Ask Ben: Finding The Last Monday Of The Month In ColdFusion

<!--- Get the current month based on the curren date. --->
<cfset dtThisMonth = CreateDate(
	Year( Now() ),
	Month( Now() ),
	1
	) />

<!---
	Now, get the last day of the current month. We
	can get this by subtracting 1 from the first day
	of the next month.
--->
<cfset dtLastDay = (
	DateAdd( "m", 1, dtThisMonth ) -
	1
	) />

<!---
	Now, the last day of the month is part of the last
	week of the month. However, there is no guarantee
	that the "Monday" of this week will be in the current
	month. If Sunday was the last day of the month, then
	Monday would be the first day of the next month.
	Regardless, let's get the date of the target day.
--->
<cfset dtMonday = (
	dtLastDay -
	DayOfWeek( dtLastDay ) +

	<!---
		This is the day of the week that we are
		trying to find (2 = Monday).
	--->
	2
	) />


<!---
	Now, we have a Monday, but we are not exactly sure if
	this Monday is in the current month. if is not, then
	we know it is the first Monday of the next month, in
	which case, subracting 7 days (one week) from it will
	give us the last Monday of the current Month.
--->
<cfif (Month( dtMonday ) NEQ Month( dtThisMonth ))>

	<!--- Subract a week. --->
	<cfset dtMonday = (dtMonday - 7) />

</cfif>


<!---
	Output the date of the last Monday. CAUTION: Our date
	math above has left us with a NUMERIC DATE, not a
	traditional date/time stamp. Therefore, be careful
	about using things like IsDate() as this numeric date
	will NOT pass these checks.
--->
<p>
	Last Monday Of Month:
	#DateFormat( dtMonday, "full" )#
</p>

<cffunction
	name="GetLastDayOfWeekOfMonth"
	access="public"
	returntype="date"
	output="false"
	hint="Returns the date of the last given weekday of the given month.">

	<!--- Define arguments. --->
	<cfargument
		name="Date"
		type="date"
		required="true"
		hint="Any date in the given month we are going to be looking at."
		/>

	<cfargument
		name="DayOfWeek"
		type="numeric"
		required="true"
		hint="The day of the week of which we want to find the last monthly occurence."
		/>

	<!--- Define the local scope. --->
	<cfset var LOCAL = StructNew() />

	<!--- Get the current month based on the given date. --->
	<cfset LOCAL.ThisMonth = CreateDate(
		Year( ARGUMENTS.Date ),
		Month( ARGUMENTS.Date ),
		1
		) />

	<!---
		Now, get the last day of the current month. We
		can get this by subtracting 1 from the first day
		of the next month.
	--->
	<cfset LOCAL.LastDay = (
		DateAdd( "m", 1, LOCAL.ThisMonth ) -
		1
		) />

	<!---
		Now, the last day of the month is part of the last
		week of the month. However, there is no guarantee
		that the target day of this week will be in the current
		month. Regardless, let's get the date of the target day
		so that at least we have something to work with.
	--->
	<cfset LOCAL.Day = (
		LOCAL.LastDay -
		DayOfWeek( LOCAL.LastDay ) +
		ARGUMENTS.DayOfWeek
		) />


	<!---
		Now, we have the target date, but we are not exactly
		sure if the target date is in the current month. if
		is not, then we know it is the first of that type of
		the next month, in which case, subracting 7 days (one
		week) from it will give us the last occurence of it in
		the current Month.
	--->
	<cfif (Month( LOCAL.Day ) NEQ Month( LOCAL.ThisMonth ))>

		<!--- Subract a week. --->
		<cfset LOCAL.Day = (LOCAL.Day - 7) />

	</cfif>


	<!--- Return the given day. --->
	<cfreturn DateFormat( LOCAL.Day ) />
</cffunction>

<p>
	<!--- Loop over every month in year. --->
	<cfloop
		index="intMonth"
		from="1"
		to="12"
		step="1">

		<!--- Get last monday. --->
		#GetLastDayOfWeekOfMonth(
			"#intMonth#/1/2007",
			2
			)#<br />

	</cfloop>
</p>