# cleanname.rb
# 
# Copyright (c) 2003 Masahiro Sakai <sakai@tom.sfc.keio.ac.jp>
# 
# This program is free software.
# You can distribute/modify this program under the same terms of ruby.
# 

#
# Usage
# -----
# 
# File.cleanname takes a filename and by lexical processing only
# returns the shortest string that names the same (possibly
# hypothetical) file. It eliminates multiple and trailing slashes, and
# it lexically interprets . and .. directory components in the name.
# 
# Bibliography
# ------------
# 
# [1]  Rob Pike, ``Lexical File Names in Plan 9 or Getting Dot-Dot Right''. 
#      Proceedings of 2000 USENIX Annual Technical Conference
#


def File.cleanname(path)
  path = path.dup
  
  # 1. reduce multile slashes to a single slash
  path.gsub!(%r!/+!, '/')
 
  # 2. Eliminate . path name elements (the current directory).
  path.gsub!(%r!(\A|/)\.(\Z|/)!, '\1')

  # 3. Eliminate .. path name elements (the parent directory) and
  # the non-. non-.., element that precedes them.
  re = %r!(\A|/)(?:[^/.]|(?:\.\.[^/])|(?:\.[^/.]))[^/]*/\.\.(\Z|/)!
  while path.gsub!(re, '\1')
  end

  # 4. Eliminate .. elements that begin a rooted
  # path, that is, replace /.. by / at the beginning
  # of a path.
  # 
  # 5. Leave intact .. elements that begin a nonrooted path.
  path.sub!(%r!\A(?:/\.\.)+!, '/')
  
  path.sub!(%r!/\Z!, '') unless path == '/' # remove trailing slash
  path.empty? ? '.' : path
end




if __FILE__ == $0
  def test(src, expected)
    dest = File.cleanname(src)
    if dest == expected
      puts "pass"
    else
      puts "fail: File.cleanname(#{src.dump})=#{dest.dump} is not equal to #{expected.dump}"
    end
  end

  def test_fix(src)
    test(src, src)
  end

  test('./', '.')
  test('../', '..')

  test('./foo', 'foo')
  test('foo/../bar', 'bar')
  test('../foo/.././bar/../.', '..')

  test_fix('../.htaccess')
  test_fix('../../foo/bar')
  test_fix('..')
  test_fix('.')
  test_fix('/')
end