MediaWiki:Access.js

// License: GPL

var controller_item_id = 96;

var wbEStruct = {
		instanceOfRelations: 'claims.P3', // location of P3 relations in wbEntity
		IDPropLoc:	'mainsnak.datavalue.value', // location of ID properties in related entity
		IDName:		'numeric-id' // ID property name which checked 
				}; 

// check if we are on a page of a loaded Entity
if ( typeof mw.config.values.wbEntity !=  "undefined" ) {
	console.log( "entity is defined" )
	// get wbEntity as json
	var obj = JSON.parse ( mw.config.values.wbEntity );
	console.log( "parsed object", obj )
	// check if we have P3 relations and iterate through
	if ( typeof check( obj, wbEStruct["instanceOfRelations"] ) != "undefined" ) {
		console.log( "object has 'instance of' relations" );
		for( var i = 0; i < dive( obj, wbEStruct["instanceOfRelations"] ).length; i++ ) {
			console.log("dived in");		
			// check if we have controller id constructed from wbEntity 
			if( dive( dive( obj, wbEStruct["instanceOfRelations"])[i] , wbEStruct["IDPropLoc"])[wbEStruct["IDName"]] === controller_item_id ) {
				console.log( "it's a controller" )		
				var $title2 = $( '.wikibase-title' ),
				qId = $title2.find( '.wikibase-title-id' ).text().replace( /[()]/g, '' );
				var api = new mw.Api();
				api.get( {
				    action: 'expandtemplates',
				    text: '{{MailtoAccess|'+qId+'}}'
				} ).done( function ( data ) {
				    mw.notify( $('<a href="'+data.expandtemplates["*"]+'"> Do a GDPR SAR to this controller!</a>') , { autoHide: false } );
				} );
			}
		}
	}
	// Else let's do nothing;
}

// helper function for diving into a part of array
function indexinterpolate(obj,i) { return  (obj[i] != undefined) ? obj[i] : obj}; 

// helper function for checking a part of an array exists
function indexcheck(obj,i) {  return  (obj[i] != undefined) ? obj[i] : undefined };

// dive selects matrix.a.b.c.d from the array called matrix and 'a.b.c.d' as string
// if a.b.c.d does not exists, it returns the substructure until the substructure exists, if d does not exist, it returns matrix.a.b.c e.g.

function dive(array, read){
	return read.split('.').reduce(indexinterpolate, array);
}

function check(array, read){
        return read.split('.').reduce(indexcheck, array);
}