GooglePChange.js

function GOOGLEPCHANGE() {
  var prices = arguments[0];
  var result = [];

  if (prices.length < 3) {
    throw "Price array should have at least rows";
  }

  for (var i = 1; i < arguments.length; i++) {
    result.push(findPriceChange_(prices, arguments[i]));
  }
  
  return result;
}

function calcDateDelta_(dt1, dt2, days) {
  return Math.abs(((dt2 - dt1) / 86400000) - days);
}

function findPriceChange_(prices, days) {
  var last = prices[prices.length - 1];
  var result = prices[prices.length - 2];
  var cur_diff = calcDateDelta_(result[0], last[0], days);

  var i = prices.length - 3;
  while (i >= 1) {
    var new_diff = calcDateDelta_(prices[i][0], last[0], days);
    if (new_diff > cur_diff) {
      break;
    }
    cur_diff = new_diff;
    result = prices[i];
    i -= 1;
  }

  if (cur_diff > 7) {
    return ["", "", ""];
  }

  return [result[0], result[1], last[1] / result[1] - 1];
}