Facetapi Tokens: Attempt to initialize tokens based on current active searchers.

Hi guys,

I've been working recently with the Meta tags module along with a setup on search_api, views, facetapi, search_api_db, etc... with a standard page setup and was wondering about the possibility of integrating the tokens provided by facetapi with the Meta tags views module (extending Meta tags).
The idea here is to be able to display values provided by the facetapi tokens in the meta tags and other head markup elements on search enabled pages.

After looking into Facetapi Bonus, which brought me to Page Title, I came up with a patch that seems to have got the maintainer's attention, requesting further documentation (See: #1830952: Introduce two new hooks to allow token types and patterns alteration).
In short, it's about introducing 2 new hooks in metatag module's api, to allow exposing tokens to metatag patterns and altering patterns before replacement.

So when I started pushing my investigations a bit further, I found out that the hook for pattern replacement, for facetapi, could potentially be avoided if proper replacement of tokens could take place in their own modules.
Which brought me to look further deeper into facetapi.tokens.inc to try to figure out why the following exposed tokens in metatag wouldn't get any value:

• facetapi_results
• facetapi_active
• facetapi_facet

It seems the reason why, for example [facetapi_active:active-value], or any other value is not replaced is because no value is passed to the $data array parameter of the facetapi_tokens function (See facetapi-7.x-1.x-dev facetapi.tokens.inc, lines 127, 171, 204), leaving the following choices:

• Working with replacements in metatag, implement hook_metatag_pattern_alter in facetapi_bonus for example, based on what already exists for page_title integration (very much a copy/paste with few adjustments).
  That's what has been suggested previously and one of the reasons for this post: #1830952: Introduce two new hooks to allow token types and patterns alteration.
• Another approach would be to try to solve the problem from the facetapi_tokens side. For example, by providing fallback replacements in case of absence of the right $data parameters (see ifs (!empty($data['....'])), lines 127, 171, 204) and this is the object of my request here.

I was wondering if it would be possible to add some kind of fallback or attempt to initialize the correct variables, based on the searchers $searchers = facetapi_get_active_searchers which would allow loading $adapter which is required for entering in any of the replacements calculation code.

We could for example add a function that would initialize the $data variable:
function facetapi_tokens_defaults($type, $data = array())

to attempt to initialize token data based on active searchers (like it's done in facetapi_bonus.page_title.inc).
facetapi_tokens_defaults would return an initialized $data array variable if any active searcher is found.
This function would be then called at the top of facetapi_tokens which would provide a default argument if nothing is passed through $data.

Currently, the function responsible for putting together token replacements based on patterns is: facetapi_tokens.
If an empty $data array is passed no value is evaluated so we could could perhaps add the following lines at the top of the function:

  // Attempt to initialize tokens based on current active searchers.
  if (empty($data[$type])) {
    $data = facetapi_tokens_defaults($type, $data);
  }

I would assume it would make sense for all the facetapi_tokens replacement values for the results returned for facetapi_results, facetapi_active, and since in a default case facetapi_facet could return information on the last selected facet (same facet as facetapi_active) with different info/properties.

If $data is provided then nothing would change from the current behavior and if the facetapi_tokens_defaults returns FALSE, then it means no searcher was found (which would be the correct result on a node list view page, for example, since it wouldn't be a search enabled page).

I have already taken a quick try and came up with the attached patch against the 1.x branch [facetapi-7.x-1.2+10-dev (2012-11-02)].
[File attached as: facetapi-initialize-default-tokens-active-searchers-0.patch]
I would greatly appreciate if you could take a bit of time to take a look at the patch and give me your feedback on this feature request.

Please let me know if you would have any questions on any points/code/aspects mentioned in this ticket or patch, I would surely be glad to provide more information.

Any testing, comments or feedback would be highly appreciated.
Thanks in advance.