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package org.glassfish.jersey.server.internal.routing;

import java.util.Collections;
import java.util.LinkedList;
import java.util.List;

import org.glassfish.jersey.process.Inflector;
import org.glassfish.jersey.process.internal.Inflecting;
import org.glassfish.jersey.server.ContainerRequest;
import org.glassfish.jersey.server.ContainerResponse;

import jersey.repackaged.com.google.common.base.Function;

/**
 * Routing tree assembly utilities.
 *
 * @author Marek Potociar (marek.potociar at oracle.com)
 */
class Routers {

    private Routers() {
        // prevents instantiation
    }

    /**
     * Creates a leaf-node {@link Router} that implements {@link org.glassfish.jersey.process.internal.Inflecting}
     * interface and returns the provided {@link org.glassfish.jersey.process.Inflector} instance
     * when the {@link org.glassfish.jersey.process.internal.Inflecting#inflector()} method is called.
     * {@link Router#apply(org.glassfish.jersey.server.ContainerRequest)} method of the created
     * hierarchical router returns the unchanged request and an empty continuation iterator.
     *
     * @param inflector a request to response transformation to be wrapped in an
     *                  {@code Router} instance.
     * @return an {@code Router} that wraps the supplied {@code Inflector}.
     */
    @SuppressWarnings("unchecked")
    public static Router asTreeAcceptor(final Inflector inflector) {
        return new InflectingRouter(inflector);
    }

    /**
     * Start building a hierarchical routing tree.
     *
     * @param transformation root transformation function.
     * @return hierarchical accepting tree builder.
     */
    public static Router.Builder acceptingTree(
            Function transformation) {
        return new RouterBuilder(transformation);
    }

    private static class InflectingRouter
            implements Router, Inflecting {

        private final Inflector inflector;

        public InflectingRouter(final Inflector inflector) {
            this.inflector = inflector;
        }

        @Override
        public Inflector inflector() {
            return inflector;
        }

        @Override
        public Continuation apply(ContainerRequest request) {
            return Continuation.of(request);
        }
    }

    private static class RouterBuilder implements Router.Builder {

        private final Function transformation;
        private List children;

        public RouterBuilder(Function transformation) {
            this.transformation = transformation;
        }

        @Override
        public Router.Builder child(Router child) {
            if (children == null) {
                children = new LinkedList();
            }
            children.add(child);

            return this;
        }

        @Override
        public Router build() {
            return (children == null)
                    ? new LinkedRouter(transformation) : new LinkedRouter(transformation, children);
        }
    }

    private static class LinkedRouter implements Router {

        private final Function transformation;
        private final List children;

        public LinkedRouter(
                Function transformation, List children) {
            this.transformation = transformation;
            this.children = children;
        }

        public LinkedRouter(Function transformation) {
            this.transformation = transformation;
            this.children = Collections.emptyList();
        }

        @Override
        public Continuation apply(ContainerRequest data) {
            return Continuation.of(transformation.apply(data), children);
        }
    }
}