degesch: add a slack plugin

Slack's IRC gateway is crap but it doesn't need to be *such* crap.

plugins/degesch/slack.lua

@@ -0,0 +1,71 @@
+--
+-- slack.lua: try to fix up UX when using the Slack IRC gateway
+--
+-- Copyright (c) 2017, Přemysl Janouch <p.janouch@gmail.com>
+--
+-- Permission to use, copy, modify, and/or distribute this software for any
+-- purpose with or without fee is hereby granted, provided that the above
+-- copyright notice and this permission notice appear in all copies.
+--
+-- THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+-- WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+-- MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+-- SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+-- WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+-- OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+-- CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+--
+
+local servers = {}
+local read_servers = function (v)
+	servers = {}
+	for name in v:lower ():gmatch "[^,]+" do
+		servers[name] = true
+	end
+end
+
+degesch.setup_config {
+	servers = {
+		type = "string_array",
+		default = "\"\"",
+		comment = "list of server names that are Slack IRC gateways",
+		on_change = read_servers
+	}
+}
+
+-- We can handle external messages about what we've supposedly sent just fine,
+-- so let's get rid of that "[username] some message sent from the web UI" crap
+degesch.hook_irc (function (hook, server, line)
+	local msg, us = degesch.parse (line), server.user
+	if not servers[server.name] or msg.command ~= "PRIVMSG" or not us
+		or msg.params[1]:lower () ~= us.nickname:lower () then return line end
+
+	-- Taking a shortcut to avoid lengthy message reassembly
+	local quoted_nick = us.nickname:gsub ("[%^%$%(%)%%%.%[%]%*%+%-%?]", "%%%0")
+	local text = line:match ("^.- PRIVMSG .- :%[" .. quoted_nick .. "%] (.*)$")
+	if not text then return line end
+	return ":" .. us.nickname .. "!" .. server.irc_user_host .. " PRIVMSG "
+		.. msg.prefix:match "^[^!@]*" .. " :" .. text
+end)
+
+degesch.hook_completion (function (hook, data, word)
+	local chan = degesch.current_buffer.channel
+	local server = degesch.current_buffer.server
+	if not chan or not servers[server.name] then return end
+
+	-- In /commands there is typically no desire at all to add the at sign
+	if data.location == 1 and data.words[1]:match "^/" then return end
+
+	-- Handle both when the at sign is already there and when it is not
+	local needle = word:gsub ("^@", ""):lower ()
+
+	local t = {}
+	for i, chan_user in ipairs (chan.users) do
+		local nick = chan_user.user.nickname
+		if data.location == 0 then nick = nick .. ":" end
+		if nick:sub (1, #needle):lower () == needle then
+			table.insert (t, "@" .. nick)
+		end
+	end
+	return t
+end)