Introduction

1. Requirements

Functional Requirements

As a user I navigate I can enter a URL and get a shortened URL
As a user if I navigate to the shortened URL I'm redirected to the original URL I entered

Generate UIDs

// 1. Use Hashing(ensures same url gets same shortened URL)
const crypto = require('crypto');
 
function hashUrl(url, length = 7) {
  const hash = crypto.createHash('sha256').update(url).digest('base64url');
  return hash.slice(0, length);
}
 
// 2. Use Id
const urlToId = new Map();
const idToUrl = new Map();
let counter = 1000;
 
const BASE62 = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
function toBase62(num) {
  let str = '';
  while (num > 0) {
    str = BASE62[num % 62] + str;
    num = Math.floor(num / 62);
  }
  return str || '0';
}
 
function shortenUrl(url) {
  if (urlToId.has(url)) {
    return toBase62(urlToId.get(url));
  }
 
  const id = counter++;
  urlToId.set(url, id);
  idToUrl.set(id, url);
  return toBase62(id);
}
 
function expandShortCode(shortCode) {
  const id = parseInt(shortCode, 62);
  return idToUrl.get(id);
}

Flip Key/Values

function flipSelective(obj) {
  const flipped = {};
  for (const [key, value] of Object.entries(obj)) {
    if (typeof value === 'number' || typeof value === 'string') {
      flipped[value] = key;
    } else {
      flipped[key] = value;
    }
  }
  return flipped;
}

API Endpoint

const express = require('express');
const app = express();
 
const urlMap = {
  'uid-123': 'https://example.com/some-long-url',
  'uid-456': 'https://google.com',
};
 
app.get('/:uid', (req, res) => {
  const { uid } = req.params;
  const redirectUrl = urlMap[uid];
 
  if (redirectUrl) {
    return res.redirect(302, redirectUrl);
  }
 
  res.status(404).send('URL not found');
});
 
const PORT = process.env.PORT || 3000;
app.listen(PORT, () => {
  console.log(`Server running on port ${PORT}`);
});