Move config handling into a provider class to make testing much easier

util/config/provider.py

@@ -0,0 +1,139 @@
+import os
+import yaml
+import logging
+import json
+
+logger = logging.getLogger(__name__)
+
+def _import_yaml(config_obj, config_file):
+  with open(config_file) as f:
+    c = yaml.safe_load(f)
+    if not c:
+      logger.debug('Empty YAML config file')
+      return
+
+    if isinstance(c, str):
+      raise Exception('Invalid YAML config file: ' + str(c))
+
+    for key in c.iterkeys():
+      if key.isupper():
+        config_obj[key] = c[key]
+
+  return config_obj
+
+
+def _export_yaml(config_obj, config_file):
+  with open(config_file, 'w') as f:
+    f.write(yaml.safe_dump(config_obj, encoding='utf-8', allow_unicode=True))
+
+
+class BaseProvider(object):
+  """ A configuration provider helps to load, save, and handle config override in the application.
+  """
+
+  def update_app_config(self, app_config):
+    """ Updates the given application config object with the loaded override config. """
+    raise NotImplementedError
+
+  def get_yaml(self):
+    """ Returns the contents of the YAML config override file, or None if none. """
+    raise NotImplementedError
+
+  def save_yaml(self, config_object):
+    """ Updates the contents of the YAML config override file to those given. """
+    raise NotImplementedError
+
+  def yaml_exists(self):
+    """ Returns true if a YAML config override file exists in the config volume. """
+    raise NotImplementedError
+
+  def volume_exists(self):
+    """ Returns whether the config override volume exists. """
+    raise NotImplementedError
+
+  def volume_file_exists(self, filename):
+    """ Returns whether the file with the given name exists under the config override volume. """
+    raise NotImplementedError
+
+  def save_volume_file(self, filename, flask_file):
+    """ Saves the given flask file to the config override volume, with the given
+        filename.
+    """
+    raise NotImplementedError
+
+
+class FileConfigProvider(BaseProvider):
+  """ Implementation of the config provider that reads the data from the file system. """
+  def __init__(self, config_volume, yaml_filename, py_filename):
+    self.config_volume = config_volume
+    self.yaml_filename = yaml_filename
+    self.py_filename = py_filename
+
+    self.yaml_path = os.path.join(config_volume, yaml_filename)
+    self.py_path = os.path.join(config_volume, py_filename)
+
+  def update_app_config(self, app_config):
+    if os.path.exists(self.py_path):
+      logger.debug('Applying config file: %s', self.py_path)
+      app_config.from_pyfile(self.py_path)
+
+    if os.path.exists(self.yaml_path):
+      logger.debug('Applying config file: %s', self.yaml_path)
+      _import_yaml(app_config, self.yaml_path)
+
+  def get_yaml(self):
+    if not os.path.exists(self.yaml_path):
+      return None
+
+    config_obj = {}
+    _import_yaml(config_obj, self.yaml_path)
+    return config_obj
+
+  def save_yaml(self, config_obj):
+    _export_yaml(config_obj, self.yaml_path)
+
+  def yaml_exists(self):
+    return self.volume_file_exists(self.yaml_filename)
+
+  def volume_exists(self):
+    return os.path.exists(self.config_volume)
+
+  def volume_file_exists(self, filename):
+    return os.path.exists(os.path.join(self.config_volume, filename))
+
+  def save_volume_file(self, filename, flask_file):
+    flask_file.save(os.path.join(self.config_volume, filename))
+
+
+class TestConfigProvider(BaseProvider):
+  """ Implementation of the config provider for testing. Everything is kept in-memory instead on
+      the real file system. """
+  def __init__(self):
+    self.files = {}
+
+  def update_app_config(self, app_config):
+    pass
+
+  def get_yaml(self):
+    if not 'config.yaml' in self.files:
+      return None
+
+    return json.loads(self.files.get('config.yaml', '{}'))
+
+  def save_yaml(self, config_obj):
+    self.files['config.yaml'] = json.dumps(config_obj)
+
+  def yaml_exists(self):
+    return 'config.yaml' in self.files
+
+  def volume_exists(self):
+    return True
+
+  def volume_file_exists(self, filename):
+    return filename in self.files
+
+  def save_volume_file(self, filename, flask_file):
+    self.files[filename] = ''
+
+  def reset_for_test(self):
+    self.files = {}