class IRB::Pager

def content_exceeds_screen_height?(content)
  screen_height, screen_width = begin
    Reline.get_screen_size
  rescue Errno::EINVAL
    [24, 80]
  end
  pageable_height = screen_height - 3 # leave some space for previous and the current prompt
  # If the content has more lines than the pageable height
  content.lines.count > pageable_height ||
    # Or if the content is a few long lines
    pageable_height * screen_width < Reline::Unicode.calculate_width(content, true)
end

def page
  if STDIN.tty? && pager = setup_pager
    begin
      pid = pager.pid
      yield pager
    ensure
      pager.close
    end
  else
    yield $stdout
  end
# When user presses Ctrl-C, IRB would raise `IRB::Abort`
# But since Pager is implemented by running paging commands like `less` in another process with `IO.popen`,
# the `IRB::Abort` exception only interrupts IRB's execution but doesn't affect the pager
# So to properly terminate the pager with Ctrl-C, we need to catch `IRB::Abort` and kill the pager process
rescue IRB::Abort
  Process.kill("TERM", pid) if pid
  nil
rescue Errno::EPIPE
end

def page_content(content)
  if content_exceeds_screen_height?(content)
    page do |io|
      io.puts content
    end
  else
    $stdout.puts content
  end
end

def setup_pager
  require 'shellwords'
  PAGE_COMMANDS.each do |pager|
    pager = Shellwords.split(pager)
    next if pager.empty?
    if pager.first == 'less' || pager.first == 'more'
      pager << '-R' unless pager.include?('-R')
    end
    begin
      io = IO.popen(pager, 'w')
    rescue
      next
    end
    if $? && $?.pid == io.pid && $?.exited? # pager didn't work
      next
    end
    return io
  end
  nil
end