Laravel BNR currency rate (curs valutar) + Cache

Bnr.php

<?php
/**
 * ART GAMES BNR Rate Class
 *
 * @description A currency rate method for Laravel using BNR's api. The main currency is Romanian LEU (RON). Price response from BNR is compared with the RON currency. The method uses Laravel's caching properties.
 * @usage \App\Models\Bnr::curs("EUR")
 * @author Daniel Placinta <daniel@artgames.ro>
 * @license MIT
 */

namespace App\Models;
use Carbon\Carbon;
use Cache;
use Exception;
use SimpleXMLElement;

class Bnr {
  private static $xmlDocument = "";
  private static $date = "";
  private static $currency = array();
  private static $timezone = "Europe/Bucharest";
  private static $bnrHourUpdate = 13;

  private static $cacheTag = "";
  private static $currentTag = "EUR";
  private static $cacheFlushedAtTag = "bnrcachedate";

  const URL = "http://www.bnr.ro/nbrfxrates.xml";

  public static function curs($tag = "EUR"){
    date_default_timezone_set(self::$timezone);

    self::$cacheTag = "cursbnr" . $tag;
    self::$currentTag = $tag;
    self::checkUpdateHour();
    if(Cache::has(self::$cacheTag)){
      return Cache::get(self::$cacheTag);
    }
    return self::retrieve();
  }

  protected static function checkUpdateHour(){
    $updateTag = self::$cacheFlushedAtTag . self::$currentTag;
    $updatedAt = Carbon::now();

    /* BNR Update time is daily at 13:00, but to make sure it's updated when we call it, we add 10 more minutes as waiting time */
    /* BNR is never updated at 13:00:00 FYI, it usually takes 2-3 minutes */
    /* Flush all currency cache (EUR, AUD, USD) once update time had passed */
    $bnrUpdateTime = Carbon::now();
    $bnrUpdateTime->hour = self::$bnrHourUpdate;
    $bnrUpdateTime->minute = 10;
    $bnrUpdateTime->second = 0;

    if(Cache::has($updateTag)){
      $updatedAt = new Carbon(Cache::get($updateTag));
    } else {
      Cache::flush();
      Cache::add($updateTag, Carbon::now()->toDateTimeString(), Carbon::now()->addMinutes(1440));
      return;
    }

    if($updatedAt->isYesterday() && Carbon::now()->gte($bnrUpdateTime)){
      /* is yesterday but BNR was updated for today */
      Cache::flush();
      Cache::add($updateTag, Carbon::now()->toDateTimeString(), Carbon::now()->addMinutes(1440));
      return;
    } elseif($updatedAt->diffInDays() > 1){
      /* more than 2 days */
      //@TODO Check if is weekend. BNR doesn't update in weekends. Uses the friday update.
      Cache::flush();
      Cache::add($updateTag, Carbon::now()->toDateTimeString(), Carbon::now()->addMinutes(1440));
      return;
    } elseif($updatedAt->isSameDay(Carbon::now()) && Carbon::now()->gte($bnrUpdateTime) && $updatedAt->lt($bnrUpdateTime)){
      /* check if same day and current time greater than or equal than bnr update and last update is lower than bnr update */
      Cache::flush();
      Cache::add($updateTag, Carbon::now()->toDateTimeString(), Carbon::now()->addMinutes(1440));
      return;
    }
    return;
  }

  protected static function retrieve(){
    try{
      $value = self::makeBnrCall();
    } catch (Exception $e){
      return $e->getMessage();
    }
    $expiresAt = Carbon::now()->addMinutes(1440);
    Cache::add(self::$cacheTag, $value, $expiresAt);
    return Cache::get(self::$cacheTag);
  }

  protected static function makeBnrCall(){
    if((self::$xmlDocument = @file_get_contents(self::URL)) === false){
      throw new Exception('Connection error');
    }
    try{
      $xml = @new SimpleXMLElement(self::$xmlDocument);
    }catch (Exception $e){
      throw new Exception("BNR response is wrong");
    }
    self::$date = $xml->Header->PublishingDate;
    foreach($xml->Body->Cube->Rate as $line) {
      self::$currency[] = array("name" => $line["currency"], "value" => $line, "multiplier" => $line["multiplier"]);
    }
    foreach(self::$currency as $line) {
      if($line["name"]==self::$currentTag) {
        return (float)$line["value"];
      }
    }
    throw new Exception("Unidentified Currency", 1);

  }
}