Convert HTML to eZ Platform Rich Text DocBook XML format

preparerichtext.php

<?php

// This is the namespace you want to use
use EzSystems\EzPlatformRichText\eZ\FieldType\RichText\Type as RichTextFieldType;

// this would be a method in your class (you'll need to inject RichTextFieldType)
// It has some extra wrangling of input not required, but makes it moarrr robust
private function prepareRichText($inputText){
    
    if($inputText === ''){
        $inputText = '<p>&nbsp;</p>';
    }

    $tidyConfig = array(
        'show-body-only' => true,
        'output-xhtml'   => true,
        'wrap'           => -1);
    
    $inputText = tidy_parse_string($inputText, $tidyConfig);

    $inputText = str_replace(array("\r\n", "\r", "\n"), "", $inputText);

    $content = ['xml' => '<?xml version="1.0" encoding="UTF-8"?><section xmlns="http://ez.no/namespaces/ezpublish5/xhtml5/edit">'. $inputText . '</section>'];

    return $this->richTextFieldType->fromHash($content);

}

// HTML content. To see full range of options (embeds, links, etc.) it's best to see the RichTextFieldType xhtml5 input test
// fixtures here: https://github.com/ezsystems/ezplatform-richtext/tree/master/tests/lib/eZ/RichText/Converter/Xslt/_fixtures/xhtml5/edit
$htmlContent = '<p>Foo <b>Bar</b>.</p><blockquote>Bar Foo</blockquote><p>Baz Bay</p>';

// This is how you would use the helpere to populare a field in a content create struct
$contentCreateStruct->setField('body', $this->prepareRichText($htmlContent));

Thank you so much for this snippet! You saved me hours of fiddling out how to approach the conversion.
Sadly in current Ibexa DXP (4.5) this is not always working anymore.

For anybody searching for this here is my updated version. The returned DOMDocument can directly be passed to ContentStruct::setField():

    use Ibexa\GraphQL\Mutation\InputHandler\FieldType\RichText\HtmlRichTextConverter;
    
    public function htmlToRichTextXml(string $html): DOMDocument
    {
        // Clean up html.
        $html = html_entity_decode($html);
        $html = str_replace(["\r\n", "\r", "\n"], '', $html);

        // @see https://api.html-tidy.org/tidy/quickref_5.8.0.html
        $tidyConfig = [
            'markup' => false,
            'show-body-only' => true,

            'doctype' => 'strict',
            'output-xhtml' => true,

            'newline' => 'LF',
            'output-bom' => false,

            'bare' => true,
            'hide-comments' => true,

            'wrap' => 0
        ];

        $tidy = tidy_parse_string($html, $tidyConfig);
        $html = tidy_get_output($tidy);

        return $this->htmlRichTextConverter->convertToXml($html);
    }

Nice to hear you found it helpful :)