In-App purchasing demo

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 #include <QFile>
 #include <QDebug>
 #include <QBuffer>
 #include <QRandomGenerator>
 #include <QtConcurrent/QtConcurrentRun>
 #include <mutex>

 #include "hangmangame.h"

 HangmanGame::HangmanGame(QObject *parent)
     : QObject(parent)
     , m_vowelsUnlocked(false)
 {
     connect(this, &HangmanGame::vowelBought, this, &HangmanGame::registerLetterBought);
     (void) QtConcurrent::run(&HangmanGame::initWordList, this);

     m_vowelsUnlocked = m_persistentSettings.value("Hangman/vowelsUnlocked", false).toBool();
     m_vowelsAvailable = m_persistentSettings.value("Hangman/vowelsAvailable", 0).toInt();
     m_wordsGiven = m_persistentSettings.value("Hangman/wordsGiven", 0).toInt();
     m_wordsGuessedCorrectly = m_persistentSettings.value("Hangman/wordsGuessedCorrectly", 0).toInt();
     m_score = m_persistentSettings.value("Hangman/score", 0).toInt();
 }

 void HangmanGame::reset()
 {
     m_lettersOwned.clear();
     emit lettersOwnedChanged();
     emit errorCountChanged();
     chooseRandomWord();
 }

 void HangmanGame::reveal()
 {
     m_lettersOwned += vowels() + consonants();
     emit errorCountChanged();
     emit lettersOwnedChanged();
 }

 void HangmanGame::gameOverReveal()
 {
     m_lettersOwned += vowels() + consonants();
     emit lettersOwnedChanged();
 }

 void HangmanGame::requestLetter(const QString &letterString)
 {
     Q_ASSERT(letterString.size() == 1);
     QChar letter = letterString.at(0);
     registerLetterBought(letter);
 }

 void HangmanGame::guessWord(const QString &word)
 {
     if (word.compare(m_word, Qt::CaseInsensitive) == 0) {
         //Determine how many vowels were earned
         setVowelsAvailable(m_vowelsAvailable + calculateEarnedVowels());
         //score is number of remaining consonants + remaining errors
         setScore(m_score + calculateEarnedPoints());
         m_lettersOwned += m_word.toUpper();
     } else {
         // Small hack to get an additional penalty for guessing wrong
         static int i=0;
         Q_ASSERT(i < 10);
         m_lettersOwned += QString::number(i++);
         emit errorCountChanged();
     }
     emit lettersOwnedChanged();
 }

 bool HangmanGame::isVowel(const QString &letter)
 {
     Q_ASSERT(letter.size() == 1);
     QChar letterChar = letter.at(0);
     return vowels().contains(letterChar);
 }

 QString HangmanGame::vowels() const
 {
     return QStringLiteral("AEIOU");
 }

 QString HangmanGame::consonants() const
 {
     return QStringLiteral("BCDFGHJKLMNPQRSTVWXYZ");
 }

 int HangmanGame::errorCount() const
 {
     int count = 0;
     for (QChar c : m_lettersOwned) {
         if (!m_word.contains(c))
             ++count;
     }
     return count;
 }

 bool HangmanGame::vowelsUnlocked() const
 {
     return m_vowelsUnlocked;
 }

 void HangmanGame::setVowelsUnlocked(bool vowelsUnlocked)
 {
     if (m_vowelsUnlocked != vowelsUnlocked) {
         m_vowelsUnlocked = vowelsUnlocked;
         m_persistentSettings.setValue("Hangman/vowelsUnlocked", m_vowelsUnlocked);
         emit vowelsUnlockedChanged(m_vowelsUnlocked);
     }
 }

 int HangmanGame::vowelsAvailable() const
 {
     return m_vowelsAvailable;
 }

 int HangmanGame::wordsGiven() const
 {
     return m_wordsGiven;
 }

 int HangmanGame::wordsGuessedCorrectly() const
 {
     return m_wordsGuessedCorrectly;
 }

 int HangmanGame::score() const
 {
     return m_score;
 }

 void HangmanGame::setScore(int score)
 {
     if (m_score != score) {
         m_score = score;
         m_persistentSettings.setValue("Hangman/score", m_score);
         emit scoreChanged(score);
     }
 }

 void HangmanGame::setWordsGiven(int count)
 {
     if (m_wordsGiven != count) {
         m_wordsGiven = count;
         m_persistentSettings.setValue("Hangman/wordsGiven", m_wordsGiven);
         emit wordsGivenChanged(count);
     }
 }

 void HangmanGame::setWordsGuessedCorrectly(int count)
 {
     if (m_wordsGuessedCorrectly != count) {
         m_wordsGuessedCorrectly = count;
         m_persistentSettings.setValue("Hangman/wordsGuessedCorrectly", m_wordsGuessedCorrectly);
         emit wordsGuessedCorrectlyChanged(count);
     }
 }

 void HangmanGame::setVowelsAvailable(int count)
 {
     if (m_vowelsAvailable != count) {
         m_vowelsAvailable = count;
         m_persistentSettings.setValue("Hangman/vowelsAvailable", m_vowelsAvailable);
         emit vowelsAvailableChanged(count);
     }
 }

 void HangmanGame::registerLetterBought(const QChar &letter)
 {
     if (m_lettersOwned.contains(letter))
         return;

     m_lettersOwned.append(letter);
     emit lettersOwnedChanged();

     if (!m_word.contains(letter))
         emit errorCountChanged();
 }

 void HangmanGame::chooseRandomWord()
 {
     const std::lock_guard<QRecursiveMutex> locker(m_lock);
     if (m_wordList.isEmpty())
         return;

     m_word = m_wordList.at(QRandomGenerator::global()->bounded(m_wordList.size()));
     emit wordChanged();
 }

 void HangmanGame::initWordList()
 {
     const std::lock_guard<QRecursiveMutex> locker(m_lock);
     QFile file(":/dict.txt");
     if (file.open(QIODevice::ReadOnly)) {
         QByteArray allData = file.readAll();
         QBuffer buffer(&allData);
         if (!buffer.open(QIODevice::ReadOnly))
             qFatal("Couldn't open buffer for reading!");

         while (!buffer.atEnd()) {
             QByteArray ba = buffer.readLine().trimmed().toUpper();
             if (!ba.isEmpty() && ba.length() < 10)
                 m_wordList.append(QString::fromLatin1(ba));
         }
     }

     chooseRandomWord();
 }

 int HangmanGame::calculateEarnedVowels()
 {
     int total = 0;
     for (int i = 0; i < m_word.length(); ++i) {
         if (isVowel(QString(m_word[i])) && !m_lettersOwned.contains(QString(m_word[i])))
             total++;
     }
     return total;
 }

 int HangmanGame::calculateEarnedPoints()
 {
     int total = 0;
     for (int i = 0; i < m_word.length(); ++i) {
         if (consonants().contains(QString(m_word[i])) && !m_lettersOwned.contains(QString(m_word[i])))
             total++;
     }
     total += 8 - errorCount();
     return total;
 }