S3Uploader.php

<?php

namespace App\Model;

use Nette;
use Aws\S3\S3Client;

class S3Uploader
{
    /** @var \Aws\S3\S3Client */
    private $s3client;

    /** @var string */
    private $bucket;
    
    public function __construct($bucket, $accessKey, $secretKey)
    {
        putenv("AWS_ACCESS_KEY_ID=$accessKey");
        putenv("AWS_SECRET_ACCESS_KEY=$secretKey");

        $this->s3client = new \Aws\S3\S3Client([
            'version' => 'latest',
            'region'  => 'us-west-2'
        ]);

        $this->bucket = $bucket;
    }

    /**
     * Upload a file to an S3 bucket
     *
     * @param string $key The key used for the uploaded object
     * @param string $file The filename to be uploaded
     * @param string $contentType The file's content type. This defaults to "application/octet-stream"
     *
     * @return string A URL to access the file publically.
     */
    public function uploadPublic ($key, $file, $contentType = 'application/octet-stream')
    {
        $result = $this->s3client->putObject([
            'Bucket'     => $this->bucket,
            'Key'        => $key,
            'SourceFile' => $file,
            'ContentType' => $contentType,
            'ACL'        => 'public-read'
        ]);

        $url = $this->s3client->getObjectUrl($this->bucket, $key);

        return $url;
    }
    
    public function getClient () {
        return $this->s3client;
    }

    public function getBucket () {
        return $this->bucket;
    }
}

Here's the blog post where I talk about using this file: https://arnesonium.com/2016/10/using-amazon-s3-as-a-nette-service/