Support spec-level permalink parsing

src/utils/permalinks/SpecPermalinkConstructor.js

@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import PermalinkConstructor from "./PermalinkConstructor";
+import PermalinkConstructor, {PermalinkParts} from "./PermalinkConstructor";
 
 export const host = "matrix.to";
 export const baseUrl = `https://${host}`;
@@ -51,4 +51,40 @@ export default class SpecPermalinkConstructor extends PermalinkConstructor {
         if (!candidates || candidates.length === 0) return '';
         return `?via=${candidates.map(c => encodeURIComponent(c)).join("&via=")}`;
     }
+
+    // Heavily inspired by/borrowed from the matrix-bot-sdk (with permission):
+    // https://github.com/turt2live/matrix-js-bot-sdk/blob/7c4665c9a25c2c8e0fe4e509f2616505b5b66a1c/src/Permalinks.ts#L33-L61
+    parsePermalink(fullUrl: string): PermalinkParts {
+        if (!fullUrl || !fullUrl.startsWith(baseUrl)) {
+            throw new Error("Does not appear to be a permalink");
+        }
+
+        const parts = fullUrl.substring(`${baseUrl}/#/`.length).split("/");
+
+        const entity = parts[0];
+        if (entity[0] === '@') {
+            // Probably a user, no further parsing needed.
+            return PermalinkParts.forUser(entity);
+        } else if (entity[0] === '+') {
+            // Probably a group, no further parsing needed.
+            return PermalinkParts.forGroup(entity);
+        } else if (entity[0] === '#' || entity[0] === '!') {
+            if (parts.length === 1) {
+                return PermalinkParts.forRoom(entity, []);
+            }
+
+            // rejoin the rest because v3 events can have slashes (annoyingly)
+            const eventIdAndQuery = parts.length > 1 ? parts.slice(1).join('/') : "";
+            const secondaryParts = eventIdAndQuery.split("?");
+
+            const eventId = secondaryParts[0];
+            const query = secondaryParts.length > 1 ? secondaryParts[1] : "";
+
+            const via = query.split("via=").filter(p => !!p);
+
+            return PermalinkParts.forEvent(entity, eventId, via);
+        } else {
+            throw new Error("Unknown entity type in permalink");
+        }
+    }
 }