User:Alexbfree/Code:GDPRMailAccess.js

const DATA_CONTROLLER_ITEM_ID = 96;  // because Q96 is data controller"
const INSTANCE_OF_PROPERTY = 'claims.P3'; // because P3 is the property "instance of"

function generateGDPRLink(qId) {
	// make an API call to expand the letter template, using this item.
	let api = new mw.Api();
    api.get( {
			    action: 'expandtemplates',
			    text: '{{User:Alexbfree/Template:GDPRMailtoAccess|qID='+qId+'}}'
			} ).done( function ( data ) {
        var expanded = $(data.expandtemplates["*"])
    	mw.notify( expanded , { autoHide: false } ); // pop up the notification with the link
	} );
}

function isDataController() {
	let retVal = false;
	if ( typeof mw.config.values.wbEntity !=  "undefined" ) // if we are on the page of a loaded entity
	{
		let obj = JSON.parse ( mw.config.values.wbEntity );
		if ( typeof check( obj, INSTANCE_OF_PROPERTY ) != "undefined" ) // if the entity has any "instance of" claim
		{
			let instance_of_claims = dive( obj, INSTANCE_OF_PROPERTY );
			for( var i = 0; i < instance_of_claims.length; i++ ) // retrieve each 'instance of' claim to check it
			{
				let the_thing_it_is_an_instance_of = dive( instance_of_claims[i] , 'mainsnak.datavalue.value');
				if (the_thing_it_is_an_instance_of['numeric-id'] === DATA_CONTROLLER_ITEM_ID ) 
				{
				  console.log('found data controller');
				  // it's a data controller
				  retVal = true; break;
				}
			}
		}
	}
	return retVal;
}

// get the ID of the current page
var $title2 = $( '.wikibase-title' );
console.log($title2.find( '.wikibase-title-id' ).text());
var qId = $title2.find( '.wikibase-title-id' ).text().replace( /[()]/g, '' );
console.log('qid is '+qId);

if (isDataController()) {
	generateGDPRLink(qID);
}