Consumir API com PHP

Modo Estrutural
<?php
$url = "https://api.hgbrasil.com/weather?key=651bb186&user_ip=remote";
$weather = json_decode(file_get_contents($url));

echo "Previsão do tempo ".$weather->results->city."<br>";
foreach($weather->results->forecast as $r2) {
    echo $r2->date." ".$r2->weekday;
    echo " Min: ".$r2->min."°C | Max: ".$r2->max."°C ";
    echo $r2->description." ".$r2->condition."<br>";
}

Modo Padronizado
index.php
<?php
/* API HG Cotações
1- No site oficial, criar conta, então chave de autenticação
2- Minha chave: Não use a mesma! 811ec71b (Ex: https://api.hgbrasil.com/finance/quotations?key=811ec71b)*/

require_once 'app/config/config.php';
require_once 'app/modules/hg-api.php';

$hg = new HG_API(HG_API_KEY);
$dolar = $hg->dolar_quotation();
var_dump($dolar);
echo("<br>".$dolar['buy']);

if($hg->is_error() == false) {
    $variation = ($dolar['variation']<0) ? 'Variação negativa' : 'Variação positiva';
}
?>

<h1>Cotação dolar</h1>
<?php if($hg->is_error()==false): ?>
    <p>U$D: <?= $dolar['buy'] ?></p>
    <p><?= $variation."(".$dolar['variation'].")" ?></p>
<?php else: ?>
    <p>Erro de serviço</p>
<?php endif; ?>

Pasta app
Subpasta config
config.php
<?php
    define('HG_API_KEY','811ec71b');
?>

Subpasta modules
hg-api.php
<?php
class HG_API {
    
    private $key = null;
    private $error = false;

    function __contruct($key = null) {
        if(!empty($key)) $this->key = $key;
    }

    function request($endpoint = '', $params = array()) {
        $uri = "https://api.hgbrasil.com/".$endpoint."?key=".$this->key."&format=json";

        if(is_array($params)) {
            foreach($params as $key => $value) {
                if(empty($value)) continue;
                $uri .= $key . '=' . urlencode($value) . '&';
            }
            $uri = substr($uri,0,-1);
            $response = @file_get_contents($uri);
            $this->error = false;
            return json_decode($response,true);
        } else {
            $this->error = true;
            return false;
        }
    }

    function is_error() {
        return $this->error;
    }

    function dolar_quotation() {
        $data = $this->request('finance/quotations');
        if(!empty($data) && is_array($data['results']['currencies']['USD'])) {
            $this->error = false;
            return $data['results']['currencies']['USD'];
        } else {
            $this->error = true;
            return false;
        }
    }
}
?>