{
  config,
  lib,
  pkgs,
  ...
}:
# The Hyprland compositor.
let # NOLINT(let_order)
  cfg = config.modules.desktop.session.hyprland; # NOLINT(let_order)
  cursor = config.stylix.cursor;
  bind = key: dispatcher: {
    _args = [
      key
      dispatcher
    ];
  };
  luaCall = function: args: mkLuaInline "${function}(${lib.concatMapStringsSep ", " toLua args})";
  terminal = "ghostty";
  execBindWith =
    key: command: options:
    bindWith key (luaCall "hl.dsp.exec_cmd" [ command ]) options;
  bindWith = key: dispatcher: options: {
    _args = [
      key
      dispatcher
      options
    ];
  };

  # Numbered-workspace switch and move for 1..9, the operator's i3 muscle memory.
  workspaceBinds = lib.concatMap (n: [
    (bind "${mod} + ${toString n}" (luaCall "hl.dsp.focus" [ { workspace = n; } ]))
    (bind "${mod} + SHIFT + ${toString n}" (luaCall "hl.dsp.window.move" [ { workspace = n; } ]))
  ]) (lib.range 1 9);

  execBind = key: command: bind key (luaCall "hl.dsp.exec_cmd" [ command ]);

  inherit (lib.generators) mkLuaInline;

  mod = "SUPER";
  toLua = lib.generators.toLua { };
  user = config.user.name;

  # Flip the tiling strategy between the two built-in layouts, since neither a
  # dispatcher nor a keyword toggles it on its own.
  toggleLayout = pkgs.writeShellScript "hypr-toggle-layout" ''
    if [ "$(hyprctl getoption -j general:layout | ${pkgs.jq}/bin/jq -r .str)" = dwindle ]; then
      hyprctl keyword general:layout master
    else
      hyprctl keyword general:layout dwindle
    fi
  '';
in
{
  options.modules.desktop.session.hyprland = {
    enable = lib.mkEnableOption "the Hyprland compositor";

    blur = lib.mkEnableOption ''
      window blur. Off by default as the single biggest battery cost on a
      laptop, left on for a host with the headroom to spend it'';
  };

  config = lib.mkIf cfg.enable {
    # This program integration owns the session, portals, and polkit, launched
    # through the universal Wayland session manager.
    programs.hyprland = {
      enable = true;
      withUWSM = true;
    };

    home-manager.users.${user}.wayland.windowManager.hyprland = {
      enable = true;

      # One package drives the whole session, so there is never a version split.
      # The program integration above installs it and the portal, leaving home-
      # manager to write only the config.
      package = null;
      portalPackage = null;

      # uwsm owns the systemd graphical-session targets.
      systemd.enable = false;

      # Write the native Lua Hyprland config. Home Manager renders the Nix
      # settings below as hl.* calls.
      configType = "lua";
      importantPrefixes = [
        "config"
        "curve"
        "animation"
      ];

      settings = {
        # Session variables handed to the compositor directly.
        # UWSM launches the session without the shell profile that would carry
        # them, so a variable the compositor or its children must see is set
        # here rather than through home-manager's sessionVariables.
        env = [
          # Chromium and Electron apps read this to select native Wayland;
          # nixpkgs wrappers (Obsidian's included) gate their Wayland flags on
          # it, so without it they run under XWayland and blur at this DPI.
          {
            _args = [
              "NIXOS_OZONE_WL"
              "1"
            ];
          }
        ]
        # Bibata ships XCursor only.
        # The hyprcursor variables name the same theme, which Hyprland
        # resolves through its XCursor fallback.
        ++ lib.optionals (cursor != null) [
          {
            _args = [
              "XCURSOR_THEME"
              cursor.name
            ];
          }
          {
            _args = [
              "XCURSOR_SIZE"
              (toString cursor.size)
            ];
          }
          {
            _args = [
              "HYPRCURSOR_THEME"
              cursor.name
            ];
          }
          {
            _args = [
              "HYPRCURSOR_SIZE"
              (toString cursor.size)
            ];
          }
        ];

        config = {
          input = {
            kb_layout = "us";
            # Caps is a second Escape.
            # Shift+Caps still toggles a real CapsLock.
            kb_options = "caps:escape_shifted_capslock";
            # Snappy key repeat.
            repeat_delay = 250;
            repeat_rate = 45;
            accel_profile = "flat";
            touchpad = {
              natural_scroll = true;
              tap_to_click = true;
              disable_while_typing = true;
            };
          };

          general = {
            gaps_in = 4;
            gaps_out = 8;
            border_size = 2;
            layout = "dwindle";
          };

          decoration = {
            rounding = 6;
            blur.enabled = cfg.blur;
          };

          # XWayland clients render at the panel's native resolution instead of
          # being raster-scaled by the compositor at the fractional monitor scale.
          xwayland.force_zero_scaling = true;

          animations.enabled = true;

          dwindle = {
            preserve_split = true;
          };
        };

        curve = {
          _args = [
            "ease"
            {
              type = "bezier";
              points = [
                [
                  0.25
                  0.1
                ]
                [
                  0.25
                  1.0
                ]
              ];
            }
          ];
        };

        # Durations are in centiseconds.
        # Short values keep the motion subtle.
        animation = [
          {
            leaf = "windows";
            enabled = true;
            speed = 3;
            bezier = "ease";
          }
          {
            leaf = "fade";
            enabled = true;
            speed = 3;
            bezier = "ease";
          }
          # Layer surfaces like the launcher fade in a touch quicker than windows.
          {
            leaf = "layersIn";
            enabled = true;
            speed = 2;
            bezier = "ease";
          }
          {
            leaf = "fadeLayersIn";
            enabled = true;
            speed = 2;
            bezier = "ease";
          }
          {
            leaf = "workspaces";
            enabled = true;
            speed = 3;
            bezier = "ease";
          }
          {
            leaf = "border";
            enabled = true;
            speed = 3;
            bezier = "ease";
          }
        ];

        bind = [
          (execBind "${mod} + Return" terminal)

          # Move focus.
          (bind "${mod} + H" (luaCall "hl.dsp.focus" [ { direction = "left"; } ]))
          (bind "${mod} + J" (luaCall "hl.dsp.focus" [ { direction = "down"; } ]))
          (bind "${mod} + K" (luaCall "hl.dsp.focus" [ { direction = "up"; } ]))
          (bind "${mod} + L" (luaCall "hl.dsp.focus" [ { direction = "right"; } ]))

          # Move the window within the layout.
          (bind "${mod} + SHIFT + H" (luaCall "hl.dsp.window.move" [ { direction = "left"; } ]))
          (bind "${mod} + SHIFT + J" (luaCall "hl.dsp.window.move" [ { direction = "down"; } ]))
          (bind "${mod} + SHIFT + K" (luaCall "hl.dsp.window.move" [ { direction = "up"; } ]))
          (bind "${mod} + SHIFT + L" (luaCall "hl.dsp.window.move" [ { direction = "right"; } ]))

          # Resize the active window.
          (bind "${mod} + ALT + H" (
            luaCall "hl.dsp.window.resize" [
              {
                x = -40;
                y = 0;
                relative = true;
              }
            ]
          ))
          (bind "${mod} + ALT + J" (
            luaCall "hl.dsp.window.resize" [
              {
                x = 0;
                y = 40;
                relative = true;
              }
            ]
          ))
          (bind "${mod} + ALT + K" (
            luaCall "hl.dsp.window.resize" [
              {
                x = 0;
                y = -40;
                relative = true;
              }
            ]
          ))
          (bind "${mod} + ALT + L" (
            luaCall "hl.dsp.window.resize" [
              {
                x = 40;
                y = 0;
                relative = true;
              }
            ]
          ))

          (bind "${mod} + Space" (luaCall "hl.dsp.window.float" [ { action = "toggle"; } ]))
          (bind "${mod} + F" (luaCall "hl.dsp.window.fullscreen" [ ]))
          # togglesplit is a dwindle layout message, reached through layout.
          (bind "${mod} + T" (luaCall "hl.dsp.layout" [ "togglesplit" ]))
          (execBind "${mod} + SHIFT + T" "${toggleLayout}")
          (bind "${mod} + SHIFT + Q" (luaCall "hl.dsp.window.close" [ ]))
          (bind "${mod} + CTRL + Q" (luaCall "hl.dsp.window.kill" [ ]))

          # Volume and brightness keys repeat while held, each raising a popup
          # through the OSD client.
          # Volume is capped at 100 percent.
          # The client floors brightness so a full hold cannot black the screen out.
          (execBindWith "XF86AudioRaiseVolume"
            "${pkgs.swayosd}/bin/swayosd-client --output-volume raise --max-volume 100"
            { repeating = true; }
          )
          (execBindWith "XF86AudioLowerVolume" "${pkgs.swayosd}/bin/swayosd-client --output-volume lower" {
            repeating = true;
          })
          (execBindWith "XF86MonBrightnessUp" "${pkgs.swayosd}/bin/swayosd-client --brightness raise" {
            repeating = true;
          })
          (execBindWith "XF86MonBrightnessDown" "${pkgs.swayosd}/bin/swayosd-client --brightness lower" {
            repeating = true;
          })

          # Mute and media transport still fire while the session is locked.
          (execBindWith "XF86AudioMute" "${pkgs.swayosd}/bin/swayosd-client --output-volume mute-toggle" {
            locked = true;
          })
          (execBindWith "XF86AudioPlay" "${pkgs.playerctl}/bin/playerctl play-pause" { locked = true; })
          (execBindWith "XF86AudioNext" "${pkgs.playerctl}/bin/playerctl next" { locked = true; })
          (execBindWith "XF86AudioPrev" "${pkgs.playerctl}/bin/playerctl previous" { locked = true; })
        ]
        ++ workspaceBinds;
      };
    };
  };
}