{ config, lib, pkgs, ... }:

let
  inherit (builtins) map;
  inherit (lib) concatMapStrings mkIf optionalString;
  # this structure roughly mirrors home-manager's `programs.neovim.plugins` option
  plugins = with pkgs.vimPlugins; [
    {
      # docs: fzf-vim (fuzzy finder): https://github.com/junegunn/fzf.vim
      plugin = fzf-vim;
    }
    {
      # treesitter syntax highlighting: https://nixos.wiki/wiki/Tree_sitters
      # docs: https://github.com/nvim-treesitter/nvim-treesitter
      # config taken from: https://github.com/i077/system/blob/master/modules/home/neovim/default.nix
      # this is required for tree-sitter to even highlight
      plugin = nvim-treesitter.withAllGrammars;
      type = "lua";
      config = ''
        require'nvim-treesitter.configs'.setup {
          highlight = {
            enable = true,
            -- disable treesitter on Rust so that we can use SyntaxRange
            -- and leverage TeX rendering in rust projects
            disable = { "rust", "tex", "latex" },
            -- disable = { "tex", "latex" },
            -- true to also use builtin vim syntax highlighting when treesitter fails
            additional_vim_regex_highlighting = false
          },
          incremental_selection = {
            enable = true,
            keymaps = {
              init_selection = "gnn",
              node_incremental = "grn",
              mcope_incremental = "grc",
              node_decremental = "grm"
            }
          },
          indent = {
            enable = true,
            disable = {}
          }
        }

        vim.o.foldmethod = 'expr'
        vim.o.foldexpr = 'nvim_treesitter#foldexpr()'
      '';
    }
    {
      # docs: tex-conceal-vim: https://github.com/KeitaNakamura/tex-conceal.vim/
      plugin = tex-conceal-vim;
      type = "viml";
      config = ''
        " present prettier fractions
        let g:tex_conceal_frac=1
      '';
    }
    {
      # source: <https://github.com/LnL7/vim-nix>
      # fixes auto-indent (incl tab size) when editing .nix files
      plugin = vim-nix;
    }
    {
      # docs: surround-nvim: https://github.com/ur4ltz/surround.nvim/
      # docs: vim-surround: https://github.com/tpope/vim-surround
      plugin = vim-surround;
    }
    {
      plugin = vim-SyntaxRange;
      type = "viml";
      config = ''
        " enable markdown-style codeblock highlighting for tex code
        autocmd BufEnter * call SyntaxRange#Include('```tex', '```', 'tex', 'NonText')
        " autocmd Syntax tex set conceallevel=2
      '';
    }
  ];
  plugin-packages = map (p: p.plugin) plugins;
  plugin-config-tex = concatMapStrings (p: optionalString (p.type or "" == "viml") p.config) plugins;
  plugin-config-lua = concatMapStrings (p: optionalString (p.type or "" == "lua") p.config) plugins;
in
{
  # private because there could be sensitive things in the swap
  sane.programs.neovim = {
    persist.private = [ ".cache/vim-swap" ];
    env.EDITOR = "vim";
    # git claims it should use EDITOR, but it doesn't!
    env.GIT_EDITOR = "vim";
  };

  programs.neovim = mkIf config.sane.programs.neovim.enabled {
    # neovim: https://github.com/neovim/neovim
    enable = true;
    viAlias = true;
    vimAlias = true;
    configure = {
      packages.myVimPackage = {
        start = plugin-packages;
      };
      customRC = ''
        " let the terminal handle mouse events, that way i get OS-level ctrl+shift+c/etc
        " this used to be default, until <https://github.com/neovim/neovim/pull/19290>
        set mouse=

        " copy/paste to system clipboard
        set clipboard=unnamedplus

        " screw tabs; always expand them into spaces
        set expandtab

        " at least don't open files with sections folded by default
        set nofoldenable

        " allow text substitutions for certain glyphs.
        " higher number = more aggressive substitution (0, 1, 2, 3)
        " i only make use of this for tex, but it's unclear how to
        " apply that *just* to tex and retain the SyntaxRange stuff.
        set conceallevel=2

        " horizontal rule under the active line
        " set cursorline

        " highlight trailing space & related syntax errors (doesn't seem to work??)
        " let c_space_errors=1
        " let python_space_errors=1

        " enable highlighting of leading/trailing spaces,
        " and especially tabs
        " source: https://www.reddit.com/r/neovim/comments/chlmfk/highlight_trailing_whitespaces_in_neovim/
        set list
        set listchars=tab:▷\·,trail:·,extends:◣,precedes:◢,nbsp:○

        """"" PLUGIN CONFIG (tex)
        ${plugin-config-tex}

        """"" PLUGIN CONFIG (lua)
        lua <<EOF
        ${plugin-config-lua}
        EOF
      '';
    };
  };
}