[Feature Request] Add custom label anchor for Sankey graphs

[leo-smi]

Add the possibility to custom change the anchor of the node text

Current:

After:

Minimum example code:

import dash
from dash import dcc, html, Input, Output
import plotly.graph_objects as go

# Inicializa o app Dash
app = dash.Dash(__name__)
app.title = "Sankey Colorido"

# ----------- Sankey básico -------------
labels = ["A1", "A2", "B1", "B2", "C1", "C2"]
sources = [0, 1, 0, 2, 3, 3]
targets = [2, 3, 3, 4, 4, 5]
values  = [8, 4, 2, 8, 4, 2]

fig = go.Figure(go.Sankey(
    arrangement="snap",
    node=dict(
        pad=15,
        thickness=20,
        line=dict(color="black", width=0.5),
        label=labels,
        color="blue"
    ),
    link=dict(
        source=sources,
        target=targets,
        value=values
    )
))

fig.update_layout(title_text="Basic Sankey Diagram", font_size=10)

# ----------- Layout Dash -------------
app.layout = html.Div([
    dcc.Graph(
        id="sankey-graph",
        figure=fig,
        style={"width":"100%", "height":"100vh"}
    )
])

# ----------- Client-side callback para alinhar labels -------------
# desloca horizontalmente e alinha à direita
app.clientside_callback(
    """
    function(figure) {
        setTimeout(() => {
            const labels = document.querySelectorAll('.sankey .node-label');
            labels.forEach(label => {
                const transform = label.getAttribute('transform');
                const match = /translate\\(([^,]+),([^)]+)\\)/.exec(transform);
                if(match){
                    const y = parseFloat(match[2]);
                    const x = -15; // deslocamento horizontal
                    label.setAttribute('transform', `translate(${x},${y})`);
                    label.setAttribute('text-anchor','end'); // alinhamento à direita
                }
            });
        }, 500); // espera renderização
        return figure;
    }
    """,
    Output('sankey-graph', 'figure'),
    Input('sankey-graph', 'figure')
)

if __name__ == "__main__":
    app.run(debug=True)

The clientside_callback is replaced after user interaction with the graph