/*
 * 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.catalina.filters;

import java.io.IOException;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;

import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletResponse;

import org.apache.catalina.util.NetMask;
import org.apache.juli.logging.Log;
import org.apache.juli.logging.LogFactory;

public final class RemoteCIDRFilter extends FilterBase {

    /**
     * text/plain MIME type: this is the MIME type we return when a
     * {@link ServletResponse} is not an {@link HttpServletResponse}
     */
    private static final String PLAIN_TEXT_MIME_TYPE = "text/plain";

    /**
     * Our logger
     */
    private final Log log = LogFactory.getLog(RemoteCIDRFilter.class); // must not be static

    /**
     * The list of allowed {@link NetMask}s
     */
    private final List<NetMask> allow = new ArrayList<>();

    /**
     * The list of denied {@link NetMask}s
     */
    private final List<NetMask> deny = new ArrayList<>();


    /**
     * Return a string representation of the {@link NetMask} list in #allow.
     *
     * @return the #allow list as a string, without the leading '[' and trailing
     *         ']'
     */
    public String getAllow() {
        return allow.toString().replace("[", "").replace("]", "");
    }


    /**
     * Fill the #allow list with the list of netmasks provided as an argument,
     * if any. Calls #fillFromInput.
     *
     * @param input The list of netmasks, as a comma separated string
     * @throws IllegalArgumentException One or more netmasks are invalid
     */
    public void setAllow(final String input) {
        final List<String> messages = fillFromInput(input, allow);

        if (messages.isEmpty()) {
            return;
        }

        for (final String message : messages) {
            log.error(message);
        }

        throw new IllegalArgumentException(sm.getString("remoteCidrFilter.invalid", "allow"));
    }


    /**
     * Return a string representation of the {@link NetMask} list in #deny.
     *
     * @return the #deny list as string, without the leading '[' and trailing
     *         ']'
     */
    public String getDeny() {
        return deny.toString().replace("[", "").replace("]", "");
    }


    /**
     * Fill the #deny list with the list of netmasks provided as an argument, if
     * any. Calls #fillFromInput.
     *
     * @param input The list of netmasks, as a comma separated string
     * @throws IllegalArgumentException One or more netmasks are invalid
     */
    public void setDeny(final String input) {
        final List<String> messages = fillFromInput(input, deny);

        if (messages.isEmpty()) {
            return;
        }

        for (final String message : messages) {
            log.error(message);
        }

        throw new IllegalArgumentException(sm.getString("remoteCidrFilter.invalid", "deny"));
    }



    @Override
    protected boolean isConfigProblemFatal() {
        // Failure to configure a security related component should always be
        // fatal.
        return true;
    }


    @Override
    public void doFilter(final ServletRequest request, final ServletResponse response, final FilterChain chain)
            throws IOException, ServletException {

        if (isAllowed(request.getRemoteAddr())) {
            chain.doFilter(request, response);
            return;
        }

        if (!(response instanceof HttpServletResponse)) {
            sendErrorWhenNotHttp(response);
            return;
        }

        ((HttpServletResponse) response).sendError(HttpServletResponse.SC_FORBIDDEN);
    }


    @Override
    public Log getLogger() {
        return log;
    }


    /**
     * Test if a remote's IP address is allowed to proceed.
     *
     * @param property The remote's IP address, as a string
     * @return true if allowed
     */
    private boolean isAllowed(final String property) {
        final InetAddress addr;

        try {
            addr = InetAddress.getByName(property);
        } catch (UnknownHostException e) {
            // This should be in the 'could never happen' category but handle it
            // to be safe.
            log.error(sm.getString("remoteCidrFilter.noRemoteIp"), e);
            return false;
        }

        for (final NetMask nm : deny) {
            if (nm.matches(addr)) {
                return false;
            }
        }

        for (final NetMask nm : allow) {
            if (nm.matches(addr)) {
                return true;
            }
        }

        // Allow if deny is specified but allow isn't
        if (!deny.isEmpty() && allow.isEmpty()) {
            return true;
        }

        // Deny this request
        return false;
    }


    private void sendErrorWhenNotHttp(ServletResponse response) throws IOException {
        final PrintWriter writer = response.getWriter();
        response.setContentType(PLAIN_TEXT_MIME_TYPE);
        writer.write(sm.getString("http.403"));
        writer.flush();
    }


    /**
     * Fill a {@link NetMask} list from a string input containing a
     * comma-separated list of (hopefully valid) {@link NetMask}s.
     *
     * @param input The input string
     * @param target The list to fill
     * @return a string list of processing errors (empty when no errors)
     */
    private List<String> fillFromInput(final String input, final List<NetMask> target) {
        target.clear();
        if (input == null || input.isEmpty()) {
            return Collections.emptyList();
        }

        final List<String> messages = new LinkedList<>();
        NetMask nm;

        for (final String s : input.split("\\s*,\\s*")) {
            try {
                nm = new NetMask(s);
                target.add(nm);
            } catch (IllegalArgumentException e) {
                messages.add(s + ": " + e.getMessage());
            }
        }

        return Collections.unmodifiableList(messages);
    }
}
