package calendarops

import (
	"errors"

	basetypes "code.apps.glenux.net/glenux/kiwimix/pkg/basetypes"
)

// DifferenceCalendarOperation is an operation that substract a calendar from
// another
type DifferenceCalendarOperation struct{}

// Ensure DifferenceCalendarOperation implements CalendarOperation
var _ CalendarOperation = (*DifferenceCalendarOperation)(nil)

func (op *DifferenceCalendarOperation) Execute(calendars ...*basetypes.Calendar) (*basetypes.Calendar, error) {
	// Check that two calendars are provided
	if len(calendars) != 2 {
		return &basetypes.Calendar{}, errors.New("difference operation requires exactly two calendars")
	}

	// Create a new calendar to store the difference
	differenceCalendar := basetypes.NewCalendar()

	// Iterate over the events in the first calendar
	for _, event1 := range calendars[0].GetEvents() {
		// Assume initially that the event is unique to the first calendar
		isUnique := true

		// Compare with the events in the second calendar
		for _, event2 := range calendars[1].GetEvents() {
			if event1.Equals(event2) {
				// If the event is also in the second calendar, it is not unique
				isUnique = false
				break
			}
		}

		// If the event is unique to the first calendar, add it to the difference calendar
		if isUnique {
			differenceCalendar.AddEvent(event1)
		}
	}

	// Return the difference calendar
	return differenceCalendar, nil
}