From 6579271439676c6b8f3a3abd978351ef91c1c947 Mon Sep 17 00:00:00 2001
From: retif <retif@decovar.dev>
Date: Fri, 9 Feb 2024 20:09:58 +0100
Subject: [PATCH] C++ wrapper library as a part of the project

---
 android/app/build.gradle.kts                  | 17 +++++++------
 android/app/jni/Android.mk                    |  6 -----
 android/app/jni/libs/arm64-v8a/.gitkeep       |  0
 android/app/src/main/cpp/CMakeLists.txt       | 25 +++++++++++++++++++
 android/app/src/main/cpp/wrapper.cpp          | 12 +++++++++
 .../java/com/example/some/MainActivity.kt     | 13 ++++++----
 6 files changed, 54 insertions(+), 19 deletions(-)
 delete mode 100644 android/app/jni/Android.mk
 delete mode 100644 android/app/jni/libs/arm64-v8a/.gitkeep
 create mode 100644 android/app/src/main/cpp/CMakeLists.txt
 create mode 100644 android/app/src/main/cpp/wrapper.cpp

diff --git a/android/app/build.gradle.kts b/android/app/build.gradle.kts
index 3eb4e56..8e11186 100644
--- a/android/app/build.gradle.kts
+++ b/android/app/build.gradle.kts
@@ -19,6 +19,12 @@ android {
             abiFilters.add("arm64-v8a")
         }
 
+//        externalNativeBuild {
+//            cmake {
+//                arguments += "-DCMAKE_BUILD_TYPE=Release"
+//            }
+//        }
+
         vectorDrawables {
             useSupportLibrary = true
         }
@@ -50,14 +56,9 @@ android {
     }
 
     externalNativeBuild {
-        ndkBuild {
-            path = file("./jni/Android.mk")
-        }
-    }
-
-    sourceSets {
-        this.getByName("main") {
-            jniLibs.srcDirs("./jni/libs")
+        cmake {
+            path = file("./src/main/cpp/CMakeLists.txt")
+            version = "3.22.1"
         }
     }
 }
diff --git a/android/app/jni/Android.mk b/android/app/jni/Android.mk
deleted file mode 100644
index 1904d26..0000000
--- a/android/app/jni/Android.mk
+++ /dev/null
@@ -1,6 +0,0 @@
-LOCAL_PATH := $(call my-dir)
-
-include $(CLEAR_VARS)
-LOCAL_MODULE := thingy
-LOCAL_SRC_FILES := libs/$(TARGET_ARCH_ABI)/libThingy.so
-include $(PREBUILT_SHARED_LIBRARY)
diff --git a/android/app/jni/libs/arm64-v8a/.gitkeep b/android/app/jni/libs/arm64-v8a/.gitkeep
deleted file mode 100644
index e69de29..0000000
diff --git a/android/app/src/main/cpp/CMakeLists.txt b/android/app/src/main/cpp/CMakeLists.txt
new file mode 100644
index 0000000..31a5222
--- /dev/null
+++ b/android/app/src/main/cpp/CMakeLists.txt
@@ -0,0 +1,25 @@
+cmake_minimum_required(VERSION 3.22.1) # it wants an exact version, so 3.22 isn't precise enough
+
+project("cpp-wrapper")
+
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED 1)
+
+# if you set CMAKE_DEBUG_POSTFIX, then you might need to hardcode the build type to Release,
+# otherwise you'll need to add the postfix value to the library name in `System.loadLibrary()`
+#set(CMAKE_DEBUG_POSTFIX "d" CACHE STRING "Filename postfix for libraries under DEBUG configuration")
+#set(CMAKE_BUILD_TYPE "Release")
+
+add_library(${CMAKE_PROJECT_NAME} SHARED) # it probably makes sense to hardcode it to SHARED right away
+
+target_sources(${CMAKE_PROJECT_NAME}
+    PRIVATE
+        wrapper.cpp
+)
+
+# target_link_libraries(${CMAKE_PROJECT_NAME}
+#     PRIVATE
+#         # these might not be needed
+#         #android
+#         #log
+# )
diff --git a/android/app/src/main/cpp/wrapper.cpp b/android/app/src/main/cpp/wrapper.cpp
new file mode 100644
index 0000000..cfd3dfd
--- /dev/null
+++ b/android/app/src/main/cpp/wrapper.cpp
@@ -0,0 +1,12 @@
+#include <jni.h>
+#include <string>
+
+extern "C" JNIEXPORT jstring JNICALL
+Java_com_example_some_MainActivity_doThingy(
+    JNIEnv *env,
+    jobject
+)
+{
+    std::string some = "some string of text from wrapper";
+    return env->NewStringUTF(some.c_str());
+}
diff --git a/android/app/src/main/java/com/example/some/MainActivity.kt b/android/app/src/main/java/com/example/some/MainActivity.kt
index c3ee8b0..10a3234 100644
--- a/android/app/src/main/java/com/example/some/MainActivity.kt
+++ b/android/app/src/main/java/com/example/some/MainActivity.kt
@@ -72,11 +72,14 @@ class MainActivity : ComponentActivity()
     companion object
     {
         init {
-            // why the fuck does it need to be a part of the file name, what's the point then
-            // of declaring LOCAL_MODULE in Android.mk?
-            // and by the way, if you'll need to load a Debug variant (libThingyd.so),
-            // then the name here would need to be Thingyd
-            System.loadLibrary("Thingy")
+            // if you, like a normal person, defined CMAKE_DEBUG_POSTFIX (to `d` value),
+            // then this thing here will fail to find the `libcpp-wrapperd.so` file,
+            // so you'll need to:
+            // - either undefine CMAKE_DEBUG_POSTFIX;
+            // - or change the name here to a d-postfixed variant;
+            // - or hardcode your wrapper library build to `-DCMAKE_BUILD_TYPE=Release`,
+            // either in `build.gradle.kts` or in CMakeLists.txt
+            System.loadLibrary("cpp-wrapper")
         }
     }
 }