class Date

# File lib/date_plus.rb, line 30
def end_of_month
  Date.civil(year, month, -1)
end

# File lib/date_plus.rb, line 26
def end_of_week
  self + (6 - cwday)
end

# File lib/date_plus.rb, line 34
def end_of_year
  Date.civil(year, -1, -1)
end

# File lib/date_plus.rb, line 53
def future_instance_of_day(day, instances_away=1)
  valid_day_or_error(day)
  fixnum_or_nil_or_error(instances_away)
  self.step(self + (31 * instances_away), step=+1).reverse_each do |current_day|
    return current_day if current_day.day === day
  end
end

# File lib/date_plus.rb, line 61
def future_instance_of_month(month_name, instances_away=1)
  valid_month_or_error(month_name)
  fixnum_or_nil_or_error(instances_away)
  months = []
  first_of_month = Date.today.start_of_month
  (instances_away * 12).times do
    months.push(first_of_month)
    first_of_month = first_of_month.next_month
  end
  months.reverse.each {|first_of_month| return first_of_month if first_of_month.month == Date.parse(month_name).month }
end

# File lib/date_plus.rb, line 45
def future_instance_of_weekday(weekday, instances_away=1)
  raise 'Argument passed is not a weekday' unless weekday.class == String || !weekday_names.include?(weekday.downcase.capitalize)
  fixnum_or_nil_or_error(instances_away)
  self.step(self + (7 * instances_away), step=+1).reverse_each do |current_day|
    return current_day if current_day.weekday_name == weekday.downcase.capitalize
  end
end

# File lib/date_plus.rb, line 73
def future_year(instances_away)
  fixnum_nil_or_error(instances_away)
  year = Date.today.start_of_year
  years = []
  (instances_away + 1).times {years.push(year); year = year.next_year}
  return years.last
end

# File lib/date_plus.rb, line 10
def month_name
  self.strftime('%B')
end

# File lib/date_plus.rb, line 40
def next_instance_of(options)
  options.each { |k, v| options[k] = v.downcase.capitalize if v.class == String }
  return check_dates_by_year(self, end_of_year, options)
end

# File lib/date_plus.rb, line 18
def start_of_month
  self - day + 1
end

# File lib/date_plus.rb, line 14
def start_of_week
  self - cwday
end

# File lib/date_plus.rb, line 22
def start_of_year
  self - yday + 1
end

# File lib/date_plus.rb, line 6
def weekday_name
  self.strftime('%A')
end

# File lib/date_plus.rb, line 99
def check_dates_by_year(start_date, end_date, options)
  start_date.step(end_date, step=+1) do |date|
    return date if options.all? { |k, v| date.valid_condition(k, v) }
  end
  next_year_start = end_date + 1
  check_dates_by_year(next_year_start, next_year_start.end_of_year, options)
end

# File lib/date_plus.rb, line 107
def fixnum_or_nil_or_error(arg)
  raise 'Argument passed is not an integer' unless arg.class == Fixnum || arg.nil?
end

# File lib/date_plus.rb, line 91
def matches_value(field, value)
  self.send(field) == value
end

# File lib/date_plus.rb, line 87
def month_names
  ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December']
end

# File lib/date_plus.rb, line 95
def valid_condition(field, condition)
  self.send(field) == condition
end

# File lib/date_plus.rb, line 111
def valid_day_or_error(arg)
  raise 'Argument passed is not a valid day' unless arg.class == Fixnum && 0 < arg && arg < 32
end

# File lib/date_plus.rb, line 115
def valid_month_or_error(arg)
  raise 'Argument passed is not a valid month' unless arg.class == String && month_names.include?(arg.downcase.capitalize)
end

# File lib/date_plus.rb, line 83
def weekday_names
  ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday']
end