add push rule settings

Fixes #126

lib/widgets/settings/keyword_field.dart

@@ -0,0 +1,70 @@
+import "package:flutter_hooks/flutter_hooks.dart";
+import "package:hooks_riverpod/hooks_riverpod.dart";
+import "package:material_ui/material_ui.dart";
+import "package:nexus/controllers/account_data.dart";
+import "package:nexus/helpers/hooks/saving.dart";
+import "package:nexus/main.dart";
+
+/// Adds a keyword, which notifies with a highlight and sound for messages
+/// containing it.
+class const KeywordField({super.key}) extends HookConsumerWidget {
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    final saving = Saving.use();
+    final controller = useTextEditingController();
+    final keyword = useValueListenable(controller).text.trim();
+    final exists = ref.watch(
+      AccountDataController.provider.select(
+        (data) => data.pushRules.global.find(.content, keyword) != null,
+      ),
+    );
+
+    // Keywords are their rules' IDs, which can't be like these
+    final error = keyword.startsWith(".")
+        ? "Can't start with a ."
+        : keyword.contains(RegExp(r"[/\\]"))
+        ? r"Can't contain / or \"
+        : exists
+        ? "Already a keyword"
+        : null;
+    final canAdd = keyword.isNotEmpty && error == null && !saving.active;
+
+    void add() {
+      if (!canAdd) return;
+      saving
+          .run(() async {
+            await ref
+                .read(AccountDataController.provider.notifier)
+                .savePushRule(
+                  .content,
+                  .new(
+                    ruleId: keyword,
+                    pattern: keyword,
+                    actions: .highlightWithSound,
+                  ),
+                );
+            if (context.mounted) controller.clear();
+          })
+          .onError(showError);
+    }
+
+    return Padding(
+      padding: .symmetric(horizontal: 16),
+      child: TextField(
+        controller: controller,
+        enabled: !saving.active,
+        onSubmitted: (_) => add(),
+        decoration: .new(
+          labelText: "New keyword",
+          helperText: "Matches whole words. * matches anything, and ? matches one character.",
+          errorText: error,
+          suffixIcon: IconButton(
+            tooltip: "Add keyword",
+            icon: Icon(Icons.add),
+            onPressed: canAdd ? add : null,
+          ),
+        ),
+      ),
+    );
+  }
+}