highestCostRelief.js

// tax lot - each group of purchases
  // long term, what price you bought at

  //portfolio of tax lots
  // relief fifo, lifo, least tax liability, highest cost
  // sellList array of objects
  // return new portfolio
  // highest cost


function highestCostRelief(portfolio, sellList) {
  portfolio.sort((a,b) => {
    if (a.price > b.price) {
      return -1;
    } 
    return 1;
  })
  const sharesToSell = {}
  sellList.forEach((item) => {
    sharesToSell[item.ticker] = (sharesToSell[item.ticker] || 0) + item.shares
  })
  portfolio.forEach((item) => {
    if (sharesToSell[item.ticker] > item.shares) {
      sharesToSell[item.ticker] -= item.shares;
      item.shares = 0;
    } else if (sharesToSell[item.ticker] <= item.shares) {
      item.shares -= sharesToSell[item.ticker];
      sharesToSell[item.ticker] = 0;
    }
  })
}

function changePortfolio (portfolio, relief, sellList) {
  const reliefMethods = {
    highestCost: highestCostRelief
  }
  if (reliefMethods[relief]) {
    highestCostRelief(portfolio, sellList)
  }
  return portfolio;
}

const portfolio = [
  {ticker: 'goog', price: 500, shares: 10, date: '05/13/2019'},
  {ticker: 'app', price: 1000, shares: 100, date: '04/03/2020'},
  {ticker: 'goog', price: 400, shares: 20, date: '04/04/2020'},
  {ticker: 'app', price: 2000, shares: 50, date: '04/03/2020'},
]

console.log(changePortfolio(portfolio, 'highestCost', [{ticker: 'goog', shares: 13}, {ticker: 'app', shares: 70}, {ticker: 'goog', shares: 1}])); 
// [ { ticker: 'app', price: 2000, shares: 0, date: '04/03/2020' }, { ticker: 'app', price: 1000, shares: 80, date: '04/03/2020' },  { ticker: 'goog', price: 500, shares: 0, date: '05/13/2019' }, { ticker: 'goog', price: 400, shares: 16, date: '04/04/2020' } ]