Jyxo\Mail\Parser::getDefaultPid PHP Method

    private function getDefaultPid(string $mimeType = 'text/html', $attempt = 1) : string
    {
        $mimeCheck = 'text/html' == $mimeType ? ['text/html', 'text/plain'] : ['text/plain', 'text/html'];
        // Tries to find text/html or text/plain in main parts
        foreach ($mimeCheck as $mime) {
            $parts = array_keys($this->structure['ftype'], $mime);
            foreach ($parts as $part) {
                if ('inline' == $this->structure['disposition'][$part] && false === strpos($this->structure['pid'][$part], '.')) {
                    return $this->structure['pid'][$part];
                }
            }
        }
        // There was nothing found in the main parts, try multipart/alternative or multipart/report
        $partLevel = 1;
        $pidLength = 1;
        foreach ($this->structure['pid'] as $partNo => $pid) {
            if ($pid === null) {
                continue;
            }
            $level = count(explode('.', $pid));
            if (!isset($multipartPid)) {
                if (1 === $level && isset($this->structure['ftype'][$partNo]) && $this->isPartMultipart($partNo, 'related')) {
                    $partLevel = 2;
                    $pidLength = 3;
                    continue;
                }
                if ($level == $partLevel && isset($this->structure['ftype'][$partNo]) && ($this->isPartMultipart($partNo, 'alternative') || $this->isPartMultipart($partNo, 'report') || $this->isPartMultipart($partNo, 'mixed'))) {
                    $multipartPid = $pid;
                    continue;
                }
            }
            if (isset($multipartPid) && $level == $partLevel + 1 && $this->structure['ftype'][$partNo] == $mimeType && $multipartPid == substr($pid, 0, $pidLength)) {
                return $pid;
            }
        }
        // Nothing was found, try next possible type
        if (1 === $attempt) {
            if ('text/html' == $mimeType) {
                return $this->getDefaultPid('text/plain', 2);
            } else {
                return $this->getDefaultPid('text/html', 2);
            }
        } else {
            // There should be a default part found in every mail; this is because of spams that are often in wrong format
            return '1';
        }
    }