/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

#include <type_traits>
#include <utility>

#import <Foundation/Foundation.h>

#import <React/RCTBridgeModule.h>
#import <React/RCTDefines.h>

/**
 * Interop type layer for RN's exportedConstants and the C++ structs generated by our typesafety codegen.
 *
 * The NativeModuleSpec will define a constantsToExport method which you can implement as follows:
 *
 * - (nonnull ModuleConstants<JS::Constants>)constantsToExport
 * {
 *   return typedConstants<JS::Constants>({ ... });
 * }
 */

// Internal container for module constants. Do not use yourself directly, instead use the typedConstants helpers below.
@interface _RCTTypedModuleConstants<StructType> : NSDictionary <NSString *, id>

+ (instancetype)newWithUnsafeDictionary:(NSDictionary<NSString *, id> *)dictionary;

@end

namespace facebook::react {

namespace detail {

// Helper to detect if T is a Builder type.
// Builder types have: nested Input struct and buildUnsafeRawValue() method.
template <typename T, typename = void>
struct IsBuilder : std::false_type {};

template <typename T>
struct IsBuilder<T, std::void_t<typename T::Input, decltype(std::declval<T>().buildUnsafeRawValue())>>
    : std::true_type {};

// Resolve Builder to its parent Constants type.
// For backwards compatibility: if T is a Builder type (e.g., JS::X::Constants::Builder),
// we resolve to the parent Constants type (JS::X::Constants).
//
// This requires Builder to have a type alias `using ResultT = Constants;` defined by codegen.
template <typename T, bool = IsBuilder<T>::value>
struct ResolveConstantsType {
  // Not a Builder, use T as-is
  using type = T;
};

// Specialization for Builder types that have ResultT defined
template <typename T>
struct ResolveConstantsType<T, true> {
  // Use T::ResultT which points to the parent Constants type (added by codegen)
  using type = typename T::ResultT;
};

} // namespace detail

// Objective-C doesn't allow arbitrary types in its lightweight generics, only object and block types. We can work
// around that by having the struct type we care about be a block-argument. The block never exists at runtime.
//
// For backwards compatibility: if T is a Builder type (e.g., JS::Module::Constants::Builder),
// ModuleConstants<Builder> resolves to the same type as ModuleConstants<Constants>.
template <typename T>
using ModuleConstants = _RCTTypedModuleConstants<void (^)(typename detail::ResolveConstantsType<T>::type)> *;

template <typename T>
ModuleConstants<T> typedConstants(typename T::Builder::Input &&value)
{
  typename T::Builder builder(std::move(value));
  return [_RCTTypedModuleConstants newWithUnsafeDictionary:builder.buildUnsafeRawValue()];
}

} // namespace facebook::react