<?php

declare(strict_types=1);

namespace App\Enum;

/**
 * How often a series repeats.
 *
 * Every rule is a whole number of days, which is what lets BookingSeries::occurrences() be a
 * plain stride from the start date. Every stride that is a multiple of 7 therefore keeps the
 * weekday fixed by construction -- that is why a series needs no weekday field at all.
 *
 * There is deliberately no calendar-monthly rule: "the 31st of each month" has no counterpart in
 * five months of the year, and it would not hold the weekday. FOUR_WEEKLY is the nearest thing
 * that behaves, at the cost of drifting against the calendar -- 13 occurrences a year, not 12,
 * which is why it is not labelled "Monatlich".
 */
enum RecurrenceRule: string
{
    case DAILY = 'daily';
    case WEEKLY = 'weekly';
    case TWO_WEEKLY = 'two_weekly';
    case FOUR_WEEKLY = 'four_weekly';

    public function label(): string
    {
        return match ($this) {
            self::DAILY => 'Täglich',
            self::WEEKLY => 'Wöchentlich',
            self::TWO_WEEKLY => 'Alle zwei Wochen',
            self::FOUR_WEEKLY => 'Alle vier Wochen',
        };
    }

    /** Days between two occurrences. */
    public function intervalDays(): int
    {
        return match ($this) {
            self::DAILY => 1,
            self::WEEKLY => 7,
            self::TWO_WEEKLY => 14,
            self::FOUR_WEEKLY => 28,
        };
    }

    /** Whether the rule lands on the same weekday every time, i.e. whether naming it adds anything. */
    public function keepsWeekday(): bool
    {
        return 0 === $this->intervalDays() % 7;
    }
}