Test vimrc configuration to turn Vim into a difftool

difftool_vimrc.vim

set nocompatible
filetype plugin indent on

set tabstop=2 softtabstop=2 shiftwidth=2 expandtab
set number
set hidden

set splitbelow
set splitright

" Additional <ESC> mappings:
" jk, in INSERT mode
" <C-c>, I'm so used to it after shell environment
inoremap jk <ESC>
noremap <C-C> <ESC>
xnoremap <C-C> <ESC>

" Set <leader> key to <Space>
nnoremap <Space> <Nop>
let mapleader=" "
let maplocalleader=","

call plug#begin('~/.vim/plugged')
  Plug 'dracula/vim', { 'as': 'dracula' }
  Plug 'airblade/vim-gitgutter'
call plug#end()

if &t_Co >= 256 || has("gui_running")
  "let g:dracula_italic=0
  let &t_8f="\<Esc>[38;2;%lu;%lu;%lum"
  let &t_8b="\<Esc>[48;2;%lu;%lu;%lum"

  if (has("termguicolors"))
    set termguicolors
  endif
endif

augroup aug_color_scheme
  au!

  autocmd ColorScheme dracula call s:PatchColorScheme()
augroup END

function s:PatchColorScheme()
  hi! link DiffChange NONE
  hi! clear DiffChange
  hi! DiffText term=NONE ctermfg=215 ctermbg=233 cterm=NONE guifg=#FFB86C guibg=#14141a gui=NONE

endfunction


" Apply a particular color scheme
" NOTE: Should go after 'autocmd ColorScheme' customization
set background=dark
colorscheme dracula

set diffopt=vertical,filler,context:3,indent-heuristic,algorithm:patience,internal


" Detect if vim is started as a diff tool (vim -d, vimdiff)
" NOTE: Does not work when you start Vim as usual and enter diff mode using :diffthis
if &diff
  let s:is_started_as_vim_diff = 1
  syntax off
  setlocal nospell
endif

augroup aug_diffs
  au!

  " Inspect whether some windows are in diff mode, and apply changes for such windows
  " Run asynchronously, to ensure '&diff' option is properly set by Vim
  au WinEnter,BufEnter * call timer_start(50, 'CheckDiffMode')

augroup END

" In diff mode:
" - Disable syntax highlighting
" - Disable spell checking
function CheckDiffMode(timer)
  let curwin = winnr()

  " Check each window
  for _win in range(1, winnr('$'))
    exe "noautocmd " . _win . "wincmd w"

    call s:change_option_in_diffmode('b:', 'syntax', 'off')
    call s:change_option_in_diffmode('w:', 'spell', 0, 1)
  endfor

  " Get back to original window
  exe "noautocmd " . curwin . "wincmd w"
endfunction

" Detect window or buffer local option is in sync with diff mode
function s:change_option_in_diffmode(scope, option, value, ...)
  let isBoolean = get(a:, "1", 0)
  let backupVarname = a:scope . "_old_" . a:option

  " Entering diff mode
  if &diff && !exists(backupVarname)
    exe "let " . backupVarname . "=&" . a:option
    call s:set_option(a:option, a:value, 1, isBoolean)
  endif

  " Exiting diff mode
  if !&diff && exists(backupVarname)
    let oldValue = eval(backupVarname)
    call s:set_option(a:option, oldValue, 1, isBoolean)
    exe "unlet " . backupVarname
  endif
endfunction

function s:set_option(option, value, ...)
  let isLocal = get(a:, "1", 0)
  let isBoolean = get(a:, "2", 0)
  if isBoolean
    exe (isLocal ? "setlocal " : "set ") . (a:value ? "" : "no") . a:option
  else
    exe (isLocal ? "setlocal " : "set ") . a:option . "=" . a:value
  endif
endfunction

nnoremap <silent> <leader>q :call <SID>QuitWindow()<CR>

function s:QuitWindow()
  if get(s:, 'is_started_as_vim_diff', 0)
    qall
    return
  endif

  quit
endfunction

nmap <expr> <Up> &diff ? '[czz' : '<Up>'
nmap <expr> <Down> &diff ? ']czz' : '<Down>'

let g:gitgutter_enabled = 1
set updatetime=1000