reading climate files

day = zero
	read first data line
		failure
			exit
		success
			requested day earlier than day read
				switch to day of year (cwrnflg = 1)
	read second data line
		failure
			exit
		success
			second day not consequtive
				exit

cwrnflg equals 0 (exact date mode)
	if requested day earlier than today and greater or equal to next day
		reset file to beginning
		read next day
		failure
			exit
	requested day greater than today 
		read forward in file
			failure
				requested day December 31
					reset file to beginning
						failure
							exit
						success
							switch to day of year (cwrnflg = 1)
				requested day not end of year
					reset file to beginning
						switch to day of year (cwrnflg = 2)

cwrnflg equals 0 (exact date mode)
	today and next day not consecutive
		today december 21
			OK
		February 28 or 29 or March 1
			switch to day of year (cwrnflg = 2)
		else
			exit
else
	check day of year
	requested day of year not equal to today day of year
		exit
		
cwrnflg greater than 0 (day of year mode)
	requested day of year 366 and next day of year 1
		return today for requested day of year
	requested day of year 1 and next day of year 366
		read next day from file
			failure
				exit
			

Alternate logic

read file until valid line
	no valid line found
		exit