A first attempt of an InstallId for Vendor/Publisher on the UAP in C++

InstallIdForPublisher.h

#pragma once

using namespace Platform;
using namespace Windows::Storage;
using namespace Windows::Storage::Streams;
using namespace Windows::Foundation;
using namespace Windows::Foundation::Collections;
using namespace Windows::Security::Cryptography;
using namespace Windows::Security::Cryptography::Core;
using namespace Windows::System::UserProfile;
using namespace concurrency;

ref class InstallIdForPublisher sealed {
public:
	static IAsyncOperation<String^>^ GetAsync(String^ folderName, String^ fileName)
	{
		auto storageFolder = ApplicationData::Current->GetPublisherCacheFolder(folderName);

		return create_async([=]() -> task<String^>
		{
			return create_task(storageFolder->TryGetItemAsync(fileName))
				.then([=](IStorageItem^ storageItem) {
				auto storageFile = dynamic_cast<StorageFile^>(storageItem);
				if (storageFile != nullptr) {
					return create_task(FileIO::ReadTextAsync(storageFile));
				}
				else {
					return create_task([]() { return ref new String(); });
				}
			})
				.then([=](String^ installId) {
				if (installId == nullptr || installId->Length() == 0) {
					installId = Generate();
					return create_task(SetAsync(folderName, fileName, installId))
						.then([installId]() -> String^ {
						return installId;
					});
				}
				else {
					return create_task([installId]() {
						return installId;
					});
				}
			});
		});
	}

private:
	static IAsyncAction^ SetAsync(String^ folderName, String^ fileName, String^ installId)
	{
		auto storageFolder = ApplicationData::Current->GetPublisherCacheFolder(folderName);

		return create_async([=]()
		{
			create_task(storageFolder->TryGetItemAsync(fileName))
				.then([=](IStorageItem^ storageItem) {
				auto storageFile = dynamic_cast<StorageFile^>(storageItem);
				if (storageFile != nullptr) {
					return create_task([storageFile]() {
						return storageFile;
					});
				}
				else {
					return create_task(storageFolder->CreateFileAsync(fileName)).then([installId](StorageFile^ storageFile) {
						return storageFile;
					});
				}
			})
				.then([=](StorageFile^ storageFile) {
				return FileIO::WriteTextAsync(storageFile, installId);
			});
		});
	}

	static String^ GenerateGuid() {
		GUID nativeGuid;
		CoCreateGuid(&nativeGuid);
		Guid guid(nativeGuid);
		return guid.ToString();
	}

	static String^ Generate()
	{
		// First try with advertising id as base for id
		auto id = AdvertisingManager::AdvertisingId;
		if (id == nullptr || id->Length() == 0) {
			// Secondly generate a new guid as base for id
			id = GenerateGuid();
		}

		auto algorithm = HashAlgorithmProvider::OpenAlgorithm("MD5");
		auto vector = CryptographicBuffer::ConvertStringToBinary(id, BinaryStringEncoding::Utf8);
		auto buffer = algorithm->HashData(vector);

		if (buffer->Length != algorithm->HashLength) {
			throw ref new Platform::Exception(0, "Failed to generate hash!");
		}

		return CryptographicBuffer::EncodeToHexString(buffer);
	}
};