Coding style.

- Move blend_color into termstr.
- Add invert method to termstr.

termstr/termstr.py

@@ -26,6 +26,15 @@ def rgb_color(rgb, is_foreground):
     return f"[{'38' if is_foreground else '48'};2;" + "%i;%i;%im" % rgb
 
 
+def blend_color(a_color, b_color, transparency):
+    a_r, a_g, a_b = a_color
+    b_r, b_g, b_b = b_color
+    complement = 1 - transparency
+    return (int(a_r * transparency + b_r * complement),
+            int(a_g * transparency + b_g * complement),
+            int(a_b * transparency + b_b * complement))
+
+
 class Color:
 
     # https://en.wikipedia.org/wiki/Natural_Color_System
@@ -38,6 +47,7 @@ class Color:
     lime = (0, 255, 0)
     yellow = (255, 211, 0)
     grey_30 = (30, 30, 30)
+    grey_40 = (40, 40, 40)
     grey_50 = (50, 50, 50)
     grey_80 = (80, 80, 80)
     grey_100 = (100, 100, 100)
@@ -378,6 +388,12 @@ class TermStr(collections.UserString):
                              is_italic=style.is_italic, is_underlined=style.is_underlined)
         return self.transform_style(set_bgcolor)
 
+    def invert(self):
+        def invert_(style):
+            return CharStyle(style.bg_color, style.fg_color, is_bold=style.is_bold,
+                             is_italic=style.is_italic, is_underlined=style.is_underlined)
+        return self.transform_style(invert_)
+
     def as_html(self):
         result = []
         styles = set()