<?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/>.

/**
 * This file responds to a login authentication request
 *
 * @package    mod_lti
 * @copyright  2019 Stephen Vickers
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

require_once(__DIR__ . '/../../config.php');
require_once($CFG->dirroot . '/mod/lti/locallib.php');

$scope = optional_param('scope', '', PARAM_TEXT);
$responsetype = optional_param('response_type', '', PARAM_TEXT);
$clientid = optional_param('client_id', '', PARAM_TEXT);
$redirecturi = optional_param('redirect_uri', '', PARAM_TEXT);
$loginhint = optional_param('login_hint', '', PARAM_TEXT);
$ltimessagehint = optional_param('lti_message_hint', 0, PARAM_INT);
$state = optional_param('state', '', PARAM_TEXT);
$responsemode = optional_param('response_mode', '', PARAM_TEXT);
$nonce = optional_param('nonce', '', PARAM_TEXT);
$prompt = optional_param('prompt', '', PARAM_TEXT);

$ok = !empty($scope) && !empty($responsetype) && !empty($clientid) &&
      !empty($redirecturi) && !empty($loginhint) &&
      !empty($nonce) && !empty($SESSION->lti_message_hint);

if (!$ok) {
    $error = 'invalid_request';
}
if ($ok && ($scope !== 'openid')) {
    $ok = false;
    $error = 'invalid_scope';
}
if ($ok && ($responsetype !== 'id_token')) {
    $ok = false;
    $error = 'unsupported_response_type';
}
if ($ok) {
    list($courseid, $typeid, $id, $titleb64, $textb64) = explode(',', $SESSION->lti_message_hint, 5);
    $ok = ($id !== $ltimessagehint);
    if (!$ok) {
        $error = 'invalid_request';
    } else {
        $config = lti_get_type_type_config($typeid);
        $ok = ($clientid === $config->lti_clientid);
        if (!$ok) {
            $error = 'unauthorized_client';
        }
    }
}
if ($ok && ($loginhint !== $USER->id)) {
    $ok = false;
    $error = 'access_denied';
}
if ($ok) {
    $uris = array_map("trim", explode("\n", $config->lti_redirectionuris));
    $ok = in_array($redirecturi, $uris);
    if (!$ok) {
        $error = 'invalid_request';
        $desc = 'Unregistered redirect_uri ' . $redirecturi;
    }
}
if ($ok) {
    if (isset($responsemode)) {
        $ok = ($responsemode === 'form_post');
        if (!$ok) {
            $error = 'invalid_request';
            $desc = 'Invalid response_mode';
        }
    } else {
        $ok = false;
        $error = 'invalid_request';
        $desc = 'Missing response_mode';
    }
}
if ($ok && !empty($prompt) && ($prompt !== 'none')) {
    $ok = false;
    $error = 'invalid_request';
    $desc = 'Invalid prompt';
}

if ($ok) {
    $course = $DB->get_record('course', array('id' => $courseid), '*', MUST_EXIST);
    if ($id) {
        $cm = get_coursemodule_from_id('lti', $id, 0, false, MUST_EXIST);
        $context = context_module::instance($cm->id);
        require_login($course, true, $cm);
        require_capability('mod/lti:view', $context);
        $lti = $DB->get_record('lti', array('id' => $cm->instance), '*', MUST_EXIST);
        list($endpoint, $params) = lti_get_launch_data($lti, $nonce);
    } else {
        require_login($course);
        $context = context_course::instance($courseid);
        require_capability('moodle/course:manageactivities', $context);
        require_capability('mod/lti:addcoursetool', $context);
        // Set the return URL. We send the launch container along to help us avoid frames-within-frames when the user returns.
        $returnurlparams = [
            'course' => $courseid,
            'id' => $typeid,
            'sesskey' => sesskey()
        ];
        $returnurl = new \moodle_url('/mod/lti/contentitem_return.php', $returnurlparams);
        // Prepare the request.
        $title = base64_decode($titleb64);
        $text = base64_decode($textb64);
        $request = lti_build_content_item_selection_request($typeid, $course, $returnurl, $title, $text,
                                                            [], [], false, false, false, false, false, $nonce);
        $endpoint = $request->url;
        $params = $request->params;
    }
} else {
    $params['error'] = $error;
    if (!empty($desc)) {
        $params['error_description'] = $desc;
    }
}
if (isset($state)) {
    $params['state'] = $state;
}
unset($SESSION->lti_message_hint);
$r = '<form action="' . $redirecturi . "\" name=\"ltiAuthForm\" id=\"ltiAuthForm\" " .
     "method=\"post\" enctype=\"application/x-www-form-urlencoded\">\n";
if (!empty($params)) {
    foreach ($params as $key => $value) {
        $key = htmlspecialchars($key);
        $value = htmlspecialchars($value);
        $r .= "  <input type=\"hidden\" name=\"{$key}\" value=\"{$value}\"/>\n";
    }
}
$r .= "</form>\n";
$r .= "<script type=\"text/javascript\">\n" .
    "//<![CDATA[\n" .
    "document.ltiAuthForm.submit();\n" .
    "//]]>\n" .
    "</script>\n";
echo $r;