Add Fluxer desktop app package

Expose Fluxer as a system package by adding a new fluxer module and
importing it
in the core packages list.

modules/core/packages/fluxer/default.nix

@@ -0,0 +1,6 @@
+{pkgs, ...}: let
+  fluxer =
+    pkgs.callPackage ./fluxer-package.nix {};
+in {
+  environment.systemPackages = [fluxer];
+}

modules/core/packages/fluxer/fluxer-package.nix

@@ -0,0 +1,35 @@
+{
+  lib,
+  appimageTools,
+  fetchurl,
+}: let
+  pname = "fluxer";
+  version = "canary";
+
+  src = fetchurl {
+    url = "https://api.fluxer.app/dl/desktop/stable/linux/x64/latest/appimage";
+    sha256 = "sha256-GdoBK+Z/d2quEIY8INM4IQy5tzzIBBM+3CgJXQn0qAw=";
+  };
+  appimageContents = appimageTools.extract {inherit pname version src;};
+in
+  appimageTools.wrapType2 {
+    inherit pname version src;
+
+    extraInstallCommands = ''
+      # mv $out/bin/${pname}-${version} $out/bin/${pname}
+      install -m 444 -D ${appimageContents}/${pname}.desktop $out/share/applications/${pname}.desktop
+      install -m 444 -D ${appimageContents}/usr/share/icons/hicolor/512x512/apps/${pname}.png \
+        $out/share/icons/hicolor/512x512/apps/${pname}.png
+      substituteInPlace $out/share/applications/${pname}.desktop \
+        --replace-fail 'Exec=AppRun' 'Exec=${pname}'
+    '';
+
+    meta = with lib; {
+      description = "Fluxer desktop app";
+      homepage = "https://github.com/fluxerapp/fluxer";
+      license = licenses.agpl3Only;
+      platforms = ["x86_64-linux"];
+      sourceProvenance = with lib.sourceTypes; [binaryNativeCode];
+      maintainers = with lib.maintainers; [garand_plg];
+    };
+  }