Write short rebalancing calculation code in Javascript or Php

Write rebalancing calculation code in Javascript or Php. The code must be data based: arrays / objects of data. The goal of the project is to write a short rebalancing calculation code in Javascript or Php. Rebalancing is when you define a portfolio of x% of stock A, y% of stock B, and z% of stock C. After a while, stocks prices change, and we need to sell some stocks and buy others, to rebalance. E.g: We have 1000$. Stock A - cost 10$, we want our portolio to have 20% of stock A - 20 stocks total value 200$. Stock B - cost 15$, we want our portolio to have 30% of stock B - 20 stocks total value 300$. Stock C - cost 50$, we want our portolio to have 50% of stock C - 10 stocks total value 500$. a year has passed, now the prices are: Stock A - 5$, worth 100$ (5*20). Stock B - 15$, still worth 300$. Stock C - 40$, worth 400$ (10*40). Total worth: 800$. Now, stock A is 12.5% of the portfolio, so we need to buy more of it to make it 20%. stock B is 37.5% of the portfolio, so we need to sell some of it to make it 30%. stock C is 50% which is the goal, so we need to do nothing. Then another year will pass, and the same calculation again...