Processing python code to get the print layout extents as a layer in qgis map

print_layout_extents_to_map_for_processing.py

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

from PyQt5.QtCore import QCoreApplication, QVariant
from qgis.core import (QgsVectorLayer, QgsFields, QgsField, QgsProject,QgsLayoutItemMap,QgsFeature,QgsGeometry,QgsCoordinateReferenceSystem,
                        QgsProcessing,
                       QgsFeatureSink,
                       QgsProcessingAlgorithm,
                       QgsProcessingParameterFeatureSource,
                       QgsProcessingParameterFeatureSink)
                       



class ExampleProcessingAlgorithm(QgsProcessingAlgorithm):
    """
    This is an example algorithm that takes a vector layer and
    creates a new identical one.

    It is meant to be used as an example of how to create your own
    algorithms and explain methods and variables used to do it. An
    algorithm like this will be available in all elements, and there
    is not need for additional work.

    All Processing algorithms should extend the QgsProcessingAlgorithm
    class.
    """

    INPUT = 'INPUT'
    OUTPUT = 'OUTPUT'

    def tr(self, string):
        """
        Returns a translatable string with the self.tr() function.
        """
        return QCoreApplication.translate('Processing', string)

    def createInstance(self):
        return ExampleProcessingAlgorithm()

    def name(self):
        """
        Returns the algorithm name, used for identifying the algorithm. This
        string should be fixed for the algorithm, and must not be localised.
        The name should be unique within each provider. Names should contain
        lowercase alphanumeric characters only and no spaces or other
        formatting characters.
        """
        return 'createExtentsFromPrintLayouts'

    def displayName(self):
        """
        Returns the translated algorithm name, which should be used for any
        user-visible display of the algorithm name.
        """
        return self.tr('Create Extents FromPrint Layouts')

    def group(self):
        """
        Returns the name of the group this algorithm belongs to. This string
        should be localised.
        """
        return self.tr('My Scripts')

    def groupId(self):
        """
        Returns the unique ID of the group this algorithm belongs to. This
        string should be fixed for the algorithm, and must not be localised.
        The group id should be unique within each provider. Group id should
        contain lowercase alphanumeric characters only and no spaces or other
        formatting characters.
        """
        return 'myscripts'

    def initAlgorithm(self, config=None):
        """
        Here we define the inputs and output of the algorithm, along
        with some other properties.
        """

        # We add a feature sink in which to store our processed features (this
        # usually takes the form of a newly created vector layer when the
        # algorithm is run in QGIS).
        self.addParameter(
            QgsProcessingParameterFeatureSink(
                self.OUTPUT,
                self.tr('Output layer')
            )
        )
    
    def fGetExtentFeaturesFromPrintLayouts(self) :
        """
        This is a function that iterates over print layouts to return a list of features, each of which represents the extent of the composer map
        As attribute, we have the name of the print layout
        """
        
        # get compositions
        projectInstance= QgsProject.instance()
        projectLayoutManager = projectInstance.layoutManager()
        comps = projectLayoutManager.printLayouts()

        # iterate over compositions
        feats = list()
        for comp in comps :
            layoutName = comp.name()
            for item in comp.items() :
                if (isinstance(item, QgsLayoutItemMap)) :
                    # geometry
                    e = item.extent()
                    feat = QgsFeature()
                    feat.setGeometry(QgsGeometry.fromRect(e))
                    # attributes
                    feat.initAttributes(1)
                    feat.setAttribute(0, QVariant(layoutName))
                    feats.append(feat)
        
        return(feats)
        
    def processAlgorithm(self, parameters, context, feedback):
        """
        Here is where the processing itself takes place.
        """

        # defining CRS
        crs = QgsCoordinateReferenceSystem()
        crs.createFromId(2154)

        # fields
        flds = QgsFields()
        flds.append(QgsField("name", QVariant.String))
        
        # sink params
        (sink, dest_id) = self.parameterAsSink(
            parameters,
            self.OUTPUT,
            context,
            flds,
            3,
           crs
        )
         
       # get features from print layouts
        feats  = self.fGetExtentFeaturesFromPrintLayouts()
        for feat in feats :
            sink.addFeature(feat, QgsFeatureSink.FastInsert)
            
        # Return the results of the algorithm
        return {self.OUTPUT: dest_id}