class Ariadne::PaginationCalculator

def calculate_total_pages
  return 1 if total_count.zero?
  (total_count.to_f / items_per_page).ceil
end

def from
  return 0 if total_count.zero?
  (page - 1) * items_per_page + 1
end

def handle_page_overflow(requested_page)
  return 1 if requested_page < 1
  return pages if requested_page > pages
  requested_page
end

def initialize(total_count:, page: 1, items_per_page: 10)
  @total_count = total_count
  @items_per_page = items_per_page
  @pages = calculate_total_pages
  @page = handle_page_overflow(page)
end

def next_page
  page < pages ? page + 1 : nil
end

def page_series
  return [] if pages <= 1
  return (1..pages).to_a if pages <= 5
  links = []
  links << 1
  if page <= 3
    # Near the beginning: 1 2 3 4 5 6 7 8 ... 20
    (2..8).each { |n| links << n if n <= pages }
    links << nil if pages > 8
    links << pages if pages > 8
  elsif page >= pages - 2
    # Near the end: 1 ... 13 14 15 16 17 18 19 20
    links << nil
    ((pages - 7)..pages).each { |n| links << n if n > 1 }
  else
    # Middle range: 1 ... 9 10 11 12 13 14 ... 20
    links << nil
    ((page - 2)..(page + 2)).each { |n| links << n }
    links << nil
    links << pages
  end
  links
end

def prev_page
  page > 1 ? page - 1 : nil
end

def to
  return 0 if total_count.zero?
  [page * items_per_page, total_count].min
end