Converter.h

/*
 * AUI Framework - Declarative UI toolkit for modern C++20
 * Copyright (C) 2020-2025 Alex2772 and Contributors
 *
 * SPDX-License-Identifier: MPL-2.0
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */
 
#pragma once
 
#include <AUI/Traits/concepts.h>
#include <AUI/Util/AStringLiteral.h>
#include "GlobalRef.h"
#include <string_view>
 
namespace aui::jni {
   template<typename T>
   struct Converter;
 
   namespace impl {
       template<typename T>
       concept convertible = std::is_void_v<T> || requires(T&& t) {
           { Converter<T>::signature } -> ::aui::convertible_to<const char*>;
           Converter<T>::toJni(t);
           { Converter<T>::fromJni(Converter<T>::toJni(t)) } -> ::aui::convertible_to<T>;
       };
   }
 
   template<typename T>
   concept convertible = ::aui::jni::impl::convertible<std::decay_t<T>>;
 
 
   template<convertible T>
   auto toJni(const T& t) -> decltype(Converter<T>::toJni(t)) {
       return Converter<T>::toJni(t);
   }
 
   template<convertible T>
   T fromJni(const auto& t) {
       return Converter<T>::fromJni(t);
   }
 
   template<typename CppType>
   using java_t_from_cpp_t = decltype(aui::jni::toJni(std::declval<CppType>()));
 
   template <>
   struct Converter<std::string> {
       static constexpr auto signature = "Ljava/lang/String;"_asl;
 
       static std::string fromJni(jobject val) {
           if (val) {
               static GlobalRef stringClass = jni::env()->GetObjectClass(val);
               static jmethodID getBytes = jni::env()->GetMethodID(stringClass.asClass(), "getBytes", "(Ljava/lang/String;)[B");
               jbyteArray b = jbyteArray(jni::env()->CallObjectMethod(val, getBytes, jni::env()->NewStringUTF("UTF-8")));
               size_t length = jni::env()->GetArrayLength(b);
               jbyte* elems = jni::env()->GetByteArrayElements(b, nullptr);
               std::string str(reinterpret_cast<char*>(elems), length);
               jni::env()->ReleaseByteArrayElements(b, elems, JNI_ABORT);
               jni::env()->DeleteLocalRef(b);
               return str;
           }
           return {};
       }
 
       static jstring toJni(std::string_view value) {
           auto bytes = env()->NewByteArray(value.length());
           if (!bytes) {
               return nullptr;
           }
 
           env()->SetByteArrayRegion(bytes, 0, value.length(), reinterpret_cast<const jbyte*>(value.data()));
 
           static jmethodID stringConstructor = env()->GetMethodID(stringClass(), "<init>", "([BLjava/lang/String;)V");
           auto str = env()->NewObject(stringClass(), stringConstructor, bytes, env()->NewStringUTF("UTF-8"));
           env()->DeleteLocalRef(bytes);
           return static_cast<jstring>(str);
       }
 
   private:
       static jclass stringClass() {
           static GlobalRef ref = jni::env()->FindClass("java/lang/String");
           return ref.asClass();
       }
   };
 
   template <>
   struct Converter<AString>: public Converter<std::string> {
       static constexpr auto signature = "Ljava/lang/String;"_asl;
 
       static jstring toJni(const AString& value) {
           return Converter<std::string>::toJni(value.toStdString());
       }
   };
 
   template<typename T, char sign>
   struct ConverterPrimitive {
       static constexpr AStringLiteral<sign> signature;
 
       static constexpr T toJni(T t) noexcept {
           return t;
       }
 
       static constexpr T fromJni(T t) noexcept {
           return t;
       }
   };
 
   template<> struct Converter<jboolean>: ConverterPrimitive<jboolean, 'Z'> {};
   template<> struct Converter<jbyte   >: ConverterPrimitive<jbyte   , 'B'> {};
   template<> struct Converter<jchar   >: ConverterPrimitive<jchar   , 'C'> {};
   template<> struct Converter<jshort  >: ConverterPrimitive<jshort  , 'S'> {};
   template<> struct Converter<jint    >: ConverterPrimitive<jint    , 'I'> {};
   template<> struct Converter<jlong   >: ConverterPrimitive<jlong   , 'J'> {};
   template<> struct Converter<jfloat  >: ConverterPrimitive<jfloat  , 'F'> {};
   template<> struct Converter<jdouble >: ConverterPrimitive<jdouble , 'D'> {};
 
   template<> struct Converter<bool>: Converter<jboolean> {};
   template<> struct Converter<void    > {
       static constexpr AStringLiteral<'V'> signature;
 
       static constexpr void fromJni() noexcept {
 
       }
   };
 
 
   template<typename T>
   concept ExposableClass = requires(T&& t) {
       { T::JAVA_CLASS_NAME } -> ::aui::convertible_to<const char*>;
   };
 
   template<ExposableClass T> struct Converter<T> {
       static constexpr auto signature = "L"_asl + T::JAVA_CLASS_NAME + ";"_asl;
 
       static T fromJni(jobject val) {
           T t;
           GlobalRef::assignLocalRef(t, val);
           return t;
       }
 
       static jobject toJni(const T& value) {
           return value.asObject();
       }
 
   };
}

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