gistfile1.applescript

--Fucntions
on add_leading_zeros(this_number, max_leading_zeros)
  set the threshold_number to (10 ^ max_leading_zeros) as integer
	if this_number is less than the threshold_number then
		set the leading_zeros to ""
		set the digit_count to the length of ((this_number div 1) as string)
		set the character_count to (max_leading_zeros + 1) - digit_count
		repeat character_count times
			set the leading_zeros to (the leading_zeros & "0") as string
		end repeat
		return (leading_zeros & (this_number as text)) as string
	else
		return this_number as text
	end if
end add_leading_zeros

--Build Year String
set y to year of (current date)
set d to my add_leading_zeros(day of (current date), 1)
set m to my add_leading_zeros(month of (current date) as integer, 1)
set myDate to y & m & d as string






activate
tell application "System Events" to tell process "Mail"
	tell text field "Subject:" of window 1
		set focused to true
		set mySubject to value
		
		set legalPrefixCharacters to {"1", "2", "3", "4", "5", "6", "7", "8", "9", "0"}
		set legalSuffixCharacters to {"-U", "-P", "-PS", "-PC", "-PD", "-R", "-S", "-TS", "9", "0"}
		
		--Get the prefix eg "20130101" and the suffix eg "-U".		
		if length of mySubject > 8 then
			set thePrefix to (characters 1 thru 8) of mySubject as text
			
			set hasMODPrefix to true
			
			--Check that the prefix is all numbers
			repeat with thisChr from 1 to (get count of characters in thePrefix)
				set theChr to character thisChr of thePrefix
				if theChr is not in legalPrefixCharacters then
					set hasMODPrefix to false
				end if
			end repeat
		else
			set hasMODPrefix to false
		end if
		--If the prefix is there, get the rest of the message and put the new prefix date in it.
		--Otherwise use the whole message and add the new prefix date.
		if hasMODPrefix is true then
			set newSubject to (myDate & "-" & (characters 10 thru -1) of mySubject as text)
		else
			set newSubject to myDate & "-" & mySubject
		end if
		
		set theSuffix to (characters -1 thru -2) of newSubject as text
		
		--If the suffix is not there, add it
		if theSuffix is not in legalSuffixCharacters then
			set newSubject to newSubject & "-U"
		end if
		
		set value to newSubject
		
	end tell
end tell