Add unified configuration handling (closes #19)

This adds loading of multiple yml files from various locations.
Namely, in order, with later files taking precendence over earlier ones
the following directories are scanned for any .yml file.
The order of the files within each directory is standard globbing order.

- $PACKAGE/etc/
- /etc/climix/
- <XDG directories>/climix, including
- ~/.config/climix/

climix/metadata.py

@@ -3,6 +3,7 @@
 from dataclasses import dataclass
 import copy
 from enum import Enum
+import glob
 from itertools import combinations
 import logging
 import os
@@ -12,6 +13,7 @@ from typing import Any, List, Mapping, Optional, Union
 
 import iris
 import pkg_resources
+import xdg.BaseDirectory
 import yaml
 
 from .index import Index
@@ -315,12 +317,28 @@ def build_index_function(spec):
     return index_function
 
 
-def load_metadata():
-    metadata_filename = os.path.join(os.path.dirname(__file__),
-                                     'etc', 'metadata.yml')
-    with open(metadata_filename) as md_file:
-        metadata = yaml.safe_load(md_file)
+def find_metadata_files_in_dir(directory):
+    if os.path.isdir(directory):
+        return glob.glob(os.path.join(directory, '*.yml'))
+    return []
+
+
+def find_metadata_files():
+    directories = [
+        os.path.join(os.path.dirname(__file__), 'etc'),
+        '/etc/climix',
+    ] + list(xdg.BaseDirectory.load_config_paths('climix'))[::-1]
+    files = sum([find_metadata_files_in_dir(directory)
+                 for directory in directories], [])
+    return files
 
-    indices = {name: build_index(idx_meta)
-               for name, idx_meta in metadata['indices'].items()}
+
+def load_metadata():
+    indices = {}
+    for metadata_path in find_metadata_files():
+        with open(metadata_path) as md_file:
+            metadata = yaml.safe_load(md_file)
+        index_metadata = metadata.get('indices', {})
+        for name, idx_meta in index_metadata.items():
+            indices[name] = build_index(idx_meta, metadata_path)
     return IndexCatalog(indices)

setup.py

@@ -37,6 +37,7 @@ setuptools.setup(
         'dask-jobqueue',
         'distributed>=2.4.0',
         'numpy',
+        'pyxdg',
         'PyYAML',
         'sentry-sdk',
         'scitools-iris>=2.2.0',