The rapid growth in population has led to substantial traffic bottlenecks in recent transportation systems. This not only causes significant air pollution, and waste in time and energy, but also signifies the issue of the auto-park scarcity. In the age of Internet of Things (IoT) and smart city ecosystems, smart parking and relevant innovative solutions are necessary towards more sustainable future cities. Smart parking with the help of sensors embedded in cars and city infrastructures can alleviate the deadlocks in parking problems and provide the best quality of services and profit to citizens. However, several design aspects should be well investigated and analyzed before implementing such solutions. In this paper, we classify the smart parking systems while considering soft and hard design factors. We overview the enabling technologies and sensors which have been commonly used in the literature. We emphasize the importance of data reliability, security, privacy and other critical design factors in such systems. Emerging parking trends in the ecosystem are investigated, while focusing on data interoperability and exchange. We also outline open research issues in the current state of smart parking systems and recommend a conceptual hybrid-parking model.