feat(env): Add env module (#270)

# What
- Add `env` module for environment-specific values
- Use in `request` module for local files

# Why
- To DRY up the code
- To fix #269

queenbee/base/request.py

@@ -4,6 +4,8 @@
 from urllib import request
 from typing import Dict
 
+from ..env.os import OS
+
 USER_AGENT_STRING = 'Queenbee'
 
 
@@ -14,20 +16,17 @@ def get_uri(url):
     elif url.startswith('http://') or url.startswith('https://'):
         return url
 
-    # a local file but is not formatted as local url
-    pre = 'file:///' if platform.system() == 'Windows' else 'file://'
-    return resolve_local_source(pre + url)
+    return resolve_local_source(OS.file_uri_prefix + url)
 
 
 def resolve_local_source(path, as_uri=True):
     """Get an absolute path for a file:// or file:/// path.
 
     Apparently both of them are used: https://en.wikipedia.org/wiki/File_URI_scheme
     """
-    sep = 'file:///' if platform.system() == 'Windows' else 'file://'
 
     try:
-        rel_path = path.split(sep)[1]
+        rel_path = path.split(OS.file_uri_prefix)[1]
     except IndexError:
         raise ValueError('Invalid local path: {path}')
 

queenbee/env/os.py

@@ -0,0 +1,18 @@
+import platform
+
+
+class OS:
+    """A simple wrapper to handle OS-specific switches.
+
+    Attributes:
+        is_windows: A boolean of whether the current system is MS Windows.
+        is_nix: A boolean of whether the current system is *nix (any Linux).
+        file_uri_prefix: A string to be used as the default prefix for URIs
+            which point to local files on the system.
+
+    """
+
+    is_windows: bool = platform.system() == 'Windows'
+    is_nix: bool = not is_windows
+
+    file_uri_prefix: str = 'file:///' if is_windows else 'file://'