from qgis.core import QgsProcessing
from qgis.core import QgsProcessingAlgorithm
from qgis.core import QgsProcessingMultiStepFeedback
from qgis.core import QgsProcessingParameterVectorLayer
from qgis.core import QgsProcessingParameterFeatureSink
import processing
 
 
class ExampleAlgo(QgsProcessingAlgorithm):
 
    def name(self):
        return 'ex_script'
 
    def displayName(self):
        return 'Example script'
 
    def group(self):
        return 'Example Scripts'
 
    def groupId(self):
        return 'examplescripts'
 
    def createInstance(self):
        return type(self)()
         
    def initAlgorithm(self, config=None):
        self.addParameter(
            QgsProcessingParameterVectorLayer(
                'input', 'INPUT', 
                types=[QgsProcessing.TypeVectorAnyGeometry]
            )
        )
        self.addParameter(
            QgsProcessingParameterFeatureSink(
                'output', 'OUTPUT', 
                type=QgsProcessing.TypeVectorPolygon
            )
        )
 
    def processAlgorithm(self, parameters, context, feedback):
        feedback = QgsProcessingMultiStepFeedback(1, feedback)
        results = {}
        outputs = {}
 
        # Buffer
        alg_params = {
            'DISSOLVE': False,
            'DISTANCE': 100,
            'END_CAP_STYLE': 0,  # Round
            'INPUT': parameters['input'],
            'JOIN_STYLE': 0,  # Round
            'MITER_LIMIT': 2,
            'SEGMENTS': 5,
            'OUTPUT': parameters['output']
        }
        outputs['Buffer'] = processing.run(
            'native:buffer', 
            alg_params, 
            context=context, 
            feedback=feedback, 
            is_child_algorithm=True)
         
        results['Output'] = outputs['Buffer']['OUTPUT']
        return results