mtl_gis_oo/scrub_layer_class.py

from qgis.core import QgsApplication, QgsField, QgsProject, \
  QgsProcessingFeedback, QgsVectorLayer, QgsVectorDataProvider, \
  QgsExpressionContext, QgsExpressionContextUtils
from qgis.analysis import QgsNativeAlgorithms
import processing


class ScrubLayer:
  def __init__(self, qgis_path, layer_path, layer_name):
    # Set the path to QGIS installation
    QgsApplication.setPrefixPath(qgis_path, True)

    # Initialize QGIS application
    qgs = QgsApplication([], False)
    qgs.initQgis()

    self.layer_path = layer_path
    self.layer_name = layer_name
    self.layer = self.load_layer()

  def load_layer(self):
    the_layer = QgsVectorLayer(self.layer_path, self.layer_name, 'ogr')
    if not the_layer.isValid():
      raise ValueError(f'Failed to load layer {self.layer_name} from {self.layer_path}')
    else:
      QgsProject.instance().addMapLayer(the_layer)
    return the_layer

  def fix_geometries(self, fixed_layer):
    QgsApplication.processingRegistry().addProvider(QgsNativeAlgorithms())
    fix_geometries_params = {
      'INPUT': self.layer,
      'METHOD': 0,
      'OUTPUT': fixed_layer
    }
    processing.run("native:fixgeometries", fix_geometries_params)

  def create_spatial_index(self):
    QgsApplication.processingRegistry().addProvider(QgsNativeAlgorithms())
    create_spatial_index_params = {
      'INPUT': self.layer,
      'OUTPUT': 'Output'
    }
    processing.run("native:createspatialindex", create_spatial_index_params)
    print(f'Creating spatial index for {self.layer_name} is completed.')

  def clip_layer(self, overlay_layer, clipped_layer):
    QgsApplication.processingRegistry().addProvider(QgsNativeAlgorithms())
    clip_layer_params = {
      'INPUT': self.layer_path,
      'OVERLAY': overlay_layer,
      'FILTER_EXPRESSION': '',
      'FILTER_EXTENT': None,
      'OUTPUT': clipped_layer
    }
    processing.run("native:clip", clip_layer_params)
    print(f'Clipping of {self.layer_name} is completed.')

  @staticmethod
  def cleanup():
    QgsApplication.exitQgis()