require 'osu_term/version'

module OSU
  # A simple helper class to turn strms into readable human names. It can also
  # determine if an strm took place during quarters, semesters, or during the
  # quarter-to-semester transition. It can also calculate the next strm.
  class Term
    include Comparable

    attr_reader :strm

    # this strm was used to to transition from quarters to semesters
    QUARTER_TO_SEMESTER_STRM = '1123'.freeze

    # Initializes a new OsuTerm based on the strm passed in.
    #
    # @param args [Hash] A hash of arguments to pass into the constructor.
    # @option args [String] :strm
    #
    # The osu term's strm number. This number has several requirements:
    # 1. The strm must be a string that's 4 digits in length.
    # 2. The first character must be 0 or 1. 0 = 1900-1999, 1 = 2000 and beyond
    # 3. strm's 2nd and 3rd char represents last two digits of the year
    # 4. the strm's last digit:
    #    - quarter:  0 (winter), 2 (Spring), 4 (Summer), or 8 (Autumn)
    #    - semester: 2 (Spring), 4 (Summer), or 8 (Autumn)
    #
    # For example, '1152' stands for "Spring 2015".
    # 1 = 2000
    # 15 = 2015
    # 2 = Spring
    #
    # @return [OsuTerm] A new OSU::Term object.
    # @raise [ArgumentError] Raised when the strm is malformed.
    def initialize(strm:)
      strm = strm.to_s
      raise ArgumentError, 'strm must be 4 digits in length' unless FOUR_DIGITS.match?(strm)
      raise ArgumentError, 'strm must start with 0 or 1' unless CENTURIES.match?(strm)

      @strm = strm

      if strm < QUARTER_TO_SEMESTER_STRM
        extend(Quarter)
        raise ArgumentError, 'strm must end in 0, 2, 4, or 8' unless Quarter::SEASONS.match?(strm)
      elsif strm == QUARTER_TO_SEMESTER_STRM
        extend(TransitionTerm)
      else
        extend(Semester)
        raise ArgumentError, 'strm must end in 2, 4, or 8' unless Semester::SEASONS.match?(strm)
      end
    end

    def name
      names[season_number].fetch(:full)
    end

    def abbr_name
      names[season_number].fetch(:abbr)
    end

    def abbr_year
      strm[1..2]
    end

    def year
      @year ||= "#{century}#{abbr_year}"
    end

    def description
      @description ||= "#{name} #{year} #{type}"
    end

    def to_s
      description
    end

    def abbreviated
      @abbreviated ||= "#{abbr_name} '#{abbr_year} #{abbr_type}"
    end

    def <=>(other)
      strm <=> other.strm
    rescue NoMethodError
      nil
    end

    def next_strm
      if transition_semester?
        '1124'
      else
        next_season_number = next_season.fetch(season_number)

        case season_number
        when 0, 2, 4
          century_and_decade = strm[0..2]

          "#{century_and_decade}#{next_season_number}"
        when 8
          century_indicator = strm[0].to_i
          next_year = decade + 1

          if next_year == 100
            [century_indicator + 1, 0, 0, next_season_number].join
          else
            century_indicator.to_s + next_year.to_s.rjust(2, '0') + next_season_number.to_s
          end
        end
      end
    end

    def next
      self.class.new(strm: next_strm)
    end

    private

    FOUR_DIGITS = /^\d{4}$/
    CENTURIES = /(0|1)/

    def season_number
      @season_number ||= strm[-1].to_i
    end

    def century
      @century ||= centuries[strm[0].to_i]
    end

    def decade
      abbr_year.to_i
    end
  end

  # Logic for OSU quarters
  module Quarter
    SEASONS = /(0|2|4|8)$/ # Winter, Spring, Summer, Autumn

    def type
      'Quarter'
    end

    def abbr_type
      'Qtr'
    end

    def quarter?
      true
    end

    def semester?
      false
    end

    def transition_semester?
      false
    end

    private

    def names
      {
        0 => { full: 'Winter', abbr: 'Wi' },
        2 => { full: 'Spring', abbr: 'Sp' },
        4 => { full: 'Summer', abbr: 'Su' },
        8 => { full: 'Autumn', abbr: 'Au' }
      }
    end

    def centuries
      {
        0 => '19',
        1 => '20'
      }
    end

    def next_season
      {
        0 => 2,
        2 => 4,
        4 => 8,
        8 => 0
      }
    end
  end

  # Logic for OSU transition terms
  module TransitionTerm
    SEASONS = /(3)$/ # Transition

    def type
      'Semester Status Recalculation'
    end

    def abbr_type
      'Sem'
    end

    def quarter?
      false
    end

    def semester?
      true
    end

    def transition_semester?
      true
    end

    private

    def names
      Hash.new(full: 'Spring', abbr: 'Sp')
    end

    def centuries
      Hash.new('20')
    end
  end

  # Logic for OSU semesters
  module Semester
    SEASONS = /(2|4|8)$/ # Spring, Summer, Autumn

    def type
      strm[-1] == SUMMER ? 'Term' : 'Semester'
    end

    def abbr_type
      strm[-1] == SUMMER ? 'Trm' : 'Sem'
    end

    def quarter?
      false
    end

    def semester?
      true
    end

    def transition_semester?
      false
    end

    private

    SUMMER = '4'.freeze

    def names
      {
        2 => { full: 'Spring', abbr: 'Sp' },
        4 => { full: 'Summer', abbr: 'Su' },
        8 => { full: 'Autumn', abbr: 'Au' }
      }
    end

    def centuries
      Hash.new('20')
    end

    def next_season
      {
        2 => 4,
        4 => 8,
        8 => 2
      }
    end
  end
end