degesch: add a "censor" plugin

So far this approach screws up highlights, which is actually a bug.

plugins/degesch/censor.lua

@@ -0,0 +1,74 @@
+--
+-- censor.lua: black out certain users' messages
+--
+-- Copyright (c) 2016, 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 to_pattern = function (mask)
+	if not mask:match ("!") then mask = mask .. "!*" end
+	if not mask:match ("@") then mask = mask .. "@*" end
+
+	-- That is, * acts like a wildcard, otherwise everything is escaped
+	return "^" .. mask:gsub ("[%^%$%(%)%%%.%[%]%+%-%?]", "%%%0")
+		:gsub ("%*", ".*") .. "$"
+end
+
+local patterns = {}
+local read_masks = function (v)
+	patterns = {}
+	local add = function (who, where)
+		local channels = patterns[who] or {}
+		table.insert (channels, where)
+		patterns[who] = channels
+	end
+	for item in v:lower ():gmatch ("[^,]+") do
+		local who, where = item:match ("^([^/]+)/*(.*)")
+		if who then add (to_pattern (who), where == "" or where) end
+	end
+end
+
+degesch.setup_config {
+	masks = {
+		type = "string_array",
+		default = "\"\"",
+		comment = "user masks (optionally \"/#channel\") to censor",
+		on_change = read_masks
+	},
+}
+
+local censor = function (line)
+	-- Taking a shortcut to avoid lengthy message reassembly
+	local start, text = line:match ("^(.- PRIVMSG .-:)(.*)$")
+	local ctcp, rest = text:match ("^(\x01%g+ )(.*)")
+	text = ctcp and ctcp .. "\x0301,01" .. rest or "\x0301,01" .. text
+	return start .. text
+end
+
+degesch.hook_irc (function (hook, server, line)
+	local msg = degesch.parse (line)
+	if msg.command ~= "PRIVMSG" then return line end
+
+	local channel = msg.params[1]:lower ()
+	for who, where in pairs (patterns) do
+		if msg.prefix:lower ():match (who) then
+			for _, x in pairs (where) do
+				if x == true or x == channel then
+					return censor (line)
+				end
+			end
+		end
+	end
+	return line
+end)