###############
LinkSplitFilter
###############

This interface allows a :ref:`Filter <extensions-filters>` to be part of the logic flow of one or more Link Splits.

LinkSplitFilters are not extensions of :doc:`/filter-interfaces/transformation-filter` and are not expected to mutate RecordInFlight instances.

Instead, their job is to evaluate each RecordInFlight and decide if it should, or should not, be sent to a given Link Split child of a running Link. They are, in some ways, a router directing traffic.

**********
Definition
**********

.. code-block:: java

	/**
	 * A Filter that is used to evaluate RecordInFlight instances to see if they should be processed by a Link Split.
	 */
	global interface LinkSplitFilter {

		/**
		 * Consider a List of RecordInFlight instances against the LinkContext they would be run against if they were allowed to proceed.
		 *
		 * @param context Details about the Link that would run if some records are accepted
		 * @param records The records to evaluate
		 *
		 * @return An ordered list of true/false, where each item is the acceptance/rejection of the corresponding index in the records parameter
		 */
		List<Boolean> evaluate(LinkContext context, List<RecordInFlight> records);
	}

*******
Example
*******

Let's say you have a Link called "AllRecords", whose job it is to pick up any records that have changed in a remote database regardless of the table they come from.

You are expecting three flavors of records:

1. Companies (which you want to put in Account)
2. People (which you want to put in Contact)
3. Invoices (which you want to put in Invoice__c)

Consequently, you have three additional Links (one for each of these types of records).

AllRecords runs, and it has 20 records that are a mix of all three types. How do you decide what to do next? That's where LinkSplitFilter comes in.

If the User selects a LinkSplitFilter when they are setting up the three Link Splits (one for each of our data types) that Filter will get a chance to give a thumbs up or down on each record.

The ``evaluate()`` method will be invoked three times, with a different LinkContext each time (corresponding to each of our child Links). The logic below would sort records appropriately.

.. code-block:: java

    public List<Boolean> evaluate(valence.LinkContext context, List<valence.RecordInFlight> records) {

		List<Boolean> results = new List<Boolean>();

        for(valence.RecordInFlight record : records) {

			// let's say that the AllRecords Link adds a field to each record called "dataType" that holds a string value indicating what flavor of record it is
			String dataType = (String)record.getOriginalPropertyValue('dataType');

			switch on dataType {
				when 'company' {
					results.add('Account'.equalsIgnoreCase(context.linkTargetName));
				}
				when 'person' {
					results.add('Contact'.equalsIgnoreCase(context.linkTargetName));
				}
				when 'invoice' {
					results.add('Invoice__c'.equalsIgnoreCase(context.linkTargetName));
				}
			}
		}

		return results;
    }