org.reactfx.util.AccumulationFacility Maven / Gradle / Ivy

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package org.reactfx.util;

import java.util.Deque;
import java.util.LinkedList;

import org.reactfx.collection.ListChangeAccumulator;
import org.reactfx.collection.ListModificationSequence;
import org.reactfx.collection.QuasiListChange;

public interface AccumulationFacility {
    A initialAccumulator(T value);
    A reduce(A accum, T value);

    interface IllegalAccumulation extends AccumulationFacility {
        @Override
        default A reduce(A accum, T value) { throw new IllegalStateException(); }
    }

    interface HomotypicAccumulation extends AccumulationFacility {
        @Override
        default T initialAccumulator(T value) { return value; }
    }

    interface NoAccumulation
    extends IllegalAccumulation, HomotypicAccumulation {}

    interface Queuing extends AccumulationFacility> {

        @Override
        default Deque initialAccumulator(T value) {
            Deque res = new LinkedList<>();
            res.add(value);
            return res;
        }

        @Override
        default Deque reduce(Deque accum, T value) {
            accum.addLast(value);
            return accum;
        }
    }

    interface RetainLatest extends HomotypicAccumulation {
        @Override
        default T reduce(T accum, T value) { return value; }
    }

    interface RetainOldest extends HomotypicAccumulation {
        @Override
        default T reduce(T accum, T value) { return accum; }
    }

    interface ListChangeAccumulation
    extends AccumulationFacility, ListModificationSequence> {

        @Override
        default ListModificationSequence initialAccumulator(
                QuasiListChange value) {
            return QuasiListChange.safeCast(value);
        }

        @Override
        default ListChangeAccumulator reduce(
                ListModificationSequence accum,
                QuasiListChange value) {
            return accum.asListChangeAccumulator().add(value);
        }
    }
}