" MIT License. Copyright (c) 2013-2018 Bailey Ling et al.
" vim: et ts=2 sts=2 sw=2

scriptencoding utf-8

let s:prototype = {}

function! s:prototype.insert_tabs(curtab) dict
  let self._tabs_position = self.get_position()
  let self._curtab = a:curtab
endfunction

function! s:prototype.build() dict
  if has_key(self, "_tabs_position")
    let tab_nr_type = get(g:, 'airline#extensions#tabline#tab_nr_type', 0)
    let num_tabs = tabpagenr('$')
    let curtab = self._curtab
    let left_tab = curtab - 1
    let right_tab = curtab + 1
    let left_position = self._tabs_position
    let right_position = self._tabs_position + 1
    let remaining_space = &columns - s:strchars(s:evaluate_tabline(self._build()))

    let left_sep_size = s:strchars(s:evaluate_tabline(self._context.left_sep))
    let left_alt_sep_size = s:strchars(s:evaluate_tabline(self._context.left_alt_sep))

    let skipped_tabs_marker = get(g:, 'airline#extensions#tabline#overflow_marker', g:airline_symbols.ellipsis)
    let skipped_tabs_marker_size = s:strchars(s:evaluate_tabline(skipped_tabs_marker))
    " The left marker will have left_alt_sep, and the right will have left_sep.
    let remaining_space -= 2 * skipped_tabs_marker_size + left_sep_size + left_alt_sep_size

    " Add the current tab
    let tab_title = self.get_title(tab_nr_type, curtab)
    let remaining_space -= s:strchars(s:evaluate_tabline(tab_title))
    " There are always two left_seps (either side of the selected tab) and all
    " other seperators are left_alt_seps.
    let remaining_space -= 2 * left_sep_size - left_alt_sep_size
    call self.insert_section(self.get_group(curtab), tab_title, left_position)

    if get(g:, 'airline#extensions#tabline#current_first', 0)
      " always have current tabpage first
      let left_position += 1
    endif

    " Add the tab to the right
    if right_tab <= num_tabs
      let tab_title = self.get_title(tab_nr_type, right_tab)
      let remaining_space -= s:strchars(s:evaluate_tabline(tab_title)) + left_alt_sep_size
      call self.insert_section(self.get_group(right_tab), tab_title, right_position)
      let right_position += 1
      let right_tab += 1
    endif

    while remaining_space > 0
      if left_tab > 0
        let tab_title = self.get_title(tab_nr_type, left_tab)
        let remaining_space -= s:strchars(s:evaluate_tabline(tab_title)) + left_alt_sep_size
        if remaining_space >= 0
          call self.insert_section(self.get_group(left_tab), tab_title, left_position)
          let right_position += 1
          let left_tab -= 1
        endif
      elseif right_tab <= num_tabs
        let tab_title = self.get_title(tab_nr_type, right_tab)
        let remaining_space -= s:strchars(s:evaluate_tabline(tab_title)) + left_alt_sep_size
        if remaining_space >= 0
          call self.insert_section(self.get_group(right_tab), tab_title, right_position)
          let right_position += 1
          let right_tab += 1
        endif
      else
        break
      endif
    endwhile

    if left_tab > 0
      if get(g:, 'airline#extensions#tabline#current_first', 0)
        let left_position -= 1
      endif
      call self.insert_raw('%#airline_tab#'.skipped_tabs_marker, left_position)
      let right_position += 1
    endif

    if right_tab <= num_tabs
      call self.insert_raw('%#airline_tab#'.skipped_tabs_marker, right_position)
    endif
  endif

  return self._build()
endfunction

function! s:evaluate_tabline(tabline)
  let tabline = a:tabline
  let tabline = substitute(tabline, '%{\([^}]\+\)}', '\=eval(submatch(1))', 'g')
  let tabline = substitute(tabline, '%#[^#]\+#', '', 'g')
  let tabline = substitute(tabline, '%(\([^)]\+\)%)', '\1', 'g')
  let tabline = substitute(tabline, '%\d\+[TX]', '', 'g')
  let tabline = substitute(tabline, '%=', '', 'g')
  let tabline = substitute(tabline, '%\d*\*', '', 'g')
  return tabline
endfunction

" Compatibility wrapper for strchars, in case this vim version does not
" have it natively
function! s:strchars(str)
  if exists('*strchars')
    return strchars(a:str)
  else
    return strlen(substitute(a:str, '.', 'a', 'g'))
  endif
endfunction

function! airline#extensions#tabline#builder#new(context)
  let builder = airline#builder#new(a:context)
  let builder._build = builder.build
  call extend(builder, s:prototype, 'force')
  return builder
endfunction