package notifier

import (
	"fmt"
	"time"

	"github.com/robfig/cron/v3"
)

// CronSchedule wraps a robfig/cron schedule to satisfy the notifier.Schedule
// interface used by StartScheduler. The spec follows the standard 5-field cron
// syntax (e.g. "0 9 * * *" for daily at 09:00 in the process local time).
type CronSchedule struct {
	spec string
	c    cron.Schedule
}

// NewCronSchedule parses a cron spec and returns a Schedule. An error is
// returned if the spec is not a valid cron expression.
func NewCronSchedule(spec string) (*CronSchedule, error) {
	c, err := cron.ParseStandard(spec)
	if err != nil {
		return nil, fmt.Errorf("parse cron schedule %q: %w", spec, err)
	}
	return &CronSchedule{spec: spec, c: c}, nil
}

// Next returns the next time the schedule fires after t.
func (s *CronSchedule) Next(t time.Time) time.Time {
	return s.c.Next(t)
}