--
-- utm-filter.lua: filter out Google Analytics bullshit from URLs
--
-- Copyright (c) 2015, Přemysl 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.
--

-- A list of useless URL parameters that don't affect page function
local banned = {
	gclid        = 1,

	utm_source   = 1,
	utm_medium   = 1,
	utm_term     = 1,
	utm_content  = 1,
	utm_campaign = 1,
}

-- Go through a parameter list and throw out any banned elements
local do_args = function (args)
	local filtered = {}
	for part in args:gmatch ("[^&]+") do
		if not banned[part:match ("^[^=]*")] then
			table.insert (filtered, part)
		end
	end
	return table.concat (filtered, "&")
end

-- Filter parameters in both the query and the fragment part of an URL
local do_single_url = function (url)
	return url:gsub ('^([^?#]*)%?([^#]*)', function (start, query)
		local clean = do_args (query)
		return #clean > 0 and start .. "?" .. clean or start
	end, 1):gsub ('^([^#]*)#(.*)', function (start, fragment)
		local clean = do_args (fragment)
		return #clean > 0 and start .. "#" .. clean or start
	end, 1)
end

local do_text = function (text)
	return text:gsub ('%f[%g]https?://%g+', do_single_url)
end

degesch.hook_irc (function (hook, server, line)
	local start, message = line:match ("^(.* :)(.*)$")
	return message and start .. do_text (message) or line
end)

degesch.hook_input (function (hook, buffer, input)
	return do_text (input)
end)