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

with lib;

let

  cfg = config.programs.neovim;

  fileType = (import ../lib/file-type.nix {
    inherit (config.home) homeDirectory;
    inherit lib pkgs;
  }).fileType;

  jsonFormat = pkgs.formats.json { };

  pluginWithConfigType = types.submodule {
    options = {
      config = mkOption {
        type = types.nullOr types.lines;
        description = lib.mdDoc
          "Script to configure this plugin. The scripting language should match type.";
        default = null;
      };

      type = mkOption {
        type =
          types.either (types.enum [ "lua" "viml" "teal" "fennel" ]) types.str;
        description = lib.mdDoc
          "Language used in config. Configurations are aggregated per-language.";
        default = "viml";
      };

      optional = mkEnableOption (lib.mdDoc "optional") // {
        description = "Don't load by default (load with :packadd)";
      };

      plugin = mkOption {
        type = types.package;
        description = lib.mdDoc "vim plugin";
      };

      runtime = mkOption {
        default = { };
        # passing actual "${xdg.configHome}/nvim" as basePath was a bit tricky
        # due to how fileType.target is implemented
        type = fileType "programs.neovim.plugins._.runtime"
          "{var}`xdg.configHome/nvim`" "nvim";
        example = literalExpression ''
          { "ftplugin/c.vim".text = "setlocal omnifunc=v:lua.vim.lsp.omnifunc"; }
        '';
        description = lib.mdDoc ''
          Set of files that have to be linked in nvim config folder.
        '';
      };
    };
  };

  allPlugins = cfg.plugins ++ optional cfg.coc.enable {
    type = "viml";
    plugin = cfg.coc.package;
    config = cfg.coc.pluginConfig;
    optional = false;
  };

  luaPackages = cfg.finalPackage.unwrapped.lua.pkgs;
  resolvedExtraLuaPackages = cfg.extraLuaPackages luaPackages;

  extraMakeWrapperArgs = lib.optionalString (cfg.extraPackages != [ ])
    ''--suffix PATH : "${lib.makeBinPath cfg.extraPackages}"'';
  extraMakeWrapperLuaCArgs =
    lib.optionalString (resolvedExtraLuaPackages != [ ]) ''
      --suffix LUA_CPATH ";" "${
        lib.concatMapStringsSep ";" luaPackages.getLuaCPath
        resolvedExtraLuaPackages
      }"'';
  extraMakeWrapperLuaArgs = lib.optionalString (resolvedExtraLuaPackages != [ ])
    ''
      --suffix LUA_PATH ";" "${
        lib.concatMapStringsSep ";" luaPackages.getLuaPath
        resolvedExtraLuaPackages
      }"'';
in {
  imports = [
    (mkRemovedOptionModule [ "programs" "neovim" "withPython" ]
      "Python2 support has been removed from neovim.")
    (mkRemovedOptionModule [ "programs" "neovim" "extraPythonPackages" ]
      "Python2 support has been removed from neovim.")
    (mkRemovedOptionModule [ "programs" "neovim" "configure" ] ''
      programs.neovim.configure is deprecated.
            Other programs.neovim options can override its settings or ignore them.
            Please use the other options at your disposal:
              configure.packages.*.opt  -> programs.neovim.plugins = [ { plugin = ...; optional = true; }]
              configure.packages.*.start  -> programs.neovim.plugins = [ { plugin = ...; }]
              configure.customRC -> programs.neovim.extraConfig
    '')
  ];

  options = {
    programs.neovim = {
      enable = mkEnableOption (lib.mdDoc "Neovim");

      viAlias = mkOption {
        type = types.bool;
        default = false;
        description = lib.mdDoc ''
          Symlink {command}`vi` to {command}`nvim` binary.
        '';
      };

      vimAlias = mkOption {
        type = types.bool;
        default = false;
        description = lib.mdDoc ''
          Symlink {command}`vim` to {command}`nvim` binary.
        '';
      };

      vimdiffAlias = mkOption {
        type = types.bool;
        default = false;
        description = lib.mdDoc ''
          Alias {command}`vimdiff` to {command}`nvim -d`.
        '';
      };

      withNodeJs = mkOption {
        type = types.bool;
        default = false;
        description = lib.mdDoc ''
          Enable node provider. Set to `true` to
          use Node plugins.
        '';
      };

      withRuby = mkOption {
        type = types.nullOr types.bool;
        default = true;
        description = lib.mdDoc ''
          Enable ruby provider.
        '';
      };

      withPython3 = mkOption {
        type = types.bool;
        default = true;
        description = lib.mdDoc ''
          Enable Python 3 provider. Set to `true` to
          use Python 3 plugins.
        '';
      };

      extraPython3Packages = mkOption {
        # In case we get a plain list, we need to turn it into a function,
        # as expected by the function in nixpkgs.
        # The only way to do so is to call `const`, which will ignore its input.
        type = with types;
          let fromType = listOf package;
          in coercedTo fromType (flip warn const ''
            Assigning a plain list to extraPython3Packages is deprecated.
                   Please assign a function taking a package set as argument, so
                     extraPython3Packages = [ pkgs.python3Packages.xxx ];
                   should become
                     extraPython3Packages = ps: [ ps.xxx ];
          '') (functionTo fromType);
        default = _: [ ];
        defaultText = literalExpression "ps: [ ]";
        example =
          literalExpression "pyPkgs: with pyPkgs; [ python-language-server ]";
        description = lib.mdDoc ''
          The extra Python 3 packages required for your plugins to work.
          This option accepts a function that takes a Python 3 package set as an argument,
          and selects the required Python 3 packages from this package set.
          See the example for more info.
        '';
      };

      # We get the Lua package from the final package and use its
      # Lua packageset to evaluate the function that this option was set to.
      # This ensures that we always use the same Lua version as the Neovim package.
      extraLuaPackages = mkOption {
        type = with types;
          let fromType = listOf package;
          in coercedTo fromType (flip warn const ''
            Assigning a plain list to extraLuaPackages is deprecated.
                   Please assign a function taking a package set as argument, so
                     extraLuaPackages = [ pkgs.lua51Packages.xxx ];
                   should become
                     extraLuaPackages = ps: [ ps.xxx ];
          '') (functionTo fromType);
        default = _: [ ];
        defaultText = literalExpression "ps: [ ]";
        example = literalExpression "luaPkgs: with luaPkgs; [ luautf8 ]";
        description = lib.mdDoc ''
          The extra Lua packages required for your plugins to work.
          This option accepts a function that takes a Lua package set as an argument,
          and selects the required Lua packages from this package set.
          See the example for more info.
        '';
      };

      generatedConfigViml = mkOption {
        type = types.lines;
        visible = true;
        readOnly = true;
        description = lib.mdDoc ''
          Generated vimscript config.
        '';
      };

      generatedConfigs = mkOption {
        type = types.attrsOf types.lines;
        visible = true;
        readOnly = true;
        example = literalExpression ''
          {
            viml = '''
              " Generated by home-manager
              map <leader> ,
            ''';

            lua = '''
              -- Generated by home-manager
              vim.opt.background = "dark"
            ''';
          }'';
        description = lib.mdDoc ''
          Generated configurations with as key their language (set via type).
        '';
      };

      package = mkOption {
        type = types.package;
        default = pkgs.neovim-unwrapped;
        defaultText = literalExpression "pkgs.neovim-unwrapped";
        description = lib.mdDoc "The package to use for the neovim binary.";
      };

      finalPackage = mkOption {
        type = types.package;
        visible = false;
        readOnly = true;
        description = lib.mdDoc "Resulting customized neovim package.";
      };

      defaultEditor = mkOption {
        type = types.bool;
        default = false;
        description = lib.mdDoc ''
          Whether to configure {command}`nvim` as the default
          editor using the {env}`EDITOR` environment variable.
        '';
      };

      extraConfig = mkOption {
        type = types.lines;
        default = "";
        example = ''
          set nobackup
        '';
        description = lib.mdDoc ''
          Custom vimrc lines.
        '';
      };

      extraLuaConfig = mkOption {
        type = types.lines;
        default = "";
        example = ''
          vim.opt.nobackup = true
        '';
        description = lib.mdDoc ''
          Custom lua lines.
        '';
      };

      extraPackages = mkOption {
        type = with types; listOf package;
        default = [ ];
        example = literalExpression "[ pkgs.shfmt ]";
        description = lib.mdDoc "Extra packages available to nvim.";
      };

      plugins = mkOption {
        type = with types; listOf (either package pluginWithConfigType);
        default = [ ];
        example = literalExpression ''
          with pkgs.vimPlugins; [
            yankring
            vim-nix
            { plugin = vim-startify;
              config = "let g:startify_change_to_vcs_root = 0";
            }
          ]
        '';
        description = lib.mdDoc ''
          List of vim plugins to install optionally associated with
          configuration to be placed in init.vim.

          This option is mutually exclusive with {var}`configure`.
        '';
      };

      coc = {
        enable = mkEnableOption (lib.mdDoc "Coc");

        package = mkOption {
          type = types.package;
          default = pkgs.vimPlugins.coc-nvim;
          defaultText = literalExpression "pkgs.vimPlugins.coc-nvim";
          description = lib.mdDoc "The package to use for the CoC plugin.";
        };

        settings = mkOption {
          inherit (jsonFormat) type;
          default = { };
          example = literalExpression ''
            {
              "suggest.noselect" = true;
              "suggest.enablePreview" = true;
              "suggest.enablePreselect" = false;
              "suggest.disableKind" = true;
              languageserver = {
                haskell = {
                  command = "haskell-language-server-wrapper";
                  args = [ "--lsp" ];
                  rootPatterns = [
                    "*.cabal"
                    "stack.yaml"
                    "cabal.project"
                    "package.yaml"
                    "hie.yaml"
                  ];
                  filetypes = [ "haskell" "lhaskell" ];
                };
              };
            };
          '';
          description = lib.mdDoc ''
            Extra configuration lines to add to
            {file}`$XDG_CONFIG_HOME/nvim/coc-settings.json`
            See
            <https://github.com/neoclide/coc.nvim/wiki/Using-the-configuration-file>
            for options.
          '';
        };

        pluginConfig = mkOption {
          type = types.lines;
          default = "";
          description = lib.mdDoc "Script to configure CoC. Must be viml.";
        };
      };
    };
  };

  config = let
    defaultPlugin = {
      type = "viml";
      plugin = null;
      config = null;
      optional = false;
      runtime = { };
    };

    # transform all plugins into a standardized attrset
    pluginsNormalized =
      map (x: defaultPlugin // (if (x ? plugin) then x else { plugin = x; }))
      allPlugins;

    suppressNotVimlConfig = p:
      if p.type != "viml" then p // { config = null; } else p;

    neovimConfig = pkgs.neovimUtils.makeNeovimConfig {
      inherit (cfg) extraPython3Packages withPython3 withRuby viAlias vimAlias;
      withNodeJs = cfg.withNodeJs || cfg.coc.enable;
      plugins = map suppressNotVimlConfig pluginsNormalized;
      customRC = cfg.extraConfig;
    };

  in mkIf cfg.enable {

    programs.neovim.generatedConfigViml = neovimConfig.neovimRcContent;

    programs.neovim.generatedConfigs = let
      grouped = lib.lists.groupBy (x: x.type) pluginsNormalized;
      concatConfigs = lib.concatMapStrings (p: p.config);
      configsOnly = lib.foldl
        (acc: p: if p.config != null then acc ++ [ p.config ] else acc) [ ];
    in mapAttrs (name: vals: lib.concatStringsSep "\n" (configsOnly vals))
    grouped;

    home.packages = [ cfg.finalPackage ];

    home.sessionVariables = mkIf cfg.defaultEditor { EDITOR = "nvim"; };

    xdg.configFile =
      let hasLuaConfig = hasAttr "lua" config.programs.neovim.generatedConfigs;
      in mkMerge (
        # writes runtime
        (map (x: x.runtime) pluginsNormalized) ++ [{
          "nvim/init.lua" = let
            luaRcContent =
              lib.optionalString (neovimConfig.neovimRcContent != "")
              "vim.cmd [[source ${
                pkgs.writeText "nvim-init-home-manager.vim"
                neovimConfig.neovimRcContent
              }]]" + config.programs.neovim.extraLuaConfig
              + lib.optionalString hasLuaConfig
              config.programs.neovim.generatedConfigs.lua;
          in mkIf (luaRcContent != "") { text = luaRcContent; };

          "nvim/coc-settings.json" = mkIf cfg.coc.enable {
            source = jsonFormat.generate "coc-settings.json" cfg.coc.settings;
          };
        }]);

    programs.neovim.finalPackage = pkgs.wrapNeovimUnstable cfg.package
      (neovimConfig // {
        wrapperArgs = (lib.escapeShellArgs neovimConfig.wrapperArgs) + " "
          + extraMakeWrapperArgs + " " + extraMakeWrapperLuaCArgs + " "
          + extraMakeWrapperLuaArgs;
        wrapRc = false;
      });

    programs.bash.shellAliases = mkIf cfg.vimdiffAlias { vimdiff = "nvim -d"; };
    programs.fish.shellAliases = mkIf cfg.vimdiffAlias { vimdiff = "nvim -d"; };
    programs.zsh.shellAliases = mkIf cfg.vimdiffAlias { vimdiff = "nvim -d"; };
  };
}