class Pagy

def self.root
  @root ||= Pathname.new(__dir__).freeze
end

def initialize(vars)
  normalize_vars(vars)
  setup_vars(count: 0, page: 1, outset: 0)
  setup_items_var
  setup_pages_var
  raise OverflowError.new(self, :page, "in 1..#{@last}", @page) if @page > @last
  @offset = (@items * (@page - 1)) + @outset
  @from   = [@offset - @outset + 1, @count].min
  @to     = [@offset - @outset + @items, @count].min
  @in     = [@to - @from + 1, @count].min
  @prev   = (@page - 1 unless @page == 1)
  @next   = @page == @last ? (1 if @vars[:cycle]) : @page + 1
end

def normalize_vars(vars)
  @vars = DEFAULT.merge(vars.delete_if { |k, v| DEFAULT.key?(k) && (v.nil? || v == '') })
end

def series(size = @vars[:size])
  return [] if size.empty?
  raise VariableError.new(self, :size, 'to contain 4 items >= 0', size) \
        unless size.size == 4 && size.all? { |num| !num.negative? rescue false } # rubocop:disable Style/RescueModifier
  # This algorithm is up to ~5x faster and ~2.3x lighter than the previous one (pagy < 4.3)
  left_gap_start  =     1 + size[0]   # rubocop:disable Layout/ExtraSpacing, Layout/SpaceAroundOperators
  left_gap_end    = @page - size[1] - 1
  right_gap_start = @page + size[2] + 1
  right_gap_end   = @last - size[3]
  left_gap_end    = right_gap_end  if left_gap_end   > right_gap_end
  right_gap_start = left_gap_start if left_gap_start > right_gap_start
  series          = []
  start           = 1
  if (left_gap_end - left_gap_start).positive?
    series.push(*start..(left_gap_start - 1), :gap)
    start = left_gap_end + 1
  end
  if (right_gap_end - right_gap_start).positive?
    series.push(*start..(right_gap_start - 1), :gap)
    start = right_gap_end + 1
  end
  series.push(*start..@last)
  series[series.index(@page)] = @page.to_s
  series
end

def setup_items_var
  setup_vars(items: 1)
end

def setup_pages_var
  @pages = @last = [(@count.to_f / @items).ceil, 1].max
end

def setup_vars(name_min)
  name_min.each do |name, min|
    raise VariableError.new(self, name, ">= #{min}", @vars[name]) \
          unless @vars[name] && instance_variable_set(:"@#{name}", @vars[name].to_i) >= min
  end
end