module.exports = {
    /**
     * @param choice {number} a choice index given by the input to $tc: `$tc('path.to.rule', choiceIndex)`
     * @param choicesLength {number} an overall amount of available choices
     * @returns a final choice index to select plural word by
     */
    ru: function (choice, choicesLength) {
        // this === VueI18n instance, so the locale property also exists here

        if (choice === 0) {
            return 0;
        }

        const teen = choice > 10 && choice < 20;
        const endsWithOne = choice % 10 === 1;

        if (choicesLength < 4) {
            return !teen && endsWithOne ? 1 : 2;
        }
        if (!teen && endsWithOne) {
            return 1;
        }
        if (!teen && choice % 10 >= 2 && choice % 10 <= 4) {
            return 2;
        }

        return choicesLength < 4 ? 2 : 3;
    },
};