dotfiles/vim/settings/folding.vim

" Folding - Modeline and Notes {{{
" vim: set sw=2 ts=2 sts=2 et tw=78 foldmarker={{{,}}} foldlevel=0 foldmethod=marker spell:
"
"   cinaeco/dotfiles Folding Settings
"
"   These are settings to make folding easier to use and look at:
"    - Indented Folds to match their first line.
"    - Stat box to right displays line count and fold level.
"    - Coloured distinctly red!
"        (sounds harsh, but actually works well with solarized-dark!)
"    - Fillchar is forced to '.' rather than '-'.
"        (easier on eyes)
"    - SpaceBar toggles folds, if any.
"        (much more convenient than the 'z' commands)
"    - SPF13-VIM provides quick foldlevel setting map: <Leader>f[0-9]
"        (useful with stat box lvl)
"
"   Note that custom foldtext will only work for vim 7.3+. For earlier
"   versions of vim, only the colouring and spacebar mapping will take effect.
"
"   TODO:
"    - Fold description is just the first line found. Haven't really
"    understood the regex, but could perhaps make it better.
"    - Fold description current truncation rule is 1/3 of the window width.
"    Perhaps this could be some less arbitrary rule?
"
" }}}

if has('folding')

  " Keyboard Shortcut {{{
    " Space as a Folding toggle in normal mode.
    nnoremap <silent> <space>     @=(foldlevel('.')?'za':"\<space>")<CR>
  " }}}

  " Fold Highlighting {{{
    " Red fold text! (Pretty good with solarized-dark)
    highlight Folded term=none cterm=none ctermfg=darkred ctermbg=none guifg=darkred guibg=none
  " }}}

  " Fold Text {{{
    set foldtext=CustomFoldText()

    function! CustomFoldText()

      " At least vim 7.3. {{{
      "  - Requirement for strdisplaywidth.
        if v:version < 703
          return foldtext()
        endif
      " }}}

      " Force dot fillchar. {{{
      "  - The complicated line is to ensure we replace the fold fillchar only.
        let &l:fillchars = substitute(&l:fillchars,',\?fold:.','','gi')
        setlocal fillchars+=fold:.
      " }}}

      " Prepare script variables. {{{
        let foldChar = matchstr(&fillchars, 'fold:\zs.')
        let currWinWidth = winwidth(0)
      " }}}

      " Prepare fold indent. {{{
      "  - Indent taken from first line in fold.
        let indentLevel = indent(v:foldstart)
        let indent = repeat(' ', indentLevel)
      " }}}

      " Prepare fold description. {{{
      "  - Truncated to 1/3 of the current window width.
        let allFoldMarkers = split(&foldmarker, ',')
        let frontFoldMarker = allFoldMarkers[0]
        let lineRaw = substitute(getline(v:foldstart), '^\s*"\?\s*\|\s*"\?\s*'.frontFoldMarker.'\d*\s*', '', 'g')
        let line = '+ '.lineRaw.' '
        let foldDesc = strpart(line, 0, currWinWidth / 3)
      " }}}

      " Prepare the stat box. {{{
      "  - Fixed stat box width at 18 characters.
      "  - Count width by display cells instead of bytes if at least vim 7.4
        let lineCount = v:foldend - v:foldstart + 1
        if v:version >= 704
          let formatForm = 'S'
        else
          let formatForm = 's'
        endif
        let statBox = '| ' . printf('%18'.formatForm, lineCount.' lines, lvl '.v:foldlevel) . ' |'
      " }}}

      " Prepare filler lines. {{{
      "  - endFiller is the fill after the stat box. Fixed at 5 characters.
      "  - midFiller is the fill between the description and stat box.
      "  - midFiller compensates for column widths generated by foldcolumn, number
      "  and relativenumber.
      "  - strdisplaywidth() seems to work. If multi-byte characters start to give
      "  trouble, consider checking the more primitive solution in strlen() help.
        let endFiller = repeat(foldChar, 5)
        let midFillerLength = winwidth(0) - strdisplaywidth(indent.foldDesc.statBox.endFiller) - &foldcolumn
        if (&number || &relativenumber)
          let midFillerLength -= &numberwidth
        endif
        let midFiller = repeat(foldChar, midFillerLength)
      " }}}

      " Output the combined fold text. {{{
        return indent.foldDesc.midFiller.statBox.endFiller
      " }}}

    endfunction
  " }}}

endif