add copy invite button to text clients

src/utils/copy.js

@@ -0,0 +1,45 @@
+/*
+Copyright 2020 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+function selectNode(node) {
+    const selection = window.getSelection();
+    selection.removeAllRanges();
+    const range = document.createRange();
+    range.selectNode(node);
+    selection.addRange(range);
+}
+
+export function copyButton(t, getCopyText, label, classNames) {
+    return t.button({className: `${classNames} icon copy`, onClick: evt => {
+        const button = evt.target;
+        const text = getCopyText();
+        const span = document.createElement("span");
+        span.innerText = text;
+        button.parentElement.appendChild(span);
+        selectNode(span);
+        if (document.execCommand("copy")) {
+            button.innerText = "Copied!";
+            button.classList.remove("copy");
+            button.classList.add("tick");
+            setTimeout(() => {
+                button.classList.remove("tick");
+                button.classList.add("copy");
+                button.innerText = label;
+            }, 2000);
+        }
+        span.parentElement.removeChild(span);
+    }}, label);
+}