# See Pagy API documentation: https://ddnexus.github.io/pagy/api/pagy

require 'pathname'

class Pagy ; VERSION = '0.6.0'

  autoload :Backend,  'pagy/backend'
  autoload :Frontend, 'pagy/frontend'

  class OutOfRangeError < StandardError; end

  # root pathname to get the path of pagy files like templates or dictionaries
  def self.root; Pathname.new(__FILE__).dirname end

  # default core vars
  VARS = { items:20, outset:0, size:[1,4,4,1] }

  # default I18n vars
  I18N = { file: Pagy.root.join('locales', 'pagy.yml').to_s, plurals: -> (c) {c==0 && 'zero' || c==1 && 'one' || 'other'} }


  attr_reader :count, :page, :items, :vars, :pages, :last, :offset, :from, :to, :prev, :next

  # merge and validate the options, do some simple aritmetic and set the instance variables
  def initialize(vars)
    @vars = VARS.merge(vars)                                              # default vars + instance vars
    @vars[:page] = (@vars[:page]||1).to_i                                 # set page to 1 if nil
    { count:0, items:1, outset:0, page:1 }.each do |k,min|                # validate core variables
      @vars[k] >= min rescue nil || raise(ArgumentError, "expected :#{k} >= #{min}; got #{@vars[k].inspect}")
      instance_variable_set(:"@#{k}", @vars.delete(k))                    # set instance variables
    end
    @pages  = @last = [(@count.to_f / @items).ceil, 1].max                # cardinal and ordinal meanings
    (1..@last).cover?(@page) || raise(OutOfRangeError, "expected :page in 1..#{@last}; got #{@page.inspect}")
    @offset = @items * (@page - 1) + @outset                              # pagination offset + outset (initial offset)
    @items  = @count % @items if @page == @last                           # adjust items for last page
    @from   = @count == 0 ? 0 : @offset+1 - @outset                       # page begins from item
    @to     = @offset + @items - @outset                                  # page ends to item
    @prev   = (@page-1 unless @page == 1)                                 # nil if no prev page
    @next   = (@page+1 unless @page == @last)                             # nil if no next page
  end

  # return the array of page numbers and :gap items e.g. [1, :gap, 7, 8, "9", 10, 11, :gap, 36]
  def series(size=@vars[:size])
    (0..3).each{|i| size[i]>=0 rescue nil || raise(ArgumentError, "expected 4 items in :size >= 0; got #{size.inspect}")}
    series = []
    [*0..size[0], *@page-size[1]..@page+size[2], *@last-size[3]+1..@last+1].sort!.each_cons(2) do |a, b|
      if    a<0 || a==b || a>@last                                        # skip out of range and duplicates
      elsif a+1 == b; series.push(a)                                      # no gap     -> no additions
      elsif a+2 == b; series.push(a, a+1)                                 # 1 page gap -> fill with missing page
      else            series.push(a, :gap)                                # n page gap -> add :gap
      end                                                                 # skip the end boundary (last+1)
    end                                                                   # shift the start boundary (0) and
    series.tap{|s| s.shift; s[s.index(@page)] = @page.to_s}               # convert the current page to String
  end

end