CC-Tweaked/projects/core/src/main/java/dan200/computercraft/core/filesystem/FileMount.java

/*
 * This file is part of ComputerCraft - http://www.computercraft.info
 * Copyright Daniel Ratcliffe, 2011-2022. Do not distribute without permission.
 * Send enquiries to dratcliffe@gmail.com
 */
package dan200.computercraft.core.filesystem;

import com.google.common.collect.Sets;
import dan200.computercraft.api.filesystem.FileOperationException;
import dan200.computercraft.api.filesystem.WritableMount;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.File;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.ClosedChannelException;
import java.nio.channels.NonReadableChannelException;
import java.nio.channels.SeekableByteChannel;
import java.nio.channels.WritableByteChannel;
import java.nio.file.*;
import java.nio.file.attribute.BasicFileAttributes;
import java.util.Collections;
import java.util.List;
import java.util.Set;

public class FileMount implements WritableMount {
    private static final Logger LOG = LoggerFactory.getLogger(FileMount.class);
    private static final long MINIMUM_FILE_SIZE = 500;
    private static final Set<OpenOption> READ_OPTIONS = Collections.singleton(StandardOpenOption.READ);
    private static final Set<OpenOption> WRITE_OPTIONS = Sets.newHashSet(StandardOpenOption.WRITE, StandardOpenOption.CREATE, StandardOpenOption.TRUNCATE_EXISTING);
    private static final Set<OpenOption> APPEND_OPTIONS = Sets.newHashSet(StandardOpenOption.WRITE, StandardOpenOption.CREATE, StandardOpenOption.APPEND);

    private class WritableCountingChannel implements WritableByteChannel {

        private final WritableByteChannel inner;
        long ignoredBytesLeft;

        WritableCountingChannel(WritableByteChannel inner, long bytesToIgnore) {
            this.inner = inner;
            ignoredBytesLeft = bytesToIgnore;
        }

        @Override
        public int write(ByteBuffer b) throws IOException {
            count(b.remaining());
            return inner.write(b);
        }

        void count(long n) throws IOException {
            ignoredBytesLeft -= n;
            if (ignoredBytesLeft < 0) {
                var newBytes = -ignoredBytesLeft;
                ignoredBytesLeft = 0;

                var bytesLeft = capacity - usedSpace;
                if (newBytes > bytesLeft) throw new IOException("Out of space");
                usedSpace += newBytes;
            }
        }

        @Override
        public boolean isOpen() {
            return inner.isOpen();
        }

        @Override
        public void close() throws IOException {
            inner.close();
        }
    }

    private class SeekableCountingChannel extends WritableCountingChannel implements SeekableByteChannel {
        private final SeekableByteChannel inner;

        SeekableCountingChannel(SeekableByteChannel inner, long bytesToIgnore) {
            super(inner, bytesToIgnore);
            this.inner = inner;
        }

        @Override
        public SeekableByteChannel position(long newPosition) throws IOException {
            if (!isOpen()) throw new ClosedChannelException();
            if (newPosition < 0) {
                throw new IllegalArgumentException("Cannot seek before the beginning of the stream");
            }

            var delta = newPosition - inner.position();
            if (delta < 0) {
                ignoredBytesLeft -= delta;
            } else {
                count(delta);
            }

            return inner.position(newPosition);
        }

        @Override
        public SeekableByteChannel truncate(long size) throws IOException {
            throw new IOException("Not yet implemented");
        }

        @Override
        public int read(ByteBuffer dst) throws ClosedChannelException {
            if (!inner.isOpen()) throw new ClosedChannelException();
            throw new NonReadableChannelException();
        }

        @Override
        public long position() throws IOException {
            return inner.position();
        }

        @Override
        public long size() throws IOException {
            return inner.size();
        }
    }

    private final File rootPath;
    private final long capacity;
    private long usedSpace;

    public FileMount(File rootPath, long capacity) {
        this.rootPath = rootPath;
        this.capacity = capacity + MINIMUM_FILE_SIZE;
        usedSpace = created() ? measureUsedSpace(this.rootPath) : MINIMUM_FILE_SIZE;
    }

    // IMount implementation

    @Override
    public boolean exists(String path) {
        if (!created()) return path.isEmpty();

        var file = getRealPath(path);
        return file.exists();
    }

    @Override
    public boolean isDirectory(String path) {
        if (!created()) return path.isEmpty();

        var file = getRealPath(path);
        return file.exists() && file.isDirectory();
    }

    @Override
    public boolean isReadOnly(String path) throws IOException {
        var file = getRealPath(path);
        while (true) {
            if (file.exists()) return !file.canWrite();
            if (file.equals(rootPath)) return false;
            file = file.getParentFile();
        }
    }

    @Override
    public void list(String path, List<String> contents) throws IOException {
        if (!created()) {
            if (!path.isEmpty()) throw new FileOperationException(path, "Not a directory");
            return;
        }

        var file = getRealPath(path);
        if (!file.exists() || !file.isDirectory()) throw new FileOperationException(path, "Not a directory");

        var paths = file.list();
        for (var subPath : paths) {
            if (new File(file, subPath).exists()) contents.add(subPath);
        }
    }

    @Override
    public long getSize(String path) throws IOException {
        if (!created()) {
            if (path.isEmpty()) return 0;
        } else {
            var file = getRealPath(path);
            if (file.exists()) return file.isDirectory() ? 0 : file.length();
        }

        throw new FileOperationException(path, "No such file");
    }

    @Override
    public SeekableByteChannel openForRead(String path) throws IOException {
        if (created()) {
            var file = getRealPath(path);
            if (file.exists() && !file.isDirectory()) return Files.newByteChannel(file.toPath(), READ_OPTIONS);
        }

        throw new FileOperationException(path, "No such file");
    }

    @Override
    public BasicFileAttributes getAttributes(String path) throws IOException {
        if (created()) {
            var file = getRealPath(path);
            if (file.exists()) return Files.readAttributes(file.toPath(), BasicFileAttributes.class);
        }

        throw new FileOperationException(path, "No such file");
    }

    // IWritableMount implementation

    @Override
    public void makeDirectory(String path) throws IOException {
        create();
        var file = getRealPath(path);
        if (file.exists()) {
            if (!file.isDirectory()) throw new FileOperationException(path, "File exists");
            return;
        }

        var dirsToCreate = 1;
        var parent = file.getParentFile();
        while (!parent.exists()) {
            ++dirsToCreate;
            parent = parent.getParentFile();
        }

        if (getRemainingSpace() < dirsToCreate * MINIMUM_FILE_SIZE) {
            throw new FileOperationException(path, "Out of space");
        }

        if (file.mkdirs()) {
            usedSpace += dirsToCreate * MINIMUM_FILE_SIZE;
        } else {
            throw new FileOperationException(path, "Access denied");
        }
    }

    @Override
    public void delete(String path) throws IOException {
        if (path.isEmpty()) throw new FileOperationException(path, "Access denied");

        if (created()) {
            var file = getRealPath(path);
            if (file.exists()) deleteRecursively(file);
        }
    }

    private void deleteRecursively(File file) throws IOException {
        // Empty directories first
        if (file.isDirectory()) {
            var children = file.list();
            for (var aChildren : children) {
                deleteRecursively(new File(file, aChildren));
            }
        }

        // Then delete
        var fileSize = file.isDirectory() ? 0 : file.length();
        var success = file.delete();
        if (success) {
            usedSpace -= Math.max(MINIMUM_FILE_SIZE, fileSize);
        } else {
            throw new IOException("Access denied");
        }
    }

    @Override
    public void rename(String source, String dest) throws IOException {
        var sourceFile = getRealPath(source);
        var destFile = getRealPath(dest);
        if (!sourceFile.exists()) throw new FileOperationException(source, "No such file");
        if (destFile.exists()) throw new FileOperationException(dest, "File exists");

        var sourcePath = sourceFile.toPath();
        var destPath = destFile.toPath();
        if (destPath.startsWith(sourcePath)) {
            throw new FileOperationException(source, "Cannot move a directory inside itself");
        }

        Files.move(sourcePath, destPath);
    }

    @Override
    public WritableByteChannel openForWrite(String path) throws IOException {
        create();
        var file = getRealPath(path);
        if (file.exists() && file.isDirectory()) throw new FileOperationException(path, "Cannot write to directory");

        if (file.exists()) {
            usedSpace -= Math.max(file.length(), MINIMUM_FILE_SIZE);
        } else if (getRemainingSpace() < MINIMUM_FILE_SIZE) {
            throw new FileOperationException(path, "Out of space");
        }
        usedSpace += MINIMUM_FILE_SIZE;

        return new SeekableCountingChannel(Files.newByteChannel(file.toPath(), WRITE_OPTIONS), MINIMUM_FILE_SIZE);
    }

    @Override
    public WritableByteChannel openForAppend(String path) throws IOException {
        if (!created()) {
            throw new FileOperationException(path, "No such file");
        }

        var file = getRealPath(path);
        if (!file.exists()) throw new FileOperationException(path, "No such file");
        if (file.isDirectory()) throw new FileOperationException(path, "Cannot write to directory");

        // Allowing seeking when appending is not recommended, so we use a separate channel.
        return new WritableCountingChannel(
            Files.newByteChannel(file.toPath(), APPEND_OPTIONS),
            Math.max(MINIMUM_FILE_SIZE - file.length(), 0)
        );
    }

    @Override
    public long getRemainingSpace() {
        return Math.max(capacity - usedSpace, 0);
    }

    @Override
    public long getCapacity() {
        return capacity - MINIMUM_FILE_SIZE;
    }

    private File getRealPath(String path) {
        return new File(rootPath, path);
    }

    private boolean created() {
        return rootPath.exists();
    }

    private void create() throws IOException {
        if (!rootPath.exists()) {
            var success = rootPath.mkdirs();
            if (!success) {
                throw new IOException("Access denied");
            }
        }
    }

    private static class Visitor extends SimpleFileVisitor<Path> {
        long size;

        @Override
        public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) {
            size += MINIMUM_FILE_SIZE;
            return FileVisitResult.CONTINUE;
        }

        @Override
        public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) {
            size += Math.max(attrs.size(), MINIMUM_FILE_SIZE);
            return FileVisitResult.CONTINUE;
        }

        @Override
        public FileVisitResult visitFileFailed(Path file, IOException exc) {
            LOG.error("Error computing file size for {}", file, exc);
            return FileVisitResult.CONTINUE;
        }
    }

    private static long measureUsedSpace(File file) {
        if (!file.exists()) return 0;

        try {
            var visitor = new Visitor();
            Files.walkFileTree(file.toPath(), visitor);
            return visitor.size;
        } catch (IOException e) {
            LOG.error("Error computing file size for {}", file, e);
            return 0;
        }
    }
}