, min u32, max u32) ?[]u32 {
 
 // min hour day month day-of-week
 fn parse_expression(exp string) ?CronExpression {
-	parts := exp.split(' ')
+	mut parts := exp.split(' ')
 
-	if parts.len != 3 {
-		return error('Expression must contain 5 space-separated parts.')
+	if parts.len < 2 || parts.len > 4 {
+		return error('Expression must contain between 2 and 4 space-separated parts.')
+	}
+
+	// For ease of use, we allow the user to only specify as many parts as they
+	// need.
+	for parts.len < 4 {
+		parts << '*'
 	}
 
 	return CronExpression{
 		minutes: parse_range(parts[0], 0, 59) ?
 		hours: parse_range(parts[1], 0, 23) ?
-		days: parse_range(parts[2], 0, 31) ?
+		days: parse_range(parts[2], 1, 31) ?
+		months: parse_range(parts[3], 1, 12) ?
 	}
 }