/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0 and the Server Side Public License, v 1; you may not use this file except
 * in compliance with, at your election, the Elastic License 2.0 or the Server
 * Side Public License, v 1.
 */

package org.elasticsearch.common.blobstore.fs;

import org.elasticsearch.common.UUIDs;
import org.elasticsearch.common.blobstore.BlobContainer;
import org.elasticsearch.common.blobstore.BlobMetadata;
import org.elasticsearch.common.blobstore.BlobPath;
import org.elasticsearch.common.blobstore.DeleteResult;
import org.elasticsearch.common.blobstore.support.AbstractBlobContainer;
import org.elasticsearch.common.blobstore.support.PlainBlobMetadata;
import org.elasticsearch.common.bytes.BytesReference;
import org.elasticsearch.common.io.Streams;
import org.elasticsearch.core.internal.io.IOUtils;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.channels.Channels;
import java.nio.channels.SeekableByteChannel;
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.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.concurrent.atomic.AtomicLong;

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 {

    private static final String TEMP_FILE_PREFIX = "pending-";

    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, BlobContainer> children() throws IOException {
        Map<String, BlobContainer> builder = new HashMap<>();
        try (DirectoryStream<Path> stream = Files.newDirectoryStream(path)) {
            for (Path file : stream) {
                if (Files.isDirectory(file)) {
                    final String name = file.getFileName().toString();
                    builder.put(name, new FsBlobContainer(blobStore, path().add(name), file));
                }
            }
        }
        return unmodifiableMap(builder);
    }

    @Override
    public Map<String, BlobMetadata> listBlobsByPrefix(String blobNamePrefix) throws IOException {
        Map<String, BlobMetadata> builder = new HashMap<>();

        blobNamePrefix = blobNamePrefix == null ? "" : blobNamePrefix;
        try (DirectoryStream<Path> stream = newDirectoryStreamIfFound(blobNamePrefix)) {
            for (Path file : stream) {
                final BasicFileAttributes attrs;
                try {
                    attrs = Files.readAttributes(file, BasicFileAttributes.class);
                } catch (FileNotFoundException | NoSuchFileException e) {
                    // The file was concurrently deleted between listing files and trying to get its attributes so we skip it here
                    continue;
                }
                if (attrs.isRegularFile()) {
                    builder.put(file.getFileName().toString(), new PlainBlobMetadata(file.getFileName().toString(), attrs.size()));
                }
            }
        }
        return unmodifiableMap(builder);
    }

    private DirectoryStream<Path> newDirectoryStreamIfFound(String blobNamePrefix) throws IOException {
        try {
            return Files.newDirectoryStream(path, blobNamePrefix + "*");
        } catch (FileNotFoundException | NoSuchFileException e) {
            // a nonexistent directory contains no blobs
            return new DirectoryStream<Path>() {
                @Override
                public Iterator<Path> iterator() {
                    return new Iterator<Path>() {
                        @Override
                        public boolean hasNext() {
                            return false;
                        }

                        @Override
                        public Path next() {
                            return null;
                        }
                    };
                }

                @Override
                public void close() {
                }
            };
        }
    }

    @Override
    public DeleteResult delete() throws IOException {
        final AtomicLong filesDeleted = new AtomicLong(0L);
        final AtomicLong bytesDeleted = new AtomicLong(0L);
        Files.walkFileTree(path, new SimpleFileVisitor<Path>() {
            @Override
            public FileVisitResult postVisitDirectory(Path dir, IOException impossible) throws IOException {
                assert impossible == null;
                Files.delete(dir);
                return FileVisitResult.CONTINUE;
            }

            @Override
            public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
                Files.delete(file);
                filesDeleted.incrementAndGet();
                bytesDeleted.addAndGet(attrs.size());
                return FileVisitResult.CONTINUE;
            }
        });
        return new DeleteResult(filesDeleted.get(), bytesDeleted.get());
    }

    @Override
    public void deleteBlobsIgnoringIfNotExists(List<String> blobNames) throws IOException {
        IOUtils.rm(blobNames.stream().map(path::resolve).toArray(Path[]::new));
    }

    @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 Files.newInputStream(resolvedPath);
        } catch (FileNotFoundException fnfe) {
            throw new NoSuchFileException("[" + name + "] blob not found");
        }
    }

    @Override
    public InputStream readBlob(String blobName, long position, long length) throws IOException {
        final SeekableByteChannel channel = Files.newByteChannel(path.resolve(blobName));
        if (position > 0L) {
            channel.position(position);
        }
        assert channel.position() == position;
        return Streams.limitStream(Channels.newInputStream(channel), length);
    }

    @Override
    public long readBlobPreferredLength() {
        // This container returns streams that are cheap to close early, so we can tell consumers to request as much data as possible.
        return Long.MAX_VALUE;
    }

    @Override
    public void writeBlob(String blobName, InputStream inputStream, long blobSize, boolean failIfAlreadyExists) throws IOException {
        final Path file = path.resolve(blobName);
        try {
            writeToPath(inputStream, file, blobSize);
        } catch (FileAlreadyExistsException faee) {
            if (failIfAlreadyExists) {
                throw faee;
            }
            deleteBlobsIgnoringIfNotExists(Collections.singletonList(blobName));
            writeToPath(inputStream, file, blobSize);
        }
        IOUtils.fsync(path, true);
    }

    @Override
    public void writeBlob(String blobName, BytesReference bytes, boolean failIfAlreadyExists) throws IOException {
        final Path file = path.resolve(blobName);
        try {
            writeToPath(bytes, file);
        } catch (FileAlreadyExistsException faee) {
            if (failIfAlreadyExists) {
                throw faee;
            }
            deleteBlobsIgnoringIfNotExists(Collections.singletonList(blobName));
            writeToPath(bytes, file);
        }
        IOUtils.fsync(path, true);
    }

    @Override
    public void writeBlobAtomic(final String blobName, BytesReference bytes, boolean failIfAlreadyExists) throws IOException {
        final String tempBlob = tempBlobName(blobName);
        final Path tempBlobPath = path.resolve(tempBlob);
        try {
            writeToPath(bytes, tempBlobPath);
            moveBlobAtomic(tempBlob, blobName, failIfAlreadyExists);
        } catch (IOException ex) {
            try {
                deleteBlobsIgnoringIfNotExists(Collections.singletonList(tempBlob));
            } catch (IOException e) {
                ex.addSuppressed(e);
            }
            throw ex;
        } finally {
            IOUtils.fsync(path, true);
        }
    }

    private void writeToPath(BytesReference bytes, Path tempBlobPath) throws IOException {
        try (OutputStream outputStream = Files.newOutputStream(tempBlobPath, StandardOpenOption.CREATE_NEW)) {
            bytes.writeTo(outputStream);
        }
        IOUtils.fsync(tempBlobPath, false);
    }

    private void writeToPath(InputStream inputStream, Path tempBlobPath, long blobSize) throws IOException {
        try (OutputStream outputStream = Files.newOutputStream(tempBlobPath, StandardOpenOption.CREATE_NEW)) {
            final int bufferSize = blobStore.bufferSizeInBytes();
            org.elasticsearch.core.internal.io.Streams.copy(
                    inputStream, outputStream, new byte[blobSize < bufferSize ? Math.toIntExact(blobSize) : bufferSize]);
        }
        IOUtils.fsync(tempBlobPath, false);
    }

    public void moveBlobAtomic(final String sourceBlobName, final String targetBlobName, final boolean failIfAlreadyExists)
        throws IOException {
        final Path sourceBlobPath = path.resolve(sourceBlobName);
        final Path targetBlobPath = path.resolve(targetBlobName);
        // 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.
        if (Files.exists(targetBlobPath)) {
            if (failIfAlreadyExists) {
                throw new FileAlreadyExistsException("blob [" + targetBlobPath + "] already exists, cannot overwrite");
            } else {
                deleteBlobsIgnoringIfNotExists(Collections.singletonList(targetBlobName));
            }
        }
        Files.move(sourceBlobPath, targetBlobPath, StandardCopyOption.ATOMIC_MOVE);
    }

    public static String tempBlobName(final String blobName) {
        return "pending-" + blobName + "-" + UUIDs.randomBase64UUID();
    }

    /**
     * Returns true if the blob is a leftover temporary blob.
     *
     * The temporary blobs might be left after failed atomic write operation.
     */
    public static boolean isTempBlobName(final String blobName) {
        return blobName.startsWith(TEMP_FILE_PREFIX);
    }
}
