local getArgs = require('Module:Arguments').getArgs

local default_error_category = "[[Category:Pages using infobox television with nonstandard dates]]"

local p = {}

function p.start_end_date_template_validation(frame)
	local args = getArgs(frame)
	local error_category = args.error_category or default_error_category

	local start_date = args.first_aired or args.released or args.airdate or args.release_date or args.airdate_overall
	if start_date then
		if not start_date:find("dtstart") then
			return error_category
		end
	end

	local end_date = args.last_aired
	if end_date then
		if not end_date:find("dtend") and end_date ~= "present" then
			return error_category
		end
	end
end

function p.dates(frame)
	local returnval
	local args = getArgs(frame)
	
	if table.getn(args) < 2 then
		if args['1'] == nil and args['2'] == nil then
			return ''
		elseif args['1'] == nil then 
			return args['2']
		elseif args['2'] == nil then 
			return args['1']
		end
	end
	
	args['1'] = args['1']:gsub("&nbsp;"," ")
	args['2'] = args['2']:gsub("&nbsp;"," ")
	
	local dmy = false
	local pr1, m1, d1, y1, su1 = string.match(args['1'], '(.-)(%u%a+)%s(%d+),%s(%d+)(.*)')
	local pr2, m2, d2, y2, su2 = string.match(args['2'], '(.-)(%u%a+)%s(%d+),%s(%d+)(.*)')
	if y1 == nil then
		dmy = true
		pr1, d1, m1, y1, su1 = string.match(args['1'], '(.-)(%d%d?)%s(%a+)%s(%d+)(.*)')
		pr2, d2, m2, y2, su2 = string.match(args['2'], '(.-)(%d%d?)%s(%a+)%s(%d+)(.*)')
	end
	
	local dash = '&nbsp;–<br />'
	if y1 ~= nil and y2 ~= nil then
		su1 = su1 or ''
		su2 = su2 or ''
		
		local MONTHS = {January=1, February=2, March=3, April=4, May=5, June=6, July=7, August=8, September=9, October=10, November=11, December=12}
		local diff = os.time({year=y2, month=MONTHS[m2], day=d2, hour=0, min=0, sec=0}) - os.time({year=y1, month=MONTHS[m1], day=d1, hour=0, min=0, sec=0})
		
		if diff < 0 then
			returnval = 'Invalid date range'
		else
			if y1 == y2 then
				if dmy == false then
					returnval = pr1 .. m1 .. ' ' .. d1 .. su1 .. dash .. pr2 .. m2 ..' '.. d2 ..', '.. y2 .. su2
				else
					returnval = pr1 .. d1 .. ' ' .. m1 .. su1 .. dash .. pr2 .. d2 .. ' ' .. m2 .. ' ' .. y2 .. su2
				end
			else
				if dmy == false then
					returnval = pr1 .. m1 .. ' ' .. d1 ..', '.. y1 .. su1 .. dash .. pr2 .. m2 .. ' '.. d2 .. ', ' .. y2 .. su2
				else
					returnval = pr1 .. d1 .. ' ' .. m1 ..' '.. y1 .. su1 .. dash .. pr2 .. d2 .. ' '.. m2 .. ' ' .. y2 .. su2
				end
			end
		end
	else
		returnval = args['1']..dash..args['2'];
	end
	
	return returnval;
end

return p