/*
 * SPDX-License-Identifier: Apache-2.0
 *
 * The OpenSearch Contributors require contributions made to
 * this file be licensed under the Apache-2.0 license or a
 * compatible open source license.
 */

/*
 * Licensed to Elasticsearch under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch licenses this file to you under
 * the Apache License, Version 2.0 (the "License"); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

/*
 * Modifications Copyright OpenSearch Contributors. See
 * GitHub history for details.
 */

package org.opensearch.rest;

import org.opensearch.client.node.NodeClient;
import org.opensearch.core.xcontent.XContent;
import org.opensearch.rest.RestRequest.Method;

import java.util.Collections;
import java.util.List;
import java.util.Objects;
import java.util.stream.Collectors;

/**
 * Handler for REST requests
 *
 * @opensearch.api
 */
@FunctionalInterface
public interface RestHandler {

    /**
     * Handles a rest request.
     * @param request The request to handle
     * @param channel The channel to write the request response to
     * @param client A client to use to make internal requests on behalf of the original request
     */
    void handleRequest(RestRequest request, RestChannel channel, NodeClient client) throws Exception;

    default boolean canTripCircuitBreaker() {
        return true;
    }

    /**
     * Indicates if the RestHandler supports content as a stream. A stream would be multiple objects delineated by
     * {@link XContent#streamSeparator()}. If a handler returns true this will affect the types of content that can be sent to
     * this endpoint.
     */
    default boolean supportsContentStream() {
        return false;
    }

    /**
     * Indicates if the RestHandler supports working with pooled buffers. If the request handler will not escape the return
     * {@link RestRequest#content()} or any buffers extracted from it then there is no need to make a copies of any pooled buffers in the
     * {@link RestRequest} instance before passing a request to this handler. If this instance does not support pooled/unsafe buffers
     * {@link RestRequest#ensureSafeBuffers()} should be called on any request before passing it to {@link #handleRequest}.
     *
     * @return true iff the handler supports requests that make use of pooled buffers
     */
    default boolean allowsUnsafeBuffers() {
        return false;
    }

    /**
     * The list of {@link Route}s that this RestHandler is responsible for handling.
     */
    default List<Route> routes() {
        return Collections.emptyList();
    }

    /**
     * A list of routes handled by this RestHandler that are deprecated and do not have a direct
     * replacement. If changing the {@code path} or {@code method} of a route,
     * use {@link #replacedRoutes()}.
     */
    default List<DeprecatedRoute> deprecatedRoutes() {
        return Collections.emptyList();
    }

    /**
     * A list of routes handled by this RestHandler that have had their {@code path} and/or
     * {@code method} changed. The pre-existing {@code route} will be registered
     * as deprecated alongside the updated {@code route}.
     */
    default List<ReplacedRoute> replacedRoutes() {
        return Collections.emptyList();
    }

    /**
     * Controls whether requests handled by this class are allowed to to access system indices by default.
     * @return {@code true} if requests handled by this class should be allowed to access system indices.
     */
    default boolean allowSystemIndexAccessByDefault() {
        return false;
    }

    static RestHandler wrapper(RestHandler delegate) {
        return new Wrapper(delegate);
    }

    /**
     * Wrapper for a handler.
     *
     * @opensearch.internal
     */
    class Wrapper implements RestHandler {
        private final RestHandler delegate;

        public Wrapper(RestHandler delegate) {
            this.delegate = Objects.requireNonNull(delegate, "RestHandler delegate can not be null");
        }

        @Override
        public String toString() {
            return delegate.toString();
        }

        @Override
        public void handleRequest(RestRequest request, RestChannel channel, NodeClient client) throws Exception {
            delegate.handleRequest(request, channel, client);
        }

        @Override
        public boolean canTripCircuitBreaker() {
            return delegate.canTripCircuitBreaker();
        }

        @Override
        public boolean supportsContentStream() {
            return delegate.supportsContentStream();
        }

        @Override
        public boolean allowsUnsafeBuffers() {
            return delegate.allowsUnsafeBuffers();
        }

        @Override
        public List<Route> routes() {
            return delegate.routes();
        }

        @Override
        public List<DeprecatedRoute> deprecatedRoutes() {
            return delegate.deprecatedRoutes();
        }

        @Override
        public List<ReplacedRoute> replacedRoutes() {
            return delegate.replacedRoutes();
        }

        @Override
        public boolean allowSystemIndexAccessByDefault() {
            return delegate.allowSystemIndexAccessByDefault();
        }
    }

    /**
     * Route for the request.
     *
     * @opensearch.internal
     */
    class Route {

        protected final String path;
        protected final Method method;

        public Route(Method method, String path) {
            this.path = path;
            this.method = method;
        }

        public String getPath() {
            return path;
        }

        public String getPathWithPathParamsReplaced() {
            return path.replaceAll("(?<=\\{).*?(?=\\})", "path_param");
        }

        public Method getMethod() {
            return method;
        }

        @Override
        public int hashCode() {
            String routeStr = "Route [method=" + method + ", path=" + getPathWithPathParamsReplaced() + "]";
            return routeStr.hashCode();
        }

        @Override
        public String toString() {
            return "Route [method=" + method + ", path=" + path + "]";
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) {
                return true;
            }
            if (o == null || getClass() != o.getClass()) {
                return false;
            }
            Route that = (Route) o;
            return Objects.equals(method, that.method)
                && Objects.equals(getPathWithPathParamsReplaced(), that.getPathWithPathParamsReplaced());
        }
    }

    /**
     * Represents an API that has been deprecated and is slated for removal.
     */
    class DeprecatedRoute extends Route {

        private final String deprecationMessage;

        public DeprecatedRoute(Method method, String path, String deprecationMessage) {
            super(method, path);
            this.deprecationMessage = deprecationMessage;
        }

        public String getDeprecationMessage() {
            return deprecationMessage;
        }
    }

    /**
     * Represents an API that has had its {@code path} or {@code method} changed. Holds both the
     * new and previous {@code path} and {@code method} combination.
     */
    class ReplacedRoute extends Route {

        private final String deprecatedPath;
        private final Method deprecatedMethod;

        /**
         * Construct replaced routes using new and deprocated methods and new and deprecated paths
         * @param method route method
         * @param path new route path
         * @param deprecatedMethod deprecated method
         * @param deprecatedPath deprecated path
         */
        public ReplacedRoute(Method method, String path, Method deprecatedMethod, String deprecatedPath) {
            super(method, path);
            this.deprecatedMethod = deprecatedMethod;
            this.deprecatedPath = deprecatedPath;
        }

        /**
         * Construct replaced routes using route method, new and deprecated paths
         * This constructor can be used when both new and deprecated paths use the same method
         * @param method route method
         * @param path new route path
         * @param deprecatedPath deprecated path
         */
        public ReplacedRoute(Method method, String path, String deprecatedPath) {
            this(method, path, method, deprecatedPath);
        }

        /**
         * Construct replaced routes using route, new and deprecated prefixes
         * @param route route
         * @param prefix new route prefix
         * @param deprecatedPrefix deprecated prefix
         */
        public ReplacedRoute(Route route, String prefix, String deprecatedPrefix) {
            this(route.getMethod(), prefix + route.getPath(), deprecatedPrefix + route.getPath());
        }

        public String getDeprecatedPath() {
            return deprecatedPath;
        }

        public Method getDeprecatedMethod() {
            return deprecatedMethod;
        }
    }

    /**
     * Construct replaced routes using routes template and prefixes for new and deprecated paths
     * @param routes routes
     * @param prefix new prefix
     * @param deprecatedPrefix deprecated prefix
     * @return new list of API routes prefixed with the prefix string
     */
    static List<ReplacedRoute> replaceRoutes(List<Route> routes, final String prefix, final String deprecatedPrefix) {
        return routes.stream().map(route -> new ReplacedRoute(route, prefix, deprecatedPrefix)).collect(Collectors.toList());
    }
}