parser: fallback zone-less source timestamps to Europe/Moscow

internal/parser/timezone.go

@@ -0,0 +1,33 @@
+package parser
+
+import (
+	"sync"
+	"time"
+)
+
+const fallbackTimezoneName = "Europe/Moscow"
+
+var (
+	fallbackTimezoneOnce sync.Once
+	fallbackTimezone     *time.Location
+)
+
+// DefaultArchiveLocation returns the timezone used for source timestamps
+// that do not contain an explicit offset.
+func DefaultArchiveLocation() *time.Location {
+	fallbackTimezoneOnce.Do(func() {
+		loc, err := time.LoadLocation(fallbackTimezoneName)
+		if err != nil {
+			fallbackTimezone = time.FixedZone("MSK", 3*60*60)
+			return
+		}
+		fallbackTimezone = loc
+	})
+	return fallbackTimezone
+}
+
+// ParseInDefaultArchiveLocation parses timestamps without timezone information
+// using Europe/Moscow as the assumed source timezone.
+func ParseInDefaultArchiveLocation(layout, value string) (time.Time, error) {
+	return time.ParseInLocation(layout, value, DefaultArchiveLocation())
+}