analytics_helper.php

<?php

use Config\Services;
use Podlibre\Ipcat\IpDb;
use GeoIp2\Database\Reader;
use Opawg\UserAgentsPhp\UserAgents;
use Config\Database;
use WhichBrowser\Parser;
/**
 * @copyright  2020 Podlibre
 * @license    https://www.gnu.org/licenses/agpl-3.0.en.html AGPL3
 * @link       https://castopod.org/
 */

use CodeIgniter\Router\Exceptions\RouterException;

if (!function_exists('base64_url_encode')) {
    /**
     * Encode Base64 for URLs
     */
    function base64_url_encode(string $input): string
    {
        return strtr(base64_encode($input), '+/=', '._-');
    }
}

if (!function_exists('base64_url_decode')) {
    /**
     * Decode Base64 from URL
     */
    function base64_url_decode(string $input): string
    {
        return base64_decode(strtr($input, '._-', '+/='));
    }
}

if (!function_exists('generate_episode_analytics_url')) {
    /**
     * Builds the episode analytics url that redirects to the audio file url
     * after analytics hit.
     *
     * @throws RouterException
     */
    function generate_episode_analytics_url(
        int $podcastId,
        int $episodeId,
        string $audioFilePath,
        float $audioFileDuration,
        int $audioFileSize,
        int $audioFileHeaderSize,
        \CodeIgniter\I18n\Time $publicationDate
    ): string {
        return url_to(
            'episode-analytics-hit',
            base64_url_encode(
                pack(
                    'I*',
                    $podcastId,
                    $episodeId,
                    // bytes_threshold: number of bytes that must be downloaded for an episode to be counted in download analytics
                    // - if file is shorter than 60sec, then it's audio_file_size
                    // - if file is longer than 60 seconds then it's audio_file_header_size + 60 seconds
                    $audioFileDuration <= 60
                        ? $audioFileSize
                        : $audioFileHeaderSize +
                            floor(
                                (($audioFileSize - $audioFileHeaderSize) /
                                    $audioFileDuration) *
                                    60,
                            ),
                    $audioFileSize,
                    $audioFileDuration,
                    strtotime($publicationDate),
                ),
            ),
            $audioFilePath,
        );
    }
}

if (!function_exists('set_user_session_deny_list_ip')) {
    /**
     * Set user country in session variable, for analytic purposes
     */
    function set_user_session_deny_list_ip(): void
    {
        $session = Services::session();
        $session->start();

        if (!$session->has('denyListIp')) {
            $session->set(
                'denyListIp',
                IpDb::find($_SERVER['REMOTE_ADDR']) != null,
            );
        }
    }
}

if (!function_exists('set_user_session_location')) {
    /**
     * Set user country in session variable, for analytic purposes
     */
    function set_user_session_location(): void
    {
        $session = Services::session();
        $session->start();

        $location = [
            'countryCode' => 'N/A',
            'regionCode' => 'N/A',
            'latitude' => null,
            'longitude' => null,
        ];

        // Finds location:
        if (!$session->has('location')) {
            try {
                $cityReader = new Reader(
                    WRITEPATH . 'uploads/GeoLite2-City/GeoLite2-City.mmdb',
                );
                $city = $cityReader->city($_SERVER['REMOTE_ADDR']);

                $location = [
                    'countryCode' => $city->country->isoCode === null
                        ? 'N/A'
                        : $city->country->isoCode,
                    'regionCode' => $city->subdivisions[0]->isoCode === null
                        ? 'N/A'
                        : $city->subdivisions[0]->isoCode,
                    'latitude' => round($city->location->latitude, 3),
                    'longitude' => round($city->location->longitude, 3),
                ];
                // If things go wrong the show must go on and the user must be able to download the file
            } catch (Exception) {
            }
            $session->set('location', $location);
        }
    }
}

if (!function_exists('set_user_session_player')) {
    /**
     * Set user player in session variable, for analytic purposes
     */
    function set_user_session_player(): void
    {
        $session = Services::session();
        $session->start();

        if (!$session->has('player')) {
            $playerFound = null;
            $userAgent = $_SERVER['HTTP_USER_AGENT'];

            try {
                $playerFound = UserAgents::find($userAgent);
                // If things go wrong the show must go on and the user must be able to download the file
            } catch (Exception) {
            }
            if ($playerFound) {
                $session->set('player', $playerFound);
            } else {
                $session->set('player', [
                    'app' => '- unknown -',
                    'device' => '',
                    'os' => '',
                    'bot' => 0,
                ]);
                // Add to unknown list
                try {
                    $db = Database::connect();
                    $procedureNameAnalyticsUnknownUseragents = $db->prefixTable(
                        'analytics_unknown_useragents',
                    );
                    $db->query(
                        "CALL {$procedureNameAnalyticsUnknownUseragents}(?)",
                        [$userAgent],
                    );
                    // If things go wrong the show must go on and the user must be able to download the file
                } catch (Exception) {
                }
            }
        }
    }
}

if (!function_exists('set_user_session_browser')) {
    /**
     * Set user browser in session variable, for analytic purposes
     */
    function set_user_session_browser(): void
    {
        $session = Services::session();
        $session->start();

        if (!$session->has('browser')) {
            $browserName = '- Other -';
            try {
                $whichbrowser = new Parser(getallheaders());
                $browserName = $whichbrowser->browser->name;
            } catch (Exception) {
                $browserName = '- Could not get browser name -';
            }
            if ($browserName == null) {
                $browserName = '- Could not get browser name -';
            }
            $session->set('browser', $browserName);
        }
    }
}

if (!function_exists('set_user_session_referer')) {
    /**
     * Set user referer in session variable, for analytic purposes
     */
    function set_user_session_referer(): void
    {
        $session = Services::session();
        $session->start();

        $newreferer = isset($_SERVER['HTTP_REFERER'])
            ? $_SERVER['HTTP_REFERER']
            : '- Direct -';
        $newreferer =
            parse_url($newreferer, PHP_URL_HOST) ===
            parse_url(current_url(false), PHP_URL_HOST)
                ? '- Direct -'
                : $newreferer;
        if (!$session->has('referer') || $newreferer != '- Direct -') {
            $session->set('referer', $newreferer);
        }
    }
}

if (!function_exists('set_user_session_entry_page')) {
    /**
     * Set user entry page in session variable, for analytic purposes
     */
    function set_user_session_entry_page(): void
    {
        $session = Services::session();
        $session->start();

        $entryPage = $_SERVER['REQUEST_URI'];
        if (!$session->has('entryPage')) {
            $session->set('entryPage', $entryPage);
        }
    }
}

if (!function_exists('podcast_hit')) {
    /**
     * Counting podcast episode downloads for analytic purposes
     * ✅ No IP address is ever stored on the server.
     * ✅ Only aggregate data is stored in the database.
     * We follow IAB Podcast Measurement Technical Guidelines Version 2.0:
     *   https://iabtechlab.com/standards/podcast-measurement-guidelines/
     *   https://iabtechlab.com/wp-content/uploads/2017/12/Podcast_Measurement_v2-Dec-20-2017.pdf
     *   ✅ Rolling 24-hour window
     *   ✅ Castopod does not do pre-load
     *   ✅ IP deny list https://github.com/client9/ipcat
     *   ✅ User-agent Filtering https://github.com/opawg/user-agents
     *   ✅ RSS User-agent https://github.com/opawg/podcast-rss-useragents
     *   ✅ Ignores 2 bytes range "Range: 0-1"  (performed by official Apple iOS Podcast app)
     *   ✅ In case of partial content, adds up all requests to check >1mn was downloaded
     *   ✅ Identifying Uniques is done with a combination of IP Address and User Agent
     * @param integer $podcastId The podcast ID
     * @param integer $episodeId The Episode ID
     * @param integer $bytesThreshold The minimum total number of bytes that must be downloaded so that an episode is counted (>1mn)
     * @param integer $fileSize The podcast complete file size
     * @param integer $duration The episode duration in seconds
     * @param int $publicationTime The episode's publication time as a UNIX timestamp
     * @param string $serviceName The name of the service that had fetched the RSS feed
     */
    function podcast_hit(
        int $podcastId,
        int $episodeId,
        int $bytesThreshold,
        int $fileSize,
        int $duration,
        int $publicationTime,
        string $serviceName
    ): void {
        $session = Services::session();
        $session->start();

        // We try to count (but if things went wrong the show should go on and the user should be able to download the file):
        try {
            // If the user IP is denied it's probably a bot:
            if ($session->get('denyListIp')) {
                $session->get('player')['bot'] = true;
            }
            //We get the HTTP header field `Range`:
            $httpRange = isset($_SERVER['HTTP_RANGE'])
                ? $_SERVER['HTTP_RANGE']
                : null;

            // We create a sha1 hash for this IP_Address+User_Agent+Episode_ID (used to count only once multiple episode downloads):
            $episodeHashId =
                '_IpUaEp_' .
                sha1(
                    $_SERVER['REMOTE_ADDR'] .
                        '_' .
                        $_SERVER['HTTP_USER_AGENT'] .
                        '_' .
                        $episodeId,
                );
            // Was this episode downloaded in the past 24h:
            $downloadedBytes = cache($episodeHashId);
            // Rolling window is 24 hours (86400 seconds):
            $rollingTTL = 86400;
            if ($downloadedBytes) {
                // In case it was already downloaded, TTL should be adjusted (rolling window is 24h since 1st download):
                $rollingTTL =
                    cache()->getMetadata($episodeHashId)['expire'] - time();
            } else {
                // If it was never downloaded that means that zero byte were downloaded:
                $downloadedBytes = 0;
            }
            // If the number of downloaded bytes was previously below the 1mn threshold we go on:
            // (Otherwise it means that this was already counted, therefore we don't do anything)
            if ($downloadedBytes < $bytesThreshold) {
                // If HTTP_RANGE is null we are downloading the complete file:
                if (!$httpRange) {
                    $downloadedBytes = $fileSize;
                } elseif ($httpRange != 'bytes=0-1') {
                    // [0-1] bytes range requests are used (by Apple) to check that file exists and that 206 partial content is working.
                    // We don't count these requests.
                    // We calculate how many bytes are being downloaded based on HTTP_RANGE values:
                    $ranges = explode(',', substr($httpRange, 6));
                    foreach ($ranges as $range) {
                        $parts = explode('-', $range);
                        $downloadedBytes += array_key_exists(1, $parts)
                            ? $fileSize
                            : (int) $parts[1] -
                                (array_key_exists(0, $parts) ? 0 : (int) $parts[0]);
                    }
                }
                // We save the number of downloaded bytes for this user and this episode:
                cache()->save($episodeHashId, $downloadedBytes, $rollingTTL);

                // If more that 1mn was downloaded, that's a hit, we send that to the database:
                if ($downloadedBytes >= $bytesThreshold) {
                    $db = Database::connect();
                    $procedureName = $db->prefixTable('analytics_podcasts');

                    $age = intdiv(time() - $publicationTime, 86400);

                    // We create a sha1 hash for this IP_Address+User_Agent+Podcast_ID (used to count unique listeners):
                    $listenerHashId =
                        '_IpUaPo_' .
                        sha1(
                            $_SERVER['REMOTE_ADDR'] .
                                '_' .
                                $_SERVER['HTTP_USER_AGENT'] .
                                '_' .
                                $podcastId,
                        );
                    $newListener = 1;
                    // Has this listener already downloaded an episode today:
                    $downloadsByUser = cache($listenerHashId);
                    // We add one download
                    if ($downloadsByUser) {
                        $newListener = 0;
                        ++$downloadsByUser;
                    } else {
                        $downloadsByUser = 1;
                    }
                    // Listener count is calculated from 00h00 to 23h59:
                    $midnightTTL = strtotime('tomorrow') - time();
                    // We save the download count for this user until midnight:
                    cache()->save(
                        $listenerHashId,
                        $downloadsByUser,
                        $midnightTTL,
                    );

                    $db->query(
                        "CALL {$procedureName}(?,?,?,?,?,?,?,?,?,?,?,?,?,?,?);",
                        [
                            $podcastId,
                            $episodeId,
                            $session->get('location')['countryCode'],
                            $session->get('location')['regionCode'],
                            $session->get('location')['latitude'],
                            $session->get('location')['longitude'],
                            $serviceName,
                            $session->get('player')['app'],
                            $session->get('player')['device'],
                            $session->get('player')['os'],
                            $session->get('player')['bot'],
                            $fileSize,
                            $duration,
                            $age,
                            $newListener,
                        ],
                    );
                }
            }
        } catch (Exception $exception) {
            // If things go wrong the show must go on and the user must be able to download the file
            log_message('critical', $exception);
        }
    }
}