feature (standalone gallery): continous check for new pictures

Adjustments by Andreas Blaesius:
- eslint fixes
- adjustments to work on latest Photobooth
- slightly adjust commit message

Change-Id: I58320492085549ad2975a4a10021567edfb02fc9

gallery.php

@@ -3,6 +3,16 @@
 require_once('lib/config.php');
 require_once('lib/db.php');
 
+// Check if there is a request for the status of the database
+if (isset($_GET['status'])){
+	// Request for DB-Status,
+	// Currently reports back the DB-Size to give the Client the ability
+	// to detect changes
+	$resp = array('dbsize'=>getDBSize());
+	exit(json_encode($resp));
+
+}
+
 $images = getImagesFromDB();
 $imagelist = ($config['newest_first'] === true) ? array_reverse($images) : $images;
 ?>
@@ -91,6 +101,7 @@
 	<script type="text/javascript" src="resources/js/theme.js"></script>
 	<script type="text/javascript" src="resources/js/core.js"></script>
 	<script type="text/javascript" src="resources/js/gallery.js"></script>
+	<script type="text/javascript" src="resources/js/gallery_updatecheck.js"></script>
 	<script src="node_modules/@andreasremdt/simple-translator/dist/umd/translator.min.js"></script>
 	<script type="text/javascript" src="resources/js/i18n.js"></script>
 </body>

lib/db.php

@@ -33,3 +33,10 @@ function isImageInDB($filename) {
 
 	return in_array($filename, $images);
 }
+
+function getDBSize(){
+	if(file_exists(DB_FILE)){
+		return (int) filesize(DB_FILE);
+	}
+	return 0;
+}

src/js/gallery_updatecheck.js

@@ -0,0 +1,47 @@
+/* globals photoBooth */
+/*
+ * This script checks for new pictures in regular intervals.
+ * If changes are detected, the page will automatically be reloaded.
+ *
+ * Needs:
+ * jQuery
+ * photoBooth Javascript
+ *
+ * Remarks:
+ * - Not made for highly demanded pages (as pages is requested regulary
+ *   and would pile up in high load with thausend of users)
+ * - Instead of reloading, adding the pictures directly would be an
+ *   improvement, but would need further changes in gallery-templates
+ *
+ */
+
+//Size of the DB - is used to determine changes
+let lastDBSize = -1;
+// Interval, the pages is checked (/ms)
+const interval = 1000 * 5;
+//URL to request for changes
+const ajaxurl = 'gallery.php/?status';
+
+/*
+ * This function will be called if there are new pictures
+ */
+
+function dbUpdated() {
+    console.log('DB is updated - refreshing');
+    //location.reload(true); //Alternative
+    photoBooth.reloadPage();
+}
+
+const checkForUpdates = function () {
+    $.getJSON({
+        url: ajaxurl,
+        success: function (result) {
+            const currentDBSize = result.dbsize;
+            if (lastDBSize != currentDBSize && lastDBSize != -1) {
+                dbUpdated();
+            }
+            lastDBSize = currentDBSize;
+        }
+    });
+};
+setInterval(checkForUpdates, interval);