Started writing cron expression parser [CI SKIP]

src/cron/expression.v

@@ -0,0 +1,55 @@
+module cron
+
+import math
+
+struct CronExpression {
+	minutes []u32
+	hours []u32
+	days []u32
+}
+
+// parse_range parses a given string into a range of integers, if possible.
+fn parse_range(s string, min u32, max u32) ?[]u32 {
+	mut out := []u32{}
+	mut start := min
+	mut interval := u32(1)
+
+	if s != '*' {
+		exps := s.split('/')
+
+		if exps.len > 1 {
+			interval = exps[1].u32()
+		}
+		// Here, s solely consists of a number, so that's the only value we
+		// should return.
+		else{
+			return [exps[0].u32()]
+		}
+
+		if exps[0] != '*' {
+			start = math.max(exps[0].u32(), min)
+		}
+	}
+
+	for start <= max {
+		out << start
+		start += interval
+	}
+
+	return out
+}
+
+// min hour day month day-of-week
+fn parse_expression(exp string) ?CronExpression {
+	parts := exp.split(' ')
+
+	if parts.len != 3 {
+		return error("Expression must contain 5 space-separated parts.")
+	}
+
+	return CronExpression{
+		minutes: parse_range(parts[0], 0, 59) ?
+		hours: parse_range(parts[1], 0, 23) ?
+		days: parse_range(parts[2], 0, 31) ?
+	}
+}