fix: use local timezone for date grouping and filtering

Author: zulerne

cmd/ccost/main.go

@@ -57,7 +57,7 @@ func main() {
 	}
 
 	if sinceStr != "" {
-		t, err := time.Parse("2006-01-02", sinceStr)
+		t, err := time.ParseInLocation("2006-01-02", sinceStr, time.Local)
 		if err != nil {
 			fmt.Fprintf(os.Stderr, "invalid --since date: %v\n", err)
 			os.Exit(1)
@@ -66,7 +66,7 @@ func main() {
 	}
 
 	if untilStr != "" {
-		t, err := time.Parse("2006-01-02", untilStr)
+		t, err := time.ParseInLocation("2006-01-02", untilStr, time.Local)
 		if err != nil {
 			fmt.Fprintf(os.Stderr, "invalid --until date: %v\n", err)
 			os.Exit(1)

internal/parser/parser.go

@@ -177,7 +177,7 @@ func parseTime(s string) (time.Time, bool) {
 			return time.Time{}, false
 		}
 	}
-	return t, true
+	return t.Local(), true
 }
 
 // dayBounds tracks min/max timestamps for a single day.
@@ -289,7 +289,7 @@ func parseFile(path string, opts Options, isMain bool) ([]Record, []Session, []s
 	var sessions []Session
 	if isMain && project != "" {
 		for date, b := range days {
-			day, _ := time.Parse("2006-01-02", date)
+			day, _ := time.ParseInLocation("2006-01-02", date, time.Local)
 			if !opts.Since.IsZero() && day.Before(opts.Since) {
 				continue
 			}