[core] Add input processing

Create infrastructure for input event handling and add i3bar event
processing. For each event, callbacks can be registered in the input
module.
Modules and widgets both identify themselves using a unique ID (the
module name for modules, a generated UUID for the widgets). This ID is
then used for registering the callbacks. This is possible since both
widgets and modules are statically allocated & do not change their IDs.

Callback actions can be either callable Python objects (in which case
the event is passed as parameter), or strings, in which case the string
is interpreted as a shell command.

see #23

bumblebee/input.py

@@ -0,0 +1,77 @@
+"""Input classes"""
+
+import sys
+import json
+import uuid
+import time
+import threading
+import bumblebee.util
+
+LEFT_MOUSE = 1
+RIGHT_MOUSE = 3
+
+def read_input(inp):
+    """Read i3bar input and execute callbacks"""
+    while inp.running:
+        line = sys.stdin.readline().strip(",").strip()
+        inp.has_event = True
+        try:
+            event = json.loads(line)
+            inp.callback(event)
+        except ValueError:
+            pass
+    inp.has_event = True
+    inp.clean_exit = True
+
+class I3BarInput(object):
+    """Process incoming events from the i3bar"""
+    def __init__(self):
+        self.running = True
+        self._thread = threading.Thread(target=read_input, args=(self,))
+        self._callbacks = {}
+        self.clean_exit = False
+        self.global_id = str(uuid.uuid4())
+        self.need_event = False
+        self.has_event = False
+
+    def start(self):
+        """Start asynchronous input processing"""
+        self._thread.start()
+
+    def alive(self):
+        """Check whether the input processing is still active"""
+        return self._thread.is_alive()
+
+    def stop(self):
+        """Stop asynchronous input processing"""
+        if self.need_event:
+            while not self.has_event:
+                time.sleep(0.1)
+        self.running = False
+        self._thread.join()
+        return self.clean_exit
+
+    def register_callback(self, obj, button, cmd):
+        """Register a callback function or system call"""
+        uid = self.global_id
+        if obj:
+            uid = obj.id
+
+        if uid not in self._callbacks:
+            self._callbacks[uid] = {}
+        self._callbacks[uid][button] = cmd
+
+    def callback(self, event):
+        """Execute callback action for an incoming event"""
+        cmd = self._callbacks.get(self.global_id, {})
+        cmd = self._callbacks.get(event["name"], cmd)
+        cmd = self._callbacks.get(event["instance"], cmd)
+        cmd = cmd.get(event["button"], None)
+        if cmd is None:
+            return
+        if callable(cmd):
+            cmd(event)
+        else:
+            bumblebee.util.execute(cmd)
+
+# vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4