alvarocastro/numeral-prefix

const transforms = {
    0(previous, [number, nextNumber]) {
        const units = {
            1: 'hena',
            2: 'di',
            3: 'tri',
            4: 'tetra',
            5: 'penta',
            6: 'hexa',
            7: 'hepta',
            8: 'octa',
            9: 'ennea'
        };
        let unit;
        if (number === 1 && nextNumber === 1) {
            unit = 'hen';
        } else if (number === 2 && nextNumber === 1) {
            unit = 'do';
        } else {
            unit = units[number];
        }

        return `${previous}${unit}`;
    },
    1(previous, [nextNumber, number]) {
        const units = {
            1: 'deca',
            2: 'icosa',
            3: 'triaconta',
            4: 'tetraconta',
            5: 'pentaconta',
            6: 'hexaconta',
            7: 'heptaconta',
            8: 'octaconta',
            9: 'enneaconta'
        };
        let unit = units[number];
        if (nextNumber > 0 && number > 1) {
            if (number === 2) {
                unit = 'icosi';
            }

            unit += 'kai';
        }

        return number === 1 ? `${previous}${unit}` : `${unit}${previous}`;
    },
    2(previous, numbers) {
        const units = {
            1: numbers[1] === 0 && numbers[0] === 0 ? 'hecto' : 'hecta',
            2: 'dihecta',
            3: 'trihecta',
            4: 'tetrahecta',
            5: 'pentahecta',
            6: 'hexahecta',
            7: 'heptahecta',
            8: 'octahecta',
            9: 'enneahecta'
        };
        const unit = units[numbers[2]];
        return `${unit}${previous}`;
    },
    3(previous, numbers) {
        const units = {
            1: 'chilia',
            2: 'dischilia',
            3: 'trischilia',
            4: 'tetrakischilia',
            5: 'pentakischilia',
            6: 'hexakischilia',
            7: 'heptakischilia',
            8: 'octakischilia',
            9: 'enneakischilia'
        };
        const unit = units[numbers[3]];
        return `${unit}${previous}`;
    },
    4(previous, numbers) {
        const units = {
            1: 'myria',
            2: 'dismyria',
            3: 'trismyria',
            4: 'tetrakismyria',
            5: 'pentakismyria',
            6: 'hexakismyria',
            7: 'heptakismyria',
            8: 'octakismyria',
            9: 'enneakismyria'
        };
        const unit = units[numbers[4]];
        return `${unit}${previous}`;
    },
    5(previous, numbers) {
        const units = {
            1: 'decakismyria',
            2: 'icosakismyria',
            3: 'triacontakismyria',
            4: 'tetracontakismyria',
            5: 'pentacontakismyria',
            6: 'hexacontakismyria',
            7: 'heptacontakismyria',
            8: 'octacontakismyria',
            9: 'enneacontakismyria'
        };
        const unit = units[numbers[5]];
        return `${unit}${previous}`;
    },
    6(previous, numbers) {
        const units = {
            1: 'hecatontakismyria',
            2: 'diacosakismyria',
            3: 'triacosakismyria',
            4: 'tetracosakismyria',
            5: 'pentacosakismyria',
            6: 'hexacosakismyria',
            7: 'heptacosakismyria',
            8: 'octacosakismyria',
            9: 'enneacosakismyria'
        };
        const unit = units[numbers[6]];
        return `${unit}${previous}`;
    },
    7(previous, numbers) {
        const units = {
            1: 'chiliakismyria',
            2: 'dischiliakismyria',
            3: 'trischiliakismyria',
            4: 'tetrakischiliakismyria',
            5: 'pentakischiliakismyria',
            6: 'hexakischiliakismyria',
            7: 'heptakischiliakismyria',
            8: 'octakischiliakismyria',
            9: 'enneakischiliakismyria'
        };
        const unit = units[numbers[7]];
        return `${unit}${previous}`;
    },
    8(previous, numbers) {
        const units = {
            1: 'myriakismyria',
            2: 'dismyriakismyria',
            3: 'trismyriakismyria',
            4: 'tetrakismyriakismyria',
            5: 'pentakismyriakismyria',
            6: 'hexakismyriakismyria',
            7: 'heptakismyriakismyria',
            8: 'octakismyriakismyria',
            9: 'enneakismyriakismyria'
        };
        const unit = units[numbers[8]];
        return `${unit}${previous}`;
    }
};

const numeralPrefix = function (number, suffix = '') {
    if (number === Number.POSITIVE_INFINITY) {
        return `apeiro${suffix}`;
    }

    if (!Number.isInteger(number)) {
        throw new TypeError('Number must be integer');
    }

    if (number <= 0) {
        throw new Error('Number must be greater than zero');
    }

    if (number > 999999999) {
        throw new Error('Number can\'t be greater than 999999999');
    }

    const numbers = number
        .toString()
        .split('')
        .map(n => Number(n))
        .reverse();

    let result = '';
    for (const [i, n] of numbers.entries()) {
        if (n > 0) {
            result = transforms[i](result, numbers, number);
        }
    }

    return result + suffix;
};

module.exports = numeralPrefix;