{ stdenv, vim, vimPlugins, vim_configurable, neovim, buildEnv, writeText, writeScriptBin
, nix-prefetch-hg, nix-prefetch-git
, fetchFromGitHub, runtimeShell
}:

/*

USAGE EXAMPLE
=============

Install Vim like this eg using nixos option environment.systemPackages which will provide
vim-with-plugins in PATH:

  vim_configurable.customize {
    name = "vim-with-plugins";

    # add custom .vimrc lines like this:
    vimrcConfig.customRC = ''
      set hidden
    '';

    # store your plugins in Vim packages
    vimrcConfig.packages.myVimPackage = with pkgs.vimPlugins; {
      # loaded on launch
      start = [ youcompleteme fugitive ];
      # manually loadable by calling `:packadd $plugin-name`
      opt = [ phpCompletion elm-vim ];
      # To automatically load a plugin when opening a filetype, add vimrc lines like:
      # autocmd FileType php :packadd phpCompletion
    };

    # plugins can also be managed by VAM
    vimrcConfig.vam.knownPlugins = pkgs.vimPlugins; # optional
    vimrcConfig.vam.pluginDictionaries = [
      # load always
      { name = "youcompleteme"; }
      { names = ["youcompleteme" "foo"]; }

      # only load when opening a .php file
      { name = "phpCompletion"; ft_regex = "^php\$"; }
      { name = "phpCompletion"; filename_regex = "^.php\$"; }

      # provide plugin which can be loaded manually:
      { name = "phpCompletion"; tag = "lazy"; }

      # full documentation at github.com/MarcWeber/vim-addon-manager
    ];

    # there is a pathogen implementation as well, but its startup is slower and [VAM] has more feature
    # vimrcConfig.pathogen.knownPlugins = vimPlugins; # optional
    # vimrcConfig.pathogen.pluginNames = ["vim-addon-nix"];
  };

WHAT IS A VIM PLUGIN?
=====================
Typical plugin files:

  plugin/P1.vim
  autoload/P1.vim
  ftplugin/xyz.vim
  doc/plugin-documentation.txt (traditional documentation)
  README(.md) (nowadays thanks to github)


Vim offers the :h rtp setting which works for most plugins. Thus adding
this to your .vimrc should make most plugins work:

  set rtp+=~/.nix-profile/share/vim-plugins/youcompleteme
  " or for p in ["youcompleteme"] | exec 'set rtp+=~/.nix-profile/share/vim-plugins/'.p | endfor

which is what the [VAM]/pathogen solutions above basically do.

Learn about about plugin Vim plugin mm managers at
http://vim-wiki.mawercer.de/wiki/topic/vim%20plugin%20managment.html.

The documentation can be accessed by Vim's :help command if it was tagged.
See vimHelpTags sample code below.

CONTRIBUTING AND CUSTOMIZING
============================
The example file pkgs/misc/vim-plugins/default.nix provides both:
* manually mantained plugins
* plugins created by VAM's nix#ExportPluginsForNix implementation

I highly recommend to lookup vim plugin attribute names at the [vim-pi] project
 which is a database containing all plugins from
vim.org and quite a lot of found at github and similar sources. vim-pi's documented purpose
is to associate vim.org script ids to human readable names so that dependencies
can be describe easily.

How to find a name?
  * http://vam.mawercer.de/ or VAM's
  * grep vim-pi
  * use VAM's completion or :AddonsInfo command

It might happen than a plugin is not known by vim-pi yet. We encourage you to
contribute to vim-pi so that plugins can be updated automatically.


CREATING DERVITATIONS AUTOMATICALLY BY PLUGIN NAME
==================================================
Most convenient is to use a ~/.vim-scripts file putting a plugin name into each line
as documented by [VAM]'s README.md
It is the same format you pass to vimrcConfig.vam.pluginDictionaries from the
usage example above.

Then create a temp vim file and insert:

  let opts = {}
  let opts.path_to_nixpkgs = '/etc/nixos/nixpkgs'
  let opts.cache_file = '/tmp/export-vim-plugin-for-nix-cache-file'
  let opts.plugin_dictionaries = map(readfile("vim-plugins"), 'eval(v:val)')
  " add more files
  " let opts.plugin_dictionaries += map(.. other file )
  call nix#ExportPluginsForNix(opts)

Then ":source %" it.

nix#ExportPluginsForNix is provided by ./vim2nix

A buffer will open containing the plugin derivation lines as well list
fitting the vimrcConfig.vam.pluginDictionaries option.

Thus the most simple usage would be:

  vim_with_plugins =
    let vim = vim_configurable;
        inherit (vimUtil.override {inherit vim}) rtpPath addRtp buildVimPlugin vimHelpTags;
        vimPlugins = [
          # the derivation list from the buffer created by nix#ExportPluginsForNix
          # don't set which will default to pkgs.vimPlugins
        ];
    in vim.customize {
      name = "vim-with-plugins";

      vimrcConfig.customRC = '' .. '';

      vimrcConfig.vam.knownPlugins = vimPlugins;
      vimrcConfig.vam.pluginDictionaries = [
          # the plugin list form ~/.vim-scripts turned into nix format added to
          # the buffer created by the nix#ExportPluginsForNix
      ];
    }

vim_with_plugins can be installed like any other application within Nix.

[VAM]    https://github.com/MarcWeber/vim-addon-manager
[vim-pi] https://bitbucket.org/vimcommunity/vim-pi
*/


let
  inherit (stdenv) lib;

  # make sure a plugin is a derivation and its dependencies are derivations. If
  # plugin already is a derivation, this is a no-op. If it is a string, it is
  # looked up in knownPlugins.
  pluginToDrv = knownPlugins: plugin:
  let
    drv =
      if builtins.isString plugin then
        # make sure `pname` is set to that we are able to convert the derivation
        # back to a string.
        ( knownPlugins.${plugin} // { pname = plugin; })
      else
        plugin;
  in
    # make sure all the dependencies of the plugin are also derivations
    drv // { dependencies = map (pluginToDrv knownPlugins) (drv.dependencies or []); };

  # transitive closure of plugin dependencies (plugin needs to be a derivation)
  transitiveClosure = plugin:
    [ plugin ] ++ (
      lib.unique (builtins.concatLists (map transitiveClosure plugin.dependencies or []))
    );

  findDependenciesRecursively = plugins: lib.concatMap transitiveClosure plugins;

  vamDictToNames = x:
      if builtins.isString x then [x]
      else (lib.optional (x ? name) x.name)
            ++ (x.names or []);

  rtpPath = "share/vim-plugins";

  vimrcFile = {
    packages ? null,
    vam ? null,
    pathogen ? null,
    plug ? null,
    customRC ? ""
  }:

    let
      /* pathogen mostly can set &rtp at startup time. Its used very commonly.
      */
      pathogenImpl = lib.optionalString (pathogen != null)
      (let
        knownPlugins = pathogen.knownPlugins or vimPlugins;

        plugins = findDependenciesRecursively (map (pluginToDrv knownPlugins) pathogen.pluginNames);

        pluginsEnv = buildEnv {
          name = "pathogen-plugin-env";
          paths = map (x: "${x}/${rtpPath}") plugins;
        };
      in
      ''
        let &rtp.=(empty(&rtp)?"":',')."${vimPlugins.pathogen.rtp}"
        execute pathogen#infect('${pluginsEnv}/{}')

        filetype indent plugin on | syn on
      '');

      /* vim-plug is an extremely popular vim plugin manager.
      */
      plugImpl = lib.optionalString (plug != null)
      (''
        source ${vimPlugins.vim-plug.rtp}/plug.vim
        call plug#begin('/dev/null')

        '' + (lib.concatMapStringsSep "\n" (pkg: "Plug '${pkg.rtp}'") plug.plugins) + ''

        call plug#end()
      '');

      /*
       vim-addon-manager = VAM

       * maps names to plugin location

       * manipulates &rtp at startup time
         or when Vim has been running for a while

       * can activate plugins laziy (eg when loading a specific filetype)

       * knows about vim plugin dependencies (addon-info.json files)

       * still is minimalistic (only loads one file), the "check out" code it also
         has only gets loaded when a plugin is requested which is not found on disk
         yet

      */
      vamImpl = lib.optionalString (vam != null)
      (let
        knownPlugins = vam.knownPlugins or vimPlugins;

        # plugins specified by the user
        specifiedPlugins = map (pluginToDrv knownPlugins) (lib.concatMap vamDictToNames vam.pluginDictionaries);
        # plugins with dependencies
        plugins = findDependenciesRecursively specifiedPlugins;

        # Vim almost reads JSON, so eventually JSON support should be added to Nix
        # TODO: proper quoting
        toNix = x:
          if (builtins.isString x) then "'${x}'"
          else if builtins.isAttrs x && builtins ? out then toNix x # a derivation
          else if builtins.isAttrs x then "{${lib.concatStringsSep ", " (lib.mapAttrsToList (n: v: "${toNix n}: ${toNix v}") x)}}"
          else if builtins.isList x then "[${lib.concatMapStringsSep ", " toNix x}]"
          else throw "turning ${lib.generators.toPretty {} x} into a VimL thing not implemented yet";

      in assert builtins.hasAttr "vim-addon-manager" knownPlugins;
      ''
        filetype indent plugin on | syn on

        let g:nix_plugin_locations = {}
        ${lib.concatMapStrings (plugin: ''
          let g:nix_plugin_locations['${plugin.pname}'] = "${plugin.rtp}"
        '') plugins}
        let g:nix_plugin_locations['vim-addon-manager'] = "${knownPlugins.vim-addon-manager.rtp}"

        let g:vim_addon_manager = {}

        if exists('g:nix_plugin_locations')
          " nix managed config

          " override default function making VAM aware of plugin locations:
          fun! NixPluginLocation(name)
            let path = get(g:nix_plugin_locations, a:name, "")
            return path == "" ? vam#DefaultPluginDirFromName(a:name) : path
          endfun
          let g:vim_addon_manager.plugin_dir_by_name = 'NixPluginLocation'
          " tell Vim about VAM:
          let &rtp.=(empty(&rtp)?"":','). g:nix_plugin_locations['vim-addon-manager']
        else
          " standalone config

          let &rtp.=(empty(&rtp)?"":',').c.plugin_root_dir.'/vim-addon-manager'
          if !isdirectory(c.plugin_root_dir.'/vim-addon-manager/autoload')
            " checkout VAM
            execute '!git clone --depth=1 https://github.com/MarcWeber/vim-addon-manager '
                \       shellescape(c.plugin_root_dir.'/vim-addon-manager', 1)
          endif
        endif

        " tell vam about which plugins to load when:
        let l = []
        ${lib.concatMapStrings (p: "call add(l, {'name': '${p.pname}'})\n") plugins}
        call vam#Scripts(l, {})
      '');

      nativeImpl = lib.optionalString (packages != null)
      (let
        link = (packageName: dir: pluginPath: "ln -sf ${pluginPath}/share/vim-plugins/* $out/pack/${packageName}/${dir}");
        packageLinks = (packageName: {start ? [], opt ? []}:
        let
          # `nativeImpl` expects packages to be derivations, not strings (as
          # opposed to older implementations that have to maintain backwards
          # compatibility). Therefore we don't need to deal with "knownPlugins"
          # and can simply pass `null`.
          depsOfOptionalPlugins = lib.subtractLists opt (findDependenciesRecursively opt);
          startWithDeps = findDependenciesRecursively start;
        in
          ["mkdir -p $out/pack/${packageName}/start"]
          # To avoid confusion, even dependencies of optional plugins are added
          # to `start` (except if they are explicitly listed as optional plugins).
          ++ (builtins.map (link packageName "start") (lib.unique (startWithDeps ++ depsOfOptionalPlugins)))
          ++ ["mkdir -p $out/pack/${packageName}/opt"]
          ++ (builtins.map (link packageName "opt") opt)
        );
        packDir = (packages:
          stdenv.mkDerivation {
            name = "vim-pack-dir";
            src = ./.;
            installPhase = lib.concatStringsSep
                             "\n"
                             (lib.flatten (lib.mapAttrsToList packageLinks packages));
            preferLocalBuild = true;
          }
        );
      in
      ''
        set packpath-=~/.vim/after
        set packpath+=${packDir packages}
        set packpath+=~/.vim/after

        filetype indent plugin on | syn on
      '');

  in writeText "vimrc" ''
  " configuration generated by NIX
  set nocompatible

  ${vamImpl}
  ${pathogenImpl}
  ${plugImpl}
  ${nativeImpl}

  ${customRC}
  '';

in

rec {
  inherit vimrcFile;

  # shell script with custom name passing [-u vimrc] [-U gvimrc] to vim
  vimWithRC = {
    vimExecutable,
    gvimExecutable,
    vimManPages,
    wrapManual,
    wrapGui,
    name ? "vim",
    vimrcFile ? null,
    gvimrcFile ? null,
    vimExecutableName,
    gvimExecutableName,
  }:
    let
      rcOption = o: file: stdenv.lib.optionalString (file != null) "-${o} ${file}";
      vimWrapperScript = writeScriptBin vimExecutableName ''
        #!${runtimeShell}
        exec ${vimExecutable} ${rcOption "u" vimrcFile} ${rcOption "U" gvimrcFile} "$@"
      '';
      gvimWrapperScript = writeScriptBin gvimExecutableName ''
        #!${stdenv.shell}
        exec ${gvimExecutable} ${rcOption "u" vimrcFile} ${rcOption "U" gvimrcFile} "$@"
      '';
    in
      buildEnv {
        inherit name;
        paths = [
          vimWrapperScript
        ] ++ lib.optional wrapGui gvimWrapperScript
          ++ lib.optional wrapManual vimManPages
        ;
      };

  # add a customize option to a vim derivation
  makeCustomizable = vim: vim // {
    customize = {
      name,
      vimrcConfig,
      wrapManual ? true,
      wrapGui ? false,
      vimExecutableName ? name,
      gvimExecutableName ? (lib.concatStrings [ "g" name ]),
    }: vimWithRC {
      vimExecutable = "${vim}/bin/vim";
      gvimExecutable = "${vim}/bin/gvim";
      inherit name wrapManual wrapGui vimExecutableName gvimExecutableName;
      vimrcFile = vimrcFile vimrcConfig;
      vimManPages = buildEnv {
        name = "vim-doc";
        paths = [ vim ];
        pathsToLink = [ "/share/man" ];
      };
    };

    override = f: makeCustomizable (vim.override f);
    overrideAttrs = f: makeCustomizable (vim.overrideAttrs f);
  };

  pluginnames2Nix = {name, namefiles} : vim_configurable.customize {
    inherit name;
    vimrcConfig.vam.knownPlugins = vimPlugins;
    vimrcConfig.vam.pluginDictionaries = ["vim2nix"];
    vimrcConfig.customRC = ''
      " Yes - this is impure and will create the cache file and checkout vim-pi
      " into ~/.vim/vim-addons
      let g:vim_addon_manager.plugin_root_dir = "/tmp/vim2nix-".$USER
      if !isdirectory(g:vim_addon_manager.plugin_root_dir)
        call mkdir(g:vim_addon_manager.plugin_root_dir)
      else
        echom repeat("=", 80)
        echom "WARNING: reusing cache directory :".g:vim_addon_manager.plugin_root_dir
        echom repeat("=", 80)
      endif
      let opts = {}
      let opts.nix_prefetch_git = "${nix-prefetch-git}/bin/nix-prefetch-git"
      let opts.nix_prefetch_hg  = "${nix-prefetch-hg}/bin/nix-prefetch-hg"
      let opts.cache_file = g:vim_addon_manager.plugin_root_dir.'/cache'
      let opts.plugin_dictionaries = []
      ${lib.concatMapStrings (file: "let opts.plugin_dictionaries += map(readfile(\"${file}\"), 'eval(v:val)')\n") namefiles }

      " uncomment for debugging failures
      " let opts.try_catch = 0

      " add more files
      " let opts.plugin_dictionaries += map(.. other file )
      call nix#ExportPluginsForNix(opts)
    '';
  };

  vim_with_vim2nix = vim_configurable.customize { name = "vim"; vimrcConfig.vam.pluginDictionaries = [ "vim-addon-vim2nix" ]; };

  inherit (import ./build-vim-plugin.nix { inherit stdenv rtpPath vim; }) buildVimPlugin buildVimPluginFrom2Nix;

  # used to figure out which python dependencies etc. neovim needs
  requiredPlugins = {
    packages ? {},
    givenKnownPlugins ? null,
    vam ? null,
    pathogen ? null,
    plug ? null, ...
  }:
    let
      # This is probably overcomplicated, but I don't understand this well enough to know what's necessary.
      knownPlugins = if givenKnownPlugins != null then givenKnownPlugins else
                     if vam != null && vam ? knownPlugins then vam.knownPlugins else
                     if pathogen != null && pathogen ? knownPlugins then pathogen.knownPlugins else
                     vimPlugins;
      pathogenPlugins = findDependenciesRecursively (map (pluginToDrv knownPlugins) pathogen.pluginNames);
      vamPlugins = findDependenciesRecursively (map (pluginToDrv knownPlugins) (lib.concatMap vamDictToNames vam.pluginDictionaries));
      nonNativePlugins = (lib.optionals (pathogen != null) pathogenPlugins)
                      ++ (lib.optionals (vam != null) vamPlugins)
                      ++ (lib.optionals (plug != null) plug.plugins);
      nativePluginsConfigs = lib.attrsets.attrValues packages;
      nativePlugins = lib.concatMap ({start?[], opt?[], knownPlugins?vimPlugins}: start++opt) nativePluginsConfigs;
    in
      nativePlugins ++ nonNativePlugins;


  # test cases:
  test_vim_with_vim_nix_using_vam = vim_configurable.customize {
   name = "vim-with-vim-addon-nix-using-vam";
    vimrcConfig.vam.pluginDictionaries = [{name = "vim-nix"; }];
  };

  test_vim_with_vim_nix_using_pathogen = vim_configurable.customize {
    name = "vim-with-vim-addon-nix-using-pathogen";
    vimrcConfig.pathogen.pluginNames = [ "vim-nix" ];
  };

  test_vim_with_vim_nix_using_plug = vim_configurable.customize {
    name = "vim-with-vim-addon-nix-using-plug";
    vimrcConfig.plug.plugins = with vimPlugins; [ vim-nix ];
  };

  test_vim_with_vim_nix = vim_configurable.customize {
    name = "vim-with-vim-addon-nix";
    vimrcConfig.packages.myVimPackage.start = with vimPlugins; [ vim-nix ];
  };

  # only neovim makes use of `requiredPlugins`, test this here
  test_nvim_with_vim_nix_using_pathogen = neovim.override {
    configure.pathogen.pluginNames = [ "vim-nix" ];
  };

  # regression test for https://github.com/NixOS/nixpkgs/issues/53112
  # The user may have specified their own plugins which may not be formatted
  # exactly as the generated ones. In particular, they may not have the `pname`
  # attribute.
  test_vim_with_custom_plugin = vim_configurable.customize {
    name = "vim_with_custom_plugin";
    vimrcConfig.vam.knownPlugins =
      vimPlugins // ({
        vim-trailing-whitespace = buildVimPluginFrom2Nix {
          name = "vim-trailing-whitespace";
          src = fetchFromGitHub {
            owner = "bronson";
            repo = "vim-trailing-whitespace";
            rev = "4c596548216b7c19971f8fc94e38ef1a2b55fee6";
            sha256 = "0f1cpnp1nxb4i5hgymjn2yn3k1jwkqmlgw1g02sq270lavp2dzs9";
          };
          # make sure string dependencies are handled
          dependencies = [ "vim-nix" ];
        };
      });
    vimrcConfig.vam.pluginDictionaries = [ { names = [ "vim-trailing-whitespace" ]; } ];
  };

  # system remote plugin manifest should be generated, deoplete should be usable
  # without the user having to do `UpdateRemotePlugins`. To test, launch neovim
  # and do `:call deoplete#enable()`. It will print an error if the remote
  # plugin is not registered.
  test_nvim_with_remote_plugin = neovim.override {
    configure.pathogen.pluginNames = with vimPlugins; [ deoplete-nvim ];
  };
}