Error at retrieving HIX value when the page content has only a video

[MizukiTemma]

Describe the Bug

HIX value cannot be retrieved when a page has only a video in its content.

Steps to Reproduce

1. Go to Testumgebung in the test system.
2. Go to the page "Integreat in Gebärdensprache (Video)"
3. See the error " HIX value could not be calculated. Please try again later."

This is locally reproducable. Copy the source code of the page and paste it in a page in the local system, you"ll see HIX benchmark API call failed: <HTTPError 400: 'Bad Request'>

Expected Behavior

No error

Actual Behavior

Error appears

Additional Information

See also #2917 If some words are added into the content, HIX value is retrieved and saved successfully.

Traceback

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[MizukiTemma]

Solution from the issue grooming: do not send the text to TextLab if the page doesn not contain real text.

[PeterNerlich]

I think we could use the combination of two conditions to determine whether we regard a page as empty, only non-textual content or content to evaluate by TextLab:

• Extract plain text – is that empty? The lxml library features HtmlElement.text_content(), a method that traverses all child nodes to extract the plain text. This is an inexpensive operation. We should trim any leading and trailing whitespace before comparing to "" for robustness.
• Do any non-text tags exist? We could walk the parsed tree ourselves and check if it contains any tags that we do not associate with text. I think it makes more sense to check for anything not expected to contain text instead of checking for a set list of specific tags like img and video, because I think the latter is much harder to make an exhaustive list. This might not hold true if we find that we already limit our content to a very small subset of possible tags during our normalization step. Tags coming to mind quickly include: div, p, br, span, i, b, em, strong, a, blockquote, ul, ol, li, mark, s, sub, sup, del, ins