/*
 * 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.
 */

package org.elasticsearch.rest;

import org.apache.lucene.search.spell.LevensteinDistance;
import org.apache.lucene.util.CollectionUtil;
import org.elasticsearch.client.node.NodeClient;
import org.elasticsearch.common.CheckedConsumer;
import org.elasticsearch.common.collect.Tuple;
import org.elasticsearch.common.component.AbstractComponent;
import org.elasticsearch.common.settings.Setting;
import org.elasticsearch.common.settings.Setting.Property;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.plugins.ActionPlugin;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Locale;
import java.util.Set;
import java.util.SortedSet;
import java.util.TreeSet;
import java.util.stream.Collectors;

/**
 * Base handler for REST requests.
 * <p>
 * This handler makes sure that the headers &amp; context of the handled {@link RestRequest requests} are copied over to
 * the transport requests executed by the associated client. While the context is fully copied over, not all the headers
 * are copied, but a selected few. It is possible to control what headers are copied over by returning them in
 * {@link ActionPlugin#getRestHeaders()}.
 */
public abstract class BaseRestHandler extends AbstractComponent implements RestHandler {

    public static final Setting<Boolean> MULTI_ALLOW_EXPLICIT_INDEX =
        Setting.boolSetting("rest.action.multi.allow_explicit_index", true, Property.NodeScope);

    protected BaseRestHandler(Settings settings) {
        super(settings);
    }

    @Override
    public final void handleRequest(RestRequest request, RestChannel channel, NodeClient client) throws Exception {
        // prepare the request for execution; has the side effect of touching the request parameters
        final RestChannelConsumer action = prepareRequest(request, client);

        // validate unconsumed params, but we must exclude params used to format the response
        // use a sorted set so the unconsumed parameters appear in a reliable sorted order
        final SortedSet<String> unconsumedParams =
            request.unconsumedParams().stream().filter(p -> !responseParams().contains(p)).collect(Collectors.toCollection(TreeSet::new));

        // validate the non-response params
        if (!unconsumedParams.isEmpty()) {
            final Set<String> candidateParams = new HashSet<>();
            candidateParams.addAll(request.consumedParams());
            candidateParams.addAll(responseParams());
            throw new IllegalArgumentException(unrecognized(request, unconsumedParams, candidateParams, "parameter"));
        }

        // execute the action
        action.accept(channel);
    }

    protected final String unrecognized(
        final RestRequest request,
        final Set<String> invalids,
        final Set<String> candidates,
        final String detail) {
        String message = String.format(
            Locale.ROOT,
            "request [%s] contains unrecognized %s%s: ",
            request.path(),
            detail,
            invalids.size() > 1 ? "s" : "");
        boolean first = true;
        for (final String invalid : invalids) {
            final LevensteinDistance ld = new LevensteinDistance();
            final List<Tuple<Float, String>> scoredParams = new ArrayList<>();
            for (final String candidate : candidates) {
                final float distance = ld.getDistance(invalid, candidate);
                if (distance > 0.5f) {
                    scoredParams.add(new Tuple<>(distance, candidate));
                }
            }
            CollectionUtil.timSort(scoredParams, (a, b) -> {
                // sort by distance in reverse order, then parameter name for equal distances
                int compare = a.v1().compareTo(b.v1());
                if (compare != 0) return -compare;
                else return a.v2().compareTo(b.v2());
            });
            if (first == false) {
                message += ", ";
            }
            message += "[" + invalid + "]";
            final List<String> keys = scoredParams.stream().map(Tuple::v2).collect(Collectors.toList());
            if (keys.isEmpty() == false) {
                message += " -> did you mean " + (keys.size() == 1 ? "[" + keys.get(0) + "]" : "any of " + keys.toString()) + "?";
            }
            first = false;
        }

        return message;
    }

    /**
     * REST requests are handled by preparing a channel consumer that represents the execution of
     * the request against a channel.
     */
    @FunctionalInterface
    protected interface RestChannelConsumer extends CheckedConsumer<RestChannel, Exception> {
    }

    /**
     * Prepare the request for execution. Implementations should consume all request params before
     * returning the runnable for actual execution. Unconsumed params will immediately terminate
     * execution of the request. However, some params are only used in processing the response;
     * implementations can override {@link BaseRestHandler#responseParams()} to indicate such
     * params.
     *
     * @param request the request to execute
     * @param client  client for executing actions on the local node
     * @return the action to execute
     * @throws IOException if an I/O exception occurred parsing the request and preparing for
     *                     execution
     */
    protected abstract RestChannelConsumer prepareRequest(RestRequest request, NodeClient client) throws IOException;

    /**
     * Parameters used for controlling the response and thus might not be consumed during
     * preparation of the request execution in
     * {@link BaseRestHandler#prepareRequest(RestRequest, NodeClient)}.
     *
     * @return a set of parameters used to control the response and thus should not trip strict
     * URL parameter checks.
     */
    protected Set<String> responseParams() {
        return Collections.emptySet();
    }

}
