Refactor run_transform function

There was a lot of code in this function so I tried to break it up into
more meaningful blocks of functionality.

backdrop/transformers/dispatch.py

@@ -31,32 +31,27 @@ def entrypoint(dataset_id, earliest, latest):
         )
 
 
-@app.task(ignore_result=True)
-def run_transform(data_set_config, transform, earliest, latest):
-    data_set = DataSet.from_group_and_type(
-        config.BACKDROP_READ_URL,
-        data_set_config['data_group'],
-        data_set_config['data_type'],
-    )
-
+def get_query_parameters(transform, earliest, latest):
     query_parameters = transform.get('query-parameters', {})
     query_parameters['flatten'] = 'true'
     query_parameters['start_at'] = earliest
     query_parameters['end_at'] = latest
 
-    data = data_set.get(query_parameters=query_parameters)
+    return query_parameters
+
 
+def get_transform_function(transform):
     function_namespace = transform['type']['function']
     function_name = function_namespace.split('.')[-1]
     module_namespace = '.'.join(function_namespace.split('.')[:-1])
 
     transform_module = importlib.import_module(module_namespace)
-    transform_function = getattr(transform_module, function_name)
+    return getattr(transform_module, function_name)
 
-    transformed_data = transform_function(data['data'], transform['options'])
 
+def get_output_dataset(transform, input_dataset):
     output_group = transform['output'].get(
-        'data-group', data_set_config['data_group'])
+        'data-group', input_dataset['data_group'])
     output_type = transform['output']['data-type']
 
     admin_api = AdminAPI(
@@ -65,10 +60,28 @@ def run_transform(data_set_config, transform, earliest, latest):
     )
     output_data_set_config = admin_api.get_data_set(output_group, output_type)
 
-    output_data_set = DataSet.from_group_and_type(
+    return DataSet.from_group_and_type(
         config.BACKDROP_WRITE_URL,
         output_group,
         output_type,
         token=output_data_set_config['bearer_token'],
     )
+
+
+@app.task(ignore_result=True)
+def run_transform(data_set_config, transform, earliest, latest):
+    data_set = DataSet.from_group_and_type(
+        config.BACKDROP_READ_URL,
+        data_set_config['data_group'],
+        data_set_config['data_type'],
+    )
+
+    data = data_set.get(
+        query_parameters=get_query_parameters(transform, earliest, latest)
+    )
+
+    transform_function = get_transform_function(transform)
+    transformed_data = transform_function(data['data'], transform['options'])
+
+    output_data_set = get_output_dataset(transform, data_set_config)
     output_data_set.post(transformed_data)