VIM: flip between test and production files (rails/rspec)

gistfile1.txt

function! FindOrCreateAlternate()
  let buflist = []
  let bufcount = bufnr("$")
  let currbufnr = 1
  let altname = AlternateFileName()
  while currbufnr <= bufcount
    if(buflisted(currbufnr))
      let currbufname = bufname(currbufnr)

      let curmatch = tolower(currbufname)

      if(altname == currbufname)
        call add(buflist, currbufnr)
      endif
    endif
    let currbufnr = currbufnr + 1
  endwhile

  if(len(buflist) > 1)
    exec ":b " . get(buflist,0)
  else
    :w
    exec ":e " . altname
  endif

endfunction

function! AlternateFileName()
  "todo: deal with projects that have /spec/app
  let current = fnamemodify(expand("%"), ':p')
  if current =~ '/spec/'
    if current =~ '/spec/javascripts/'
      let altname = substitute(current, "/spec/","/public/", 'g')
      let altname = substitute(altname, "\Spec\.js", ".js",'g')
    else
      let altname = substitute(current, "/spec/lib/","/lib/", 'g')
      let altname = substitute(altname, "/spec/","/app/", 'g')
      let altname = substitute(altname, "\.erb_spec\.rb", ".erb",'g')
      let altname = substitute(altname, "_spec\.rb", ".rb",'g')
    endif
  elseif current =~ '/test/'
    " todo: deal with this
  else
    if current =~ '/javascripts/'
      let altname = substitute(current, "/public/","/spec/", 'g')
      let altname = substitute(altname, ".js", "Spec.js", 'g')
    else
      let altname = substitute(current, "/app/","/spec/", 'g')
      let altname = substitute(altname, "/lib/", "/spec/lib/", "g")

      let altname = substitute(altname, "\.rb", "_spec.rb", 'g')
    endif
  endif

  return altname
endfunction

function! TestToggleNewTabVertical()
  :vsplit
  call FindOrCreateAlternate()
endfunction

function! TestToggleNewTabHorizontal()
  :split
  call FindOrCreateAlternate()
endfunction

" flip between test/subject (same window, vsp, sp)
nnoremap <leader>tt :call FindOrCreateAlternate()<CR>
nnoremap <leader>tv :call TestToggleNewTabVertical()<CR>
nnoremap <leader>th :call TestToggleNewTabHorizontal()<CR>