function! s:AlternateFile()
  let fn = substitute(expand('%'), "^".getcwd()."/", "", "")
  let head = fnamemodify(fn, ':h')
  let tail = fnamemodify(fn, ':t')

  if match(head, '^lib') >= 0
    return substitute(head, '^lib', 'test', '').'/test_'.tail
  elseif match(head, '^test') >= 0
    return substitute(head, '^test', 'lib', '').'/'.substitute(tail, '^test_', '', '')
  endif
  return ''
endfunction

function! s:Alternate(cmd)
  let file = s:AlternateFile()
  "if file != '' && filereadable(file)
    if a:cmd == 'T'
      let cmd = 'tabe'
    elseif a:cmd == 'S'
      let cmd = 'sp'
    else
      let cmd = 'e'
    endif
    exe ':'.cmd.' '.file
  "else
    "echomsg 'No alternate file is defined: '.file
  "endif
endfunction

function! s:Init(path)
  try
    command A  :call s:Alternate('')
    command AE :call s:Alternate('E')
    command AS :call s:Alternate('S')
    command AV :call s:Alternate('V')
    command AT :call s:Alternate('T')
  catch /^Vim\%((\a\+)\)\=:E174/
  endtry
endfunction

function! s:Detect()
  let dir = getcwd()
  if filereadable(dir . '/config/environment.rb')
    " don't load if this is a rails project
    return 0
  endif

  if filereadable(dir . '/Rakefile') && isdirectory(dir . '/lib') && filereadable(dir . '/test/helper.rb')
    return s:Init(dir)
  endif

  return 0
endfunction

augroup nonRailsRubyDetect
  autocmd VimEnter * call s:Detect()
augroup END