# MIT License
# Copyright (c) 2019 Robert Helgesson
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
{
  config,
  lib,
  pkgs,
  ...
}:
with lib; let
  cfg = config.programs.emacs.init;

  packageFunctionType = mkOptionType {
    name = "packageFunction";
    description = "function from epkgs to package";
    check = isFunction;
    merge = mergeOneOption;
  };

  usePackageType = types.submodule ({
    name,
    config,
    ...
  }: {
    options = {
      enable = mkEnableOption "Emacs package ${name}";

      package = mkOption {
        type =
          types.either (types.str // {description = "name of package";})
          packageFunctionType;
        default = name;
        description = ''
          The package to use for this module. Either the package name
          within the Emacs package set or a function taking the Emacs
          package set and returning a package.
        '';
      };

      defer = mkOption {
        type = types.either types.bool types.ints.positive;
        default = false;
        description = ''
          The <option>:defer</option> setting.
        '';
      };

      defines = mkOption {
        type = types.listOf types.str;
        default = [];
        description = ''
          The entries to use for <option>:defines</option>.
        '';
      };

      demand = mkOption {
        type = types.bool;
        default = false;
        description = ''
          The <option>:demand</option> setting.
        '';
      };

      diminish = mkOption {
        type = types.listOf types.str;
        default = [];
        description = ''
          The entries to use for <option>:diminish</option>.
        '';
      };

      chords = mkOption {
        type = types.attrsOf types.str;
        default = {};
        example = {
          "jj" = "ace-jump-char-mode";
          "jk" = "ace-jump-word-mode";
        };
        description = ''
          The entries to use for <option>:chords</option>.
        '';
      };

      functions = mkOption {
        type = types.listOf types.str;
        default = [];
        description = ''
          The entries to use for <option>:functions</option>.
        '';
      };

      mode = mkOption {
        type = types.listOf types.str;
        default = [];
        description = ''
          The entries to use for <option>:mode</option>.
        '';
      };

      after = mkOption {
        type = types.listOf types.str;
        default = [];
        description = ''
          The entries to use for <option>:after</option>.
        '';
      };

      bind = mkOption {
        type = types.attrsOf types.str;
        default = {};
        example = {
          "M-<up>" = "drag-stuff-up";
          "M-<down>" = "drag-stuff-down";
        };
        description = ''
          The entries to use for <option>:bind</option>.
        '';
      };

      bindLocal = mkOption {
        type = types.attrsOf (types.attrsOf types.str);
        default = {};
        example = {
          helm-command-map = {"C-c h" = "helm-execute-persistent-action";};
        };
        description = ''
          The entries to use for local keymaps in <option>:bind</option>.
        '';
      };

      bindKeyMap = mkOption {
        type = types.attrsOf types.str;
        default = {};
        example = {"C-c p" = "projectile-command-map";};
        description = ''
          The entries to use for <option>:bind-keymap</option>.
        '';
      };

      command = mkOption {
        type = types.listOf types.str;
        default = [];
        description = ''
          The entries to use for <option>:commands</option>.
        '';
      };

      config = mkOption {
        type = types.lines;
        default = "";
        description = ''
          Code to place in the <option>:config</option> section.
        '';
      };

      extraConfig = mkOption {
        type = types.lines;
        default = "";
        description = ''
          Additional lines to place in the use-package configuration.
        '';
      };

      hook = mkOption {
        type = types.listOf types.str;
        default = [];
        description = ''
          The entries to use for <option>:hook</option>.
        '';
      };

      earlyInit = mkOption {
        type = types.lines;
        default = "";
        description = ''
          Lines to add to <option>programs.emacs.init.earlyInit</option> when
          this package is enabled.
          </para><para>
          Note, the package is not automatically loaded so you will have to
          <literal>require</literal> the necessary features yourself.
        '';
      };

      init = mkOption {
        type = types.lines;
        default = "";
        description = ''
          The entries to use for <option>:init</option>.
        '';
      };

      extraPackages = mkOption {
        type = types.listOf types.package;
        default = [];
        description = ''
          Extra packages to add to <option>home.packages</option>.
        '';
      };

      assembly = mkOption {
        type = types.lines;
        readOnly = true;
        internal = true;
        description = "The final use-package code.";
      };
    };

    config = mkIf config.enable {
      assembly = let
        quoted = v: ''"${escape [''"''] v}"'';
        mkBindHelper = cmd: prefix: bs:
          optionals (bs != {}) ([":${cmd} (${prefix}"]
            ++ mapAttrsToList (n: v: "  (${quoted n} . ${v})") bs
            ++ [")"]);

        mkAfter = vs: optional (vs != []) ":after (${toString vs})";
        mkCommand = vs: optional (vs != []) ":commands (${toString vs})";
        mkDefines = vs: optional (vs != []) ":defines (${toString vs})";
        mkDiminish = vs: optional (vs != []) ":diminish (${toString vs})";
        mkMode = map (v: ":mode ${v}");
        mkFunctions = vs: optional (vs != []) ":functions (${toString vs})";
        mkBind = mkBindHelper "bind" "";
        mkBindLocal = bs: let
          mkMap = n: v: mkBindHelper "bind" ":map ${n}" v;
        in
          flatten (mapAttrsToList mkMap bs);
        mkBindKeyMap = mkBindHelper "bind-keymap" "";
        mkChords = mkBindHelper "chords" "";
        mkHook = map (v: ":hook ${v}");
        mkDefer = v:
          if isBool v
          then optional v ":defer t"
          else [":defer ${toString v}"];
        mkDemand = v: optional v ":demand t";
      in
        concatStringsSep "\n  "
        (["(use-package ${name}"]
          ++ mkAfter config.after
          ++ mkBind config.bind
          ++ mkBindKeyMap config.bindKeyMap
          ++ mkBindLocal config.bindLocal
          ++ mkChords config.chords
          ++ mkCommand config.command
          ++ mkDefer config.defer
          ++ mkDefines config.defines
          ++ mkFunctions config.functions
          ++ mkDemand config.demand
          ++ mkDiminish config.diminish
          ++ mkHook config.hook
          ++ mkMode config.mode
          ++ optionals (config.init != "") [":init" config.init]
          ++ optionals (config.config != "") [":config" config.config]
          ++ optional (config.extraConfig != "") config.extraConfig)
        + ")";
    };
  });

  usePackageStr = name: pkgConfStr: ''
    (use-package ${name}
      ${pkgConfStr})
  '';

  mkRecommendedOption = type: extraDescription:
    mkOption {
      type = types.bool;
      default = false;
      example = true;
      description =
        ''
          Whether to enable recommended ${type} settings.
        ''
        + optionalString (extraDescription != "") ''
          </para><para>
          ${extraDescription}
        '';
    };

  # Recommended GC settings.
  gcSettings = ''
    (defun hm/reduce-gc ()
      "Reduce the frequency of garbage collection."
      (setq gc-cons-threshold most-positive-fixnum
            gc-cons-percentage 0.6))

    (defun hm/restore-gc ()
      "Restore the frequency of garbage collection."
      (setq gc-cons-threshold 16777216
            gc-cons-percentage 0.1))

    ;; Make GC more rare during init, while minibuffer is active, and
    ;; when shutting down. In the latter two cases we try doing the
    ;; reduction early in the hook.
    (hm/reduce-gc)
    (add-hook 'minibuffer-setup-hook #'hm/reduce-gc -50)
    (add-hook 'kill-emacs-hook #'hm/reduce-gc -50)

    ;; But make it more regular after startup and after closing minibuffer.
    (add-hook 'emacs-startup-hook #'hm/restore-gc)
    (add-hook 'minibuffer-exit-hook #'hm/restore-gc)

    ;; Avoid unnecessary regexp matching while loading .el files.
    (defvar hm/file-name-handler-alist file-name-handler-alist)
    (setq file-name-handler-alist nil)

    (defun hm/restore-file-name-handler-alist ()
      "Restores the file-name-handler-alist variable."
      (setq file-name-handler-alist hm/file-name-handler-alist)
      (makunbound 'hm/file-name-handler-alist))

    (add-hook 'emacs-startup-hook #'hm/restore-file-name-handler-alist)
  '';

  # Whether the configuration makes use of `:diminish`.
  hasDiminish = any (p: p.diminish != []) (attrValues cfg.usePackage);

  # Whether the configuration makes use of `:bind`.
  hasBind =
    any (p: p.bind != {} || p.bindLocal != {} || p.bindKeyMap != {})
    (attrValues cfg.usePackage);

  # Whether the configuration makes use of `:chords`.
  hasChords = any (p: p.chords != {}) (attrValues cfg.usePackage);

  usePackageSetup =
    ''
      (eval-when-compile
        (require 'use-package)
        ;; To help fixing issues during startup.
        (setq use-package-verbose ${
        if cfg.usePackageVerbose
        then "t"
        else "nil"
      }))

    ''
    + optionalString hasDiminish ''
      ;; For :diminish in (use-package).
      (require 'diminish)
    ''
    + optionalString hasBind ''
      ;; For :bind in (use-package).
      (require 'bind-key)

      ;; Fixes "Symbol’s function definition is void: use-package-autoload-keymap".
      (autoload #'use-package-autoload-keymap "use-package-bind-key")
    ''
    + optionalString hasChords ''
      ;; For :chords in (use-package).
      (use-package use-package-chords
        :config (key-chord-mode 1))
    '';

  earlyInitFile = ''
    ;;; hm-early-init.el --- Emacs configuration à la Home Manager -*- lexical-binding: t; -*-
    ;;
    ;;; Commentary:
    ;;
    ;; The early init component of the Home Manager Emacs configuration.
    ;;
    ;;; Code:

    ${cfg.earlyInit}

    (provide 'hm-early-init)
    ;; hm-early-init.el ends here
  '';

  initFile =
    ''
      ;;; hm-init.el --- Emacs configuration à la Home Manager -*- lexical-binding: t; -*-
      ;;
      ;;; Commentary:
      ;;
      ;; A configuration generated from a Nix based configuration by
      ;; Home Manager.
      ;;
      ;;; Code:

      ${optionalString cfg.startupTimer ''
        (defun hm/print-startup-stats ()
          "Prints some basic startup statistics."
          (let ((elapsed (float-time (time-subtract after-init-time
                                                    before-init-time))))
            (message "Startup took %.2fs with %d GCs" elapsed gcs-done)))
        (add-hook 'emacs-startup-hook #'hm/print-startup-stats)
      ''}

      ${cfg.prelude}

      ${usePackageSetup}
    ''
    + concatStringsSep "\n\n" (map (getAttr "assembly")
      (filter (getAttr "enable") (attrValues cfg.usePackage)))
    + ''

      ${cfg.postlude}

      (provide 'hm-init)
      ;; hm-init.el ends here
    '';
in {
  options.programs.emacs.init = {
    enable = mkEnableOption "Emacs configuration";

    recommendedGcSettings = mkRecommendedOption "garbage collection" ''
      This will reduce garbage collection frequency during startup and
      while the minibuffer is active.
    '';

    startupTimer = mkEnableOption "Emacs startup duration timer";

    earlyInit = mkOption {
      type = types.lines;
      default = "";
      description = ''
        Configuration lines to add in <filename>early-init.el</filename>.
      '';
    };

    prelude = mkOption {
      type = types.lines;
      default = "";
      description = ''
        Configuration lines to add in the beginning of
        <filename>init.el</filename>.
      '';
    };

    postlude = mkOption {
      type = types.lines;
      default = "";
      description = ''
        Configuration lines to add in the end of
        <filename>init.el</filename>.
      '';
    };

    packageQuickstart = mkOption {
      type = types.bool;
      default = true;
      description = ''
        Whether to enable package-quickstart. This will make sure that
        <literal>package.el</literal> is activated and all autoloads are
        available.
        </para><para>
        If disabled you can save quite a few milliseconds on the startup time,
        but you will most likely have to tweak the <literal>command</literal>
        option of various packages.
        </para><para>
        As an example, running <literal>(emacs-init-time)</literal> on an Emacs
        configuration with this option enabled reported ~300ms. Disabling the
        option dropped the init time to ~200ms.
      '';
    };

    usePackageVerbose = mkEnableOption "verbose use-package mode";

    usePackage = mkOption {
      type = types.attrsOf usePackageType;
      default = {};
      example = literalExpression ''
        {
          dhall-mode = {
            mode = [ '''"\\.dhall\\'"''' ];
          };
        }
      '';
      description = ''
        Attribute set of use-package configurations.
      '';
    };
  };

  config = mkIf (config.programs.emacs.enable && cfg.enable) {
    # Collect the extra packages that should be included in the user profile.
    # These are typically tools called by Emacs packages.
    home.packages =
      concatMap (v: v.extraPackages)
      (filter (getAttr "enable") (builtins.attrValues cfg.usePackage));

    programs.emacs.init.earlyInit = let
      standardEarlyInit = mkBefore ''
        ${optionalString cfg.recommendedGcSettings gcSettings}

        ${
          if cfg.packageQuickstart
          then ''
            (setq package-quickstart t
                  package-quickstart-file "hm-package-quickstart.el")
          ''
          else ''
            (setq package-enable-at-startup nil)
          ''
        }

        ;; Avoid expensive frame resizing. Inspired by Doom Emacs.
        (setq frame-inhibit-implied-resize t)
      '';

      # Collect the early initialization strings for each package.
      packageEarlyInits =
        map (p: p.earlyInit)
        (filter (p: p.earlyInit != "") (builtins.attrValues cfg.usePackage));
    in
      mkMerge ([standardEarlyInit] ++ packageEarlyInits);

    programs.emacs.extraPackages = epkgs: let
      getPkg = v:
        if isFunction v
        then [(v epkgs)]
        else optional (isString v && hasAttr v epkgs) epkgs.${v};

      packages =
        concatMap (v: getPkg (v.package))
        (filter (getAttr "enable") (builtins.attrValues cfg.usePackage));
    in [
      (epkgs.trivialBuild {
        pname = "hm-early-init";
        src = pkgs.writeText "hm-early-init.el" earlyInitFile;
        packageRequires = packages;
        preferLocalBuild = true;
        allowSubstitutes = false;
      })

      (epkgs.trivialBuild {
        pname = "hm-init";
        src = pkgs.writeText "hm-init.el" initFile;
        packageRequires =
          [epkgs.use-package]
          ++ packages
          ++ optional hasBind epkgs.bind-key
          ++ optional hasDiminish epkgs.diminish
          ++ optional hasChords epkgs.use-package-chords;
        preferLocalBuild = true;
        allowSubstitutes = false;
        preBuild = ''
          # Do a bit of basic formatting of the generated init file.
          emacs -Q --batch \
            --eval '(find-file "hm-init.el")' \
            --eval '(let ((indent-tabs-mode nil) (lisp-indent-offset 2)) (indent-region (point-min) (point-max)))' \
            --eval '(write-file "hm-init.el")'

          ${optionalString cfg.packageQuickstart ''
            # Generate a package quickstart file to make autoloads and such
            # available.
            emacs -Q --batch \
              --eval "(require 'package)" \
              --eval "(setq package-quickstart-file \"hm-package-quickstart.el\")" \
              --eval "(package-quickstart-refresh)"

            # We know what we're doing?
            sed -i '/no-byte-compile: t/d' hm-package-quickstart.el
          ''}
        '';
      })
    ];

    home.file = {
      ".emacs.d/early-init.el".text = ''
        (require 'hm-early-init)
        (provide 'early-init)
      '';

      ".emacs.d/init.el".text = ''
        (require 'hm-init)
        (provide 'init)
      '';
    };
  };
}