Get date of each week start

weeks_between.rb

def weeks_between(start_at, finish_at)
  results = []

  week_start = start_at.beginning_of_week
  week_end   = start_at.end_of_week

  while week_end <= finish_at.end_of_week
    # Collect these
    results << [week_start, week_end]

    # Update dates
    week_start = week_end + 1.second
    week_end = week_start.end_of_week
  end

  results
end

weeks = weeks_between(Time.parse('2020-08-03'), Time.parse('2021-12-31')).map(&:first).map(&:to_date).map(&:iso8601)