/*
 * 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.common.settings;

import org.elasticsearch.common.Strings;
import org.elasticsearch.common.component.AbstractComponent;
import org.elasticsearch.common.regex.Regex;
import org.elasticsearch.common.xcontent.ToXContent.Params;
import org.elasticsearch.rest.RestRequest;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

/**
 * A class that allows to filter settings objects by simple regular expression patterns or full settings keys.
 * It's used for response filtering on the rest layer to for instance filter out sensitive information like access keys.
 */
public final class SettingsFilter extends AbstractComponent {
    /**
     * Can be used to specify settings filter that will be used to filter out matching settings in toXContent method
     */
    public static String SETTINGS_FILTER_PARAM = "settings_filter";

    private final Set<String> patterns;
    private final String patternString;

    public SettingsFilter(Settings settings, Collection<String> patterns) {
        super(settings);
        for (String pattern : patterns) {
            if (isValidPattern(pattern) == false) {
                throw new IllegalArgumentException("invalid pattern: " + pattern);
            }
        }
        this.patterns = Collections.unmodifiableSet(new HashSet<>(patterns));
        patternString = Strings.collectionToDelimitedString(patterns, ",");
    }

    /**
     * Returns a set of patterns
     */
    public Set<String> getPatterns() {
        return patterns;
    }

    /**
     * Returns <code>true</code> iff the given string is either a valid settings key pattern or a simple regular expression
     * @see Regex
     * @see AbstractScopedSettings#isValidKey(String)
     */
    public static boolean isValidPattern(String pattern) {
        return AbstractScopedSettings.isValidKey(pattern) || Regex.isSimpleMatchPattern(pattern);
    }

    public void addFilterSettingParams(RestRequest request) {
        if (patterns.isEmpty() == false) {
            request.params().put(SETTINGS_FILTER_PARAM, patternString);
        }
    }

    public static Settings filterSettings(Params params, Settings settings) {
        String patterns = params.param(SETTINGS_FILTER_PARAM);
        final Settings filteredSettings;
        if (patterns != null && patterns.isEmpty() == false) {
            filteredSettings = filterSettings(Strings.commaDelimitedListToSet(patterns), settings);
        } else {
            filteredSettings = settings;
        }
        return filteredSettings;
    }

    public Settings filter(Settings settings) {
        return filterSettings(patterns, settings);
    }

    private static Settings filterSettings(Iterable<String> patterns, Settings settings) {
        Settings.Builder builder = Settings.builder().put(settings);
        List<String> simpleMatchPatternList = new ArrayList<>();
        for (String pattern : patterns) {
            if (Regex.isSimpleMatchPattern(pattern)) {
                simpleMatchPatternList.add(pattern);
            } else {
                builder.remove(pattern);
            }
        }
        if (!simpleMatchPatternList.isEmpty()) {
            String[] simpleMatchPatterns = simpleMatchPatternList.toArray(new String[simpleMatchPatternList.size()]);
            Iterator<Entry<String, String>> iterator = builder.internalMap().entrySet().iterator();
            while (iterator.hasNext()) {
                Map.Entry<String, String> current = iterator.next();
                if (Regex.simpleMatch(simpleMatchPatterns, current.getKey())) {
                    iterator.remove();
                }
            }
        }
        return builder.build();
    }
}