A bot command to fork a thread

[jkomoros]

If someone replies to any message in any channel and uses the magic command, then the bot should create a new thread starting with the message that it's in reply to.

At the beginning, it will be a slash command reply that is in reply to the message that should be the new OP.

The thread OP should be a copy/paste of the message, with a link back to the original (using a channel reference, an actual link, and an @mention of the user).

In the future (once #35) is supported, when we can rename threads by tfidf words, then it should be possible to fork a thread merely by hitting the 🍴 emoji reaction on a post and have it auto named based on the contents of the OP.

Originally captured in #19

[jkomoros]

• Switch to using a version of discordgo that supports slash commands
• Fix the slash command permissions error
• Figure out how to get the slash command to show up when composing a a reply to another message in the UI (is this not possible?)
• Fix Have a command to have the bot rename a thread based on distinctive words #35 (so threads created will automatically have reasonable names)
• When seeing a 🧵 emoji, create a fork automatically in a fixed channel ID
• The channel fork cache has to keep channelD + messageID for both sides (you can't fetch a message via just a messageID)
• Save out forked message caches when they're updated
• The IDF cache indexes forked messages when it sees them and keeps track of the originalMessageID --> forkedID
• The IDF cache should be persisted in memory (especially if we need to look into it for forks, and it's not huge memory) and periodically rebuilt.
• Bug: the forked message is not persited anymore, so if you kill the bot and restart and the cache is recent enough, it won't contain the forked messages that happened since last rebuild. One option is to delete the IDF cache when it needs to be rebuilt. Another option is to have the timestamp be IN the file, not literal metadata in filesystem, so we can distinguish when an IDF needs to be regenerated, while still persisting fork information just fine.
• When a message that is forked is edited, update the content in the forked version
• Handle read outs of emojis that are not built-in in forked messages
• When a message that is forked is deleted, delete the forks (or not?)
• When a message that is a fork of another is deleted, forget about it
• When seeing the fork emoji don't fork if it's already been forked
• After forking, undo the thread and needle
• BUG: AutoTopWords last line can panic if there aren't that many words total
• When an emoji reaction comes in on a message that is forked, update the emoji reactions for each
• When a forked message is created, reply back to the last message in the fork chain with a link to the new forked thing
• When hitting the thread emoji, reply to that message and ask what the thread title should be and then fork it to that thread.
• Do the clippings for normal emoji reactions (when they lose the emoji they need to be a clipping, delete the clipping, and every additional emoji copy over the emojis)
• The fork reply should mention that you can use a :needle to fork multiple items if only one was provided
• When a 🧵 emoji reaction comes, fork just that item
• Also start at a :sewing-needle and copy down to he thread. (remind people in the "thread created" response that the can do that) (look upwards only until you get to a sewing needle or the thread so you don't copy too much) (ignore messages that aren't normal or replies)
• When deploying to production also allow the applications.command oauth scope (following instructions in readme)
• newBot should return a bot and an err, not panic
• Once tehre's a new release of discordgo that supports slash commands, switch to that and off of the specific commit import

[jkomoros]

Well darn it, looks like slash commands are not legal to issue in the UI when responding to a message, and there's no type of field in a slash command for a given message ID. So we'll need to figure out a different interaction pattern than replying to a message you want to use as an OP with the '/fork' command.

This machinery with slash commands is useful, so I don't want to get rid of. Maybe have an /archive command to start, which just archives a thread?