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_last_var
  raise OverflowError.new(self, :page, "in 1..#{@last}", @page) if @page > @last
  setup_offset_var
  @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], **_)
  series = []
  if size.is_a?(Array) && 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]
    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
    start           = 1
    if (left_gap_end - left_gap_start).positive?
      series.push(*start...left_gap_start, :gap)
      start = left_gap_end + 1
    end
    if (right_gap_end - right_gap_start).positive?
      series.push(*start...right_gap_start, :gap)
      start = right_gap_end + 1
    end
    series.push(*start..@last)
  elsif size.is_a?(Integer) && size.positive?    # only central series
    # The simplest and fastest algorithm
    size  = @last if size > @last                # reduce the max size to @last
    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 = (start..start + size - 1).to_a
  else
    return [] if size.empty?
    raise VariableError.new(self, :size, 'to be a single positive Integer or an Array of 4', size)
  end
  series[series.index(@page)] = @page.to_s
  series
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