How to parameterize 'Select By Location' in QGIS processing plugin

Question

Can someone help me understand how to properly parameterize the 'Select by Location' geoprocessing tool when implementing it in a QGIS processing plugin. I have been following the tutorial on building a processing plugin, however I get an 'Unable to execute algorithm' error when I try to run my processing plugin. At thi point, I just want to be able to parameterize and run a the basic geoprocessing tool 'Select by Location' before I start changing things.....

Here is a snippet of code from the two functions used to define the parameters, and implement the processAlgorithm.

As written, I receive the error: Unable to execute algorithm Incorrect parameter value for INPUT

I have compared the output in the log window for the 'Select by Location' tool in Vector-->Research--> Select by location, which looks like this:

Input parameters:
{ 'INPUT' : "crs='EPSG:4326' url='https://services3.arcgis.com/T4QMspbfLg3qTGWY/ArcGIS/rest/services/Fire_History_Perimeters_Public/FeatureServer/0'", 
  'INTERSECT' : '/media/williamkessler/extradrive1/BearToothGroup/Data/Airports_and_drivetime/Airports.gpkg|layername=1hr_Isochrone', 
  'METHOD' : 0, 
  'PREDICATE' : [0] }
  
  Execution completed in 0.44 seconds
  Results:
  {'OUTPUT': 'FH_Perimeter_f0404e04_0298_4fb3_bd78_5534a7d1fe4f'}

and what comes from my tool:

Input parameters:
  { 'INPUT' : "arcgisfeatureserver://crs='EPSG:4326' url='https://services3.arcgis.com/T4QMspbfLg3qTGWY/ArcGIS/rest/services/Fire_History_Perimeters_Public/FeatureServer/0'", 
  'Intersecting Layer' : '/media/williamkessler/extradrive1/BearToothGroup/Data/Airports_and_drivetime/Airports.gpkg|layername=1hr_Isochrone', 
  'METHOD': 0,
  'Predicate' : [0] }'

  Unable to execute algorithm
  Incorrect parameter value for INPUT
  Execution failed after 0.05 seconds

The only difference I can see, is a difference in how the CRS is specified? How do I change this? Will it solve my issue?

def initAlgorithm(self, config):
    """
    Here we define the inputs and output of the algorithm, along
    with some other properties.
    """
    # I add the input vector features source. It can have any kind of geometry.
    self.addParameter(
        QgsProcessingParameterFeatureSource(
            self.INPUT,
            self.tr('Input layer'),
            [QgsProcessing.TypeVectorAnyGeometry]
        )
    )

    # I add the vector features source to compare the input against. It can have any kind of geometry.
    self.addParameter(
        QgsProcessingParameterFeatureSource(
            self.INTERSECT,
            self.tr('INTERSECTING layer'),
            [QgsProcessing.TypeVectorAnyGeometry]
        )
    )

    # I specify the geometric predicate to base the selection on. It  is an enum parameter with multiselect (the same as in the basic 'select by location tool' 
    self.addParameter(
        QgsProcessingParameterEnum(
            name = self.PRED, 
            description = self.tr('Geometric Predicate'), 
            options = ["Intersect","Contain","Disjoint","Equal","Touch","Overlap","Are Within", "Cross"],
            defaultValue = "Intersect",
            allowMultiple = True,
        )
    )
    
    # 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 processAlgorithm(self, parameters, context, feedback):
    """
    Here is where the processing itself takes place.
    """

    # Retrieve the feature source and sink. The 'dest_id' variable is used
    # to uniquely identify the feature sink, and must be included in the
    # dictionary returned by the processAlgorithm function.
    source = self.parameterAsSource(parameters, self.INPUT, context)

    (sink, dest_id) = self.parameterAsSink(parameters, self.OUTPUT,
            context, source.fields(), source.wkbType(), source.sourceCrs())

    intersect = self.parameterAsSource(parameters, self.INTERSECT, context)

    predicate = self.parameterAsSource(parameters, self.PRED, context)

    # method = self.parameterAsSource(parameters, self.METHOD, context)

    # Compute the number of steps to display within the progress bar and
    # get features from source
    total = 100.0 / source.featureCount() if source.featureCount() else 0
    features = source.getFeatures()
    
    ## Here is where I attempt to implement the 'select by location' processing tool: 
    processing.run("qgis:selectbylocation", {'INPUT':source, 'PREDICATE': predicate, 'INTERSECT': intersect, 'METHOD':0})

 '''
    # for current, feature in enumerate(features):
    #     # Stop the algorithm if cancel button has been clicked
    #     if feedback.isCanceled():
    #         break

    #     # Add a feature in the sink
    #     # sink.addFeature(feature, QgsFeatureSink.FastInsert)

    #     # processing.run("qgis:selectbylocation", {'INPUT':feature, 'PREDICATE': predicate, 'INTERSECT': intersect, 'METHOD':0})
    #     # Update the progress bar
    #     feedback.setProgress(int(current * total))

    # Return the results of the algorithm. In this case our only result is
    # the feature sink which contains the processed features, but some
    # algorithms may return multiple feature sinks, calculated numeric
    # statistics, etc. These should all be included in the returned
    # dictionary, with keys matching the feature corresponding parameter
    # or output names.
    return {self.OUTPUT: dest_id}

Answer 1

I figured out the answer to my own question. It's a two parter- I had the inputs misspecified- the processessing tool I was trying to call requires vectorLayers as input, not 'FeatureSource'

   self.addParameter(
    QgsProcessingParameterFeatureSource(
        self.INPUT,
        self.tr('Input layer'),
        [QgsProcessing.TypeVectorAnyGeometry]
    )
)

becomes:

  self.addParameter(
    QgsProcessingParameterVectorLayer(
        self.INPUT,
        self.tr('Input layer'),
        [QgsProcessing.TypeVectorAnyGeometry]
    )
)

and,

When calling your parameters in the processAlgorithm function, the class called needs to match the parameter type. For instance:

source = self.parameterAsSource(parameters, self.INPUT, context)

predicate = self.parameterAsSource(parameters, self.PRED, context)

should be:

source = self.parameterAsVectorLayer(parameters, self.INPUT, context)

predicate = self.parameterAsEnum(parameters, self.PRED, context)