/*
 * 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.blobstore.fs;

import org.apache.lucene.util.IOUtils;
import org.elasticsearch.common.blobstore.BlobMetaData;
import org.elasticsearch.common.blobstore.BlobPath;
import org.elasticsearch.common.blobstore.support.AbstractBlobContainer;
import org.elasticsearch.common.blobstore.support.PlainBlobMetaData;
import org.elasticsearch.common.io.Streams;

import java.io.BufferedInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.file.DirectoryStream;
import java.nio.file.FileAlreadyExistsException;
import java.nio.file.FileVisitResult;
import java.nio.file.Files;
import java.nio.file.NoSuchFileException;
import java.nio.file.Path;
import java.nio.file.SimpleFileVisitor;
import java.nio.file.StandardCopyOption;
import java.nio.file.StandardOpenOption;
import java.nio.file.attribute.BasicFileAttributes;
import java.util.HashMap;
import java.util.Map;

import static java.util.Collections.unmodifiableMap;

/**
 * A file system based implementation of {@link org.elasticsearch.common.blobstore.BlobContainer}.
 * All blobs in the container are stored on a file system, the location of which is specified by the {@link BlobPath}.
 *
 * Note that the methods in this implementation of {@link org.elasticsearch.common.blobstore.BlobContainer} may
 * additionally throw a {@link java.lang.SecurityException} if the configured {@link java.lang.SecurityManager}
 * does not permit read and/or write access to the underlying files.
 */
public class FsBlobContainer extends AbstractBlobContainer {

    protected final FsBlobStore blobStore;

    protected final Path path;

    public FsBlobContainer(FsBlobStore blobStore, BlobPath blobPath, Path path) {
        super(blobPath);
        this.blobStore = blobStore;
        this.path = path;
    }

    @Override
    public Map<String, BlobMetaData> listBlobs() throws IOException {
        return listBlobsByPrefix(null);
    }

    @Override
    public Map<String, BlobMetaData> listBlobsByPrefix(String blobNamePrefix) throws IOException {
        // If we get duplicate files we should just take the last entry
        Map<String, BlobMetaData> builder = new HashMap<>();

        blobNamePrefix = blobNamePrefix == null ? "" : blobNamePrefix;
        try (DirectoryStream<Path> stream = Files.newDirectoryStream(path, blobNamePrefix + "*")) {
            for (Path file : stream) {
                final BasicFileAttributes attrs = Files.readAttributes(file, BasicFileAttributes.class);
                if (attrs.isRegularFile()) {
                    builder.put(file.getFileName().toString(), new PlainBlobMetaData(file.getFileName().toString(), attrs.size()));
                }
            }
        }
        return unmodifiableMap(builder);
    }

    @Override
    public void deleteBlob(String blobName) throws IOException {
        Path blobPath = path.resolve(blobName);
        if (Files.isDirectory(blobPath)) {
            // delete directory recursively as long as it is empty (only contains empty directories),
            // which is the reason we aren't deleting any files, only the directories on the post-visit
            Files.walkFileTree(blobPath, new SimpleFileVisitor<Path>() {
                @Override
                public FileVisitResult postVisitDirectory(Path dir, IOException exc) throws IOException {
                    Files.delete(dir);
                    return FileVisitResult.CONTINUE;
                }
            });
        } else {
            Files.delete(blobPath);
        }
    }

    @Override
    public boolean blobExists(String blobName) {
        return Files.exists(path.resolve(blobName));
    }

    @Override
    public InputStream readBlob(String name) throws IOException {
        final Path resolvedPath = path.resolve(name);
        try {
            return new BufferedInputStream(Files.newInputStream(resolvedPath), blobStore.bufferSizeInBytes());
        } catch (FileNotFoundException fnfe) {
            throw new NoSuchFileException("[" + name + "] blob not found");
        }
    }

    @Override
    public void writeBlob(String blobName, InputStream inputStream, long blobSize) throws IOException {
        if (blobExists(blobName)) {
            throw new FileAlreadyExistsException("blob [" + blobName + "] already exists, cannot overwrite");
        }
        final Path file = path.resolve(blobName);
        try (OutputStream outputStream = Files.newOutputStream(file, StandardOpenOption.CREATE_NEW)) {
            Streams.copy(inputStream, outputStream, new byte[blobStore.bufferSizeInBytes()]);
        }
        IOUtils.fsync(file, false);
        IOUtils.fsync(path, true);
    }

    @Override
    public void move(String source, String target) throws IOException {
        Path sourcePath = path.resolve(source);
        Path targetPath = path.resolve(target);
        // If the target file exists then Files.move() behaviour is implementation specific
        // the existing file might be replaced or this method fails by throwing an IOException.
        assert !Files.exists(targetPath);
        Files.move(sourcePath, targetPath, StandardCopyOption.ATOMIC_MOVE);
        IOUtils.fsync(path, true);
    }
}
