add ISODuration type for ISO8061 duration compatibility

duration.go

@@ -0,0 +1,99 @@
+package clocktime
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"time"
+
+	"github.com/sosodev/duration"
+)
+
+// ISODuration wraps a time.Duration to provide custom JSON and SQL
+// serialization and full ISO8061 compatibility. Note: ISODuration is limited
+// to the same range as time.Duration despite ISO8061 supporting larger durations.
+type ISODuration time.Duration
+
+// NewISODuration creates a new duration from numeric components.
+func NewISODuration(hours, minutes, seconds int) ISODuration {
+	return ISODuration(
+		time.Hour*time.Duration(hours) +
+			time.Minute*time.Duration(minutes) +
+			time.Second*time.Duration(seconds),
+	)
+}
+
+// DurationFromISOString parses an ISO8601 duration string (e.g., "PT1H30M45S")
+// and returns an ISODuration.
+func DurationFromISOString(s string) (ISODuration, error) {
+	d, err := duration.Parse(s)
+	if err != nil {
+		return 0, fmt.Errorf("error parsing ISO8061 duration: %w", err)
+	}
+	return ISODuration(d.ToTimeDuration()), nil
+}
+
+// ISODurationFromDuration converts a time.Duration to an ISODuration.
+func ISODurationFromDuration(d time.Duration) ISODuration {
+	return ISODuration(d)
+}
+
+// String returns the ISO8601 string representation of the ISODuration.
+func (d ISODuration) String() string {
+	td := time.Duration(d)
+	isoDur := duration.FromTimeDuration(td)
+	return isoDur.String()
+}
+
+// Duration returns the time.Duration representation of the ISODuration.
+func (d ISODuration) Duration() time.Duration {
+	return time.Duration(d)
+}
+
+// MarshalJSON implements the json.Marshaler interface for ISODuration,
+// serializing it as an ISO8601 duration string.
+func (d ISODuration) MarshalJSON() ([]byte, error) {
+	return json.Marshal("\"" + d.String() + "\"")
+}
+
+// UnmarshalJSON implements the json.Unmarshaler interface for ISODuration,
+// parsing an ISO8601 duration string.
+func (d *ISODuration) UnmarshalJSON(data []byte) error {
+	var s string
+	if err := json.Unmarshal(data, &s); err != nil {
+		return err
+	}
+	parsedDur, err := DurationFromISOString(s)
+	if err != nil {
+		return err
+	}
+	*d = parsedDur
+	return nil
+}
+
+// MarshalGQL implements the graphql.Marshaler interface for ISODuration,
+// serializing it as an ISO8601 duration string.
+func (d ISODuration) MarshalGQL(w io.Writer) {
+	fmt.Fprint(w, "\""+d.String()+"\"")
+}
+
+// UnmarshalGQL implements the graphql.Unmarshaler interface for ISODuration,
+// parsing an ISO8601 duration string. nil values are treated as zero duration.
+func (d *ISODuration) UnmarshalGQL(value any) error {
+	if value == nil {
+		*d = ISODuration(0)
+		return nil
+	}
+
+	s, ok := value.(string)
+	if !ok {
+		return fmt.Errorf("ISODuration must be a string")
+	}
+
+	parsedDur, err := DurationFromISOString(s)
+	if err != nil {
+		return err
+	}
+	*d = parsedDur
+	return nil
+}