--
-- prime.lua: highlight prime numbers in messages
--
-- Copyright (c) 2020, Přemysl Eric Janouch <p@janouch.name>
--
-- Permission to use, copy, modify, and/or distribute this software for any
-- purpose with or without fee is hereby granted.
--
-- 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.
--

-- The prime test is actually very fast, so there is no DoS concern
local is_prime = function (n)
	if tonumber (n) < 2 then return false end
	for i = 2, n ^ (1 / 2) do if (n % i) == 0 then return false end end
	return true
end

local do_interlink = function (run)
	-- Let's not cripple formatting, colours especially
	-- TODO: we can just employ the same approach as in do_text and skip over
	if run:find ('%c') then return run end

	return run:gsub ("%f[%w_]%d+%f[^%w_]", function (number)
		if is_prime (number) then return "\x1f" .. number .. "\x1f" end
		return number
	end)
end

local do_text = 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))
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
end)