Add configuration and CLI foundation

internal/timeutil/parse.go

@@ -0,0 +1,49 @@
+package timeutil
+
+import (
+	"fmt"
+	"strings"
+	"time"
+)
+
+const DateLayout = "2006-01-02"
+const LocalDateTimeLayout = "2006-01-02T15:04"
+
+func LoadLocation(name string) (*time.Location, error) {
+	location, err := time.LoadLocation(name)
+	if err == nil {
+		return location, nil
+	}
+	if strings.Contains(name, "/") {
+		return nil, fmt.Errorf("load timezone %q: %w", name, err)
+	}
+	location, chicagoErr := time.LoadLocation("America/" + name)
+	if chicagoErr == nil {
+		return location, nil
+	}
+	return nil, fmt.Errorf("load timezone %q: %w", name, err)
+}
+
+func LocalDate(now time.Time, location *time.Location) time.Time {
+	local := now.In(location)
+	return time.Date(local.Year(), local.Month(), local.Day(), 0, 0, 0, 0, location)
+}
+
+func ParseLocalDate(value string, location *time.Location) (time.Time, error) {
+	parsed, err := time.ParseInLocation(DateLayout, value, location)
+	if err != nil {
+		return time.Time{}, fmt.Errorf("parse date %q as YYYY-MM-DD: %w", value, err)
+	}
+	return parsed, nil
+}
+
+func ParseStormTime(value string, location *time.Location) (time.Time, error) {
+	if parsed, err := time.Parse(time.RFC3339, value); err == nil {
+		return parsed, nil
+	}
+	parsed, err := time.ParseInLocation(LocalDateTimeLayout, value, location)
+	if err != nil {
+		return time.Time{}, fmt.Errorf("parse storm time %q as YYYY-MM-DDTHH:MM or RFC3339: %w", value, err)
+	}
+	return parsed, nil
+}