feat(command): open external editor command in composing message

OPEN_EXTERNAL_EDITOR command paste the composing message in a python tempfile,
run external editor over it and wait the exit before update the message.

$ZULIP_EDITOR_COMMAND and fallback $EDITOR are use for the external editor
command.

Author: mek-yt

docs/hotkeys.md

@@ -81,6 +81,7 @@
 |Autocomplete @mentions, #stream_names, :emoji: and topics|<kbd>ctrl</kbd> + <kbd>f</kbd>|
 |Cycle through autocomplete suggestions in reverse|<kbd>ctrl</kbd> + <kbd>r</kbd>|
 |Narrow to compose box message recipient|<kbd>meta</kbd> + <kbd>.</kbd>|
+|Open the message in external editor|<kbd>ctrl</kbd> + <kbd>o</kbd>|
 |Jump to the beginning of line|<kbd>ctrl</kbd> + <kbd>a</kbd>|
 |Jump to the end of line|<kbd>ctrl</kbd> + <kbd>e</kbd>|
 |Jump backward one word|<kbd>meta</kbd> + <kbd>b</kbd>|

zulipterminal/config/keys.py

@@ -310,6 +310,11 @@ class KeyBinding(TypedDict):
         'help_text': 'View user information (From Users list)',
         'key_category': 'general',
     },
+    'OPEN_EXTERNAL_EDITOR': {
+        'keys': ['ctrl o'],
+        'help_text': 'Open the message in external editor',
+        'key_category': 'msg_compose',
+    },
     'BEGINNING_OF_LINE': {
         'keys': ['ctrl a'],
         'help_text': 'Jump to the beginning of line',

zulipterminal/ui_tools/boxes.py

@@ -2,10 +2,14 @@
 UI boxes for entering text: WriteBox, MessageSearchBox, PanelSearchBox
 """
 
+import os
 import re
+import shutil
+import subprocess
 import unicodedata
 from collections import Counter
 from datetime import datetime, timedelta
+from tempfile import NamedTemporaryFile
 from time import sleep
 from typing import Any, Callable, Dict, List, NamedTuple, Optional, Tuple
 
@@ -810,6 +814,33 @@ def keypress(self, size: urwid_Size, key: str) -> Optional[str]:
         elif is_command_key("MARKDOWN_HELP", key):
             self.view.controller.show_markdown_help()
             return key
+        elif is_command_key("OPEN_EXTERNAL_EDITOR", key):
+            editor = os.environ.get("ZULIP_EDITOR_COMMAND", os.environ.get("EDITOR"))
+            if editor is None:
+                self.view.controller.report_error(
+                    "Configure $EDITOR or $ZULIP_EDITOR_COMMAND shell environment."
+                )
+                return key
+            editor_splits = editor.split(" ")
+            fullpath_program = shutil.which(editor_splits[0])
+            if fullpath_program is None:
+                self.view.controller.report_error(
+                    "Editor program not found, check $EDITOR "
+                    "or $ZULIP_EDITOR_COMMAND."
+                )
+                return key
+            editor_splits[0] = fullpath_program
+            edit_tempfile = NamedTemporaryFile(suffix=".md")
+            with open(edit_tempfile.name, mode="w") as edit_writer:
+                edit_writer.write(self.msg_write_box.edit_text)
+            self.view.controller.loop.screen.stop()
+            editor_splits.append(edit_tempfile.name)
+            subprocess.call(editor_splits)
+            with open(edit_tempfile.name, mode="r") as edit_reader:
+                self.msg_write_box.edit_text = edit_reader.read().rstrip()
+            edit_tempfile.close()
+            self.view.controller.loop.screen.start()
+            return key
         elif is_command_key("SAVE_AS_DRAFT", key):
             if self.msg_edit_state is None:
                 if self.compose_box_status == "open_with_private":