# -*- coding: utf-8 -*-

from qgis.analysis import (
    QgsGeometrySnapper
)
from qgis.core import (
    QgsFeature,
    QgsGeometry,
    QgsProject,
    QgsVectorLayer,
)


def create_scratch_reference_layer():
    """Create a scratch reference layer to snap to"""

    r1 = QgsVectorLayer(
        path='Polygon',
        baseName='x',
        providerLib='memory'
    )

    refGeom = QgsGeometry.fromWkt(
        wkt="Polygon((0 0, 10 0, 10 10, 0 10, 0 0))"
    )

    ff = QgsFeature(
        id=0
    )

    ff.setGeometry(
        geometry=refGeom
    )

    flist = [ff]

    r1.dataProvider().addFeatures(
        flist=flist
    )

    # QgsProject.instance().addMapLayer(mapLayer=r1)

    return r1


polygonGeom = QgsGeometry.fromWkt(
    wkt="Polygon((0.1 -0.1, 10.1 0, 9.9 10.1, 0 10, 0.1 -0.1))"
)

snapper = QgsGeometrySnapper(
    referenceSource=create_scratch_reference_layer()
)

result = snapper.snapGeometry(
    geometry=polygonGeom,
    snapTolerance=1
)

print("result =", result)