[core/themes] Add theme loading

Load a theme from a JSON file.

bumblebee/error.py

@@ -8,4 +8,8 @@ class ModuleLoadError(BaseError):
     """Raised whenever loading a module fails"""
     pass
 
+class ThemeLoadError(BaseError):
+    """Raised whenever loading a theme fails"""
+    pass
+
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bumblebee/theme.py

@@ -1,7 +1,30 @@
 """Theme support"""
 
+import os
+import json
+
+import bumblebee.error
+
+def theme_path():
+    """Return the path of the theme directory"""
+    return os.path.dirname("{}/../themes/".format(os.path.dirname(os.path.realpath(__file__))))
+
 class Theme(object):
     """Represents a collection of icons and colors"""
-    pass
+    def __init__(self, name):
+        self._theme = self.load(name)
+
+    def load(self, name):
+        """Load and parse a theme file"""
+        path = theme_path()
+        themefile = "{}/{}.json".format(path, name)
+        if os.path.isfile(themefile):
+            try:
+                with open(themefile) as data:
+                    return json.load(data)
+            except ValueError as exception:
+                raise bumblebee.error.ThemeLoadError("JSON error: {}".format(exception))
+        else:
+            raise bumblebee.error.ThemeLoadError("no such theme: {}".format(name))
 
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