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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF 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.apache.sshd.common;

import java.util.AbstractMap.SimpleImmutableEntry;
import java.util.Collection;
import java.util.Map;
import java.util.Objects;
import java.util.Properties;
import java.util.Set;
import java.util.TreeSet;
import java.util.stream.Collectors;

import org.apache.sshd.common.util.GenericUtils;
import org.apache.sshd.common.util.MapEntryUtils;

/**
 * A wrapper that exposes a read-only {@link Map} access to the system properties. Any attempt to modify it will throw
 * {@link UnsupportedOperationException}. The mapper uses the {@link #SYSPROPS_MAPPED_PREFIX} to filter and access' only
 * these properties, ignoring all others
 *
 * @author Apache MINA SSHD Project
 */
public final class SyspropsMapWrapper implements Map {
    /**
     * Prefix of properties used by the mapper to identify SSHD related settings
     */
    public static final String SYSPROPS_MAPPED_PREFIX = "org.apache.sshd.config";

    /**
     * Exposes the "raw" system properties as a {@link PropertyResolver} without any further filtering
     */
    public static final PropertyResolver RAW_PROPS_RESOLVER = PropertyResolverUtils.toPropertyResolver(System.getProperties());

    /**
     * The one and only wrapper instance
     */
    public static final SyspropsMapWrapper INSTANCE = new SyspropsMapWrapper();

    /**
     * A {@link PropertyResolver} with no parent that exposes the system properties
     */
    public static final PropertyResolver SYSPROPS_RESOLVER = new PropertyResolver() {
        @Override
        public Map getProperties() {
            return SyspropsMapWrapper.INSTANCE;
        }

        @Override
        public PropertyResolver getParentPropertyResolver() {
            return null;
        }

        @Override
        public String toString() {
            return "SYSPROPS";
        }
    };

    private SyspropsMapWrapper() {
        super();
    }

    @Override
    public void clear() {
        throw new UnsupportedOperationException("sysprops#clear() N/A");
    }

    @Override
    public boolean containsKey(Object key) {
        return get(key) != null;
    }

    @Override
    public boolean containsValue(Object value) {
        // not the most efficient implementation, but we do not expect it to be called much
        Properties props = System.getProperties();
        for (String key : props.stringPropertyNames()) {
            if (!isMappedSyspropKey(key)) {
                continue;
            }

            Object v = props.getProperty(key);
            if (Objects.equals(v, value)) {
                return true;
            }
        }

        return false;
    }

    @Override
    public Set> entrySet() {
        Properties props = System.getProperties();
        // return a copy in order to avoid concurrent modifications
        Set> entries = new TreeSet<>(MapEntryUtils.byKeyEntryComparator());
        for (String key : props.stringPropertyNames()) {
            if (!isMappedSyspropKey(key)) {
                continue;
            }

            Object v = props.getProperty(key);
            if (v != null) {
                String unmappedKey = getUnmappedSyspropKey(key);
                entries.add(new SimpleImmutableEntry<>(unmappedKey, v));
            }
        }

        return entries;
    }

    @Override
    public Object get(Object key) {
        String propName = getMappedSyspropKey(key);
        return (key instanceof String) ? System.getProperty(propName) : null;
    }

    @Override
    public boolean isEmpty() {
        return GenericUtils.isEmpty(keySet());
    }

    @Override
    public Set keySet() {
        return System.getProperties()
                .stringPropertyNames()
                .stream()
                // filter out any non-SSHD properties
                .filter(SyspropsMapWrapper::isMappedSyspropKey)
                .map(SyspropsMapWrapper::getUnmappedSyspropKey)
                .collect(Collectors.toSet());
    }

    @Override
    public Object put(String key, Object value) {
        throw new UnsupportedOperationException("sysprops#put(" + key + ")[" + value + "] N/A");
    }

    @Override
    public void putAll(Map m) {
        throw new UnsupportedOperationException("sysprops#putAll(" + m + ") N/A");
    }

    @Override
    public Object remove(Object key) {
        throw new UnsupportedOperationException("sysprops#remove(" + key + ") N/A");
    }

    @Override
    public int size() {
        return GenericUtils.size(keySet());
    }

    @Override
    public Collection