Find any particular day of the month with Ruby - ruby

Question

I'm trying to build in a calendar system into my app. The problem I'm currently on is once a month schedule. Basically if a person schedules on the second Wednesday of the month I want to automatically update the schedule to the second Wednesday of the next month. I've tried just adding + 1.month but that doesn't achieve exactly what I want. Because it moves it to the next month date not day of the week. Does anyone know how I can achieve this. Here is what I'm currently doing that is not right.
def call
schedule.update!(
end_at: end_at_next_month,
start_at: start_at_next_month,
status: "monthly",
arranged: true
)
end
private
def schedule
context.schedule
end
def end_at_next_month
schedule.end_at + 1.month
end
def start_at_next_month
schedule.start_at + 1.month
end
end

Answer 1

require 'date'
def date_of_nth_wday(month, year, wday, nth)
base_date = Date.new(year, month)
base_wday = base_date.wday
ret_date = base_date +
( wday > base_wday ? wday - base_wday : 7 - base_wday + wday) +
7*(nth-1)
ret_date.month == month ? ret_date : nil
end
Obtain the date of the second Sunday of August, 2017
date_of_nth_wday(8, 2017, 0, 2)
#=> #<Date: 2017-08-13 ((2457979j,0s,0n),+0s,2299161j)>
Obtain the date of the third Friday of August, 2017
date_of_nth_wday(8, 2017, 5, 3)
#=> #<Date: 2017-08-18 ((2457984j,0s,0n),+0s,2299161j)>
Obtain the date of the fifth Monday of August, 2017
date_of_nth_wday(8, 2017, 1, 5)
#=> nil (there are only 4 Mondays in August, 2017)

Answer 2

You can try something like this:
DAYS_MAPPING = { 0=>"Sunday",
1=>"Monday",
2=>"Tuesday",
3=>"Wednesday",
4=>"Thursday",
5=>"Friday",
6=>"Saturday" }
# Returns week of month in integer
# for example: 1 for matching day of 1st week of the month
def get_week_number(date)
week_number = date.strftime('%U').to_i - date.beginning_of_month.strftime('%U').to_i
offset = (Date.parse(DAYS_MAPPING[date.wday]) < date.beginning_of_month) ? 0 : 1
week_number + offset
end
def specific_day_of_next_month(schedule)
# wday => day of week in integer
# for example: 0 for Sunday; 1 for Monday & so on ...
wday = schedule.wday
week_number = get_week_number(schedule)
next_month = schedule + 1.month
days = (next_month.beginning_of_month..next_month.end_of_month).select { |d| d.wday == wday }
days[week_number-1]
end
Example 1:
schedule = Date.today
# => Sat, 01 Jul 2017 (First Saturday of July)
specific_day_of_next_month(schedule)
# => Sat, 05 Aug 2017 (First Saturday of August)
Example 2:
schedule = Date.new(2017, 7, 10)
# => Mon, 10 Jul 2017 (Second Monday of July)
specific_day_of_next_month(schedule)
# => Mon, 14 Aug 2017 (Second Monday of August)

Answer 3

Your title is different to your explanation in the text. With my example you don't get the last friday, but you could select the 1,2,3,4,5th wednesday (or any other day) of a month.
require 'date'
class Date
#~ class DateError < ArgumentError; end
#Get the third monday in march 2008: new_by_mday( 2008, 3, 1, 3)
#
#Based on http://forum.ruby-portal.de/viewtopic.php?f=1&t=6157
def self.new_by_mday(year, month, weekday, nr)
raise( ArgumentError, "No number for weekday/nr") unless weekday.respond_to?(:between?) and nr.respond_to?(:between?)
raise( ArgumentError, "Number not in Range 1..5: #{nr}") unless nr.between?(1,5)
raise( ArgumentError, "Weekday not between 0 (Sunday)and 6 (Saturday): #{nr}") unless weekday.between?(0,6)
day = (weekday-Date.new(year, month, 1).wday)%7 + (nr-1)*7 + 1
if nr == 5
lastday = (Date.new(year, (month)%12+1, 1)-1).day # each december has the same no. of days
raise "There are not 5 weekdays with number #{weekday} in month #{month}" if day > lastday
end
Date.new(year, month, day)
end
end
#2nd monday (weekday 1) in july
p Date.new_by_mday(2017,7,1,2)
If you look for a gem: date_tools supports ths function.