module TopNLoader

# File lib/top_n_loader.rb, line 7
def load_associations(base_klass, ids, relation, limit:, order: nil)
  validate_ar_class! :base_klass, base_klass
  validate_limit! limit
  return Hash.new { [] } if ids.empty? || limit.zero?
  klass = base_klass.reflect_on_association(relation.to_sym).klass
  order_option = { limit: limit, **parse_order(klass, order) }
  sql = SQLBuilder.top_n_association_sql base_klass, klass, relation, **order_option
  records = klass.find_by_sql([sql, ids])
  format_result(records, klass: klass, **order_option)
end

# File lib/top_n_loader.rb, line 18
def load_groups(klass, column, keys, limit:, order: nil, condition: nil)
  validate_ar_class! :klass, klass
  validate_limit! limit
  return Hash.new { [] } if keys.empty? || limit.zero?
  options = {
    klass: klass,
    group_column: column,
    limit: limit,
    **parse_order(klass, order)
  }
  records = klass.find_by_sql(
    SQLBuilder.top_n_group_sql(
      group_keys: keys,
      condition: condition,
      **options
    )
  )
  format_result records, **options
end

# File lib/top_n_loader.rb, line 66
def format_result(records, klass:, group_column: nil, limit:, order_mode:, order_key:)
  primary_key = klass.primary_key
  type = klass.attribute_types[group_column.to_s] if group_column
  result = records.group_by do |record|
    key = record.top_n_group_key
    type ? type.cast(key) : key unless key.nil?
  end
  result.transform_values! do |grouped_records|
    existings, blanks = grouped_records.partition { |o| o[order_key] }
    existings.sort_by! { |o| [o[order_key], o[primary_key]] }
    blanks.sort_by! { |o| o[primary_key] }
    ordered = blanks + existings
    ordered.reverse! if order_mode == :desc
    ordered.take limit
  end
  Hash.new { [] }.update result
end

# File lib/top_n_loader.rb, line 49
def parse_order(klass, order)
  key, mode = begin
    case order
    when Hash
      raise ArgumentError, 'invalid order' unless order.size == 1
      order.first
    when Symbol
      [klass.primary_key, order]
    when NilClass
      [klass.primary_key, :asc]
    end
  end
  raise ArgumentError, "invalid order key: #{key}" unless klass.has_attribute? key
  raise ArgumentError, "invalid order mode: #{mode.inspect}" unless %i[asc desc].include? mode
  { order_key: key, order_mode: mode }
end

# File lib/top_n_loader.rb, line 40
def validate_ar_class!(var_name, klass)
  return if klass.is_a?(Class) && klass < ActiveRecord::Base
  raise ArgumentError, "#{var_name} should be a subclass of ActiveRecord::Base"
end

# File lib/top_n_loader.rb, line 45
def validate_limit!(limit)
  raise ArgumentError, 'negative limit' if limit < 0
end