app: Add component to store enabled state of an app in kvstore

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/app.py

@@ -463,6 +463,33 @@ class Info(FollowerComponent):
             clients_module.validate(clients)
 
 
+class EnableState(LeaderComponent):
+    """A component to hold the enable state of an app using a simple flag."""
+
+    @property
+    def key(self):
+        """Return the storage key."""
+        if not self.app_id:
+            raise KeyError('Component must be added to an app before use.')
+
+        return f'{self.app_id}_enable'
+
+    def is_enabled(self):
+        """Return whether the app/component is enabled."""
+        from plinth import kvstore
+        return kvstore.get_default(self.key, False)
+
+    def enable(self):
+        """Store that the app/component is enabled."""
+        from plinth import kvstore
+        kvstore.set(self.key, True)
+
+    def disable(self):
+        """Store that the app/component is enabled."""
+        from plinth import kvstore
+        kvstore.set(self.key, False)
+
+
 def apps_init():
     """Create apps by constructing them with components."""
     from . import module_loader  # noqa  # Avoid circular import

plinth/tests/test_app.py

@@ -9,7 +9,7 @@ from unittest.mock import Mock, call, patch
 
 import pytest
 
-from plinth.app import (App, Component, FollowerComponent, Info,
+from plinth.app import (App, Component, EnableState, FollowerComponent, Info,
                         LeaderComponent, apps_init)
 
 # pylint: disable=protected-access
@@ -427,6 +427,28 @@ def test_info_clients_validation():
     Info('test-app', 3, clients=clients)
 
 
+def test_enable_state_key(app_with_components):
+    """Test getting the storage key for enable state component."""
+    component = EnableState('enable-state-1')
+    with pytest.raises(KeyError):
+        assert component.key
+
+    app_with_components.add(component)
+    assert component.key == app_with_components.app_id + '_enable'
+
+
+@pytest.mark.django_db
+def test_enable_state_enable_disable(app_with_components):
+    """Test enabling/disabling enable state component."""
+    component = EnableState('enable-state-1')
+    app_with_components.add(component)
+    assert not component.is_enabled()
+    component.enable()
+    assert component.is_enabled()
+    component.disable()
+    assert not component.is_enabled()
+
+
 class ModuleTest1:
     """A test module with an app."""