```python exec
import reflex as rx
from typing import Any
```

# Complex Example

In this more complex example we will be wrapping `reactflow` a library for building node based applications like flow charts, diagrams, graphs, etc.

## Import

Lets start by importing the library [reactflow](https://www.npmjs.com/package/reactflow). Lets make a seperate file called `reactflow.py` and add the following code:

```python
from reflex.components.component import Component
from typing import Any, Dict, List, Union
from reflex.vars import Var

class ReactFlowLib(Component):
    """A component that wraps a react flow lib."""

    library = "reactflow"

    def _get_custom_code(self) -> str:
        return """import 'reactflow/dist/style.css';
        """
```

Notice we also use the `_get_custom_code` method to import the css file that is needed for the styling of the library.

## Components

For this tutorial we will wrap three components from Reactflow: `ReactFlow`, `Background`, and `Controls`. Lets start with the `ReactFlow` component.

Here we will define the `tag` and the `vars` that we will need to use the component.

We will also define the `get_event_triggers` method to specify the events that the component will trigger. For this tutorial we will use `on_edges_change` and `on_connect`, but you can find all the events that the component triggers in the [reactflow docs](https://reactflow.dev/docs/api/react-flow-props/#onnodeschange).

```python
from reflex.components.component import Component
from typing import Any, Dict, List, Union
from reflex.vars import Var

class ReactFlowLib(Component):
    ...

class ReactFlow(ReactFlowLib):

    tag = "ReactFlow"

    nodes: Var[List[Dict[str, Any]]]

    edges: Var[List[Dict[str, Any]]]

    fit_view: Var[bool]

    nodes_draggable: Var[bool]

    nodes_connectable: Var[bool]

    nodes_focusable: Var[bool]

    def get_event_triggers(self) -> dict[str, Any]:
        return {
            **super().get_event_triggers(),
            "on_edges_change": lambda e0: [e0],
            "on_connect": lambda e0: [e0],
        }
```

Now lets add the `Background` and `Controls` components. We will also create the components using the `create` method so that we can use them in our app.

```python
from reflex.components.component import Component
from typing import Any, Dict, List, Union
from reflex.vars import Var

class ReactFlowLib(Component):
    ...

class ReactFlow(ReactFlowLib):
    ...

class Background(ReactFlowLib):

    tag = "Background"

    color: Var[str]

    gap: Var[int]

    size: Var[int]

    variant: Var[str]

class Controls(ReactFlowLib):

    tag = "Controls"

react_flow = ReactFlow.create
background = Background.create
controls = Controls.create
```

## Building the App

Now that we have our components lets build the app.

Lets start by defining the initial nodes and edges that we will use in our app.

```python
import reflex as rx
from .react_flow import react_flow, background, controls
import random
from typing import Any, Dict, List


initial_nodes = [
    \{
        'id': '1',
        'type': 'input',
        'data': \{'label': '150'},
        'position': \{'x': 250, 'y': 25},
    },
    \{
        'id': '2',
        'data': \{'label': '25'},
        'position': \{'x': 100, 'y': 125},
    },
    \{
        'id': '3',
        'type': 'output',
        'data': \{'label': '5'},
        'position': \{'x': 250, 'y': 250},
    },
]

initial_edges = [
    \{'id': 'e1-2', 'source': '1', 'target': '2', 'label': '*', 'animated': True},
    \{'id': 'e2-3', 'source': '2', 'target': '3', 'label': '+', 'animated': True},
]
```

Next we will define the state of our app. We have three event handlers: `add_random_node`, `clear_graph`, and `on_edges_change`.

The `on_edges_change` event handler will be called when an edge is changed. In this case we will use it to delete an edge if it already exists, and add the new edge. It takes in a single argument `new_edge` which is a dictionary containing the `source` and `target` of the edge.

```python
class State(rx.State):
    """The app state."""
    nodes: List[Dict[str, Any]] = initial_nodes
    edges: List[Dict[str, Any]] = initial_edges
    
    def add_random_node(self):
        new_node_id = f'\{len(self.nodes) + 1\}'
        node_type = random.choice(['default'])
        # Label is random number
        label = new_node_id
        x = random.randint(0, 500)
        y = random.randint(0, 500)

        new_node = {
            'id': new_node_id,
            'type': node_type,
            'data': \{'label': label},
            'position': \{'x': x, 'y': y},
            'draggable': True,
        }
        self.nodes.append(new_node)

    def clear_graph(self):
        self.nodes = []  # Clear the nodes list
        self.edges = []  # Clear the edges list

    def on_edges_change(self, new_edge):
        # Iterate over the existing edges
        for i, edge in enumerate(self.edges):
            # If we find an edge with the same ID as the new edge
            if edge["id"] == f"e\{new_edge['source']}-\{new_edge['target']}":
                # Delete the existing edge
                del self.edges[i]
                break

        # Add the new edge
        self.edges.append({
            "id": f"e\{new_edge['source']}-\{new_edge['target']}",
            "source": new_edge["source"],
            "target": new_edge["target"],
            "label": random.choice(["+", "-", "*", "/"]),
            "animated": True,
        })
```

Now lets define the UI of our app. We will use the `react_flow` component and pass in the `nodes` and `edges` from our state. We will also add the `on_connect` event handler to the `react_flow` component to handle when an edge is connected.

```python
def index() -> rx.Component:
    return rx.vstack(
        react_flow(
            background(),
            controls(),
            nodes_draggable=True,
            nodes_connectable=True,
            on_connect=lambda e0: State.on_edges_change(e0),
            nodes=State.nodes,
            edges=State.edges,
            fit_view=True,
        ),
        rx.hstack(
            rx.button("Clear graph", on_click=State.clear_graph, width="100%"),
            rx.button("Add node", on_click=State.add_random_node, width="100%"),
            width="100%",
        ),
        height="30em",
        width="100%",
    )


# Add state and page to the app.
app = rx.App()
app.add_page(index)
```

```python exec
import reflex as rx
from reflex.components.component import Component
from typing import Any, Dict, List, Union
from reflex.vars import Var
import random

class ReactFlowLib(Component):
    """A component that wraps a react flow lib."""

    library = "reactflow"

    def _get_custom_code(self) -> str:
        return """import 'reactflow/dist/style.css';
        """

class ReactFlow(ReactFlowLib):

    tag = "ReactFlow"

    nodes: Var[List[Dict[str, Any]]]

    edges: Var[List[Dict[str, Any]]]

    fit_view: Var[bool]

    nodes_draggable: Var[bool]

    nodes_connectable: Var[bool]

    nodes_focusable: Var[bool]

    def get_event_triggers(self) -> dict[str, Any]:
        return {
            **super().get_event_triggers(),
            "on_edges_change": lambda e0: [e0],
            "on_connect": lambda e0: [e0],
        }


class Background(ReactFlowLib):

    tag = "Background"

    color: Var[str]

    gap: Var[int]

    size: Var[int]

    variant: Var[str]

class Controls(ReactFlowLib):

    tag = "Controls"

react_flow = ReactFlow.create
background = Background.create
controls = Controls.create

initial_nodes = [
    {
        'id': '1',
        'type': 'input',
        'data': {'label': '150'},
        'position': {'x': 250, 'y': 25},
    },
    {
        'id': '2',
        'data': {'label': '25'},
        'position': {'x': 100, 'y': 125},
    },
    {
        'id': '3',
        'type': 'output',
        'data': {'label': '5'},
        'position': {'x': 250, 'y': 250},
    },
]

initial_edges = [
    {'id': 'e1-2', 'source': '1', 'target': '2', 'label': '*', 'animated': True},
    {'id': 'e2-3', 'source': '2', 'target': '3', 'label': '+', 'animated': True},
]


class ReactFlowState(rx.State):
    """The app state."""
    nodes: List[Dict[str, Any]] = initial_nodes
    edges: List[Dict[str, Any]] = initial_edges
    
    def add_random_node(self):
        new_node_id = f'{len(self.nodes) + 1}'
        node_type = random.choice(['default'])
        # Label is random number
        label = new_node_id
        x = random.randint(0, 250)
        y = random.randint(0, 250)

        new_node = {
            'id': new_node_id,
            'type': node_type,
            'data': {'label': label},
            'position': {'x': x, 'y': y},
            'draggable': True,
        }
        print(new_node)
        self.nodes.append(new_node)

    def clear_graph(self):
        self.nodes = []  # Clear the nodes list
        self.edges = []  # Clear the edges list

    def on_edges_change(self, new_edge):
        # Iterate over the existing edges
        for i, edge in enumerate(self.edges):
            # If we find an edge with the same ID as the new edge
            if edge["id"] == f"e{new_edge['source']}-{new_edge['target']}":
                # Delete the existing edge
                del self.edges[i]
                break

        # Add the new edge
        self.edges.append({
            "id": f"e{new_edge['source']}-{new_edge['target']}",
            "source": new_edge["source"],
            "target": new_edge["target"],
            "label": random.choice(["+", "-", "*", "/"]),
            "animated": True,
        })
```

Here is an example of the app running:

```python eval
rx.vstack(
        react_flow(
            background(),
            controls(),
            nodes_draggable=True,
            nodes_connectable=True,
            on_connect=lambda e0: ReactFlowState.on_edges_change(e0),
            nodes=ReactFlowState.nodes,
            edges=ReactFlowState.edges,
            fit_view=True,
        ),
        rx.hstack(
            rx.button("Clear graph", on_click=ReactFlowState.clear_graph, width="100%"),
            rx.button("Add node", on_click=ReactFlowState.add_random_node, width="100%"),
            width="100%",
        ),
        height="30em",
        width="100%",
    )
```