module.exports = function(fi, country) {
    if (fi == null) return true;
    if (typeof fi != 'string') return false;

    fi = fi.toUpperCase();
    country = country ? country.toLowerCase() : 'es';

    let len = fi.length;

    let validators = {
        es: {
            regExp: /^[A-Z0-9]\d{7}[A-Z0-9]$/,
            validate: () => {
                let isCif = /[A-W]/.test(fi.charAt(0));
                let lastDigit = fi.charAt(len - 1);
                let computedDigit;

                if (isCif) {
                    let numbers = fi.substring(1, 8)
                        .split('')
                        .map(x => parseInt(x));

                    let pairSum = numbers
                        .filter((_, i) => i % 2 != 0)
                        .reduce((a, x) => a + x);

                    let oddSum = numbers
                        .filter((_, i) => i % 2 == 0)
                        .map(x => x * 2)
                        .join('')
                        .split('')
                        .map(x => parseInt(x))
                        .reduce((a, x) => a + x);

                    let sum = (pairSum + oddSum).toString();
                    let units = parseInt(sum.charAt(sum.length - 1));
                    let control = units == 0 ? 0 : 10 - units;
                    let index = 'JABCDEFGHI'.indexOf(lastDigit);
                    computedDigit = index == -1 ? control.toString() : index;
                } else {
                    // Foreign NIF
                    let index = 'XYZ'.indexOf(fi.charAt(0));
                    let nif = index == -1 ? fi : index.toString() + fi.substring(1);

                    let rest = parseInt(nif.substring(0, 8)) % 23;
                    computedDigit = 'TRWAGMYFPDXBNJZSQVHLCKE'.charAt(rest);
                }

                return computedDigit == lastDigit;
            }
        },
        fr: {
            regExp: /^[A-Z0-9]{2}\d{9}$/
        },
        it: {
            regExp: /^\d{11}$/
        },
        pt: {
            regExp: /^\d{9}$/
        }
    };

    let validator = validators[country];

    if (!validator)
        return false;

    return validator.regExp.test(fi)
        && (!validator.validate || validator.validate());
};