Laravel MongoDB - aggregation, ordering query

I am wondering how could I achieve a specific result.

Starting of I am using https://github.com/jenssegers/laravel-mongodb

The code sample below is used to get an array of documents that contains my specific slug in the rewards node. And till that point, everything works as intended.

 $array = [
            'rewards.slug' => ['$eq' => 'example_slug'],
            'expired' => ['$gte' => \Carbon\Carbon::now()->toDateTimeString()]
        ];
        $models = Master::raw(function ($collection) use (&$array) {
            return $collection->find(
                $array, ["typeMap" => ['root' => 'array', 'document' => 'array']])
                ->toArray();
        });

My example document

{
    "_id": {
        "$oid": "5be4464eafad20007245543f"
    },
    "some_int_value": 100,
    "some_string_value": "String",
    "rewards": [
        {
            "slug": "example_slug",
            "name": "Example slug",
            "quantity": 4,
            "estimated": {
                "value": 18750
            }
        },
        {
            "slug": "example_slug",
            "name": "Example slug",
            "quantity": 1,
            "estimated": {
                "value": 100
            }
        },
        {
            "slug": "other_example",
            "name": "Other slug example",
            "quantity": 1,
            "estimated": {
                "value": 100
            }
        }
    ],
    "expires": "2018-11-08 20:20:45",
}

Desired result

I would like to implement some more complex query, which would do the following.

• Retrieve documents that : pseudo select all documents that contain reward "slug": "example_slug", sum the quantity of them, return greater than X quantity documents, order by sum quantity desc
• and a very similar one to the above select all documents that contain reward "slug": "example_slug", sum estimated.value, return greater than X estimated.value documents, order by sum of estimated.value desc

If you do need more explanation feel free to ask, I feel like I don't even know where to start with this one.

All help is greatly appreciated

via Chebli Mohamed