Show notification on new changes to pre-empt edit conflicts

Solves #1418.

modules/friendlytag.js

@@ -289,6 +289,7 @@ Twinkle.tag.callback = function friendlytagCallback() {
 	var result = form.render();
 	Window.setContent(result);
 	Window.display();
+	Twinkle.notifyOnChanges();
 
 	// for quick filter:
 	$allCheckboxDivs = $(result).find('[name$=tags]').parent();

modules/twinkleprod.js

@@ -109,6 +109,7 @@ Twinkle.prod.callback = function twinkleprodCallback() {
 	evt.initEvent('change', true, true);
 	result.prodtype[0].dispatchEvent(evt);
 
+	Twinkle.notifyOnChanges();
 };
 
 

modules/twinklespeedy.js

@@ -225,6 +225,8 @@ Twinkle.speedy.initDialog = function twinklespeedyInitDialog(callbackfunc) {
 
 	// Check for prior deletions.  Just once, upon init
 	Twinkle.speedy.callback.priorDeletionCount();
+
+	Twinkle.notifyOnChanges();
 };
 
 Twinkle.speedy.callback.modeChanged = function twinklespeedyCallbackModeChanged(form) {

modules/twinklexfd.js

@@ -221,6 +221,7 @@ Twinkle.xfd.callback = function twinklexfdCallback() {
 	var result = form.render();
 	Window.setContent(result);
 	Window.display();
+	Twinkle.notifyOnChanges();
 	result.previewer = new Morebits.wiki.preview($(result).find('div#twinklexfd-previewbox').last()[0]);
 
 	// We must init the controls

twinkle.js

@@ -467,6 +467,38 @@ Twinkle.makeFindSourcesDiv = function makeSourcesDiv(divID) {
 	}
 };
 
+Twinkle.notifyOnChanges = function pollChanges() {
+	let interval = setInterval(function () {
+		let api = new mw.Api();
+		api.get({
+			action: 'query',
+			format: 'json',
+			prop: 'revisions',
+			titles: Morebits.pageNameNorm,
+			formatversion: '2',
+			rvprop: 'ids',
+			rvslots: 'main',
+			rvstartid: mw.config.get('wgCurRevisionId') + 1,
+			rvdir: 'newer'
+		}).then(function (response) {
+			if (response.query.pages[0].missing) {
+				mw.notify('[Twinkle] This page has just been deleted!', {
+					type: 'error',
+					autoHide: false
+				});
+				clearInterval(interval);
+			}
+			if (response.query.pages[0].revisions) {
+				mw.notify('[Twinkle] Page has been edited in the meantime. Reload to see latest changes.', {
+					type: 'warn',
+					autoHide: false
+				});
+				clearInterval(interval);
+			}
+		});
+	}, 5000);
+};
+
 /** Twinkle-specific utility functions shared by multiple modules */
 // Used in batch, unlink, and deprod to sort pages by namespace, as
 // json formatversion=2 sorts by pageid instead (#1251)