Hidden setting to override the text editor.

Note that people who run gtimelog straight from Git will need to
manually run ``make`` to recompile the gsettings schema, or gtimelog
will segfault when you press Ctrl+E.

Also note that using `gsettings` is a pain when the schema is not
installed globally, but you can use

    dconf write /org/gtimelog/editor '"gvim %s"'

and then tweak it with dconf-editor.

Error handling is missing: if you set editor to gvim and gvim is not
installed, you'll see a Python traceback on the console.

Application.prepare_args() is a separate static method so I could write
unit tests for it, but I haven't done so.

Closes #113.

CHANGES.rst

@@ -40,6 +40,11 @@ Changelog
 - Grouped task entries can now be sorted by start date, name, duration or
   according to tasks.txt order (GH: #228).
 
+- There's a new hidden setting to override the text editor (GH: #113).
+  You can use ``gsettings set org.gtimelog editor gvim`` (or dconf-editor).
+  More complicated settings like ``'gnome-terminal -e "vim %s"'`` also work
+  (``%s`` is replaced with the file name).
+
 
 0.11.3 (2019-04-23)
 ~~~~~~~~~~~~~~~~~~~

src/gtimelog/data/org.gtimelog.gschema.xml

@@ -38,7 +38,7 @@
 
         <key name="log-order" enum="org.gtimelog.LogOrder">
             <default>"start-time"</default>
-	    <summary>Log Tasks/Groups order</summary>
+            <summary>Log Tasks/Groups order</summary>
             <description>Order of tasks and groups in Log view</description>
         </key>
 
@@ -163,6 +163,12 @@
             <description>If true, the task entry will use the standard GTK+ completion.  If false, it'll only use the custom prefix completion on PageUp/PageDown.</description>
         </key>
 
+        <key name="editor" type="s">
+            <default>""</default>
+            <summary>Text editor to use for editing timelog.txt or tasks.txt</summary>
+            <description>If blank, gtimelog will use your system default editor.  If the value contains '%s', it will be replaced with the filename, otherwise the filename will be appended as an extra argument.</description>
+        </key>
+
     </schema>
 
 </schemalist>

src/gtimelog/main.py

@@ -1,4 +1,6 @@
 """An application for keeping track of your time."""
+import shlex
+import subprocess
 import sys
 import time
 
@@ -307,9 +309,30 @@ def do_startup(self):
     def on_quit(self, action, parameter):
         self.quit()
 
+    @staticmethod
+    def prepare_args(program, filename):
+        args = shlex.split(program)
+        had_percent_s = False
+        for i, arg in enumerate(args):
+            if '%s' in arg:
+                args[i] = arg.replace('%s', filename)
+                had_percent_s = True
+        if not had_percent_s:
+            args.append(filename)
+        return args
+
+    def run_in_background(self, program, filename):
+        args = self.prepare_args(program, filename)
+        subprocess.Popen(args)
+        # XXX: error handling!
+
     def open_in_editor(self, filename):
         self.create_if_missing(filename)
-        if os.name == 'nt':
+        gsettings = Gio.Settings.new("org.gtimelog")
+        editor = gsettings.get_string('editor')
+        if editor:
+            self.run_in_background(editor, filename)
+        elif os.name == 'nt':
             os.startfile(filename)
         else:
             uri = GLib.filename_to_uri(filename, None)