{ depot, pkgs, lib, ... }:

# TODO(wpcarro): See if it's possible to expose emacsclient on PATH, so that I
# don't need to depend on wpcarros-emacs and emacs in my NixOS configurations.
let
  inherit (builtins) path;
  inherit (depot.third_party.nixpkgs) emacsPackagesGen emacs27;
  inherit (depot.users) wpcarro;
  inherit (pkgs) writeShellScript writeShellScriptBin;
  inherit (lib) mapAttrsToList;
  inherit (lib.strings) concatStringsSep makeBinPath;

  emacsBinPath = makeBinPath (
    wpcarro.common.shell-utils ++
    (with pkgs; [
      clipmenu
      ispell
      nix
      pass
      scrot
      xorg.xset
    ]));

  emacsWithPackages = (emacsPackagesGen emacs27).emacsWithPackages;

  wpcarrosEmacs = emacsWithPackages (epkgs:
    (with epkgs.tvlPackages; [
      tvl
    ]) ++

    (with epkgs.elpaPackages; [
      exwm
    ]) ++

    (with epkgs.melpaPackages; [
      org-bullets
      sly
      notmuch
      elm-mode
      ts
      vterm
      base16-theme
      password-store
      # TODO(wpcarro): Prefer an Emacs client for clipmenud.
      clipmon
      evil
      evil-collection
      evil-commentary
      evil-surround
      key-chord
      # TODO(wpcarro): Assess whether or not I need this with Nix.
      add-node-modules-path
      web-mode
      rjsx-mode
      tide
      prettier-js
      flycheck
      diminish
      doom-themes
      telephone-line
      which-key
      all-the-icons
      all-the-icons-ivy
      ivy
      ivy-pass
      ivy-prescient
      restclient
      package-lint
      parsec
      magit-popup
      direnv
      alert
      nix-mode
      racer
      rust-mode
      rainbow-delimiters
      racket-mode
      lispyville
      elisp-slime-nav
      py-yapf
      reason-mode
      elixir-mode
      go-mode
      company
      markdown-mode
      refine
      deferred
      magit
      request
      pcre2el
      helpful
      # TODO(wpcarro): Determine if Nix solves this problem.
      exec-path-from-shell
      yasnippet
      projectile
      deadgrep
      counsel
      counsel-projectile
      # TODO(wpcarro): Learn what this is.
      engine-mode
      eglot
      dap-mode
      lsp-ui
      suggest
      paradox
      flymake-shellcheck
      fish-mode
      tuareg
      haskell-mode
      use-package
      general
      clojure-mode
      cider
      f
      dash
      company
      counsel
      flycheck
      emojify
    ]));

  vendorDir = path {
    path = ./.emacs.d/vendor;
    name = "emacs-vendor";
  };

  # TODO(wpcarro): byte-compile these by packaging each as an Elisp library.
  wpcDir = path {
    path = ./.emacs.d/wpc;
    name = "emacs-libs";
  };

  wpcPackageEl = path {
    path = ./.emacs.d/wpc/wpc-package.el;
    name = "wpc-package.el";
  };

  initEl = path {
    path = ./.emacs.d/init.el;
    name = "init.el";
  };

  loadPath = concatStringsSep ":" [
    wpcDir
    vendorDir
    # TODO(wpcarro): Explain why the trailing ":" is needed.
    "${wpcarrosEmacs.deps}/share/emacs/site-lisp:"
  ];

  # Transform an attrset into "export k=v" statements.
  makeEnvVars = env: concatStringsSep "\n"
    (mapAttrsToList (k: v: "export ${k}=\"${v}\"") env);

  withEmacsPath = { emacsBin, env ? {} }:
    writeShellScriptBin "wpcarros-emacs" ''
      export XMODIFIERS=emacs
      export PATH="${emacsBinPath}:$PATH"
      export EMACSLOADPATH="${loadPath}"
      ${makeEnvVars env}
      exec ${emacsBin} \
        --debug-init \
        --no-init-file \
        --no-site-file \
        --no-site-lisp \
        --load ${initEl} \
        "$@"
    '';
in {
  inherit initEl withEmacsPath;

  # I need to start my Emacs from CI without the call to `--load ${initEl}`.
  runScript = { script }:
    writeShellScript "run-emacs-script" ''
      export PATH="${emacsBinPath}:$PATH"
      export EMACSLOADPATH="${wpcDir}:${vendorDir}:${wpcarrosEmacs.deps}/share/emacs/site-lisp"
      exec ${wpcarrosEmacs}/bin/emacs \
        --no-site-file \
        --no-site-lisp \
        --no-init-file \
        --script ${script} \
        "$@"
    '';

  nixos = withEmacsPath {
    emacsBin = "${wpcarrosEmacs}/bin/emacs";
  };

  meta.targets = [ "nixos" ];
}