home-manager/modules/programs/feh.nix

{
  config,
  lib,
  pkgs,
  ...
}:
let
  inherit (lib)
    filterAttrs
    mapAttrsToList
    mkOption
    types
    ;

  cfg = config.programs.feh;

  bindingsOf = t: with types; attrsOf (nullOr (either t (listOf t)));

  renderThemes =
    options:
    let
      render = mapAttrsToList (theme: options: "${theme} ${lib.escapeShellArgs options}");
    in
    lib.concatStringsSep "\n" (render options);

  renderBindings =
    bindings:
    let
      enabled = filterAttrs (n: v: v != null) bindings;
      disabled = filterAttrs (n: v: v == null) bindings;
      render = mapAttrsToList renderBinding;
    in
    lib.concatStringsSep "\n" (render disabled ++ render enabled);

  renderBinding =
    func: key:
    if key == null then
      func
    else if lib.isList key then
      lib.concatStringsSep " " ([ func ] ++ map toString key)
    else
      "${func} ${toString key}";

in
{
  options.programs.feh = {
    enable = lib.mkEnableOption "feh - a fast and light image viewer";

    package = lib.mkPackageOption pkgs "feh" { nullable = true; };

    buttons = mkOption {
      default = { };
      type = with types; bindingsOf (either str int);
      example = {
        zoom_in = 4;
        zoom_out = "C-4";
        prev_img = [
          3
          "C-3"
        ];
      };
      description = ''
        Override feh's default mouse button mapping. If you want to disable an
        action, set its value to null. If you want to bind multiple buttons to
        an action, set its value to a list.
        See <https://man.finalrewind.org/1/feh/#BUTTONS_CONFIG_SYNTAX> for
        default bindings and available commands.
      '';
    };

    keybindings = mkOption {
      default = { };
      type = bindingsOf types.str;
      example = {
        zoom_in = "plus";
        zoom_out = "minus";
        prev_img = [
          "h"
          "Left"
        ];
      };
      description = ''
        Override feh's default keybindings. If you want to disable a keybinding
        set its value to null. If you want to bind multiple keys to an action,
        set its value to a list.
        See <https://man.finalrewind.org/1/feh/#KEYS_CONFIG_SYNTAX> for
        default bindings and available commands.
      '';
    };

    themes = mkOption {
      default = { };
      type = with types; attrsOf (listOf str);
      example = {
        feh = [
          "--image-bg"
          "black"
        ];
        webcam = [
          "--multiwindow"
          "--reload"
          "20"
        ];
        present = [
          "--full-screen"
          "--sort"
          "name"
          "--hide-pointer"
        ];
        booth = [
          "--full-screen"
          "--hide-pointer"
          "--slideshow-delay"
          "20"
        ];
        imagemap = [
          "-rVq"
          "--thumb-width"
          "40"
          "--thumb-height"
          "30"
          "--index-info"
          "%n\\n%wx%h"
        ];
        example = [
          "--info"
          "foo bar"
        ];
      };
      description = ''
        Define themes for feh.
        See <https://man.finalrewind.org/1/feh/#THEMES_CONFIG_SYNTAX> for
        important guidelines and limitations related to theme configuration.
      '';
    };

  };

  config = lib.mkIf cfg.enable {
    assertions = [
      {
        assertion = ((filterAttrs (n: v: v == "") cfg.keybindings) == { });
        message = "To disable a keybinding, use `null` instead of an empty string.";
      }
    ];

    home.packages = lib.mkIf (cfg.package != null) [ cfg.package ];

    xdg.configFile."feh/buttons" = lib.mkIf (cfg.buttons != { }) {
      text = renderBindings cfg.buttons + "\n";
    };

    xdg.configFile."feh/keys" = lib.mkIf (cfg.keybindings != { }) {
      text = renderBindings cfg.keybindings + "\n";
    };

    xdg.configFile."feh/themes" = lib.mkIf (cfg.themes != { }) {
      text = renderThemes cfg.themes + "\n";
    };
  };
}