vim-airline/autoload/airline/builder.vim

" MIT license. Copyright (c) 2013 Bailey Ling.
" vim: et ts=2 sts=2 sw=2 fdm=indent

function! airline#builder#new(active, highlighter)
  let builder = {}
  let builder._sections = []
  let builder._active = a:active
  let builder._highlighter = a:highlighter

  function! builder.split(gutter)
    call add(self._sections, ['|', a:gutter])
  endfunction

  function! builder.add_section(group, contents)
    call add(self._sections, ['airline_'.a:group, a:contents])
  endfunction

  function! builder.add_raw(text)
    call add(self._sections, ['_', a:text])
  endfunction

  function! builder._group(group)
    return self._active ? a:group : a:group.'_inactive'
  endfunction

  function! builder.build()
    let line = '%{airline#check_mode()}'
    let side = 0
    let prev_group = ''
    for section in self._sections
      if section[0] == '|'
        let side = 1
        let line .= '%#'.prev_group.'#'.section[1]
        let prev_group = ''
        continue
      endif
      if section[0] == '_'
        let line .= section[1]
        continue
      endif

      if prev_group != ''
        call self._highlighter.add_separator(self._group(prev_group), self._group(section[0]))
        let line .= side == 0
              \ ? '%#'.self._group(section[0]).'_to_'.self._group(prev_group).'#'
              \ : '%#'.self._group(prev_group).'_to_'.self._group(section[0]).'#'
        let line .= side == 0
              \ ? self._active ? g:airline_left_sep : g:airline_left_alt_sep
              \ : self._active ? g:airline_right_sep : g:airline_right_alt_sep
      endif

      let line .= '%#'.self._group(section[0]).'#'.section[1]
      let prev_group = section[0]
    endfor

    return {
          \ 'statusline': line,
          \ }
  endfunction

  return builder
endfunction