Make Android Build script Linux compatible

Author: alexanderwiederin

scripts/uniffi_bindgen_generate_kotlin_android.sh

@@ -1,11 +1,37 @@
 #!/bin/bash
+
 BINDINGS_DIR="bindings/kotlin"
 TARGET_DIR="target"
 PROJECT_DIR="ldk-node-android"
-PACKAGE_DIR="org/lightningdevkit/ldknode"
 UNIFFI_BINDGEN_BIN="cargo run --manifest-path bindings/uniffi-bindgen/Cargo.toml"
-ANDROID_NDK_ROOT="/opt/homebrew/share/android-ndk"
-LLVM_ARCH_PATH="darwin-x86_64"
+
+export_variable_if_not_present() {
+  local name="$1"
+  local value="$2"
+
+  # Check if the variable is already set
+  if [ -z "${!name}" ]; then
+    export "$name=$value"
+    echo "Exported $name=$value"
+  else
+    echo "$name is already set to ${!name}, not exporting."
+  fi
+}
+
+case "$OSTYPE" in
+    linux-gnu)
+      export_variable_if_not_present "ANDROID_NDK_ROOT" "/opt/android-ndk"
+      export_variable_if_not_present "LLVM_ARCH_PATH" "linux-x86_64"
+      ;;
+    darwin*)
+      export_variable_if_not_present "ANDROID_NDK_ROOT" "/opt/homebrew/share/android-ndk"
+      export_variable_if_not_present "LLVM_ARCH_PATH" "darwin-x86_64"
+      ;;
+    *)
+      echo "Unknown operating system: $OSTYPE"
+      ;;
+    esac
+
 PATH="$ANDROID_NDK_ROOT/toolchains/llvm/prebuilt/$LLVM_ARCH_PATH/bin:$PATH"
 
 rustup target add x86_64-linux-android aarch64-linux-android armv7-linux-androideabi