// Package timeutil provides JSON-serializable time utilities.
package timeutil

import (
	"encoding/json"
	"errors"
	"time"
)

// Duration is a wrapper around time.Duration that supports JSON marshaling/unmarshaling.
//
// When marshaling to JSON, it outputs the duration as a string using time.Duration.String().
// When unmarshaling from JSON, it accepts both:
//   - String values that can be parsed by time.ParseDuration (e.g., "30s", "5m", "1h30m")
//   - Numeric values that represent nanoseconds as a float64
//
// This makes it compatible with configuration files and APIs that need to represent
// durations in a human-readable format.
//
// Example usage:
//
//	type Config struct {
//		Timeout timeutil.Duration `json:"timeout"`
//	}
//
//	// JSON: {"timeout": "30s"}
//	// or:   {"timeout": 30000000000}
type Duration struct {
	time.Duration
}

// MarshalJSON implements json.Marshaler.
// It marshals the duration as a string using time.Duration.String().
func (d Duration) MarshalJSON() ([]byte, error) {
	return json.Marshal(time.Duration(d.Duration).String())
}

// UnmarshalJSON implements json.Unmarshaler.
// It accepts both string values (parsed via time.ParseDuration) and
// numeric values (interpreted as nanoseconds).
func (d *Duration) UnmarshalJSON(b []byte) error {
	var v any
	if err := json.Unmarshal(b, &v); err != nil {
		return err
	}
	switch value := v.(type) {
	case float64:
		*d = Duration{time.Duration(value)}
		return nil
	case string:
		tmp, err := time.ParseDuration(value)
		if err != nil {
			return err
		}
		*d = Duration{tmp}
		return nil
	default:
		return errors.New("invalid duration")
	}
}