{
  description = "APKs demonstrating class shadowing.";
  inputs = {
    nixpkgs.url = github:nixos/nixpkgs/nixos-unstable;
    flake-utils.url = github:numtide/flake-utils;
  };

  outputs = { self, nixpkgs, flake-utils }: 
    flake-utils.lib.eachDefaultSystem (system:
    let
      pkgs = import nixpkgs {
        system = system;
        config = {
          android_sdk.accept_license = true;
          allowUnfree = true;
        };
      };
      jdk = pkgs.javaPackages.compiler.openjdk17;
      android-env = pkgs.androidenv.composeAndroidPackages {
        buildToolsVersions = [ "34.0.0" ];
        platformVersions = [ "34" ];
      };
      platforms = "${builtins.head android-env.platforms}/libexec/android-sdk/platforms/android-34";
      build-tools = "${builtins.head android-env.build-tools}/libexec/android-sdk/build-tools/34.0.0";

      javaCompile = folder: pkgs.stdenvNoCC.mkDerivation {
        name = "java-class-${folder}";
        src = self;
        buildInputs = [ jdk android-env.androidsdk ];
        phases = ["unpackPhase" "buildPhase"];
        buildPhase = ''
          mkdir $out
          javac -classpath ${platforms}/android.jar $(find ${folder} -type f -name '*.java') -d $out/
        '';
      };
      java2dex = drv: pkgs.stdenvNoCC.mkDerivation {
        name = "${drv}-classes.dex";
        srcs = drv;
        # jdk env needed for d8
        buildInputs = [ jdk android-env.androidsdk ];
        phases = ["unpackPhase" "buildPhase" "installPhase"];
        buildPhase = ''
          mkdir build
          d8 --classpath ${platforms}/android.jar $(find . -name '*.class') --output build/
        '';
        installPhase = ''
          mv build/classes.dex $out
        '';
      };
      make-manifest = package : name: pkgs.stdenvNoCC.mkDerivation {
        name = "AndroidManifest-${package}.xml";
        srcs = self;
        #buildInputs = [ ];
        phases = ["unpackPhase" "buildPhase"];
        buildPhase = ''
          mkdir $out
          cat AndroidManifest.xml | sed 's/PACKAGE/${package}/' | sed 's/NAME/${name}/' > $out/AndroidManifest.xml
        '';
      };
      keypass = "P@ssw0rd!";
      keystore = pkgs.stdenvNoCC.mkDerivation {
        name = "shadowing.keystore";
        buildInputs = [ jdk ];
        phases = ["buildPhase"];
        buildPhase = ''
          keytool -genkeypair -validity 1000 -dname "CN=SomeKey,O=SomeOne,C=FR" -keystore $out -storepass '${keypass}' -keypass '${keypass}' -alias SignKey -keyalg RSA -v
        '';
      };
      make-apk = {
        package,
        name,
        classes,
      } : let 
        manifest = make-manifest package name;
      in pkgs.stdenvNoCC.mkDerivation {
        name = "${package}";
        buildInputs = [ jdk android-env.androidsdk ];
        phases = ["buildPhase" "installPhase"];
        buildPhase = ''
          mkdir -p build/apk_files

          ${pkgs.lib.strings.concatMapStringsSep "\n" ( item:
              "cp ${item.drv} build/apk_files/${item.name}"
          ) classes}

          # link classes.dex not working?
          # ${build-tools}/aapt2 link -v ---manifest ${manifest}/AndroidManifest.xml -I ${platforms}/android.jar -o build/app.apk build/apk_files/

          ${build-tools}/aapt package -v -f -M ${manifest}/AndroidManifest.xml -I ${platforms}/android.jar -F build/app.apk build/apk_files/
          ${build-tools}/zipalign -f 4 build/app.apk build/app.aligned.apk
          ${build-tools}/apksigner sign -ks ${keystore} --v2-signing-enabled true --in build/app.aligned.apk --out build/${package}.apk --ks-pass 'pass:${keypass}'
        '';
        installPhase = ''
          mkdir $out
          cp build/${package}.apk $out/
          cp build/${package}.apk.idsig $out/
        '';
      };

      java-classes-main = pkgs.stdenvNoCC.mkDerivation {
        name = "java-class-main";
        src = self;
        buildInputs = [ jdk android-env.androidsdk ];
        phases = ["unpackPhase" "buildPhase"];
        buildPhase = ''
          mkdir $out
          javac -classpath ${platforms}/android.jar $(find java/main -type f -name '*.java') $(find java/actual -type f -name '*.java') -d $out/
          find java/actual/ -type f -name '*.java' | while read f ; do
            class_file=$(echo $f | sed "s#java/actual/##" | sed 's/.java/.class/')
            rm $out/$class_file
          done
        '';
      };
      java-classes-actual = javaCompile "java/actual";
      java-classes-dummy = javaCompile "java/dummy";
      java-classes-empty = javaCompile "java/empty";

      main-actual-classes-dex = java2dex (pkgs.symlinkJoin {
        name = "classes-main-actual";
        paths = [ java-classes-main java-classes-actual ];
      });
      main-dummy-classes-dex = java2dex (pkgs.symlinkJoin {
        name = "classes-main-dummy";
        paths = [ java-classes-main java-classes-dummy ];
      });
      main-classes-dex = java2dex java-classes-main;
      actual-classes-dex = java2dex java-classes-actual;
      dummy-classes-dex = java2dex java-classes-dummy;
      empty-classes-dex = java2dex java-classes-empty;
      
    in {

      packages = rec {
        control = make-apk {
          package = "com.example.shadowing.control";
          name = "Shadowing C";
          classes = [
            { name = "classes.dex"; drv = main-actual-classes-dex; }
          ];
        };
        # classes.dex vs classes2.dex
        shdw1 = make-apk {
          package = "com.example.shadowing.one";
          name = "Shadowing 1";
          classes = [
            { name = "classes.dex"; drv = main-actual-classes-dex; }
            { name = "classes2.dex"; drv = dummy-classes-dex; }
          ];
        };
        # classes2.dex vs classes3.dex
        shdw2 = make-apk {
          package = "com.example.shadowing.two";
          name = "Shadowing 2";
          classes = [
            { name = "classes.dex"; drv = main-classes-dex; }
            { name = "classes2.dex"; drv = actual-classes-dex; }
            { name = "classes3.dex"; drv = dummy-classes-dex; }
          ];
        };
        # classes2.dex vs classes1.dex
        shdw3 = make-apk {
          package = "com.example.shadowing.three";
          name = "Shadowing 3";
          classes = [
            { name = "classes.dex"; drv = main-classes-dex; }
            { name = "classes1.dex"; drv = dummy-classes-dex; }
            { name = "classes2.dex"; drv = actual-classes-dex; }
          ];
        };
        # classes10.dex vs classes2.dex
        shdw4 = make-apk {
          package = "com.example.shadowing.four";
          name = "Shadowing 4";
          classes = [
            { name = "classes.dex"; drv = main-classes-dex; }
            { name = "classes2.dex"; drv = actual-classes-dex; }
            { name = "classes3.dex"; drv = empty-classes-dex; }
            { name = "classes4.dex"; drv = empty-classes-dex; }
            { name = "classes5.dex"; drv = empty-classes-dex; }
            { name = "classes6.dex"; drv = empty-classes-dex; }
            { name = "classes7.dex"; drv = empty-classes-dex; }
            { name = "classes8.dex"; drv = empty-classes-dex; }
            { name = "classes9.dex"; drv = empty-classes-dex; }
            { name = "classes10.dex"; drv = dummy-classes-dex; }
          ];
        };
        default = pkgs.symlinkJoin {
          name = "all-shadowing-apks";
          paths = [ control shdw1 shdw2 shdw3 shdw4];
        };
      };

      devShells.default = pkgs.mkShellNoCC {
          packages = [ jdk android-env.androidsdk ];
          #shellHook = ''
          #'';
      };
    })
  ;
}