/*
 * 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.config.keys.loader;

import java.io.IOException;
import java.io.StreamCorruptedException;
import java.security.GeneralSecurityException;
import java.security.KeyPair;
import java.util.AbstractMap.SimpleImmutableEntry;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;

import org.apache.sshd.common.NamedResource;
import org.apache.sshd.common.config.keys.FilePasswordProvider;
import org.apache.sshd.common.session.SessionContext;
import org.apache.sshd.common.util.GenericUtils;
import org.apache.sshd.common.util.ValidateUtils;

/**
 * @author <a href="mailto:dev@mina.apache.org">Apache MINA SSHD Project</a>
 */
public abstract class AbstractKeyPairResourceParser implements KeyPairResourceParser {

    private final List<String> beginners;
    private final List<String> enders;
    private final List<List<String>> endingMarkers;

    /**
     * @param beginners The markers that indicate the beginning of a parsing block
     * @param enders    The <U>matching</U> (by position) markers that indicate the end of a parsing block
     */
    protected AbstractKeyPairResourceParser(List<String> beginners, List<String> enders) {
        this.beginners = ValidateUtils.checkNotNullAndNotEmpty(beginners, "No begin markers");
        this.enders = ValidateUtils.checkNotNullAndNotEmpty(enders, "No end markers");
        ValidateUtils.checkTrue(
                beginners.size() == enders.size(),
                "Mismatched begin(%d)/end(%d) markers sizes",
                beginners.size(), enders.size());
        endingMarkers = new ArrayList<>(enders.size());
        enders.forEach(m -> endingMarkers.add(Collections.singletonList(m)));
    }

    public List<String> getBeginners() {
        return beginners;
    }

    public List<String> getEnders() {
        return enders;
    }

    /**
     * @return A {@link List} of same size as the ending markers, where each ending marker is encapsulated inside a
     *         singleton list and resides as the <U>same index</U> as the marker it encapsulates
     */
    public List<List<String>> getEndingMarkers() {
        return endingMarkers;
    }

    @Override
    public boolean canExtractKeyPairs(NamedResource resourceKey, List<String> lines)
            throws IOException, GeneralSecurityException {
        return KeyPairResourceParser.containsMarkerLine(lines, getBeginners());
    }

    @Override
    public Collection<KeyPair> loadKeyPairs(SessionContext session,
                                            NamedResource resourceKey,
                                            FilePasswordProvider passwordProvider,
                                            List<String> lines)
            throws IOException, GeneralSecurityException {
        Collection<KeyPair> keyPairs = new LinkedList<>();
        List<String> beginMarkers = getBeginners();
        List<List<String>> endMarkers = getEndingMarkers();
        for (Map.Entry<Integer, Integer> markerPos = KeyPairResourceParser.findMarkerLine(lines, beginMarkers);
             markerPos != null;) {
            int startIndex = markerPos.getKey();
            String startLine = lines.get(startIndex);
            startIndex++;
            int markerIndex = markerPos.getValue();
            List<String> ender = endMarkers.get(markerIndex);
            markerPos = KeyPairResourceParser.findMarkerLine(lines, startIndex, ender);
            if (markerPos == null) {
                throw new StreamCorruptedException("Missing end marker (" + ender + ") after line #" + startIndex);
            }
            int endIndex = markerPos.getKey();
            String endLine = lines.get(endIndex);
            Map.Entry<? extends Map<String, String>, ? extends List<String>> result = separateDataLinesFromHeaders(
                    session, resourceKey, startLine, endLine, lines.subList(startIndex, endIndex));
            Map<String, String> headers = result.getKey();
            List<String> dataLines = result.getValue();
            Collection<KeyPair> kps = extractKeyPairs(session, resourceKey, startLine, endLine, passwordProvider,
                    (dataLines == null) ? Collections.emptyList() : dataLines,
                    (headers == null) ? Collections.emptyMap() : headers);
            if (GenericUtils.isNotEmpty(kps)) {
                if (GenericUtils.isEmpty(keyPairs)) {
                    keyPairs = new LinkedList<>(kps);
                } else {
                    keyPairs.addAll(kps);
                }
            }
            markerPos = KeyPairResourceParser.findMarkerLine(lines, endIndex + 1, beginMarkers);
        }
        return keyPairs;
    }

    protected Map.Entry<Map<String, String>, List<String>> separateDataLinesFromHeaders(
            SessionContext session, NamedResource resourceKey, String startLine, String endLine, List<String> dataLines)
            throws IOException, GeneralSecurityException {
        return new SimpleImmutableEntry<>(Collections.emptyMap(), dataLines);
    }

    /**
     * Extracts the key pairs within a <U>single</U> delimited by markers block of lines. By default cleans up the empty
     * lines, joins them and converts them from BASE64
     *
     * @param  session                  The {@link SessionContext} for invoking this load command - may be {@code null}
     *                                  if not invoked within a session context (e.g., offline tool or session unknown).
     * @param  resourceKey              A hint as to the origin of the text lines
     * @param  beginMarker              The line containing the begin marker
     * @param  endMarker                The line containing the end marker
     * @param  passwordProvider         The {@link FilePasswordProvider} to use in case the data is encrypted - may be
     *                                  {@code null} if no encrypted
     * @param  lines                    The block of lines between the markers
     * @param  headers                  Any headers that may have been available when data was read
     * @return                          The extracted {@link KeyPair}s - may be {@code null}/empty if none.
     * @throws IOException              If failed to parse the data
     * @throws GeneralSecurityException If failed to generate the keys
     */
    public Collection<KeyPair> extractKeyPairs(SessionContext session,
                                               NamedResource resourceKey,
                                               String beginMarker,
                                               String endMarker,
                                               FilePasswordProvider passwordProvider,
                                               List<String> lines,
                                               Map<String, String> headers)
            throws IOException, GeneralSecurityException {
        byte[] dataBytes = KeyPairResourceParser.extractDataBytes(lines);
        try {
            return extractKeyPairs(session, resourceKey, beginMarker, endMarker, passwordProvider, dataBytes, headers);
        } finally {
            Arrays.fill(dataBytes, (byte) 0); // clean up sensitive data a.s.a.p.
        }
    }

    /**
     * @param  session                  The {@link SessionContext} for invoking this load command - may be {@code null}
     *                                  if not invoked within a session context (e.g., offline tool or session unknown).
     * @param  resourceKey              A hint as to the origin of the text lines
     * @param  beginMarker              The line containing the begin marker
     * @param  endMarker                The line containing the end marker
     * @param  passwordProvider         The {@link FilePasswordProvider} to use in case the data is encrypted - may be
     *                                  {@code null} if no encrypted
     * @param  bytes                    The bytes from the lines containing the data
     * @param  headers                  Any headers that may have been available when data was read
     * @return                          The extracted {@link KeyPair}s - may be {@code null}/empty if none.
     * @throws IOException              If failed to parse the data
     * @throws GeneralSecurityException If failed to generate the keys
     */
    public abstract Collection<KeyPair> extractKeyPairs(SessionContext session,
                                               NamedResource resourceKey,
                                               String beginMarker,
                                               String endMarker,
                                               FilePasswordProvider passwordProvider,
                                               byte[] bytes,
                                               Map<String, String> headers)
            throws IOException, GeneralSecurityException;
}
