module InterpretDate

# File lib/interpret_date.rb, line 6
def interpret_date(date_input, buffer = 10)
  # the number of years previous turn of the century + buffer number of years
  @century_divider = Date.today.year + buffer - current_century
  convert_date(date_input)
end

# File lib/interpret_date.rb, line 12
def interpret_dob_date(date_input)
  # the number of years since previous turn of the century
  @century_divider = Date.today.year - current_century
  convert_date(date_input)
end

# File lib/interpret_date.rb, line 29
def contains_only_eight_digits(value)
  /^\d{8}$/ =~ value
end

# File lib/interpret_date.rb, line 25
def contains_only_six_digits(value)
  /^\d{6}$/ =~ value
end

# File lib/interpret_date.rb, line 33
def convert_date(date_input)
  # Only run the interpret_date code if we have a non-nil string,
  # otherwise, use #to_date to strip any time or timezone info
  return date_input.to_date unless date_input.is_a?(String) || date_input.nil?

  if contains_only_six_digits(date_input)
    # The date_input only contains digits, and must
    # be in the form MMDDYY
    month = date_input[0,2].to_i
    day   = date_input[2,2].to_i
    year  = date_input[4,2].to_i
  elsif contains_only_eight_digits(date_input)
    # The date_input only contains digits, and must
    # be in the form MMDDYYYY
    month = date_input[0,2].to_i
    day   = date_input[2,2].to_i
    year  = date_input[4,4].to_i
  elsif db_formatted_date(date_input)
    year, month, day = date_input.split("-").collect { |element| element.to_i }
  elsif slash_based_date(date_input)
    # Break the string apart using the delimiters '-', '/', and '.', making each element an integer
    month, day, year = date_input.split(/[-\.\/]+/).collect { |element| element.to_i }
  else
    return nil
  end

  # Do not allow a three-digit year
  return nil if year.to_s.size == 3

  # Modify two-digit years
  if year < 100
    # @century_divider represents the year where we
    # divide 2 digit years from the last century or the current one
    if year > @century_divider
      year += current_century - 100
    else
      year += current_century
    end
  end

  begin
    Date.new(year, month, day)
  rescue
    nil
  end
end

# File lib/interpret_date.rb, line 20
def current_century
  year = Date.today.year
  "#{year.to_s[0..1]}00".to_i
end

# File lib/interpret_date.rb, line 95
def db_formatted_date(value)
  /^\d{4}-\d{2}-\d{2}$/ =~ value
end

# File lib/interpret_date.rb, line 90
def slash_based_date(value)
  /^\d{1,2}([-\.\/]+)\d{1,2}\1\d{2,4}$/ =~ value
end