_README.md

How to create a Ruby Gem

Why create a gem?

• For code reuse
• For isolation (easy to test, black box input/output)
• For important and/or complex code
• For community features and feedback (if open sourced)

Example code to turn into a gem

pry

require_relative 'month_ordinals'
month_ordinals = MonthOrdinals.for 2016
month_ordinals[:first][:friday]
_[7]

month_ordinals = MonthOrdinals.for 2016..2017
month_ordinals

Scaffold Gem:

bundle gem month_ordinals
cd month_ordinals
ls -1A

This adds a gemspec, Rakefile (for testing and releasing), stub for your library's code, semver version.rb, minitest, travis.yml, bin/setup and bin/console, an MIT license and a git repository.

Edit gemspec summary, description, homepage, remove private gem protection, add gems:

vi *gemspec

Edit bin/console and bin/setup (add .git/safe and pry)

vi bin/setup bin/console

Commit scaffold:

git commit -am 'Initial commit'

Add code:

mkdir lib/month_ordinals/ext
vi lib/month_ordinals.rb
git add -p
git commit -v -S
git create ericboehs/month_ordinals
git push -u

Play and Test

bin/console

rake
# or
m test/month_ordinals_test.rb:5

Publish

rake -T

rake release

Updating

vi -p lib/month_ordinals.rb lib/month_ordinals/version.rb
git add -p
git commit -v
rake release

Resources

• gem install bundler
• gem install pry-awesome_print
• gem install m
• gem install hub
• gem install gist
• mkdir -p .git/safe: tpope tweet, .zshrc
• Vim gqq: :help gq
• tpope/vim-abolish
• christoomey/vim-tmux-runner
• gemfury

Create this gist

gist _README.md month_ordinals.rb

month_ordinals.rb

require "minitest/autorun"
require "date"

class MonthOrdinals
  ORDINALS = %i(first second third fourth fifth last)
  WEEKDAYS = %i(sunday monday tuesday wednesday thursday friday saturday)

  def self.for years
    years = years..years unless years.is_a? Range
    ORDINALS.map { |ordinal| { ordinal => years_map(years, ORDINALS.index(ordinal)) } }.reduce Hash.new, :merge
  end

  private

  def self.years_map years, ordinal
    years.map { |year| weekdays_map year, ordinal }.reduce Hash.new, :deep_array_merge
  end

  def self.weekdays_map year, ordinal
    WEEKDAYS.map { |weekday| [weekday, months_map(year, ordinal, WEEKDAYS.index(weekday))] }.to_h
  end

  def self.months_map year, ordinal, day_of_week, months=1..12
    months.map do |month|
      date =
        if ordinal == 5
          last_day_of_month day_of_week, year, month
        else
          ordinal_day_of_month ordinal, day_of_week, year, month
        end
      date if date.month == month
    end.compact
  end

  def self.last_day_of_month day_of_week, year, month
    date = Date.new year, month, -1
    offset = date.wday - day_of_week
    date -= offset % 7
  end

  def self.ordinal_day_of_month ordinal, day_of_week, year, month
    date = Date.new year, month, 1
    offset = day_of_week - date.wday
    date += offset % 7
    date += 7 * ordinal
  end
end

class ::Hash
  def deep_array_merge second
    merger = proc do |key, v1, v2|
      if Hash === v1 && Hash === v2
        v1.merge v2, &merger
      elsif v1.is_a?(Array) && v2.is_a?(Array)
        v1 + v2
      end
    end

    self.merge second, &merger
  end
end

class MonthOrdinalsTest < MiniTest::Test
  def test_first_sundays
    expected_month_ordinals = [
      Date.new(2001, 1, 7), Date.new(2001, 2, 4), Date.new(2001, 3, 4),
      Date.new(2001, 4, 1), Date.new(2001, 5, 6), Date.new(2001, 6, 3)
    ]
    month_ordinals = MonthOrdinals.for 2001..2002

    assert_empty expected_month_ordinals - month_ordinals[:first][:sunday]
  end

  def test_third_tuesdays
    skip
  end

  def test_last_fridays
    expected_month_ordinals = [
      Date.new(2001, 1, 26), Date.new(2001, 2, 23), Date.new(2001, 3, 30),
      Date.new(2001, 4, 27), Date.new(2001, 5, 25), Date.new(2001, 6, 29)
    ]
    month_ordinals = MonthOrdinals.for 2001..2002

    assert_empty expected_month_ordinals - month_ordinals[:last][:friday]
  end
end

Finished gem:
http://github.com/ericboehs/month_ordinals
https://rubygems.org/gems/month_ordinals