add bundle.py to create single-file bbj client

python is able to import modules from a zip file. if the zip file
contains __main__.py it will even run it as a script! this lets us bundle
bbj's frontend together with its sole external dependency (urwid) to
create a single executable file that'll run anywhere with python
installed, no virtualenv needed.

the only downside is that python can't import shared objects (.so) from a
zip file, so urwid can't use its C-accelerated str_util module and has
to fall back to the python version. which is slower, probably.

bundle.py

@@ -0,0 +1,32 @@
+import zipfile
+import glob
+import os
+
+
+# TODO: should we include .pyc files?
+# TODO: add urwid source into the repo somewhere
+
+files = {
+    '__main__.py': 'clients/urwid/main.py',
+    'network.py': 'clients/network_client.py',
+    'urwid': 'env/lib/python3.8/site-packages/urwid/*.py',
+}
+
+with open('bbj_demo', 'wb') as f:
+    f.write(b"#!/usr/bin/env python3\n")
+    with zipfile.ZipFile(f, 'w', compression=zipfile.ZIP_DEFLATED) as z:
+        z.comment = b'BBJ'
+        for name, source in files.items():
+            if '*' in source:
+                dirname = name
+                for path in sorted(glob.glob(source)):
+                    name = dirname + '/' + os.path.basename(path)
+                    z.write(path, name)
+            else:
+                z.write(source, name)
+try:
+    mask = os.umask(0)
+    os.umask(mask)
+except OSError:
+    mask = 0
+os.chmod(z.filename, 0o777&~mask)

clients/urwid/main.py

@@ -793,7 +793,7 @@ class App(object):
         """
         if self.mode == "thread":
             # mark the current position in this thread before going back to the index
-            mark()
+            self.mark()
 
         self.body.attr_map = {None: "default"}
         self.mode = "index"
@@ -859,7 +859,7 @@ class App(object):
             self.walker += self.make_message_body(message)
         self.set_default_header()
         self.set_default_footer()
-        self.goto_post(mark(thread_id))
+        self.goto_mark(thread_id)
 
 
     def toggle_client_pin(self):
@@ -983,10 +983,10 @@ class App(object):
                 self.last_index_pos = self.get_focus_post(True).thread["thread_id"]
             self.index()
         else:
-            mark()
+            self.mark()
             thread = self.thread["thread_id"]
             self.thread_load(None, thread)
-            self.goto_post(mark(thread))
+            self.goto_mark(thread)
         self.temp_footer_message("Refreshed content!", 1)
 
 
@@ -1021,10 +1021,31 @@ class App(object):
                 width=30, height=6)
 
         else:
-            mark()
+            self.mark()
             self.index()
 
 
+    def mark(self, thread_id=None):
+        if self.mode != "thread":
+            return
+
+        if thread_id is None:
+            thread_id = self.thread['thread_id']
+        pos = self.get_focus_post()
+        mark(thread_id, pos, default=0)
+        return pos
+
+
+    def goto_mark(self, thread_id=None):
+        if self.mode != "thread":
+            return
+
+        if thread_id is None:
+            thread_id = self.thread['thread_id']
+        pos = mark(thread_id, default=0)
+        self.goto_post(pos)
+
+
     def get_focus_post(self, return_widget=False):
         pos = self.box.get_focus_path()[0]
         if self.mode == "thread":
@@ -2501,11 +2522,16 @@ def bbjrc(mode, **params):
     return values
 
 
-def mark(directive=True):
+def mark(key, value=None, default=None):
     """
-    Set and retrieve positional marks for threads.
+    Sets a value in the markfile and returns the old value (or default).
     This uses a seperate file from the preferences
     to keep it free from clutter.
+
+    The key must be a string, and the value must be
+    json-encodable. If value isn't provided (or is None)
+    then this doesn't set anything and it is only a
+    read operation.
     """
     try:
         with open(markpath, "r") as _in:
@@ -2513,19 +2539,14 @@ def mark(directive=True):
     except FileNotFoundError:
         values = {}
 
-    if directive == True and app.mode == "thread":
-        pos = app.get_focus_post()
-        values[app.thread["thread_id"]] = pos
+    old = values.get(key, default)
+
+    if value is not None and value != old:
+        values[key] = value
         with open(markpath, "w") as _out:
             json.dump(values, _out)
-        return pos
-
-    elif isinstance(directive, str):
-        try:
-            return values[directive]
-        except KeyError:
-            return 0
 
+    return old
 
 def load_client_pins():
     """