Ignore channel canvases

Channel canvases are exported as `canvas_in_the_conversation.json` files
in the channel directory. These files contain "canvas" objects
(`filetype="quip"`) which are exported in much the same way as normal
file uploads. However, because the canvases are meant to be living
documents, they have no `ts` key in them. This lack of a `ts` was
causing import errors.

To resolve this, the channel message loader now only loads messages from
filenames matching the pattern `*-*-*.json`, which excludes the channel
canvas file.

Fixes #28

README.md

@@ -28,6 +28,7 @@ Limitations
 - No private messages will be imported
 - Reactions to messages will be shown in a custom embed, not as normal reactions
 - No embeds from Slack (can contain images, buttons, etc) will be preserved.
+- No canvases from Slack will be preserved.
 - File uploads will be done in two messages. The first is the message content, the second is a
   message containing the title of the uploaded file and attaching it.
 

slack_to_discord/importer.py

@@ -165,7 +165,7 @@ def mention_repl(m):
 
     messages = {}
     file_ts_map = {}
-    for file in sorted(glob.glob(os.path.join(channel_dir, "*.json"))):
+    for file in sorted(glob.glob(os.path.join(channel_dir, "*-*-*.json"))):
         with open(file, "rb") as fp:
             data = json.load(fp)
         for d in sorted(data, key=lambda x: x["ts"]):