module Tournaments
  class GenerateGroupMatches
    def self.call(tournament:, start_at: nil)
      new(tournament, start_at: start_at).call
    end

    def initialize(tournament, start_at: nil)
      @tournament = tournament
      @start_at = start_at
    end

    def call
      Tournaments::Entitlements.new(@tournament.club).assert_writable!
      created = []
      cursor = @start_at || Time.zone.local(@tournament.starts_on.year, @tournament.starts_on.month, @tournament.starts_on.day, 9, 0, 0)
      courts = @tournament.court_list
      court_idx = 0

      @tournament.groups.includes(:participants).order(:position).each do |group|
        pairs = round_robin(group.participants.to_a)
        pairs.each do |home, away|
          next if home.blank? || away.blank?

          match = Tournaments::ScheduleMatch.call(
            tournament: @tournament,
            attrs: {
              home_participant_id: home.id,
              away_participant_id: away.id,
              tournament_group_id: group.id,
              court: courts[court_idx % courts.size],
              scheduled_at: cursor
            }
          )
          created << match
          court_idx += 1
          if (court_idx % courts.size).zero?
            cursor += 1.hour
            cursor = next_day_morning(cursor) if cursor.to_date > @tournament.ends_on
          end
        end
      end
      created
    end

    private

    def round_robin(participants)
      list = participants.dup
      return [] if list.size < 2

      list << nil if list.size.odd?
      n = list.size
      rounds = n - 1
      pairs = []
      rounds.times do
        (n / 2).times do |i|
          a = list[i]
          b = list[n - 1 - i]
          pairs << [a, b] if a && b
        end
        list = [list[0]] + [list[-1]] + list[1..-2]
      end
      pairs
    end

    def next_day_morning(time)
      nxt = time.to_date + 1.day
      nxt = @tournament.starts_on if nxt > @tournament.ends_on
      Time.zone.local(nxt.year, nxt.month, nxt.day, 9, 0, 0)
    end
  end
end