add support for up2k hooks

contrib/plugins/up2k-hooks.js

@@ -0,0 +1,45 @@
+// hooks into up2k
+
+function up2k_namefilter(good_files, nil_files, bad_files, hooks) {
+    // is called when stuff is dropped into the browser,
+    // after iterating through the directory tree and discovering all files,
+    // before the upload confirmation dialogue is shown
+
+    // good_files will successfully upload
+    // nil_files are empty files and will show an alert in the final hook
+    // bad_files are unreadable and cannot be uploaded
+    var file_lists = [good_files, nil_files, bad_files];
+
+    // build a list of filenames
+    var filenames = [];
+    for (var lst of file_lists)
+        for (var ent of lst)
+            filenames.push(ent[1]);
+
+    toast.inf(5, "running database query...");
+
+    // simulate delay while passing the list to some api for checking
+    setTimeout(function () {
+
+        // only keep webm files as an example
+        var new_lists = [];
+        for (var lst of file_lists) {
+            var keep = [];
+            new_lists.push(keep);
+
+            for (var ent of lst)
+                if (/\.webm$/.test(ent[1]))
+                    keep.push(ent);
+        }
+
+        // finally, call the next hook in the chain
+        [good_files, nil_files, bad_files] = new_lists;
+        hooks[0](good_files, nil_files, bad_files, hooks.slice(1));
+
+    }, 1000);
+}
+
+// register
+up2k_hooks.push(function () {
+    up2k.gotallfiles.unshift(up2k_namefilter);
+});