{
  config,
  lib,
  pkgs,
  ...
}:
let
  inherit (lib)
    concatStringsSep
    literalExpression
    mkIf
    mkOption
    optionalString
    types
    ;

  cfg = config.services.kanshi;

  directivesTag = types.attrTag {
    profile = mkOption {
      type = profileModule;
      description = ''
        profile attribute set.
      '';
    };
    output = mkOption {
      type = outputModule;
      description = ''
        output attribute set.
      '';
    };
    include = mkOption {
      type = types.str;
      description = ''
        Include as another file from _path_.
        Expands shell syntax (see *wordexp*(3) for details).
      '';
    };
  };

  tagToStr =
    x:
    if x ? profile then
      profileStr x.profile
    else if x ? output then
      outputStr x.output
    else if x ? include then
      ''include "${x.include}"''
    else
      throw "Unknown tags ${lib.attrNames x}";

  directivesStr = concatStringsSep "\n" (map tagToStr cfg.settings);

  oldDirectivesStr = ''
    ${concatStringsSep "\n" (lib.mapAttrsToList (n: v: profileStr (v // { name = n; })) cfg.profiles)}
    ${cfg.extraConfig}
  '';

  outputModule = types.submodule {
    options = {

      criteria = mkOption {
        type = types.str;
        description = ''
          The criteria can either be an output name, an output description or "*".
          The latter can be used to match any output.

          On
          {manpage}`sway(1)`,
          output names and descriptions can be obtained via
          `swaymsg -t get_outputs`.
        '';
      };

      status = mkOption {
        type = types.nullOr (
          types.enum [
            "enable"
            "disable"
          ]
        );
        default = null;
        description = ''
          Enables or disables the specified output.
        '';
      };

      mode = mkOption {
        type = types.nullOr types.str;
        default = null;
        example = "1920x1080@60Hz";
        description = ''
          &lt;width&gt;x&lt;height&gt;[@&lt;rate&gt;[Hz]]

          Configures the specified output to use the specified mode.
          Modes are a combination of width and height (in pixels) and
          a refresh rate (in Hz) that your display can be configured to use.
        '';
      };

      position = mkOption {
        type = types.nullOr types.str;
        default = null;
        example = "1600,0";
        description = ''
          &lt;x&gt;,&lt;y&gt;

          Places the output at the specified position in the global coordinates
          space.
        '';
      };

      scale = mkOption {
        type = types.nullOr types.float;
        default = null;
        example = 2;
        description = ''
          Scales the output by the specified scale factor.
        '';
      };

      transform = mkOption {
        type = types.nullOr (
          types.enum [
            "normal"
            "90"
            "180"
            "270"
            "flipped"
            "flipped-90"
            "flipped-180"
            "flipped-270"
          ]
        );
        default = null;
        description = ''
          Sets the output transform.
        '';
      };

      alias = mkOption {
        type = types.nullOr types.str;
        default = null;
        example = "laptopMonitor";
        description = ''
          Defines an alias for the output
        '';
      };

      adaptiveSync = mkOption {
        type = types.nullOr types.bool;
        default = null;
        example = true;
        description = ''
          Enables or disables adaptive synchronization
          (aka. Variable Refresh Rate).
        '';
      };
    };
  };

  outputStr =
    {
      criteria,
      status,
      mode,
      position,
      scale,
      transform,
      adaptiveSync,
      alias,
      ...
    }:
    ''output "${criteria}"''
    + optionalString (status != null) " ${status}"
    + optionalString (mode != null) " mode ${mode}"
    + optionalString (position != null) " position ${position}"
    + optionalString (scale != null) " scale ${toString scale}"
    + optionalString (transform != null) " transform ${transform}"
    + optionalString (adaptiveSync != null) " adaptive_sync ${if adaptiveSync then "on" else "off"}"
    + optionalString (alias != null) " alias \$${alias}";

  profileModule = types.submodule {
    options = {
      outputs = mkOption {
        type = types.listOf outputModule;
        default = [ ];
        description = ''
          Outputs configuration.
        '';
      };

      name = mkOption {
        type = types.str;
        default = "";
        description = ''
          Profile name
        '';
      };

      exec = mkOption {
        type = with types; coercedTo str lib.singleton (listOf str);
        default = [ ];
        example = "[ \${pkg.sway}/bin/swaymsg workspace 1, move workspace to eDP-1 ]";
        description = ''
          Commands executed after the profile is successfully applied.
          Note that if you provide multiple commands, they will be
          executed asynchronously with no guaranteed ordering.
        '';
      };
    };
  };

  profileStr =
    { outputs, exec, ... }@args:
    ''
      profile ${args.name or ""} {
        ${concatStringsSep "\n  " (map outputStr outputs ++ map (cmd: "exec ${cmd}") exec)}
      }
    '';
in
{

  meta.maintainers = [ ];

  options.services.kanshi = {
    enable = lib.mkEnableOption "kanshi, a Wayland daemon that automatically configures outputs";

    package = lib.mkPackageOption pkgs "kanshi" { };

    profiles = mkOption {
      type = types.attrsOf profileModule;
      default = { };
      description = ''
        Attribute set of profiles.
      '';
      example = {
        undocked = {
          outputs = [
            {
              criteria = "eDP-1";
            }
          ];
        };
        docked = {
          outputs = [
            {
              criteria = "eDP-1";
            }
            {
              criteria = "Some Company ASDF 4242";
              transform = "90";
            }
          ];
        };
      };
    };

    extraConfig = mkOption {
      type = types.lines;
      default = "";
      description = ''
        Extra configuration lines to append to the kanshi
        configuration file.
      '';
    };

    settings = mkOption {
      type = types.listOf directivesTag;
      default = [ ];
      description = ''
        Ordered list of directives.
        See kanshi(5) for information.
      '';
      example = literalExpression ''
        [
          { include = "path/to/included/files"; }
          { output.criteria = "eDP-1";
            output.scale = 2;
          }
          { profile.name = "undocked";
            profile.outputs = [
              {
                criteria = "eDP-1";
              }
            ];
          }
          { profile.name = "docked";
            profile.outputs = [
              {
                criteria = "eDP-1";
              }
              {
                criteria = "Some Company ASDF 4242";
                transform = "90";
              }
            ];
          }
        ]
      '';
    };

    systemdTarget = mkOption {
      type = types.str;
      default = config.wayland.systemd.target;
      defaultText = literalExpression "config.wayland.systemd.target";
      description = ''
        Systemd target to bind to.
      '';
    };
  };

  config = mkIf cfg.enable (
    lib.mkMerge [
      {
        assertions = [
          (lib.hm.assertions.assertPlatform "services.kanshi" pkgs lib.platforms.linux)
          {
            assertion = (cfg.profiles == { } && cfg.extraConfig == "") || (lib.length cfg.settings) == 0;
            message = "Cannot mix kanshi.settings with kanshi.profiles or kanshi.extraConfig";
          }
          {
            assertion =
              let
                profiles = lib.filter (x: x ? profile) cfg.settings;
              in
              lib.length (lib.filter (x: lib.any (a: a ? alias && a.alias != null) x.profile.outputs) profiles)
              == 0;
            message = "Output kanshi.*.output.alias can only be defined on global scope";
          }
        ];
      }

      (mkIf (cfg.profiles != { }) {
        warnings = [
          "kanshi.profiles option is deprecated. Use kanshi.settings instead."
        ];
      })

      (mkIf (cfg.extraConfig != "") {
        warnings = [
          "kanshi.extraConfig option is deprecated. Use kanshi.settings instead."
        ];
      })

      {
        home.packages = [ cfg.package ];

        xdg.configFile."kanshi/config" =
          let
            generatedConfigStr =
              if cfg.profiles == { } && cfg.extraConfig == "" then directivesStr else oldDirectivesStr;
          in
          mkIf (generatedConfigStr != "") { text = generatedConfigStr; };

        systemd.user.services.kanshi = {
          Unit = {
            Description = "Dynamic output configuration";
            Documentation = "man:kanshi(1)";
            ConditionEnvironment = "WAYLAND_DISPLAY";
            PartOf = cfg.systemdTarget;
            Requires = cfg.systemdTarget;
            After = cfg.systemdTarget;
          };

          Service = {
            Type = "simple";
            ExecStart = "${cfg.package}/bin/kanshi";
            Restart = "always";
          };

          Install = {
            WantedBy = [ cfg.systemdTarget ];
          };
        };
      }
    ]
  );
}
