from qgis.core import QgsProject
from qgis.utils import iface


def transparency_slider(layers):
    """Add the opacity slider to any new layer added in QGIS."""
    for layer in QgsProject.instance().mapLayers().values():
        if (
            layer.customProperty("embeddedWidgets/count") != 1
            or layer.customProperty("embeddedWidgets/0/id") != "transparency"
        ):
            layer.setCustomProperty("embeddedWidgets/count", 1)
            layer.setCustomProperty("embeddedWidgets/0/id", "transparency")
        else:
            pass
        iface.layerTreeView().refreshLayerSymbology(layer.id())


def initTransparencySlider():
    """Initialize the transparency slider connection when QGIS is ready."""
    QgsProject.instance().layersAdded.connect(transparency_slider)
    # Also apply to any existing layers on startup
    transparency_slider(QgsProject.instance().mapLayers().values())


# Add the initialization function to be run when QGIS is ready
iface.initializationCompleted.connect(initTransparencySlider)