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package org.zalando.riptide.capture;

import javax.annotation.Nullable;
import java.util.Optional;
import java.util.concurrent.atomic.AtomicReference;

final class DefaultCapture implements Capture {

    /**
     * A reference holding the captured value. It can represent three different states:
     * 
     *     {@code null}: not captured
     *     {@code Optional.empty()}: captured null
     *     {@code Optional.of(..)}: captured non-null
     * 
     */
    private final AtomicReference> reference = new AtomicReference<>();

    @Override
    public void capture(@Nullable final T result) {
        final boolean captured = reference.compareAndSet(null, Optional.ofNullable(result));

        if (!captured) {
            throw new IllegalStateException("Already captured");
        }
    }

    @Override
    @SuppressWarnings("OptionalAssignedToNull")
    public T retrieve() {
        @Nullable final Optional value = reference.get();

        if (value == null) {
            throw new CaptureException();
        }

        return value.orElse(null);
    }

}