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/*
 * Licensed to the University Corporation for Advanced Internet Development, 
 * Inc. (UCAID) under one or more contributor license agreements.  See the 
 * NOTICE file distributed with this work for additional information regarding
 * copyright ownership. The UCAID 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.opensaml.saml.metadata.resolver.impl;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Timer;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;

import net.shibboleth.utilities.java.support.component.ComponentInitializationException;
import net.shibboleth.utilities.java.support.component.ComponentSupport;
import net.shibboleth.utilities.java.support.resolver.ResolverException;

import org.apache.http.client.HttpClient;
import org.opensaml.core.xml.XMLObject;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.w3c.dom.Document;

import com.google.common.io.Files;

/**
 * A URL metadata provider that caches a copy of the retrieved metadata to disk so that, in the event that the metadata
 * may not be pulled from the URL it may be pulled from disk using the last fetched data. If the backing file does not
 * already exist it will be created.
 * 
 * It is the responsibility of the caller to re-initialize, via {@link #initialize()}, if any properties of this
 * provider are changed.
 */
public class FileBackedHTTPMetadataResolver extends HTTPMetadataResolver {

    /** Class logger. */
    @Nonnull private final Logger log = LoggerFactory.getLogger(FileBackedHTTPMetadataResolver.class);

    /** File containing the backup of the metadata. */
    @Nullable private File metadataBackupFile;
    
    /**
     * Constructor.
     * 
     * @param client HTTP client used to fetch remote metadata
     * @param metadataURL the URL to fetch the metadata
     * @param backupFilePath the file that will keep a backup copy of the metadata,
     * 
     * @throws ResolverException thrown if the URL is not a valid URL, the metadata can not be retrieved from
     *             the URL
     */
    public FileBackedHTTPMetadataResolver(HttpClient client, String metadataURL, String backupFilePath) 
            throws ResolverException {
        this(null, client, metadataURL, backupFilePath);
    }

    /**
     * Constructor.
     * 
     * @param client HTTP client used to fetch remote metadata
     * @param backgroundTaskTimer timer used to schedule background metadata refresh tasks
     * @param metadataURL the URL to fetch the metadata
     * @param backupFilePath the file that will keep a backup copy of the metadata,
     * 
     * @throws ResolverException thrown if the URL is not a valid URL, the metadata can not be retrieved from
     *             the URL
     */
    public FileBackedHTTPMetadataResolver(Timer backgroundTaskTimer, HttpClient client, String metadataURL,
            String backupFilePath) throws ResolverException {
        super(backgroundTaskTimer, client, metadataURL);
        setBackupFile(backupFilePath);
    }
    
    /** {@inheritDoc} */
    protected void doDestroy() {
        metadataBackupFile = null;

        super.doDestroy();
    }

    /** {@inheritDoc} */
    protected void initMetadataResolver() throws ComponentInitializationException {
        try {
            validateBackupFile(metadataBackupFile);
        } catch (final ResolverException e) {
            if (isFailFastInitialization()) {
                log.error("Metadata backup file path was invalid, initialization is fatal");
                throw new ComponentInitializationException("Metadata backup file path was invalid", e);
            } else {
                log.error("Metadata backup file path was invalid, continuing without known good backup file");
            }
        }
        
        super.initMetadataResolver();
    }

    /**
     * Sets the file used to backup metadata. The given file path is checked to see if it is a read/writable file if it
     * exists or if can be created if it does not exist.
     * 
     * @param backupFilePath path to the backup file
     * 
     * @throws ResolverException thrown if the backup file is not read/writable or creatable
     */
    protected void setBackupFile(String backupFilePath) throws ResolverException {
        ComponentSupport.ifInitializedThrowUnmodifiabledComponentException(this);
        ComponentSupport.ifDestroyedThrowDestroyedComponentException(this);

        final File backingFile = new File(backupFilePath);
        metadataBackupFile = backingFile;
    }

    /**
     * Validate the basic properties of the specified metadata backup file, for example that it 
     * exists and/or can be created; that it is not a directory; and that it is readable and writable.
     *
     * @param backupFile the file to evaluate
     * @throws ResolverException if file does not pass basic properties required of a metadata backup file
     */
    protected void validateBackupFile(File backupFile) throws ResolverException {
        if (!backupFile.exists()) {
            try {
                backupFile.createNewFile();
            } catch (final IOException e) {
                final String msg = "Unable to create backing file " + backupFile.getAbsolutePath();
                log.error(msg, e);
                throw new ResolverException(msg, e);
            }
        }

        if (backupFile.isDirectory()) {
            throw new ResolverException("Filepath " + backupFile.getAbsolutePath()
                    + " is a directory and may not be used as a backing metadata file");
        }

        if (!backupFile.canRead()) {
            throw new ResolverException("Filepath " + backupFile.getAbsolutePath()
                    + " exists but can not be read by this user");
        }

        if (!backupFile.canWrite()) {
            throw new ResolverException("Filepath " + backupFile.getAbsolutePath()
                    + " exists but can not be written to by this user");
        }
    }

    /** {@inheritDoc} */
    protected byte[] fetchMetadata() throws ResolverException {
        try {
            return super.fetchMetadata();
        } catch (ResolverException e) {
            if (metadataBackupFile.exists()) {
                log.warn("Problem reading metadata from remote source, processing existing backup file: {}", 
                        metadataBackupFile.getAbsolutePath());
                try {
                    return Files.toByteArray(metadataBackupFile);
                } catch (final IOException ioe) {
                    final String errMsg = "Unable to retrieve metadata from backup file "
                            + metadataBackupFile.getAbsolutePath();
                    log.error(errMsg, ioe);
                    throw new ResolverException(errMsg, ioe);
                }
            } else {
                log.error("Unable to read metadata from remote server and backup does not exist");
                throw new ResolverException("Unable to read metadata from remote server and backup does not exist");
            }
        }
    }

    /** {@inheritDoc} */
    protected void postProcessMetadata(byte[] metadataBytes, Document metadataDom, XMLObject originalMetadata, 
            XMLObject filteredMetadata) throws ResolverException {
        try {
            validateBackupFile(metadataBackupFile);
            try (final FileOutputStream out = new FileOutputStream(metadataBackupFile)) {
                out.write(metadataBytes);
                out.flush();
            }
        } catch (final ResolverException e) {
            log.error("Unable to write metadata to backup file: {}", metadataBackupFile.getAbsoluteFile(), e);
        } catch (final IOException e) {
            log.error("Unable to write metadata to backup file: {}", metadataBackupFile.getAbsoluteFile(), e);
        } finally {
            super.postProcessMetadata(metadataBytes, metadataDom, originalMetadata, filteredMetadata);
        }
    }
}