alvarocastro/roll

const round = require('@alvarocastro/round');
const mexp = require('math-expression-evaluator');

const rollDice = function (sides) {
    return Math.ceil(roll.random() * sides);
};

const parseDice = function (diceString) {
    const re = /(\d*)d(\d+|%)/;
    const [, countString, sidesString] = re.exec(diceString);

    return {
        sides: sidesString === '%' ? 100 : Number(sidesString),
        count: countString ? Number(countString) : 1
    };
};

const roll = function (rollString, rollCallback = () => {}) {
    const rollStringRegex = /^(\d*)d(\d+|%)(([+\-/*bw])(\d+))?(([+\-/*])(\d+|(\d*)d(\d+|%)(([+\-/*bw])(\d+))?))*$/;

    if (!rollStringRegex.test(rollString)) {
        throw new Error(`"${rollString}" is not a valid roll`);
    }

    const formula = rollString.replace(/(\d*)d(\d+|%)/g, diceString => {
        const dice = parseDice(diceString);

        const rolls = [];
        for (let i = 0; i < dice.count; i++) {
            const roll = rollDice(dice.sides);
            rolls.push(roll);
        }

        rollCallback(`${dice.count}d${dice.sides}`, rolls);
        return `(${rolls.join('+')})`;
    });

    const result = mexp.eval(formula);
    return round(result);
};

roll.detailed = function (rollString, rollCallback = () => {}) {
    const rolls = [];
    const result = roll(rollString, (roll, result) => {
        rollCallback(roll, result);
        rolls.push({
            roll,
            result
        });
    });

    return {
        rolls,
        result
    };
};

roll.random = function () {
    return Math.random();
};

module.exports = roll;