Add Hook plugin to run commands on events

This plugin allows users to execute scripts on
different events, as well as forward any
arguments from the events to the script.

beetsplug/hook.py

@@ -0,0 +1,100 @@
+# This file is part of beets.
+# Copyright 2015, Adrian Sampson.
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+
+"""Allows custom commands to be run when an event is emitted by beets"""
+from __future__ import (division, absolute_import, print_function,
+                        unicode_literals)
+
+import subprocess
+import sys
+
+from beets.plugins import BeetsPlugin
+
+
+def create_hook_function(command, shell, substitute_args):
+
+    # TODO: Find a better way of piping STDOUT/STDERR/STDIN between the process
+    #       and the user.
+    #
+    #       The issue with our current method is that we can only pesudo-pipe
+    #       one (two if we count STDERR being piped to STDOUT) stream at a
+    #       time, meaning we can't have both output and input simultaneously.
+    #       This is due to how Popen.std(out/err) works, as
+    #       Popen.std(out/err).readline() waits until a newline has been output
+    #       to the stream before returning.
+
+    def hook_function(**kwargs):
+        hook_command = command
+
+        for key in kwargs:
+            if key in substitute_args:
+                hook_command = hook_command.replace(substitute_args[key],
+                                                    str(kwargs[key]))
+
+        process = subprocess.Popen(hook_command,
+                                   stdout=subprocess.PIPE,
+                                   stderr=subprocess.STDOUT,
+                                   shell=shell)
+
+        while process.poll() is None:
+            sys.stdout.write(process.stdout.readline())
+
+        # Ensure there's nothing left in the stream
+        sys.stdout.write(process.stdout.readline())
+
+    return hook_function
+
+
+class HookPlugin(BeetsPlugin):
+    """Allows custom commands to be run when an event is emitted by beets"""
+    def __init__(self):
+        super(HookPlugin, self).__init__()
+
+        self.config.add({
+            'hooks': [],
+            'substitute_event': '%EVENT%',
+            'shell': True
+        })
+
+        hooks = self.config['hooks'].get(list)
+        global_substitute_event = self.config['substitute_event'].get()
+        global_shell = self.config['shell'].get(bool)
+
+        for hook_index in range(len(hooks)):
+            hook = self.config['hooks'][hook_index]
+
+            hook_event = hook['event'].get()
+            hook_command = hook['command'].get()
+
+            if 'substitute_event' in hook:
+                original = hook['substitute_event'].get()
+            else:
+                original = global_substitute_event
+
+            if 'shell' in hook:
+                shell = hook['shell'].get(bool)
+            else:
+                shell = global_shell
+
+            if 'substitute_args' in hook:
+                substitute_args = hook['substitute_args'].get(dict)
+            else:
+                substitute_args = {}
+
+            hook_command = hook_command.replace(original, hook_event)
+            hook_function = create_hook_function(hook_command,
+                                                 shell,
+                                                 substitute_args)
+
+            self.register_listener(hook_event, hook_function)