feat(replies): enable based on redaction implementation

* Close #86
* https://matrix.org/docs/spec/client_server/latest#rich-replies
* Modify to `/reply-matrix` to avoid clash with `/reply` used by `wee-slack`

main.py

@@ -73,7 +73,8 @@ from matrix.commands import (hook_commands, hook_page_up,
                              matrix_redact_command_cb, matrix_topic_command_cb,
                              matrix_olm_command_cb, matrix_devices_command_cb,
                              matrix_room_command_cb, matrix_uploads_command_cb,
-                             matrix_upload_command_cb, matrix_send_anyways_cb)
+                             matrix_upload_command_cb, matrix_send_anyways_cb,
+                             matrix_reply_command_cb)
 from matrix.completion import (init_completion, matrix_command_completion_cb,
                                matrix_debug_completion_cb,
                                matrix_message_completion_cb,

matrix/commands.py

@@ -285,6 +285,27 @@ def hook_commands():
         "",
     )
 
+    W.hook_command(
+        # Command name and short description
+        "reply-matrix",
+        "reply to a message",
+        # Synopsis
+        ('<event-id>[:"<message-part>"] [<reply>]'),
+        # Description
+        (
+            "    event-id: event id of the message that will be replied to\n"
+            "message-part: an initial part of the message (ignored, only "
+            "used\n"
+            "              as visual feedback when using completion)\n"
+            "       reply: the reply\n"
+        ),
+        # Completions
+        ("%(matrix_messages)"),
+        # Function name
+        "matrix_reply_command_cb",
+        "",
+    )
+
     W.hook_command(
         # Command name and short description
         "topic",
@@ -1321,6 +1342,64 @@ def matrix_redact_command_cb(data, buffer, args):
     return W.WEECHAT_RC_OK
 
 
+@utf8_decode
+def matrix_reply_command_cb(data, buffer, args):
+    def predicate(event_id, line):
+        event_tag = SCRIPT_NAME + "_id_{}".format(event_id)
+        tags = line.tags
+
+        if event_tag in tags:
+            return True
+        return False
+
+    for server in SERVERS.values():
+        if buffer in server.buffers.values():
+            room_buffer = server.find_room_from_ptr(buffer)
+
+            # Intentional use of `parse_redact_args` which serves the
+            # necessary purpose
+            event_id, reply = parse_redact_args(args)
+
+            if not event_id:
+                message = (
+                    "{prefix}matrix: Invalid command "
+                    "arguments (see /help reply)"
+                ).format(prefix=W.prefix("error"))
+                W.prnt("", message)
+                return W.WEECHAT_RC_ERROR
+
+            lines = room_buffer.weechat_buffer.find_lines(
+                partial(predicate, event_id), max_lines=1
+            )
+
+            if not lines:
+                room_buffer.error(
+                    "No such message with event id "
+                    "{event_id} found.".format(event_id=event_id))
+                return W.WEECHAT_RC_OK
+
+            formatted_data = Formatted.from_input_line(reply)
+            server.room_send_message(
+                room_buffer,
+                formatted_data,
+                "m.text",
+                in_reply_to_event_id=event_id,
+            )
+            room_buffer.last_message = None
+
+            return W.WEECHAT_RC_OK
+
+        if buffer == server.server_buffer:
+            message = (
+                '{prefix}matrix: command "reply" must be '
+                "executed on a Matrix channel buffer"
+            ).format(prefix=W.prefix("error"))
+            W.prnt("", message)
+            return W.WEECHAT_RC_OK
+
+    return W.WEECHAT_RC_OK
+
+
 def matrix_command_help(args):
     if not args:
         message = (

matrix/server.py

@@ -1118,6 +1118,7 @@ class MatrixServer(object):
         formatted,    # type: Formatted
         msgtype="m.text",  # type: str
         ignore_unverified_devices=False,  # type: bool
+        in_reply_to_event_id="",  # type: str
     ):
         # type: (...) -> bool
         room = room_buffer.room
@@ -1126,9 +1127,13 @@ class MatrixServer(object):
 
         content = {"msgtype": msgtype, "body": formatted.to_plain()}
 
-        if formatted.is_formatted():
+        if formatted.is_formatted() or in_reply_to_event_id:
             content["format"] = "org.matrix.custom.html"
             content["formatted_body"] = formatted.to_html()
+            if in_reply_to_event_id:
+                content["m.relates_to"] = {
+                    "m.in_reply_to": {"event_id": in_reply_to_event_id}
+                }
 
         try:
             uuid = self.room_send_event(