satori-services/public/exrate.php

<?php
$config = parse_ini_file(__DIR__ . '/../config/flashii.ini');
require_once $config['msz-path'] . '/lib/index/index.php';

try {
    $db = \Index\Data\DbTools::create($config['exrate-dsn2']);
    $db->execute('SET SESSION time_zone = \'+00:00\', sql_mode = \'STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION\';');
} catch(Exception $ex) {
    die((string)$ex);
}

define('EXRATE_INTER', 'EUR');
define('EXRATE_COMMON', [
    'EUR', 'AUD', 'GBP', 'CAD', 'USD', 'JPY', 'PLN', 'SGD', 'RUB', 'ILS',
]);

$from   = strtoupper((string)filter_input(INPUT_GET, 'from'));
$to     = strtoupper((string)filter_input(INPUT_GET, 'to'));
$amount = (string)(filter_input(INPUT_GET, 'amount', FILTER_SANITIZE_NUMBER_FLOAT, FILTER_FLAG_ALLOW_FRACTION) ?? '1');

if((!empty($to) && strlen($to) !== 3) || strlen($from) !== 3) {
    http_response_code(400);
    die('Invalid currency specified.');
}

$needsRefresh = $db->query('SELECT MAX(rate_stored) > NOW() - INTERVAL 1 DAY FROM `exchange-rates` LIMIT 1');
$needsRefresh->next();
$needsRefresh = $needsRefresh->isNull(0) || $needsRefresh->getInteger(0) < 1;

if($needsRefresh) {
    $data = json_decode(file_get_contents('https://api.exchangerate.host/latest?base=' . EXRATE_INTER), true);
    if($data !== null) {
        $db->execute('TRUNCATE `exchange-rates`');
        $insertCurrency = $db->prepare('INSERT INTO `exchange-rates` (rate_from, rate_to, rate_value) VALUES (?, ?, ?)');
        foreach($data['rates'] as $currency => $rate) {
            $insertCurrency->reset();
            $insertCurrency->addParameter(1, $data['base']);
            $insertCurrency->addParameter(2, $currency);
            $insertCurrency->addParameter(3, $rate);
            $insertCurrency->execute();
        }
    }
}

$result = new stdClass;
$result->from = $from;
$result->to = $to;
$result->amount = (float)$amount;

if($from === $to) {
    $result->result = $result->amount;
} else {
    $convertCurrency = $db->prepare(sprintf(
        'SELECT (SELECT (? / rate_value) FROM `exchange-rates` WHERE rate_from = "%1$s" AND rate_to = ?) * rate_value FROM `exchange-rates` WHERE rate_from = "%1$s" AND rate_to = ?',
        EXRATE_INTER
    ));

    if(empty($to)) {
        $result->results = [];
        foreach(EXRATE_COMMON as $commonCurrency) {
            if($commonCurrency === $from)
                continue;

            $result->results[] = $current = new stdClass;
            $current->to = $commonCurrency;

            $convertCurrency->reset();
            $convertCurrency->addParameter(1, $amount);
            $convertCurrency->addParameter(2, $from);
            $convertCurrency->addParameter(3, $commonCurrency);
            $convertCurrency->execute();

            $convertResult = $convertCurrency->getResult();
            $convertResult->next();

            $current->result = $convertResult->getFloat(0);
        }
    } else {
        $convertCurrency->addParameter(1, $amount);
        $convertCurrency->addParameter(2, $from);
        $convertCurrency->addParameter(3, $to);
        $convertCurrency->execute();

        $convertResult = $convertCurrency->getResult();
        $convertResult->next();

        $result->result = $convertResult->getFloat(0);
    }
}

http_response_code(200);
header('Content-Type: application/json');
echo json_encode($result);