pager_preview_test.rb

require 'irb'
require 'stringio'

def count_lines(ascii_text, width)
  ascii_text.lines.sum{|l| [(l.chomp.size-1)/40+1,1].max }
end
10000.times do |i|
  width = 40
  height= 20
  out = IRB::Pager::PageOverflowIO.new(width, height, ->*{})
  chars = [*'a'..'f', "\n"]
  escs = ["\e[1m", "\e[31;42m", ""]
  buf = StringIO.new
  rand(2..50).times do
    s = (rand**3*100).floor.times.map{chars.sample+escs.sample}.join
    if rand < 0.95
      out.write(s)
      buf.write(s)
    else
      out.puts(s)
      buf.puts(s)
    end
  end
  ascii_all = out.string.gsub(/\e\[[\d;]+m/,'')
  ascii_firstpage = (out.first_page_lines&.join||out.string).gsub(/\e\[[\d;]+m/,'')
  raise unless out.string == buf.string
  if out.multipage?
    p i => :multipage
    raise unless count_lines(ascii_firstpage, width) == height
    raise unless count_lines(ascii_all[0, ascii_firstpage.size + 1], width) != height
    raise unless ascii_all.start_with?(ascii_firstpage)
  else
    p i => :single
    raise unless count_lines(ascii_firstpage, width) <= height
  end
end