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

let
  inherit (lib)
    concatStringsSep
    escapeShellArgs
    filterAttrs
    getName
    getVersion
    hasAttr
    hasSuffix
    isString
    literalExpression
    maintainers
    mapAttrs'
    mkEnableOption
    mkIf
    mkOption
    mkPackageOption
    nameValuePair
    optional
    types
    ;
  inherit (pkgs)
    formats
    runCommand
    symlinkJoin
    ;

  jsonFormat = formats.json { };

  cfg = config.programs.gram;

  extensionsDir = runCommand "gram-extensions" { } ''
    set -euo pipefail

    drvs=(${escapeShellArgs cfg.extensionPackages})
    paths=(/share/gram/extensions /share/zed/extensions)

    mkdir $out/

    for drv in "''${drvs[@]}"; do
      for path in "''${paths[@]}"; do
        if [ -e "$drv/$path" ]; then
          ln -s "$drv/$path"/* $out/
        fi
      done
    done
  '';
in

{
  meta.maintainers = with maintainers; [ mikaeladev ];

  options.programs.gram = {
    enable = mkEnableOption "Gram";

    # packages #

    package = mkPackageOption pkgs "gram" { nullable = true; };

    extraPackages = mkOption {
      type = with types; listOf package;
      default = [ ];
      example = literalExpression "with pkgs; [ nil ]";
      description = ''
        List of extra packages available to Gram.
      '';
    };

    extensionPackages = mkOption {
      type = with types; listOf package;
      default = [ ];
      example = literalExpression "with gram-extensions; [ catppuccin ]";
      description = ''
        List of extension packages to install.

        See also:
        - <https://codeberg.org/niklaskorz/nix-gram-extensions>
        - <https://github.com/DuskSystems/nix-zed-extensions>
      '';
    };

    # single-file configs #

    settings = mkOption {
      type = with types; either (attrsOf jsonFormat.type) lines;
      default = { };
      example = {
        buffer_font_family = "JetBrains Mono";
        buffer_font_weight = 400;
        buffer_font_size = 14;
      };
      description = ''
        Set of [settings] to write to {file}`settings.jsonc`.

        [settings]: https://gram-editor.com/docs/configuring-gram/
      '';
    };

    debugger = mkOption {
      type = with types; either (listOf jsonFormat.type) lines;
      default = [ ];
      example = [
        {
          label = "Example Start debugger config";
          adapter = "Example adapter name";
          request = "launch";
          program = "path_to_program";
          cwd = "$GRAM_WORKTREE_ROOT";
        }
      ];
      description = ''
        List of [debug tasks] to write to {file}`debug.jsonc`.

        [debug tasks]: https://gram-editor.com/docs/debugger/
      '';
    };

    keymaps = mkOption {
      type = with types; either (listOf jsonFormat.type) lines;
      default = [ ];
      example = [
        {
          bindings = {
            ctrl-right = "editor::SelectLargerSyntaxNode";
            ctrl-left = "editor::SelectSmallerSyntaxNode";
          };
        }
        {
          context = "ProjectPanel && not_editing";
          bindings.o = "project_panel::Open";
        }
      ];
      description = ''
        List of [key bindings] to write to {file}`keymap.jsonc`.

        [key bindings]: https://gram-editor.com/docs/key-bindings/
      '';
    };

    tasks = mkOption {
      type = with types; either (listOf jsonFormat.type) lines;
      default = [ ];
      example = [
        {
          label = "Example task";
          command = ''for i in {1..5}; do echo "Hello $i/5"; sleep 1; done'';
          env.foo = "bar";
          use_new_terminal = false;
          allow_concurrent_runs = false;
          reveal = "always";
          hide = "never";
          shell = "system";
          show_summary = true;
          show_command = true;
          save = "none";
        }
      ];
      description = ''
        List of [tasks] to write to {file}`tasks.jsonc`.

        [tasks]: https://gram-editor.com/docs/tasks/
      '';
    };

    # multi-file configs #

    snippets = mkOption {
      type = with types; attrsOf (either (attrsOf jsonFormat.type) lines);
      default = { };
      example = {
        html = {
          "Define doctype" = {
            prefix = "doctype";
            description = "Defines the document type";
            body = [
              "<!DOCTYPE>"
              "$1"
            ];
          };
        };
        javascript = {
          "Log to console" = {
            prefix = "log";
            description = "Logs to console";
            body = [
              ''console.info("Hello, ''${1:World}!")''
              "$0"
            ];
          };
        };
      };
      description = ''
        Set of [snippets] to write to {file}`snippets/‹name›.json`.

        [snippets]: https://gram-editor.com/docs/snippets/
      '';
    };

    themes = mkOption {
      type = with types; attrsOf (either (attrsOf jsonFormat.type) lines);
      default = { };
      example = literalExpression ''
        {
          my-cool-theme = {
            name = "My Cool Theme";
            author = "You!";
            themes = [
              {
                name = "My Cool Dark Theme";
                appearance = "dark";
                style = {
                  "editor.background" = "#000";
                  # ...
                };
              }
              {
                name = "My Cool Light Theme";
                appearance = "light";
                style = {
                  "editor.background" = "#fff";
                  # ...
                };
              }
            ];
          };
        }
      '';
      description = ''
        Set of [local themes] to write to {file}`themes/‹name›.json`.

        [local themes]: https://gram-editor.com/docs/themes/
      '';
    };
  };

  config = mkIf cfg.enable {
    assertions = [
      {
        assertion = cfg.extraPackages != [ ] -> cfg.package != null;
        message = ''
          The `programs.gram.extraPackages` option requires that `programs.gram.package`
          not be null.
        '';
      }
    ]
    ++ (
      let
        mkSnippetException = scope: substitute: {
          assertion = !((hasAttr scope cfg.snippets) || (hasAttr (scope + ".json") cfg.snippets));
          message = ''
            The snippet scope defined at `programs.gram.snippets.${scope}` is incorrect,
            use `programs.gram.snippets.${substitute}` instead.

            (reasoning: <https://gram-editor.com/docs/snippets/>)
          '';
        };
      in
      [
        (mkSnippetException "global" "snippets")
        (mkSnippetException "jsx" "javascript")
        (mkSnippetException "plain" "plaintext")
      ]
    );

    home.packages = optional (cfg.package != null) (
      if cfg.extraPackages == [ ] && cfg.extensionPackages == [ ] then
        cfg.package
      else
        (symlinkJoin {
          pname = "${getName cfg.package}-wrapped";
          version = getVersion cfg.package;
          paths = [ cfg.package ];
          preferLocalBuild = true;
          nativeBuildInputs = [ pkgs.makeWrapper ];
          postBuild =
            let
              optionalArgs =
                (optional (cfg.extraPackages != [ ]) "--suffix PATH : ${lib.makeBinPath cfg.extraPackages}")
                ++ (optional (cfg.extensionPackages != [ ]) "--set GRAM_SYSTEM_EXTENSIONS_DIR ${extensionsDir}");
            in
            ''
              wrapProgram $out/bin/${cfg.package.meta.mainProgram or "gram"} \
                ${concatStringsSep " " optionalArgs}
            '';
        })
    );

    home.sessionVariables = mkIf (cfg.package == null && cfg.extensionPackages != [ ]) {
      GRAM_SYSTEM_EXTENSIONS_DIR = extensionsDir;
    };

    xdg.configFile =
      let
        withSuffix = suffix: value: if (hasSuffix suffix value) then value else (value + suffix);

        mkFileValue =
          name: value:
          if isString value then { text = value; } else { source = jsonFormat.generate name value; };

        mapConfigAttrs =
          prefix: suffix:
          mapAttrs' (
            name: value:
            let
              suffixedName = withSuffix suffix name;
            in
            nameValuePair (prefix + suffixedName) (mkFileValue suffixedName value)
          );

        singleFileConfigs = filterAttrs (_: value: value != null) {
          settings = if (cfg.settings != { }) then cfg.settings else null;
          debug = if (cfg.debugger != [ ]) then cfg.debugger else null;
          keymap = if (cfg.keymaps != [ ]) then cfg.keymaps else null;
          tasks = if (cfg.tasks != [ ]) then cfg.tasks else null;
        };
      in
      (mapConfigAttrs "gram/" ".jsonc" singleFileConfigs)
      // (mapConfigAttrs "gram/snippets/" ".json" cfg.snippets)
      // (mapConfigAttrs "gram/themes/" ".json" cfg.themes);
  };
}