# 🥳 AppFlowy - Event Driven System 

* Goals of the System
* Some Design Considerations
* High Level Design
* Component Design 

## 🎯 Goals of the System
The AppFlowy project is an attempt to build a high performance application. Here are the top-level requirements for out system.

1. **High Performance.** 
2. **Cross-platform.**
3. **Reliability**
4. **Safety**


## 🤔 Some Design Considerations

## 📜 High Level Design

## 📚 Component Design

### 📙 Event Dispatch

```
                        Frontend                                                     FLowySDK
                                                             │                                              ┌─────────┐
                                                             │                                          ┌7─▶│Handler A│
                                                             │                                          │   └─────────┘
                                                             │                             ┌─────────┐  │   ┌─────────┐
┌──────┐    ┌────┐    ┌──────────────┐                       │                        ┌───▶│Module A │──┼──▶│Handler B│
│Widget│─1─▶│Bloc│─2─▶│ Repository A │─3─┐                   │                        │    └─────────┘  │   └─────────┘
└──────┘    └────┘    └──────────────┘   │                   │                        │                 │   ┌─────────┐
                      ┌──────────────┐   │    ┌───────┐    ┌─┴──┐     ┌───────────┐   │    ┌─────────┐  └──▶│Handler C│
                      │ Repository B │───┼───▶│ Event │─4─▶│FFI │─5──▶│Dispatcher │─6─┼───▶│Module B │      └─────────┘
                      └──────────────┘   │    └───────┘    └─┬──┘     └───────────┘   │    └─────────┘
                      ┌──────────────┐   │                   │                        │
                      │ Repository C │───┘                   │                        │    ┌─────────┐
                      └──────────────┘                       │                        └───▶│Module C │
                                                             │                             └─────────┘
                                                             │
                                                             │
```
Here are the event flow: 
1. User click on the `Widget`(The user interface) that invokes the `Bloc` actions
2. `Bloc` calls the repositories to perform additional operations to handle the actions.
3. `Repository` offers the functionalities by combining the event, defined in the `FlowySDK`.
4. `Events` will be passed in the `FlowySDK` through the [FFI](https://en.wikipedia.org/wiki/Foreign_function_interface) interface.
5. `Dispatcher` parses the event and generates the specific action scheduled in the `FlowySDK` runtime.
6. `Dispatcher` find the event handler declared by the modules.
7. `Handler` consumes the event and generates the response. The response will be returned to the widget through the `FFI`.

The event flow will be discussed in two parts: the frontend implemented in flutter and the FlowySDK implemented in Rust.

#### FlowySDK



#### Frontend
The Frontend follows the DDD design pattern, you can recap from [**here**](DOMAIN_DRIVEN_DESIGN.md).
```
    ┌──────┐        ┌────┐        ┌──────────────┐
    │Widget│──1────▶│Bloc│──2────▶│ Repository A │─3──┐
    └──────┘        └────┘        └──────────────┘    │
                                  ┌──────────────┐    │     ┌───────┐
                                  │ Repository B │────┼────▶│ Event │
                                  └──────────────┘    │     └───────┘
                                  ┌──────────────┐    │
                                  │ Repository C │────┘
                                  └──────────────┘
```