Add tail command

mmcli.py

@@ -244,6 +244,80 @@ def cat(mm_api: mattermost.MMApi, cmdline_args):
 		print_initial_messages()
 
 
+def tail(mm_api: mattermost.MMApi, cmdline_args):
+
+	team, channel = resolve_team_channel(mm_api, cmdline_args.channel)
+
+	if not cmdline_args.ids:
+		users = list(mm_api.get_users())
+		def attribute(key_value):
+			key, value = key_value
+			if key == "channel_id":
+				assert value == channel["id"]
+				return "channel", channel["name"]
+			if key == "user_id":
+				return "username", first(u["username"] for u in users if u["id"] == value)
+			return key_value
+	else:
+		def attribute(key_value):
+			return key_value
+
+
+	# In a list to allow overwriting from within print_initial_messages without using global
+	backlog = [ [] ]
+	backlog_lock = threading.Lock()
+
+	def print_initial_messages():
+		data_page = mm_api._get(f"/v4/channels/{channel['id']}/posts")
+		order = data_page["order"]
+		posts = [
+			data_page["posts"][post_id]
+			for post_id in reversed(order)
+		]
+
+		for post in posts:
+			print(str_for_post(attribute, post, cmdline_args))
+
+		with backlog_lock:
+			for post in backlog[0]:
+				print(str_for_post(attribute, post, cmdline_args))
+			backlog[0] = None
+
+	if cmdline_args.follow:
+		def simple_websocket_callback(_mmws, event_data):
+			if event_data.get("event") == "posted":
+				post = json.loads(event_data["data"]["post"])
+				if post["channel_id"] != channel["id"]:
+					return
+				print(str_for_post(attribute, post, cmdline_args), flush=True)
+
+		def initial_websocket_callback(mmws: MMws, event_data):
+			if event_data.get("event") == "posted":
+				post = json.loads(event_data["data"]["post"])
+				if post["channel_id"] != channel["id"]:
+					return
+				with backlog_lock:
+					if backlog[0] is not None:
+						backlog[0].append(post)
+						return
+					else:
+						mmws.ws_handler = simple_websocket_callback
+						simple_websocket_callback(mmws, event_data)
+
+		ws_url = http_to_ws(mm_api._url) + "/v4/websocket"
+		mmws = MMws(initial_websocket_callback, mm_api.access_token, ws_url)
+
+		thread = threading.Thread(target=print_initial_messages)
+		thread.setDaemon(True)
+		thread.start()
+
+		mmws.run_websocket()
+
+	else:
+		print_initial_messages()
+
+
+
 def ls(mm_api: mattermost.MMApi, cmdline_args):
 	# TODO --follow doesn't work for channel creation and deletion yet
 
@@ -407,6 +481,7 @@ def str_for_chan(attribute, channel, cmdline_args):
 ACTIONS = {
 	"login": {"function": login, "accesstoken_required": False},
 	"cat": {"function": cat},
+	"tail": {"function": tail},
 	"ls": {"function": ls},
 	"send": {"function": send},
 	"rm": {"function": rm},
@@ -477,6 +552,10 @@ Security note: Other programs and users can typically read which arguments you g
 	parser_cat.add_argument("--since", help="all after timestamp")
 	parser_cat.add_argument("-f", "--follow", action="store_true", help="keep running, printing new posts as they come in")
 
+	parser_tail = subparsers.add_parser("tail", help="list newest messages in channel")
+	parser_tail.add_argument("channel", help="URL names of team and channel: '<team>/<channel>'")
+	parser_tail.add_argument("-f", "--follow", action="store_true", help="keep running, printing new posts as they come in")
+
 	parser_ls = subparsers.add_parser("ls", help="list channels")
 	parser_ls.add_argument("team", help="URL name of team")
 	parser_ls.add_argument("-f", "--follow", action="store_true", help="keep running, printing changes to channels as they come in")