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 * Java implementation of the SciJava Ops matching engine.
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package org.scijava.ops.engine.matcher.reduce;

import java.util.Collections;
import java.util.List;
import java.util.Objects;
import java.util.Optional;
import java.util.ServiceLoader;
import java.util.function.LongFunction;
import java.util.stream.Collectors;
import java.util.stream.LongStream;

import org.scijava.ops.api.OpInfo;
import org.scijava.ops.engine.OpInfoGenerator;
import org.scijava.struct.Member;

public class ReducedOpInfoGenerator implements OpInfoGenerator {

	public static final List<InfoReducer> infoReducers = ServiceLoader.load(
		InfoReducer.class).stream().map(ServiceLoader.Provider::get).collect(
			Collectors.toList());

	@Override
	public boolean canGenerateFrom(Object o) {
		// We can only generate OpInfos from other OpInfos
		if (!(o instanceof OpInfo)) return false;
        var info = (OpInfo) o;
		// We only benefit from OpInfos with optional parameters
        var allParamsRequired = info.inputs().parallelStream() //
			.allMatch(Member::isRequired); //
		if (allParamsRequired) return false;
		// If we have a InfoReducer, then we can reduce
		return infoReducers //
			.parallelStream() //
			.anyMatch(reducer -> reducer.canReduce(info));
	}

	@Override
	public List<OpInfo> generateInfosFrom(Object o) {
		if (!(o instanceof OpInfo)) return Collections.emptyList();
		return reduce((OpInfo) o);
	}

	private List<OpInfo> reduce(OpInfo info) {
		// Find the correct InfoReducer
		Optional<? extends InfoReducer> optionalReducer = infoReducers //
			.parallelStream() //
			.filter(infoReducer -> infoReducer.canReduce(info)) //
			.findAny();
		if (optionalReducer.isEmpty()) return Collections.emptyList();
		// We can only reduce as many times as we have optional params
        var numReductions = (int) info.struct().members().parallelStream() //
			.filter(m -> !m.isRequired()) //
			.count(); //
		// add a ReducedOpInfo for all possible reductions
        var reducer = optionalReducer.get();
		LongFunction<OpInfo> func = l -> reducer.reduce(info, (int) l);
		return LongStream.range(1, numReductions + 1) //
			.mapToObj(func) //
			.filter(Objects::nonNull) //
			.collect(Collectors.toList());
	}

}
