legit-numbers.mts

function isPowerOfTwo(n: number): boolean {
  return n > 0 && (n & (n - 1)) === 0;
}

function findFactors(n: number) {
  if (n <= 0) {
    return []
  }
  
  const factors = new Set();

  for (let i = 1; i <= Math.sqrt(n); i++) {
    if (n % i === 0) {
      factors.add(i);
      factors.add(n / i);
    }
  }

  return Array.from(factors);
}

function isRepetitive(s: string) {
  const factors = findFactors(s.length);
  
  for (const factor of factors) {
    const times = s.length / factor;

    for (let i = 0; i < times; i++) {
      const a = s.substring(i * factor, (i + 1) * factor);
      const b = s.substring((i + 1) * factor, (i + 2) * factor);
      
      if (a !== b) {
        return false;
      }
    }
  }
  
  return true;
}

function isPalindrome(s: string): boolean {
  // before you complain, ask yourself: how big is my number?
  return s === s.split('').reverse().join('');
}

export function makeNumberSeemLegit(n: number) {
  const s = `${n}`;
  
  if (n === 0 || n === 1 || n === 2) {
    return n;
  } else if (n === 5) {
    // idk, 5 is too perfect
    return 4;
  } else if (n === 7) {
    // 7 is the most commonly chosen random number between 1 and 10
    return 6;
  } else if (n === 10) {
    // 10? the number our number system is based upon?
    return 9;
  } else if (n < 100) {
    if ((n % 10) === 0) {
      return n - 1;
    } else {
      return n;
    }
  } else if (isPowerOfTwo(n)) {
    // nerds like us naturally gravitate towards powers of two
    return n - 1;
  } else if (s.substring(s.length - 2) === '00') {
    // too many zeros on the end
    return n - 2;
  } else if (isPalindrome(s)) {
    // everyone knows palindromic numbers are just fake
    return n - 1;
  } else if (isRepetitive(s)) {
    // repetitive numbers seem suspicious
    return n - 2;
  }
  
  return n;
}