prime.lua: skip colour sequences, add config

Colour sequence skipping is somewhat involved, we might want to
add a helper generator to the "degesch" Lua library, in the form of
{substring, is_formatting}.

formatter_parse_mirc() isn't useful, a pure Lua implementation
would be more appropriate (where do we put that?)

plugins/degesch/prime.lua

@@ -15,36 +15,54 @@
 -- CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 --
 
+local smallest, highlight = 0, "\x1f"
+degesch.setup_config {
+	smallest = {
+		type = "integer",
+		default = "0",
+		comment = "smallest number to scan for primality",
+		on_change = function (v) smallest = math.max (v, 2) end
+	},
+	highlight = {
+		type = "string",
+		default = "\"\\x1f\"",
+		comment = "the attribute to use for highlights",
+		on_change = function (v) highlight = v end
+	},
+}
+
 -- The prime test is actually very fast, so there is no DoS concern
-local is_prime = function (n)
+local do_intercolour = function (text)
-	if tonumber (n) < 2 then return false end
+	return tostring (text:gsub ("%f[%w_]%d+", function (n)
-	for i = 2, n ^ (1 / 2) do if (n % i) == 0 then return false end end
+		if tonumber (n) < smallest then return nil end
-	return true
+		for i = 2, n ^ (1 / 2) do if (n % i) == 0 then return nil end end
+		return highlight .. n .. highlight
+	end))
 end
 
-local do_interlink = function (run)
+local do_interlink = function (text)
-	-- Let's not cripple formatting, colours especially
+	local rebuilt, last = {""}, 1
-	-- TODO: we can just employ the same approach as in do_text and skip over
+	for start in text:gmatch ('()\x03') do
-	if run:find ('%c') then return run end
+		table.insert (rebuilt, do_intercolour (text:sub (last, start - 1)))
-
+		local sub = text:sub (start + 1)
-	return run:gsub ("%f[%w_]%d+%f[^%w_]", function (number)
+		last = start + (sub:match ('^%d%d?,%d%d?()') or sub:match ('^%d?%d?()'))
-		if is_prime (number) then return "\x1f" .. number .. "\x1f" end
+		table.insert (rebuilt, text:sub (start, last - 1))
-		return number
+	end
-	end)
+	return table.concat (rebuilt) .. do_intercolour (text:sub (last))
 end
 
-local do_text = function (text)
+local do_message = function (text)
 	local rebuilt, last = {""}, 1
 	for run, link, endpos in text:gmatch ('(.-)(%f[%g]https?://%g+)()') do
 		last = endpos
 		table.insert (rebuilt, do_interlink (run) .. link)
 	end
-	return table.concat (rebuilt, "") .. do_interlink (text:sub (last))
+	return table.concat (rebuilt) .. do_interlink (text:sub (last))
 end
 
 -- XXX: sadly it won't typically highlight primes in our own messages,
 -- unless IRCv3 echo-message is on
 degesch.hook_irc (function (hook, server, line)
 	local start, message = line:match ("^(.- PRIVMSG .- :)(.*)$")
-	return message and start .. do_text (message) or line
+	return message and start .. do_message (message) or line
 end)