require("iuplua")

function checkDateFormat(str_date)
	str_date = string.gsub(str_date, "^%s*(.-)%s*$", "%1")
	local check = string.find(str_date, "^%d?%d.%d?%d.%d%d%d%d$")
	if not check then
		return nil
	end
	local day, month, year = string.match(str_date, "(%d?%d).(%d?%d).(%d%d%d%d)")
	if day==nil or month==nil or year==nil then
		return nil
	end
	return 1, tonumber(day), tonumber(month), tonumber(year)
end

function validateDate(day, month, year)
	local leapYear = 0

	if day and day < 1 or day>31 or month and month < 1 or month > 12 then
		return nil
	end

	if year % 400 == 0 or year % 4 == 0 and year % 100 ~= 0 then
		leapYear = 1
	end

	if month == 2 and leapYear and day > 29 then
		return nil
	end

	if month == 2 and not leapYear and day > 28 then
		return nil
	end

	if (month == 4 or month == 6 or month == 9 or month == 11) and day > 30 then
		return nil
	end

  return 1
end

function startBeforeEnd(startDay, startMonth, startYear, endDay, endMonth, endYear)

  if startYear < endYear then
    return 1
  end

  if  startYear == endYear and startMonth < endMonth then
    return 1
  end

  if  startYear == endYear and startMonth == endMonth and startDay <= endDay then
    return 1
  end

  return nil
end

--********************************** Main *****************************************

lst_flight = iup.list{"one-way flight", "return flight"; dropdown = "YES", value = 1, expand = "HORIZONTAL"}
txt_startDate = iup.text{expand = "HORIZONTAL", value = "22.09.1957"}
txt_returnDate = iup.text{expand = "HORIZONTAL", active="NO", value = "22.09.1957"}
btn_book = iup.button{title = "Book", expand = "HORIZONTAL"}

dlg = iup.dialog{iup.vbox{lst_flight, txt_startDate, txt_returnDate, btn_book; gap="10"}, title = "Book Flight", size = "150", margin = "10x10"}

function btn_book:action()
  local flightType = lst_flight.value
  if lst_flight.value == "1" then
    iup.Message("Attention!", "You have booked a one-way flight on "..txt_startDate.value..".")
  else
    iup.Message("Attention!", "You have booked a return flight on "..txt_startDate.value..
                            " and "..txt_returnDate.value..".")
 end
end

function lst_flight:valuechanged_cb()
	if self.value == "1" then
		txt_returnDate.active = "NO"
	else
		txt_returnDate.active = "YES"
	end
end

function checkDate(self)
	local check, day, month, year = checkDateFormat(self.value)
	if  not check then
		self.bgcolor = "255 0 0"
		self.valid = nil
		return
	end
	
	local valid = validateDate(day, month, year)
	if  not valid then
		self.bgcolor = "255 0 0"
		self.valid = nil
		return
	end

	self.bgcolor = "255 255 255"
	self.valid = 1
	self.day = day
	self.month = month
	self.year = year
end

function txt_startDate:valuechanged_cb()
	checkDate(self)
	if self.valid and txt_returnDate.active == "NO" or
	   (txt_returnDate.valid and startBeforeEnd(self.day, self.month, self.year,
		                                        txt_returnDate.day, txt_returnDate.month, txt_returnDate.year)) then
		btn_book.active = "YES"
	else
		btn_book.active = "NO"
	end
end

function txt_returnDate:valuechanged_cb()
	checkDate(self)
	if self.valid and txt_startDate.valid and
	   startBeforeEnd(txt_startDate.day, txt_startDate.month, txt_startDate.year,
		              self.day, self.month, self.year) then
		btn_book.active = "YES"
	else
		btn_book.active = "NO"
	end
end

dlg:showxy( iup.CENTER, iup.CENTER )

if (iup.MainLoopLevel()==0) then
  iup.MainLoop()
end