Implement builtin handler for configuring frontend

tfw/components/frontend/__init__.py

@@ -3,3 +3,4 @@ from .frontend_proxy_handler import FrontendProxyHandler
 from .frontend_ready_handler import FrontendReadyHandler
 from .message_queue_handler import MessageQueueHandler
 from .message_sender import MessageSender
+from .frontend_config_handler import FrontendConfigHandler

tfw/components/frontend/frontend_config_handler/__init__.py

@@ -0,0 +1 @@
+from .frontend_config_handler import FrontendConfigHandler

tfw/components/frontend/frontend_config_handler/frontend_config_handler.py

@@ -0,0 +1,36 @@
+from yaml import safe_load
+
+from tfw.internals.networking import Scope
+
+
+class FrontendConfigHandler:
+    keys = ['frontend.ready']
+
+    def __init__(self, config_path):
+        self._config_path = config_path
+
+    def handle_event(self, _, connector):
+        # pylint: disable=no-self-use
+        for message in self._config_messages:
+            connector.send_message(message)
+        connector.send_message({'key': 'frontend.ready'}, scope=Scope.WEBSOCKET)
+
+    @property
+    def _config_messages(self):
+        config = safe_load(self._config_str)
+        return [
+            self._create_config_message(k, v)
+            for k, v in config.items()
+        ]
+
+    @property
+    def _config_str(self):
+        with open(self._config_path, 'r') as ifile:
+            return ifile.read()
+
+    @staticmethod
+    def _create_config_message(key, value):
+        return {
+            'key': f'frontend.{key}',
+            **value
+        }

tfw/components/frontend/frontend_config_handler/test_frontend_config_handler.py

@@ -0,0 +1,40 @@
+from textwrap import dedent
+
+from .frontend_config_handler import FrontendConfigHandler
+
+
+class MockFrontendConfigHandler(FrontendConfigHandler):
+    @property
+    def _config_str(self):
+        return dedent('''
+        cat:
+            someConfigKey: lel
+            otherStuff:    42
+        foo:
+            hey:           yaaay
+        ''')
+
+
+class MockConnector:
+    def __init__(self):
+        self.messages = []
+
+    def send_message(self, message, **_):
+        self.messages.append(message)
+
+
+def test_frontend_config_handler():
+    connector = MockConnector()
+    handler = MockFrontendConfigHandler('')
+
+    handler.handle_event({'key': 'frontend.ready'}, connector)
+    assert connector.messages[0] == {
+        'key': 'frontend.cat',
+        'someConfigKey': 'lel',
+        'otherStuff': 42
+    }
+    assert connector.messages[1] == {
+        'key': 'frontend.foo',
+        'hey': 'yaaay'
+    }
+    assert connector.messages[-1] == {'key': 'frontend.ready'}