KESA - Event Sourcing Illustrated: A Jigsaw Puzzle Game Perspective

In the dynamic world of software development, managing and maintaining the state of an application poses significant challenges. Event sourcing, an innovative architectural pattern, steps in to revolutionize this process, which offers a robust foundation for understanding not only where the system stands, but also how it got there, significantly enhancing both transparency and traceability.

What is Event Sourcing?

Event sourcing is an architectural pattern that captures changes to an entity's state through a chronological series of events. This approach diverges from traditional methodologies that emphasize storing the current state, by instead focusing on the sequence of events that lead to that state.

Event Sourcing utilizes concepts such as events, event streams, event stores, and event handlers to manage and process these changes. Further, it offers benefits such as immutable event logs, auditability, event replay for state reconstruction, consistency, improved scalability, fault tolerance, and support for event-driven architectures.

Jigsaw Puzzle Game Project Overview

To illustrate the practical application of event sourcing, we present a simple, engaging example: a digital jigsaw puzzle game. This single-player game is developed to highlight the principles and advantages of event sourcing and event-driven architectures, where a player interacts with a web interface to assemble a jigsaw puzzle.

Play the game here: Fidenz Kesa

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Find the full project explainer video here: https://youtu.be/4O9VukIrtCI

Implementing Event Sourcing in Jigsaw Puzzle Game

The table below demonstrates the implementation of event sourcing features within the Jigsaw Puzzle Game application, which has been intentionally over-engineered to effectively illustrate event sourcing capabilities using a jigsaw puzzle game as an example.

Event Sourcing Feature	Application Implementation	Benefits in the Game Context
Entity	The "JigsawPuzzleGame" entity is designed to represent the current state of a gaming session.	Encapsulates the game logic and helps validating events for an ongoing gaming session
Event	Each game action triggering an event sent from the front-end to the back-end such as: Game Started Event, Piece Added Event, Piece Removed Event.	Facilitates real-time game interactions and state management
Event Stream	A gaming session begins with a Start Game Event, marking the commencement of an event stream. Subsequent events, including Piece Added Events and Piece Removed Events, will be sequentially numbered in chronological order.	Ensures ordered, reliable processing of game actions
Event Handlers	Event handlers are designed to react to various events, taking actions such as processing data and updating “JigsawPuzzleGame” entity.	Enables dynamic game state management based on player actions
Event Store	Events are stored in the event store and can be retrieved as needed. Once saved, these events are immutable. Each event record includes essential information such as the unique game session ID, event type, event stream ID, and event data, among other details.	Provides durability and historical tracking of game actions
Immutable Event Log	Event Store implementation provide chronologically ordered immutable events of a gaming session	Accurate tracking of puzzle progress
Event Replay	A Player can use the Event List to go back in time to a specific point in the game. This can be done by selecting an event from the event list. The system then reverse all subsequent events by applying their opposite, thus restoring the puzzle to the desired state	Ability to revert puzzle state and understand puzzle assembly
Consistency and Eventual Consistency	Storing events in chronological order with event stream ID and event type	Distinguishes between the various events that occur within a gaming session.

Conclusion

The jigsaw puzzle game serves as a practical and engaging example to illustrate the principles of event sourcing. By understanding how each action in the game translates into an event and contributes to the puzzle's state, we can appreciate the power and utility of event sourcing in software development. As technology evolves, it's exciting to ponder how event sourcing will shape the future of data management and application design.

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