Use best first creator for OpenURL author, not just first position

This also fixes Google Scholar Search lookup to use an author not in first creator
position [1].

[1] https://forums.zotero.org/discussion/58384/

chrome/content/zotero/xpcom/data/items.js

@@ -955,6 +955,30 @@ Zotero.Items = function() {
 	});
 	
 	
+	/**
+	 * Given API JSON for an item, return the best first creator, regardless of creator order
+	 *
+	 * @return {Object|false} - Creator in API JSON format, or false
+	 */
+	this.getFirstCreatorFromJSON = function (json) {
+		var primaryCreatorType = Zotero.CreatorTypes.getName(
+			Zotero.CreatorTypes.getPrimaryIDForType(
+				Zotero.ItemTypes.getID(json.itemType)
+			)
+		);
+		let firstCreator = json.creators.find(creator => {
+			return creator.creatorType == primaryCreatorType || creator.creatorType == 'author';
+		});
+		if (!firstCreator) {
+			firstCreator = json.creators.find(creator => creator.creatorType == 'editor');
+		}
+		if (!firstCreator) {
+			return false;
+		}
+		return firstCreator;
+	};
+	
+	
 	/*
 	 * Generate SQL to retrieve firstCreator field
 	 *

chrome/content/zotero/xpcom/openurl.js

@@ -205,7 +205,7 @@ Zotero.OpenURL = new function() {
 		
 		if(item.creators && item.creators.length) {
 			// encode first author as first and last
-			var firstCreator = item.creators[0];
+			let firstCreator = Zotero.Items.getFirstCreatorFromJSON(item);
 			if(item.itemType == "patent") {
 				_mapTag(firstCreator.firstName, "invfirst");
 				_mapTag(firstCreator.lastName, "invlast");

test/tests/openurlTest.js

@@ -0,0 +1,23 @@
+"use strict";
+
+describe("Zotero.OpenURL", function() {
+	describe("#createContextObject()", function () {
+		it("should use firstCreator for author", function* () {
+			var item = createUnsavedDataObject('item');
+			item.setCreators([
+				{
+					firstName: "Aaa",
+					lastName: "Editor",
+					creatorType: 'editor'
+				},
+				{
+					firstName: "Bbb",
+					lastName: "Author",
+					creatorType: 'author'
+				}
+			]);
+			var co = Zotero.OpenURL.createContextObject(item, "1.0");
+			assert.include(co, '&rft.aufirst=Bbb&rft.aulast=Author&');
+		});
+	});
+});