old_contents: from flask import Blueprint, jsonify, request
  
  from usb.models import db, Redirect, DeviceType
  from usb.shortener import get_short_id, get_short_url
  
  api = Blueprint('api', __name__)
  
  
  @api.route('/links')
  def get_links():
      return jsonify({}), 200
  
  
  @api.route('/links', methods=['POST'])
  def shorten_url():
      short_id = get_short_id()
      long_url = request.json['url']
      for device_type in DeviceType:
          db.session.add(Redirect(short_id, device_type, long_url))
      db.session.commit()
      short_url = get_short_url(short_id)
      return jsonify(url=short_url), 200
  
new_contents: from flask import Blueprint, jsonify, request
  
  from usb.models import db, Redirect, DeviceType
  from usb.shortener import get_short_id, get_short_url
  
  api = Blueprint('api', __name__)
  
  
  @api.route('/links')
  def get_links():
      return jsonify({}), 200
  
  
  @api.route('/links', methods=['POST'])
  def shorten_url():
      short_id = get_short_id()
      long_url = request.json['url']
      redirect = Redirect.query.filter_by(url=long_url).first()
      if redirect:
          short_url = get_short_url(redirect.short)
          return jsonify(url=short_url), 409
      for device_type in DeviceType:
          db.session.add(Redirect(short_id, device_type, long_url))
      db.session.commit()
      short_url = get_short_url(short_id)
      return jsonify(url=short_url), 200
  
subject: Return short URL if it's already exists