Salaray Pattern Generator: Tool for creating sets of data for salaries paid in different patterns (weekly, two weekly, four weekly and monthly)

salary_pattern_generator.rb

require 'active_support'
require 'active_support/core_ext/integer/time'

class SalaryPatternGenerator
  def self.generate(*args)
    new(*args).generate
  end

  attr_reader :period, :salary, :day_offset, :salary_offset, :start_at

  def initialize(period:, salary:, day_offset:nil, salary_offset:nil, start_at:Time.now.utc)
    @period = period
    @salary = salary
    @salary_offset = salary_offset
    @day_offset = day_offset
    @start_at = start_at
  end

  def generate
    case period
    when :monthly
      generate_monthly
    when :weekly
      generate_weekly
    when :two_weekly
      generate_weekly(2)
    when :four_weekly
      generate_weekly(4)
    end
  end

  def generate_monthly
    dates_for 0..2, :month
  end

  def generate_weekly(step=1)
    weeks = ((start_at_normalized - 3.months.ago) / 1.week).to_i
    dates_for (0..weeks).step(step), :week
  end

  def dates_for(points, method)
    points.to_a
    points.each_with_object({}) do |n,h|
      time = sample_day(n.__send__(method).ago + start_offset)
      h[time] = sample_salary
    end
  end

  def sample_day(day)
    return day unless day_offset
    offset = sample_around 0, day_offset
    day + offset.days
  end

  def sample_salary
    return salary unless salary_offset
    sample_around salary, salary_offset
  end

  def sample_around(middle, offset)
    first = middle - offset
    last = middle + offset
    (first..last).to_a.sample
  end

  def start_offset
    @start_offset ||= start_at_normalized - Time.now.utc.beginning_of_day
  end

  def start_at_normalized
    @start_at_normalized ||= (start_at.utc.beginning_of_day + 1.day)
  end
end

start_at = Time.parse('2019-06-30 00:00:00').utc

puts 'Raw data of monthly salary with day offset'
m = SalaryPatternGenerator.generate(period: :monthly, salary: 1000, day_offset: 2, start_at: start_at)
p m

puts 'Weekly salary values showing effect of salary offset'
w = SalaryPatternGenerator.generate(period: :weekly, salary: 200, salary_offset: 10, start_at: start_at)
p w.values
puts 'Weekly days showing pattern back from start_at'
p w.keys.map(&:day)

puts 'Two weekly days showing pattern back from start_at'
ww = SalaryPatternGenerator.generate(period: :two_weekly, salary: 200, start_at: start_at)
p ww.keys.map(&:day)

puts 'Four weekly days showing pattern back from start_at'
wwww = SalaryPatternGenerator.generate(period: :four_weekly, salary: 200, start_at: start_at)
p wwww.keys.map(&:day)