<?php
// This file is part of Moodle - http://moodle.org/
//
// Moodle is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Moodle is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.

/**
 * AWS helper class. Contains useful functions when interacting with the SDK.
 *
 * @package    core
 * @author     Peter Burnett <peterburnett@catalyst-au.net>
 * @copyright  2020 Catalyst IT
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

namespace core\aws;

use Aws\CommandInterface;
use Aws\AwsClient;
use Psr\Http\Message\RequestInterface;

/**
 * This class contains functions that help plugins to interact with the AWS SDK.
 *
 * @copyright  2020 Catalyst IT
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
class aws_helper {

    /**
     * This creates a proxy string suitable for use with the AWS SDK.
     *
     * @return string the string to use for proxy settings.
     */
    public static function get_proxy_string(): string {
        global $CFG;
        $proxy = '';
        if (empty($CFG->proxytype)) {
            return $proxy;
        }
        if ($CFG->proxytype === 'SOCKS5') {
            // If it is a SOCKS proxy, append the protocol info.
            $protocol = 'socks5://';
        } else {
            $protocol = '';
        }
        if (!empty($CFG->proxyhost)) {
            $proxy = $CFG->proxyhost;
            if (!empty($CFG->proxyport)) {
                $proxy .= ':'. $CFG->proxyport;
            }
            if (!empty($CFG->proxyuser) && !empty($CFG->proxypassword)) {
                $proxy = $protocol . $CFG->proxyuser . ':' . $CFG->proxypassword . '@' . $proxy;
            }
        }
        return $proxy;
    }

    /**
     * Configure the provided AWS client to route traffic via the moodle proxy for any hosts not excluded.
     *
     * @param AwsClient $client
     * @return AwsClient
     */
    public static function configure_client_proxy(AwsClient $client): AwsClient {
        $client->getHandlerList()->appendBuild(self::add_proxy_when_required(), 'proxy_bypass');
        return $client;
    }

    /**
     * Generate a middleware higher order function to wrap the handler and append proxy configuration based on target.
     *
     * @return callable Middleware high order callable.
     */
    protected static function add_proxy_when_required(): callable {
        return function (callable $fn) {
            return function (CommandInterface $command, ?RequestInterface $request = null) use ($fn) {
                if (isset($request)) {
                    $target = (string) $request->getUri();
                    if (!is_proxybypass($target)) {
                        $command['@http']['proxy'] = self::get_proxy_string();
                    }
                }

                $promise = $fn($command, $request);
                return $promise;
            };
        };
    }
}