Module:Diff days

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require('strict');
local get_args = require ('Module:Arguments').getArgs;
local lang_object = mw.getContentLanguage();

--[[--------------------------< D I F F _ D A Y S >------------------------------------------------------------

return difference between two date/time strings <t1>, and <t2>, in days to <precision> decimal places.  Converts
each date/time string to a unix timestamp (seconds), subtracts <t1> from <t2>, divides the difference by the number
of seconds in a day (86400) and returns a formatted string to <precision> decimal places.  The default precision
is 3 decimal places.  A positive result is returned when <t2> is the same as, or is 'later' (more recent) than,
<t1>; negative results else.

to call this from a template:
	{{#invoke:diff days|diff_days|<t1>|<t2>|precision=}}
where <t1> and <t2> are date/time strings acceptable to the MediaWiki #time parser

]]

local function diff_days (frame)
	local args_t = get_args (frame);
	local t1 = args_t[1];														-- t1 is 'start' time
	local t2 = args_t[2];														-- t2 is 'end' time
	local precision = tonumber (args_t.precision) or 3;							-- number of decimal places to show; default is 3
	if 0 > precision then
		return '<span style="color:#d33">invalid precision: ' .. precision .. '</span>';
	end

	if not t1 or not t2 then
		return '<span style="color:#d33">both of t1 and t2 required</span>';
	end

	local good;
	local time1, time2;															-- to hold Unix time stamps representing the dates

	good, time1 = pcall (lang_object.formatDate, lang_object, 'U', t1 );		-- convert t1 value to unix timestamp 
	if not good then
		return '<span style="color:#d33">invalid time: ' .. t1 .. '</span>';
	end

	good, time2 = pcall (lang_object.formatDate, lang_object, 'U', t2 );		-- convert t2 value to unix timestamp 
	if not good then
		return '<span style="color:#d33">invalid time: ' .. t2 .. '</span>';
	end

	return string.format ('%.'.. precision .. 'f', (time2 - time1)/86400);
end

--[[--------------------------< E X P O R T E D   F U N C T I O N >--------------------------------------------
]]

return {
	diff_days = diff_days
	}