{ config, pkgs, ... }:
{

  # neovim
  programs.neovim = {
    enable        = true;
    defaultEditor = true;
    viAlias       = true;
    vimAlias      = true;

    # neovim config
    extraConfig = ''

      " Use tab for trigger completion with characters ahead and navigate.
      inoremap <silent><expr> <TAB>
        \ pumvisible() ? "\<C-n>" :
        \ <SID>check_back_space() ? "\<TAB>" :
        \ coc#refresh()
      inoremap <expr><S-TAB> pumvisible() ? "\<C-p>" : "\<C-h>"
      function! s:check_back_space() abort
        let col = col('.') - 1
        return !col || getline('.')[col - 1]  =~# '\s'
      endfunction

      " Use <c-space> to trigger completion.
      if has('nvim')
        inoremap <silent><expr> <c-space> coc#refresh()
      else
        inoremap <silent><expr> <c-@> coc#refresh()
      endif

      " clipboard
      set clipboard+=unnamedplus

      " cursor
      set guicursor=a:hor20-Cursor
      set guicursor=v:block-Cursor

      " terminal title
      set title

      " auto-complete
      set completeopt=menu,menuone,longest

      " show number
      set number
    '';

    # lua config
    extraLuaConfig = ''

      -- set mapleader
      vim.g.mapleader = ' '
      vim.g.maplocalleader = ' '

      -- set vim options
      vim.opt.backspace  = '2'
      vim.opt.laststatus = 2
      vim.opt.cursorline = true

      -- set scrolloff
      vim.opt.scrolloff = 10

      -- indentation
      vim.opt.tabstop     = 2
      vim.opt.shiftwidth  = 2
      vim.opt.expandtab   = true
      vim.opt.smartindent = true

      -- load plugins
      require("neo-tree").setup({
        filesystem = {
          filtered_items = {
            hide_dotfiles = false,
            hide_gitignored = false,
          },
        },
        window = {
          position = "left",
          width = 36,
        },
      })
      require("neo-tree.sources.manager").show("filesystem")

      -- function for new line
      _G.add_new_line = function()
        local n_lines = vim.api.nvim_buf_line_count(0)
        local last_nonblank = vim.fn.prevnonblank(n_lines)
        if last_nonblank <= n_lines then vim.api.nvim_buf_set_lines(0, last_nonblank, n_lines, true, { ''' }) end
      end

      vim.cmd([[
        augroup AddNewlineOnSave
          autocmd!
          autocmd BufWritePre * lua _G.add_new_line()
        augroup END
      ]])
    '';

    # auto-complete
    coc = {
      enable   = true;
      settings = {
        "suggest.noselect"        = true;
        "suggest.enablePreview"   = true;
        "suggest.enablePreselect" = true;
        "suggest.disableKind"     = true;

        "diagnostic.errorSign" = "✘";
        "diagnostic.infoSign"  = "ℹ";
        "diagnostic.hintSign"  = "➤";
      };
    };

    # plugins
    plugins = with pkgs.vimPlugins; [
      neo-tree-nvim
    ];
  };
}