How to find the date number given the Year, month, day of the week and the week it falls on in ruby - ruby

Question

So i'm new to ruby and not to familiar with the syntax of the Date gem, but is there a way to find the date of a moving holiday like fathers day?
So my current class for the moving holidays looks like this:
class MovingHoliday < Holiday
def initialize (name, month, day_of_week, week, year=2016)
#name = name
#month = month
#day_of_week = day_of_week
#week = week
#year = year
#my_date = Date.new(year, month, day)
end
end
and my input looks like this:
fathers_day = MovingHoliday.new("Fathers Day", 6, "sunday", 4, year)
The 6 is the month, "sunday" is well the day_of_the_week, and 4 is the week it falls on.
I just can't figure out the syntax if there is any that would/could do conversion for this.
And I can't use any gems other then rubys Date.

Answer 1

class MovingHoliday < Holiday
def initialize (name, month, day_of_week, week, year=2016)
#name = name
#month = month
#day_of_week = day_of_week
#week = week
#year = year
#my_date = Date.new(year, month, 1)
#my_date += 1 while !my_date.send("#{day_of_week}?")
#my_date += (7 * (week - 1))
end
end
Not pretty, but it works. It takes the first of the month, moves up a day until it's the correct day of the week, and then increases by the appropriate number of weeks.
As it stands, it assumes that you're given an actual day of the week. You'll probably want to sanitize the input in some manner or convert from "sunday" to 0 (my_date.wday returns 0 for sunday, 1 for monday, etc)

Answer 2

date in Ruby is not a gem, it's part of the standard library, it's just not loaded unless you require it. (In Ruby, require is used for both purposes, loading gems and loading parts of the standard library that are not loaded by default.)
I don't know of any built-in functionality that would calculate the date for you, I think you'd have to write that yourself, since you don't want to consider other gems.