add support for creating rooms

Fixes #81

lib/helpers/extensions/create_room.dart

@@ -0,0 +1,111 @@
+import "dart:async";
+
+import "package:collection/collection.dart";
+import "package:flutter_riverpod/flutter_riverpod.dart";
+import "package:material_ui/material_ui.dart";
+import "package:nexus/controllers/client.dart";
+import "package:nexus/controllers/rooms.dart";
+import "package:nexus/controllers/sidebar_page.dart";
+import "package:nexus/controllers/spaces.dart";
+import "package:nexus/helpers/extensions/focus_room.dart";
+import "package:nexus/helpers/extensions/get_all_child_rooms.dart";
+import "package:nexus/helpers/extensions/with_progress_snackbar.dart";
+import "package:nexus/models/requests/create_room.dart";
+
+extension CreateRoom on BuildContext {
+  /// Creates a room, showing progress and errors in snackbars, and opens it
+  /// once it has synced. [request] may be a future, so any lookups needed to
+  /// build it happen while the progress snackbar is shown.
+  ///
+  /// Returns the created room's ID, or null if creating it failed.
+  Future<String?> createRoom(
+    CreateRoomRequest request, {
+    required String name,
+  }) async {
+    final container = ProviderScope.containerOf(this);
+    final messenger = ScaffoldMessenger.of(this);
+
+    final result = await withProgressSnackbar("Creating $name...", () async {
+      final roomId = await container
+          .read(ClientController.provider.notifier)
+          .createRoom(request);
+
+      // Wait for the room to show up in the room list (under DMs, if it's
+      // one) before opening it.
+      final synced = Completer<bool>();
+      final subscription = container.listen(
+        SpacesController.provider.select(
+          (async) =>
+              async.value?.any(
+                (space) =>
+                    space.id == roomId ||
+                    ((!request.isDirect || space.id == "dms") &&
+                        space.allChildRooms.any(
+                          (room) => room.metadata?.id == roomId,
+                        )),
+              ) ??
+              false,
+        ),
+        (_, found) {
+          if (found && !synced.isCompleted) synced.complete(true);
+        },
+        fireImmediately: true,
+      );
+
+      return (
+        roomId,
+        await synced.future
+            .timeout(const .new(seconds: 15), onTimeout: () => false)
+            .whenComplete(subscription.close),
+      );
+    });
+    if (result == null) return null;
+
+    final (roomId, synced) = result;
+    if (synced && await container.focusRoom(roomId)) {
+      container.read(SidebarPageController.provider.notifier).set(.rooms);
+    } else {
+      messenger.showSnackBar(
+        .new(
+          content: Text("Created $name, but it hasn't finished syncing yet."),
+        ),
+      );
+    }
+
+    return roomId;
+  }
+
+  /// Opens the existing DM with [userId], or creates one if there isn't one.
+  Future<void> startDirectMessage(
+    String userId, {
+    required String name,
+    bool encrypted = true,
+    String? inviteReason,
+  }) async {
+    final container = ProviderScope.containerOf(this);
+    final existing = container
+        .read(RoomsController.provider)
+        .values
+        .firstWhereOrNull((room) => room.metadata?.dmUserId == userId)
+        ?.metadata
+        ?.id;
+
+    if (existing != null) {
+      if (await container.focusRoom(existing)) {
+        container.read(SidebarPageController.provider.notifier).set(.rooms);
+      }
+      return;
+    }
+
+    await createRoom(
+      .new(
+        isDirect: true,
+        preset: .trustedPrivateChat,
+        invite: .new([userId]),
+        inviteReason: inviteReason,
+        initialState: encrypted ? .new([.encryption]) : const .empty(),
+      ),
+      name: "a DM with $name",
+    );
+  }
+}