From 31549aa7ebc3096f040becf57e530145c2e9950d Mon Sep 17 00:00:00 2001
From: Joscha <joscha@plugh.de>
Date: Thu, 16 May 2019 09:14:16 +0000
Subject: [PATCH] Add ConfigView

with python magic to make this possible:

c = Config({"a.b": "c"})
c.view.a.b == "c"
---
 cheuph/euphoria/config.py | 44 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 43 insertions(+), 1 deletion(-)

diff --git a/cheuph/euphoria/config.py b/cheuph/euphoria/config.py
index f00a7df..585fdd7 100644
--- a/cheuph/euphoria/config.py
+++ b/cheuph/euphoria/config.py
@@ -1,6 +1,6 @@
 from typing import Any, Dict
 
-__all__ = ["Config"]
+__all__ = ["Fields", "Config", "ConfigView"]
 
 Fields = Dict[str, Any]
 
@@ -86,3 +86,45 @@ class Config:
                 self.fields.pop(key)
         else:
             self.fields[key] = value
+
+    @property
+    def view(self) -> "ConfigView":
+        return ConfigView(
+                self.to_tree(self.default_fields),
+                self.to_tree(self.fields),
+        )
+
+class ConfigView:
+    def __init__(self,
+            default_fields: Any,
+            fields: Any,
+            prefix: str = "",
+            ) -> None:
+
+        self._default_fields = default_fields
+        self._fields = fields
+        self._prefix = prefix
+
+    def __getattr__(self, name: str) -> Any:
+        """
+        This function assumes that _default_fields and _fields have the same
+        dict structure.
+        """
+
+        default_field = self._default_fields.get(name)
+        field = self._fields.get(name)
+
+        if isinstance(field, dict) or isinstance(default_field, dict):
+            # At least one is a dict, the other is either also a dict of the
+            # same structure or None.
+            default_field = default_field or {}
+            field = field or {}
+
+            return ConfigView(default_field, field, f"{self._prefix}{name}.")
+
+        value = default_field if field is None else field
+
+        if value is None:
+            raise ConfigException(f"Field {self._prefix}{name} does not exist")
+
+        return value