Support the customization of timezone

README.md

@@ -54,5 +54,4 @@ Hyphens define ranges. For example, 2000-2010 indicates every year between 2000
 
 ## Details
 
-* At this moment, the package supports only **UTC** timezone.
 * The return value of `Next` and `Prev` is zero if the pattern doesn't match in five years.

_example/location.go

@@ -0,0 +1,13 @@
+package main
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/gitploy-io/cronexpr"
+)
+
+func main() {
+	nextTime := cronexpr.MustParseInLocation("0 * * * *", "Asia/Seoul").Next(time.Now())
+	fmt.Printf("Parse the cron expression in the KR timezone: %s", nextTime)
+}

parser.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"strconv"
 	"strings"
+	"time"
 )
 
 type (
@@ -55,6 +56,44 @@ var (
 	}
 )
 
+// MustParse returns the same result as Parse but it panic
+// when something is wrong.
+func MustParseInLocation(expr string, locName string) *Schedule {
+	loc, err := time.LoadLocation(locName)
+	if err != nil {
+		panic(err)
+	}
+
+	schdule, err := Parse(expr)
+	if err != nil {
+		panic(err)
+	}
+
+	schdule.Location = loc
+	return schdule
+}
+
+// ParseInLocation parse the expression in the location and
+// returns a new schedule representing the given spec.
+// It returns an error when loading the location is failed or
+// the syntax of the expression is wrong.
+func ParseInLocation(expr string, locName string) (*Schedule, error) {
+	loc, err := time.LoadLocation(locName)
+	if err != nil {
+		return nil, err
+	}
+
+	schdule, err := Parse(expr)
+	if err != nil {
+		return nil, err
+	}
+
+	schdule.Location = loc
+	return schdule, nil
+}
+
+// MustParse returns the same result as Parse but it panic
+// when the syntax of expression is wrong.
 func MustParse(expr string) *Schedule {
 	s, err := Parse(expr)
 	if err != nil {
@@ -64,6 +103,9 @@ func MustParse(expr string) *Schedule {
 	return s
 }
 
+// Parse parses the expression and returns a new schedule representing the given spec.
+// And the default location of a schedule is "UTC".
+// It returns an error when the syntax of expression is wrong.
 func Parse(expr string) (*Schedule, error) {
 	err := verifyExpr(expr)
 	if err != nil {

schedule.go

@@ -8,13 +8,19 @@ type (
 	Schedule struct {
 		Minute, Hour, Dom, Month, Dow bitset
 
-		// TODO: support the timezone option
-		// Location *time.Location
+		Location *time.Location
 	}
 )
 
+// Next returns the next time matched with the expression.
 func (s *Schedule) Next(t time.Time) time.Time {
 	loc := time.UTC
+	if s.Location != nil {
+		loc = s.Location
+	}
+
+	origLoc := t.Location()
+	t.In(loc)
 
 	added := false
 
@@ -88,11 +94,18 @@ L:
 		}
 	}
 
-	return t
+	return t.In(origLoc)
 }
 
+// Next returns the previous time matched with the expression.
 func (s *Schedule) Prev(t time.Time) time.Time {
 	loc := time.UTC
+	if s.Location != nil {
+		loc = s.Location
+	}
+
+	origLoc := t.Location()
+	t.In(loc)
 
 	subtracted := false
 
@@ -167,7 +180,7 @@ L:
 		}
 	}
 
-	return t
+	return t.In(origLoc)
 }
 
 // dayMatches returns true if the schedule's day-of-week and day-of-month