[output] Add support for click-events in i3

The i3 output now has a separate thread that continuously monitors stdin
for incoming click events. The generic output class also has methods for
registering callbacks (as commands). For now, by default, scroll events
will be used to emulate the next/previous workspace.

bumblebee/outputs/i3.py

@@ -1,16 +1,44 @@
 from __future__ import unicode_literals
 
+import os
+import sys
 import json
+import shlex
+import threading
+import subprocess
 import bumblebee.output
 
+def read_input(output):
+    while True:
+        line = sys.stdin.readline().strip(",").strip()
+        if line == "[": continue
+        if line == "]": break
+
+        DEVNULL = open(os.devnull, 'wb')
+
+        event = json.loads(line)
+        cb = output.callback(event)
+        if cb:
+            cb = cb.format(
+                name = event.get("name", ""),
+                instance = event.get("instance", ""),
+                button = event.get("button", -1)
+            )
+            subprocess.call(shlex.split(cb), stdout=DEVNULL, stderr=DEVNULL)
+
 class i3bar(bumblebee.output.Output):
     def __init__(self, theme):
-
         super(i3bar, self).__init__(theme)
         self._data = []
 
+        self.add_callback("i3-msg workspace prev", 4)
+        self.add_callback("i3-msg workspace next", 5)
+
+        self._thread = threading.Thread(target=read_input, args=(self,))
+        self._thread.start()
+
     def start(self):
-        return json.dumps({ "version": 1 }) + "["
+        return json.dumps({ "version": 1, "click_events": True }) + "["
 
     def add(self, obj):
         theme = self.theme()
@@ -21,6 +49,8 @@ class i3bar(bumblebee.output.Output):
                 u"full_text": "{}{}{}".format(theme.prefix(obj), d, theme.suffix(obj)),
                 "color": theme.color(obj),
                 "background": theme.background(obj),
+                "name": obj.__module__.replace("bumblebee.modules.",""),
+                "instance": obj.instance() if hasattr(obj, "instance") else None,
             }
 
             if theme.urgent(obj) and obj.critical():