BuyPreferencesImpl.kt

class BuyPreferencesImpl(context: Context) : BuyPreferences {
    companion object {
        private val PREFERENCES_FILENAME = "BUY_PREFERENCES"
        private val BUY_COUNT_KEY = "BUY_COUNT_KEY"
    }

    private val sharedPreferences = context.getSharedPreferences(
        PREFERENCES_FILENAME, 
        Context.MODE_PRIVATE
    )

    override fun incrementBuyCount() {
        val count = getBuyCount()
        sharedPreferences.edit().putInt(BUY_COUNT_KEY, count + 1).apply()
    }

    override fun getBuyCount(): Int {
        return sharedPreferences.getInt(BUY_COUNT_KEY, 0)
    }
}