<?php
// Setup instructions:
// composer require gocardless/gocardless-pro
// composer require symfony/serializer-pack
use GoCardlessPro\Resources\Event;
use Symfony\Component\Serializer\Encoder\JsonEncoder;
use Symfony\Component\Serializer\Encoder\XmlEncoder;
use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;
use Symfony\Component\Serializer\Serializer;

require_once 'vendor/autoload.php';

// This - I hope - mimics the Symfony framework default Serializer configuration
$encoders = [new XmlEncoder(), new JsonEncoder()];
$normalizers = [new ObjectNormalizer()];
$serializer = new Serializer($normalizers, $encoders);
// End configuring the serializer

// Begin configuring the object to serialize
$json = '{"id":"EV0000000000000","created_at":"2019-08-06T20:09:15.731Z","action":"active","resource_type":"mandates","details":{"origin":"gocardless","cause":"mandate_activated","description":"The time window after submission for the banks to refuse a mandate has ended without any errors being received, so this mandate is now active."},"links":{"mandate":"MD00000000000"},"metadata":[],"model_name":"Event"}';
$event = new Event(json_decode($json));

echo "Expected\n";
// Get rid of the line breaks:
echo json_encode(json_decode($json));

echo "\n\nActual\n";
echo $serializer->serialize($event, 'json');

Expected
{"id":"EV0000000000000","created_at":"2019-08-06T20:09:15.731Z","action":"active","resource_type":"mandates","details":{"origin":"gocardless","cause":"mandate_activated","description":"The time window after submission for the banks to refuse a mandate has ended without any errors being received, so this mandate is now active."},"links":{"mandate":"MD00000000000"},"metadata":[],"model_name":"Event"}

Actual
{"api_response":null}

<?php
// Setup instructions:
// composer require gocardless/gocardless-pro
// composer require symfony/serializer-pack
use GoCardlessPro\Resources\Event;
use Symfony\Component\Serializer\Encoder\JsonEncoder;
use Symfony\Component\Serializer\Encoder\XmlEncoder;
use Symfony\Component\Serializer\Normalizer\PropertyNormalizer;
use Symfony\Component\Serializer\Serializer;

require_once 'vendor/autoload.php';

// Custom Serializer configuration
$encoders = [new XmlEncoder(), new JsonEncoder()];
$normalizers = [new PropertyNormalizer()];
$serializer = new Serializer($normalizers, $encoders);
// End configuring the serializer

$json = '{"id":"EV0000000000000","created_at":"2019-08-06T20:09:15.731Z","action":"active","resource_type":"mandates","details":{"origin":"gocardless","cause":"mandate_activated","description":"The time window after submission for the banks to refuse a mandate has ended without any errors being received, so this mandate is now active."},"links":{"mandate":"MD00000000000"},"metadata":[],"model_name":"Event"}';
// All problems can be fixed if I could change this to $event = new Event(json_decode($json, true));
// But I can't - the library that creates these objects doesn't
// So I need the serializer to handle stdClass objects
$event = new Event(json_decode($json));

echo "Expected\n";
// Get rid of the line breaks:
echo json_encode(json_decode($json));

echo "\n\nActual\n";
// IMO this should work, but it throws an exception:
// PHP Fatal error:  Uncaught Symfony\Component\Serializer\Exception\NotNormalizableValueException: Could not normalize object of type stdClass, no supporting normalizer found.
#echo $serializer->serialize($event, 'json');

// So I try doing my own conversions:
// It still throws the same exception
$callback = function ($innerObject, $outerObject, string $attributeName, string $format = null, array $context = []) {
    return $innerObject instanceof \stdClass ? (array)$innerObject : $innerObject;
};
echo $serializer->serialize($event, 'json', [
    'callbacks' => [
        // This assumes I know all the object properties that are stdClass - which I won't
        'details' => $callback,
        'links' => $callback,
        'metadata' => $callback,
        'data' => $callback,
    ]
]);

Expected
{"id":"EV0000000000000","created_at":"2019-08-06T20:09:15.731Z","action":"active","resource_type":"mandates","details":{"origin":"gocardless","cause":"mandate_activated","description":"The time window after submission for the banks to refuse a mandate has ended without any errors being received, so this mandate is now active."},"links":{"mandate":"MD00000000000"},"metadata":[],"model_name":"Event"}

Actual
PHP Fatal error:  Uncaught Symfony\Component\Serializer\Exception\NotNormalizableValueException: Could not normalize object of type stdClass, no supporting normalizer found. in Z:\path\to\vendor\symfony\serializer\Serializer.php:173
Stack trace:
#0 Z:\path\to\vendor\symfony\serializer\Serializer.php(162): Symfony\Component\Serializer\Serializer->normalize(Object(stdClass), 'json', Array)
#1 Z:\path\to\vendor\symfony\serializer\Normalizer\AbstractObjectNormalizer.php(206): Symfony\Component\Serializer\Serializer->normalize(Array, 'json', Array)
#2 Z:\path\to\vendor\symfony\serializer\Serializer.php(152): Symfony\Component\Serializer\Normalizer\AbstractObjectNormalizer->normalize(Object(GoCardlessPro\Resources\Event), 'json', Array)
#3 Z:\path\to\vendor\symfony\serializer\Serializer.php(125): Symfony\Component\Serializer\Serializer->normalize in Z:\path\to\vendor\symfony\serializer\Serializer.php on line 173

Fatal error: Uncaught Symfony\Component\Serializer\Exception\NotNormalizableValueException: Could not normalize object of type stdClass, no supporting normalizer found. in Z:\path\to\vendor\symfony\serializer\Serializer.php on line 173

Symfony\Component\Serializer\Exception\NotNormalizableValueException: Could not normalize object of type stdClass, no supporting normalizer found. in Z:\path\to\vendor\symfony\serializer\Serializer.php on line 173

Call Stack:
    0.0002     405288   1. {main}() Z:\path\to\index.php:0
    0.0130    1260760   2. Symfony\Component\Serializer\Serializer->serialize() Z:\path\to\index.php:45
    0.0131    1261136   3. Symfony\Component\Serializer\Serializer->normalize() Z:\path\to\vendor\symfony\serializer\Serializer.php:125
    0.0131    1262264   4. Symfony\Component\Serializer\Normalizer\PropertyNormalizer->normalize() Z:\path\to\vendor\symfony\serializer\Serializer.php:152
    0.0138    1267416   5. Symfony\Component\Serializer\Serializer->normalize() Z:\path\to\vendor\symfony\serializer\Normalizer\AbstractObjectNormalizer.php:206
    0.0138    1267792   6. Symfony\Component\Serializer\Serializer->normalize() Z:\path\to\vendor\symfony\serializer\Serializer.php:162