Improve URL Previews

only show 2 by default with expand/collapse mechanism
show all hashes again, but dedup requests
clean up hide mechanism, instead of one `x` per preview have one per group

src/components/views/rooms/LinkPreviewGroup.tsx

@@ -0,0 +1,76 @@
+/*
+Copyright 2021 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.
+*/
+
+import React, { useEffect } from "react";
+import { MatrixEvent } from "matrix-js-sdk/src/models/event";
+
+import { useStateToggle } from "../../../hooks/useStateToggle";
+import LinkPreviewWidget from "./LinkPreviewWidget";
+import AccessibleButton from "../elements/AccessibleButton";
+import { _t } from "../../../languageHandler";
+
+const INITIAL_NUM_PREVIEWS = 2;
+
+interface IProps {
+    links: string[]; // the URLs to be previewed
+    mxEvent: MatrixEvent; // the Event associated with the preview
+    onCancelClick?(): void; // called when the preview's cancel ('hide') button is clicked
+    onHeightChanged?(): void; // called when the preview's contents has loaded
+}
+
+const LinkPreviewGroup: React.FC<IProps> = ({ links, mxEvent, onCancelClick, onHeightChanged }) => {
+    const [expanded, toggleExpanded] = useStateToggle();
+    useEffect(() => {
+        onHeightChanged();
+    }, [onHeightChanged, expanded]);
+
+    const shownLinks = expanded ? links : links.slice(0, INITIAL_NUM_PREVIEWS);
+
+    let toggleButton;
+    if (links.length > INITIAL_NUM_PREVIEWS) {
+        toggleButton = <AccessibleButton onClick={toggleExpanded}>
+            { expanded
+                ? _t("Collapse")
+                : _t("Show %(count)s other previews", { count: links.length - shownLinks.length }) }
+        </AccessibleButton>;
+    }
+
+    return <div className="mx_LinkPreviewGroup">
+        { shownLinks.map((link, i) => (
+            <LinkPreviewWidget key={link} link={link} mxEvent={mxEvent} onHeightChanged={onHeightChanged}>
+                { i === 0 ? (
+                    <AccessibleButton
+                        className="mx_LinkPreviewGroup_hide"
+                        onClick={onCancelClick}
+                        aria-label={_t("Close preview")}
+                    >
+                        <img
+                            className="mx_filterFlipColor"
+                            alt=""
+                            role="presentation"
+                            src={require("../../../../res/img/cancel.svg")}
+                            width="18"
+                            height="18"
+                        />
+                    </AccessibleButton>
+                ): undefined }
+            </LinkPreviewWidget>
+        )) }
+        { toggleButton }
+    </div>;
+};
+
+export default LinkPreviewGroup;