package ca.spottedleaf.concurrentutil.completable;

import ca.spottedleaf.concurrentutil.collection.MultiThreadedQueue;
import ca.spottedleaf.concurrentutil.executor.Cancellable;
import ca.spottedleaf.concurrentutil.util.ConcurrentUtil;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.function.BiConsumer;

public final class CallbackCompletable<T> {

    private static final Logger LOGGER = LoggerFactory.getLogger(CallbackCompletable.class);

    private final MultiThreadedQueue<BiConsumer<T, Throwable>> waiters = new MultiThreadedQueue<>();
    private T result;
    private Throwable throwable;
    private volatile boolean completed;

    public boolean isCompleted() {
        return this.completed;
    }

    /**
     * Note: Can only use after calling {@link #addAsynchronousWaiter(BiConsumer)}, as this function performs zero
     * synchronisation
     */
    public T getResult() {
        return this.result;
    }

    /**
     * Note: Can only use after calling {@link #addAsynchronousWaiter(BiConsumer)}, as this function performs zero
     * synchronisation
     */
    public Throwable getThrowable() {
        return this.throwable;
    }

    /**
     * Adds a waiter that should only be completed asynchronously by the complete() calls. If complete()
     * has already been called, returns {@code null} and does not invoke the specified consumer.
     * @param consumer Consumer to be executed on completion
     * @throws NullPointerException If consumer is null
     * @return A cancellable which will control the execution of the specified consumer
     */
    public Cancellable addAsynchronousWaiter(final BiConsumer<T, Throwable> consumer) {
        if (this.waiters.add(consumer)) {
            return new CancellableImpl(consumer);
        }
        return null;
    }

    private void completeAllWaiters(final T result, final Throwable throwable) {
        this.completed = true;
        BiConsumer<T, Throwable> waiter;
        while ((waiter = this.waiters.pollOrBlockAdds()) != null) {
            this.completeWaiter(waiter, result, throwable);
        }
    }

    private void completeWaiter(final BiConsumer<T, Throwable> consumer, final T result, final Throwable throwable) {
        try {
            consumer.accept(result, throwable);
        } catch (final Throwable throwable2) {
            LOGGER.error("Failed to complete callback " + ConcurrentUtil.genericToString(consumer), throwable2);
        }
    }

    /**
     * Adds a waiter that will be completed asynchronously by the complete() calls. If complete()
     * has already been called, then invokes the consumer synchronously with the completed result.
     * @param consumer Consumer to be executed on completion
     * @throws NullPointerException If consumer is null
     * @return A cancellable which will control the execution of the specified consumer
     */
    public Cancellable addWaiter(final BiConsumer<T, Throwable> consumer) {
        if (this.waiters.add(consumer)) {
            return new CancellableImpl(consumer);
        }
        this.completeWaiter(consumer, this.result, this.throwable);
        return new CancellableImpl(consumer);
    }

    public void complete(final T result) {
        this.result = result;
        this.completeAllWaiters(result, null);
    }

    public void completeWithThrowable(final Throwable throwable) {
        if (throwable == null) {
            throw new NullPointerException("Throwable cannot be null");
        }
        this.throwable = throwable;
        this.completeAllWaiters(null, throwable);
    }

    private final class CancellableImpl implements Cancellable {

        private final BiConsumer<T, Throwable> waiter;

        private CancellableImpl(final BiConsumer<T, Throwable> waiter) {
            this.waiter = waiter;
        }

        @Override
        public boolean cancel() {
            return CallbackCompletable.this.waiters.remove(this.waiter);
        }
    }
}