class Pagy

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

def initialize(vars)
  normalize_vars(vars)
  setup_vars(count: 0, page: 1, outset: 0)
  setup_items_var
  setup_offset_var
  setup_last_var
  raise OverflowError.new(self, :page, "in 1..#{@last}", @page) if @page > @last
  @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 label
  @page.to_s
end

def label_for(page)
  page.to_s
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], **_)
  raise VariableError.new(self, :size, 'to be an Integer >= 0', size) \
        unless size.is_a?(Integer) && size >= 0
  return [] if size.zero?
  [].tap do |series|
    if size >= @last
      series.push(*1..@last)
    else
      left  = ((size - 1) / 2.0).floor             # left half might be 1 page shorter for even size
      start = if @page <= left                     # beginning pages
                1
              elsif @page > (@last - size + left)  # end pages
                @last - size + 1
              else                                 # intermediate pages
                @page - left
              end
      series.push(*start...start + size)
      # Set first and last pages plus gaps when needed, respecting the size
      if vars[:ends] && size >= 7
        series[0]  = 1     unless series[0]  == 1
        series[1]  = :gap  unless series[1]  == 2
        series[-2] = :gap  unless series[-2] == @last - 1
        series[-1] = @last unless series[-1] == @last
      end
    end
    series[series.index(@page)] = @page.to_s
  end
end

def setup_items_var
  setup_vars(items: 1)
end

def setup_last_var
  @last = [(@count.to_f / @items).ceil, 1].max
  @last = vars[:max_pages] if vars[:max_pages] && @last > vars[:max_pages]
end

def setup_offset_var
  @offset = (@items * (@page - 1)) + @outset  # may be already set from gear_box
end

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