feat: nix shell setup

.envrc

@@ -0,0 +1 @@
+use flake

.gitignore

@@ -25,6 +25,11 @@ out/
 .gradle/
 build/
 
+# Nix / direnv
+.direnv/
+result
+result-*
+
 # Python cache
 __pycache__/
 

flake.nix

@@ -0,0 +1,50 @@
+{
+  description = "uchar element x — reproducible dev environment";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-25.11";
+
+    flake-parts.url = "github:hercules-ci/flake-parts";
+
+    android-nixpkgs = {
+      url = "github:tadfisher/android-nixpkgs";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+  };
+
+  outputs =
+    { self, flake-parts, ... }@inputs:
+    flake-parts.lib.mkFlake { inherit inputs; } (
+      { ... }:
+      {
+        systems = [
+          "x86_64-linux"
+          "aarch64-linux"
+          "x86_64-darwin"
+          "aarch64-darwin"
+        ];
+
+        perSystem =
+          { pkgs, system, ... }:
+          {
+            _module.args.pkgs = import inputs.nixpkgs {
+              inherit system;
+              config.allowUnfree = true;
+              config.android_sdk.accept_license = true;
+              overlays = [
+                (final: prev: {
+                  android = inputs.android-nixpkgs;
+                })
+              ];
+            };
+
+            formatter = pkgs.alejandra;
+
+            devShells.default = import ./nix/shell.nix {
+              inherit pkgs inputs system;
+              formatter = pkgs.alejandra;
+            };
+          };
+      }
+    );
+}

nix/shell.nix

@@ -0,0 +1,81 @@
+{
+  pkgs,
+  inputs,
+  system,
+  formatter ? pkgs.alejandra,
+  ...
+}:
+let
+  isLinux = pkgs.stdenv.isLinux;
+  pinnedJDK = pkgs.jdk21_headless;
+
+  androidCustomPackage = inputs.android-nixpkgs.sdk.${system} (
+    sdkPkgs: with sdkPkgs; [
+      cmdline-tools-latest
+      platform-tools
+      build-tools-36-0-0
+      platforms-android-36
+      emulator
+      system-images-android-36-google-apis-playstore-x86-64
+    ]
+  );
+
+  androidEmulator = pkgs.androidenv.emulateApp {
+    name = "emulator";
+    platformVersion = "36";
+    abiVersion = "x86_64";
+    systemImageType = "google_apis_playstore";
+    configOptions = {
+      "hw.gpu.enabled" = "yes";
+      "hw.gpu.mode" = "swiftshader_indirect";
+      "hw.keyboard" = "yes";
+    };
+  };
+
+  androidEmulatorNoGPU = pkgs.androidenv.emulateApp {
+    name = "emulator";
+    platformVersion = "36";
+    abiVersion = "x86_64";
+    systemImageType = "google_apis_playstore";
+    configOptions = {
+      "hw.gpu.enabled" = "no";
+      "hw.keyboard" = "yes";
+    };
+  };
+in
+pkgs.mkShell {
+  packages = [
+    pinnedJDK
+    androidCustomPackage
+    pkgs.ktlint
+    pkgs.git
+    pkgs.coreutils
+    formatter
+  ]
+  ++ pkgs.lib.optionals isLinux [
+    (pkgs.writeScriptBin "android-emulator" ''
+      ${androidEmulator}/bin/run-test-emulator
+    '')
+    (pkgs.writeScriptBin "android-emulator-no-gpu" ''
+      ${androidEmulatorNoGPU}/bin/run-test-emulator
+    '')
+  ];
+
+  env = {
+    ANDROID_HOME = "${androidCustomPackage}/share/android-sdk";
+    ANDROID_SDK_ROOT = "${androidCustomPackage}/share/android-sdk";
+    JAVA_HOME = pinnedJDK.home;
+    GRADLE_OPTS = "-Dorg.gradle.project.android.aapt2FromMavenOverride=${androidCustomPackage}/share/android-sdk/build-tools/36.0.0/aapt2";
+  };
+
+  shellHook = ''
+    echo "---------------------------------------------------------------------------------------------------"
+    echo " Uchar Element X Android dev shell."
+    echo " JDK:           $(java -version 2>&1 | head -1)"
+    echo " ANDROID_HOME:  $ANDROID_HOME"
+    ${pkgs.lib.optionalString isLinux ''
+      echo " Emulator:      run 'android-emulator' else 'android-emulator-no-gpu'"
+    ''}
+    echo "---------------------------------------------------------------------------------------------------"
+  '';
+}