[core] Add debugging capabilities

* If an exception is thrown, catch it and show a (somewhat) nice error
  message in the i3bar instead of the normal content
* Add a flag "-d" for debugging into a debug log. Currently, this only
  logs commandline calls as they occur and their return values, as well
  as exceptions.

fixes #58

bumblebee-status

@@ -1,6 +1,8 @@
 #!/usr/bin/env python
 
+import os
 import sys
+import logging
 import bumblebee.theme
 import bumblebee.engine
 import bumblebee.config
@@ -8,17 +10,42 @@ import bumblebee.output
 import bumblebee.input
 
 def main():
+    logging.basicConfig(
+        level=logging.DEBUG,
+        format="[%(asctime)s] %(levelname)-8s %(message)s",
+        filename="{}/debug.log".format(os.path.dirname(os.path.realpath(__file__)))
+    )
     config = bumblebee.config.Config(sys.argv[1:])
     theme = bumblebee.theme.Theme(config.theme())
     output = bumblebee.output.I3BarOutput(theme=theme)
     inp = bumblebee.input.I3BarInput()
+    engine = None
+
+    try:
         engine = bumblebee.engine.Engine(
             config=config,
             output=output,
             inp=inp,
         )
-
         engine.run()
+    except BaseException as e:
+        logging.exception(e)
+        if output.started():
+            output.flush()
+            output.end()
+        else:
+            output.start()
+        import time
+        while True:
+            output.begin()
+            error = bumblebee.modules.error.Module(engine, config)
+            error.set("exception occurred: {}".format(e))
+            widget = error.widgets()[0]
+            widget.link_module(error)
+            output.draw(widget, error)
+            output.flush()
+            output.end()
+            time.sleep(1)
 #    try:
 #    except KeyboardInterrupt as error:
 #        inp.stop()

bumblebee/config.py

@@ -4,7 +4,9 @@ This module provides configuration information (loaded modules,
 module parameters, etc.) to all other components
 """
 
+import os
 import sys
+import logging
 import argparse
 import textwrap
 import importlib
@@ -14,6 +16,7 @@ MODULE_HELP = "Specify a space-separated list of modules to load. The order of t
 THEME_HELP = "Specify the theme to use for drawing modules"
 PARAMETER_HELP = "Provide configuration parameters in the form of <module>.<key>=<value>"
 LIST_HELP = "Display a list of either available themes or available modules along with their parameters."
+DEBUG_HELP = "Enable debug log ('debug.log' located in the same directory as the bumblebee-status executable)"
 
 class print_usage(argparse.Action):
     def __init__(self, option_strings, dest, nargs=None, **kwargs):
@@ -51,6 +54,8 @@ def create_parser():
         help=PARAMETER_HELP)
     parser.add_argument("-l", "--list", choices=["modules", "themes"], action=print_usage,
         help=LIST_HELP)
+    parser.add_argument("-d", "--debug", action="store_true",
+        help=DEBUG_HELP)
     return parser
 
 class Config(bumblebee.store.Store):
@@ -64,6 +69,9 @@ class Config(bumblebee.store.Store):
         parser = create_parser()
         self._args = parser.parse_args(args if args else [])
 
+        if not self._args.debug:
+            logger = logging.getLogger().disabled = True
+
         for param in self._args.parameters:
             key, value = param.split("=")
             self.set(key, value)

bumblebee/modules/error.py

@@ -0,0 +1,26 @@
+# pylint: disable=C0111,R0903
+
+"""Draws an error widget.
+"""
+
+import bumblebee.input
+import bumblebee.output
+import bumblebee.engine
+
+class Module(bumblebee.engine.Module):
+    def __init__(self, engine, config):
+        super(Module, self).__init__(engine, config,
+            bumblebee.output.Widget(full_text=self.text)
+        )
+        self._text = ""
+
+    def set(self, text):
+        self._text = text
+
+    def text(self, widget):
+        return self._text
+
+    def state(self, widget):
+        return ["critical"]
+
+# vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4

bumblebee/output.py

@@ -50,9 +50,14 @@ class I3BarOutput(object):
     def __init__(self, theme):
         self._theme = theme
         self._widgets = []
+        self._started = False
+
+    def started(self):
+        return self._started
 
     def start(self):
         """Print start preamble for i3bar protocol"""
+        self._started = True
         sys.stdout.write(json.dumps({"version": 1, "click_events": True}) + "[\n")
 
     def stop(self):

bumblebee/util.py

@@ -1,4 +1,5 @@
 import shlex
+import logging
 import subprocess
 
 try:
@@ -8,17 +9,21 @@ except ImportError:
     pass
 
 def execute(cmd, wait=True):
+    logging.info("executing command '{}'".format(cmd))
     args = shlex.split(cmd)
     proc = subprocess.Popen(args, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
+    rv = None
 
     if wait:
         out, _ = proc.communicate()
         if proc.returncode != 0:
             raise RuntimeError("{} exited with {}".format(cmd, proc.returncode))
         if type(out) == str:
-            return out
+            rv = out
-        return out.decode("utf-8")
+        else:
-    return None
+            rv = out.decode("utf-8")
+    logging.info("command returned '{}'".format("" if not rv else rv))
+    return rv
 
 def bytefmt(num):
     for unit in [ "", "Ki", "Mi", "Gi" ]: