[core] Add support for custom colorsets (e.g. pywal)

In a theme file, it is now possible to provide an array of "color
definitions", which allow you to use names instead of colors throughout
the theme file.

Currently, only the colorset "wal" is supported, which reads all colors
from the wal JSON file (~/.cache/wal/colors.json) and makes them usable
in the theme (as "foreground", "background", "cursor", "color12", etc.).

An example of this can be found in the theme wal-powerline.

see #185

bumblebee/theme.py

@@ -25,17 +25,20 @@ def themes():
 class Theme(object):
     """Represents a collection of icons and colors"""
     def __init__(self, name):
-        self._init(self.load(name))
         self._widget = None
         self._cycle_idx = 0
         self._cycle = {}
         self._prevbg = None
+        self._colorset = {}
+        self._init(self.load(name))
 
     def _init(self, data):
         """Initialize theme from data structure"""
         self._theme = data
         for iconset in data.get("icons", []):
             self._merge(data, self._load_icons(iconset))
+        for colorset in data.get("colors", []):
+            self._merge(self._colorset, self._load_colors(colorset))
         self._defaults = data.get("defaults", {})
         self._cycles = self._theme.get("cycle", [])
         self.reset()
@@ -99,6 +102,21 @@ class Theme(object):
         """Return the SBW"""
         return self._get(widget, "separator-block-width", None)
 
+    def _load_wal_colors(self):
+        walfile = os.path.expanduser("~/.cache/wal/colors.json")
+        result = {}
+        with io.open(walfile) as data:
+            colors = json.load(data)
+            for field in ["special", "colors"]:
+                for key in colors[field]:
+                    result[key] = colors[field][key]
+        return result
+
+    def _load_colors(self, name):
+        """Load colors for a theme"""
+        if name == "wal":
+            return self._load_wal_colors()
+
     def _load_icons(self, name):
         """Load icons for a theme"""
         path = "{}/icons/".format(theme_path())
@@ -110,7 +128,7 @@ class Theme(object):
 
         if os.path.isfile(themefile):
             try:
-                with io.open(themefile,encoding="utf-8") as data:
+                with io.open(themefile, encoding="utf-8") as data:
                     return json.load(data)
             except ValueError as exception:
                 raise bumblebee.error.ThemeLoadError("JSON error: {}".format(exception))
@@ -155,7 +173,9 @@ class Theme(object):
             widget.set(key, (idx + 1) % len(value))
             value = value[idx]
 
-        return value
+        if isinstance(value, list) or isinstance(value, dict):
+            return value
+        return self._colorset.get(value, value)
 
     # algorithm copied from
     # http://blog.impressiver.com/post/31434674390/deep-merge-multiple-python-dicts

themes/wal-powerline.json

@@ -0,0 +1,42 @@
+{
+	"icons": [ "awesome-fonts" ],
+	"colors": [ "wal" ],
+	"defaults": {
+		"separator-block-width": 0,
+		"critical": {
+			"fg": "cursor",
+			"bg": "color5"
+		},
+		"warning": {
+			"fg": "cursor",
+			"bg": "color6"
+		},
+		"default_separators": false
+	},
+	"cycle": [
+		{
+			"fg": "foreground",
+			"bg": "background"
+		},
+		{
+			"fg": "background",
+			"bg": "foreground"
+		}
+	],
+	"dnf": {
+		"good": {
+			"fg": "background",
+			"bg": "color3"
+		}
+	},
+	"battery": {
+		"charged": {
+			"fg": "background",
+			"bg": "color3"
+		},
+		"AC": {
+			"fg": "background",
+			"bg": "color3"
+		}
+	}
+}