flexible-digit.js

function getNumber(digit = 4) {
  return () =>
    Math.floor(
      Math.random() * Math.pow(10, digit)
    );
}

function getNumInRange(digit = 4) {
  return function(numberGenerator) {
    return function recursiveQuery() {
      const newPin = numberGenerator();

      return newPin <= Math.pow(10, digit - 1)
        ? recursiveQuery()
        : newPin;
    };
  };
}

function checkConsecutive(nPlus1, n) {
  return nPlus1 - n !== 1;
}

function checkValidity(arr) {
  let isValid = true;
  let next = 0;
  return function checkResursive(idx = 0) {
    next = idx + 1;
    isValid =
      isValid &&
      checkConsecutive(arr[idx + 1], arr[idx]);

    return next === arr.length - 1
      ? isValid
      : checkResursive(next);
  };
}

function getPin(digit) {
  return pinGenerator => {
    return function ensureInShape() {
      const pin = pinGenerator();
      const stringArr = pin.toString().split('');

      const noDuplicate =
        new Set(stringArr).size === digit;

      const noConsecutive = checkValidity(
        stringArr.map(item => parseInt(item))
      )();

      return noDuplicate && noConsecutive
        ? pin
        : ensureInShape();
    };
  };
}

function getSolution(howMany) {
  const result = new Set();
  return pinGenerator => {
    return function getEach() {
      result.add(pinGenerator());
      if (result.size === howMany) {
        return result;
      } else {
        return getEach();
      }
    };
  };
}

const generator = digits =>
  getPin(digits)(
    getNumInRange(digits)(getNumber(digits))
  );

module.exports = {
  getSolution,
  generator
};