Datatable extractor causes duplicated table headers

[fabiodrg]

In some tables, the Datatable extractor fails to remove the original header before appending a new <thead>

The problem is that tables in Sigarra are not consistent from HTML point of view. Some use the tr > th elements, others use the more structural tags thead, tbody, etc.

Note: If I understand it correctly, we need to ensure the presence of a <thead> otherwise the DataTables library won't work properly. The remaining of the table is not relevant. I.e., the body of the table can either be wrapped around a tbody or be listed in multiple tr elements.

So, I think we just need to handle the following cases:

Example with <thead>

<table>
  ... // <caption>, <colgroup> can appear here
  <thead>
    <tr>
    ... // one or more table rows
  </thead>
  ... // one or multiple <tr> or <tbody> and lastly an optional <tfooter>
</table>

Interpretation: If we have a table > thead, then we don't have to do anything! The library should work just fine. We don't care about the table body structure.

Example with <tr>s only

<table>
  ... // <caption>, <colgroup> can appear here
  <tr>
    <th>...</th>
    <th>...</th>
    ...
  </tr>
</table>

Interpretation: If we happen to have table > tr > th, then we need to transform the table. We replace tr by a theader tag and that's it. To be more precise, we need to ensure that all direct childrens of the table row are table headers. Table headers can also be used for rows. I think it's enough to see if the first table row only has th childs, just to avoid iterating over all rows. I mean, does it make sense that a header appears in the middle of the table? Technically it works and browsers render it, but I can't imagine a use-case.

References:

• https://developer.mozilla.org/en-US/docs/Web/HTML/Element/table
• https://developer.mozilla.org/en-US/docs/Web/HTML/Element/thead
• https://developer.mozilla.org/en-US/docs/Web/HTML/Element/th
• https://www.datatables.net/examples/plug-ins/sorting_manual