feishin: fix darwin builds

Addresses the comment
https://github.com/NixOS/nixpkgs/pull/303638#issuecomment-2052463043
following #303638.

pkgs/applications/audio/feishin/default.nix

@@ -1,8 +1,10 @@
 {
   lib,
+  stdenv,
   buildNpmPackage,
   fetchFromGitHub,
   electron_27,
+  darwin,
   copyDesktopItems,
   makeDesktopItem,
   ...
@@ -21,8 +23,7 @@ let
   electron = electron_27;
 in
 buildNpmPackage {
-  pname = "feishin";
-  inherit version;
+  inherit pname version;
 
   inherit src;
   npmDepsHash = "sha256-+pr9fWg/9kxkYMmthtqhjgF6MOomSQxVCO5V8tHHRdE=";
@@ -32,13 +33,21 @@ buildNpmPackage {
 
   env.ELECTRON_SKIP_BINARY_DOWNLOAD = "1";
 
-  nativeBuildInputs = [ copyDesktopItems ];
+  nativeBuildInputs =
+    lib.optionals (stdenv.isLinux) [ copyDesktopItems ]
+    ++ lib.optionals stdenv.isDarwin [ darwin.autoSignDarwinBinariesHook ];
 
-  postPatch = ''
+  postPatch =
+    ''
       # release/app dependencies are installed on preConfigure
       substituteInPlace package.json \
         --replace-fail "electron-builder install-app-deps &&" ""
 
+      # Don't check for updates.
+      substituteInPlace src/main/main.ts \
+        --replace-fail "autoUpdater.checkForUpdatesAndNotify();" ""
+    ''
+    + lib.optionalString stdenv.isLinux ''
       # https://github.com/electron/electron/issues/31121
       substituteInPlace src/main/main.ts \
         --replace-fail "process.resourcesPath" "'$out/share/feishin/resources'"
@@ -67,17 +76,35 @@ buildNpmPackage {
       done
     '';
 
-  postBuild = ''
+  postBuild =
+    lib.optionalString stdenv.isDarwin ''
+      # electron-builder appears to build directly on top of Electron.app, by overwriting the files in the bundle.
+      cp -r ${electron}/Applications/Electron.app ./
+      find ./Electron.app -name 'Info.plist' | xargs -d '\n' chmod +rw
+
+      # Disable code signing during build on macOS.
+      # https://github.com/electron-userland/electron-builder/blob/fa6fc16/docs/code-signing.md#how-to-disable-code-signing-during-the-build-process-on-macos
+      export CSC_IDENTITY_AUTO_DISCOVERY=false
+      sed -i "/afterSign/d" package.json
+    ''
+    + ''
       npm exec electron-builder -- \
         --dir \
-      -c.electronDist=${electron}/libexec/electron \
+        -c.electronDist=${if stdenv.isDarwin then "./" else "${electron}/libexec/electron"} \
         -c.electronVersion=${electron.version} \
         -c.npmRebuild=false
     '';
 
-  installPhase = ''
+  installPhase =
+    ''
       runHook preInstall
-
+    ''
+    + lib.optionalString stdenv.isDarwin ''
+      mkdir -p $out/{Applications,bin}
+      cp -r release/build/**/Feishin.app $out/Applications/
+      makeWrapper $out/Applications/Feishin.app/Contents/MacOS/Feishin $out/bin/feishin
+    ''
+    + lib.optionalString stdenv.isLinux ''
       mkdir -p $out/share/feishin
       pushd release/build/*/
       cp -r locales resources{,.pak} $out/share/feishin
@@ -98,7 +125,8 @@ buildNpmPackage {
           $out/share/feishin/resources/assets/icons/"$size"x"$size".png \
           $out/share/icons/hicolor/"$size"x"$size"/apps/${pname}.png
       done
-
+    ''
+    + ''
       runHook postInstall
     '';