/* This code is part of Freenet. It is distributed under the GNU General
 * Public License, version 2 (or at your option any later version). See
 * http://www.gnu.org/ for further details of the GPL. */
package freenet.support.io;

import java.io.BufferedInputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.RandomAccessFile;
import java.io.Serializable;

import freenet.client.async.ClientContext;
import freenet.support.api.Bucket;

/**
 * FIXME: implement a hash verifying version of this.
 */
public class ReadOnlyFileSliceBucket implements Bucket, Serializable {

    private static final long serialVersionUID = 1L;
    private final File file;
	private final long startAt;
	private final long length;

	/**
	 * zero arg c'tor for db4o on jamvm / serialization
	 */
	@SuppressWarnings("unused")
	private ReadOnlyFileSliceBucket() {
		startAt = 0;
		length = 0;
		file = null;
	}

	public ReadOnlyFileSliceBucket(File f, long startAt, long length) {
		this.file = new File(f.getPath()); // copy so we can delete it
		this.startAt = startAt;
		this.length = length;
	}

    @Override
	public OutputStream getOutputStream() throws IOException {
		throw new IOException("Bucket is read-only");
	}

    @Override
    public OutputStream getOutputStreamUnbuffered() throws IOException {
        throw new IOException("Bucket is read-only");
    }

	@Override
	public InputStream getInputStream() throws IOException {
		return new BufferedInputStream(getInputStreamUnbuffered());
	}

    @Override
    public InputStream getInputStreamUnbuffered() throws IOException {
        return new MyInputStream();
    }

	@Override
	public String getName() {
		return "ROFS:" + file.getAbsolutePath() + ':' + startAt + ':' + length;
	}

	@Override
	public long size() {
		return length;
	}

	@Override
	public boolean isReadOnly() {
		return true;
	}

	@Override
	public void setReadOnly() {
	// Do nothing
	}

	private class MyInputStream extends InputStream {

		private RandomAccessFile f;
		private long ptr; // relative to startAt

		MyInputStream() throws IOException {
			try {
				this.f = new RandomAccessFile(file, "r");
				f.seek(startAt);
				if(f.length() < (startAt + length))
					throw new ReadOnlyFileSliceBucketException("File truncated? Length " + f.length() + " but start at " + startAt + " for " + length + " bytes");
				ptr = 0;
			} catch(FileNotFoundException e) {
				throw new ReadOnlyFileSliceBucketException(e);
			}
		}

		@Override
		public int read() throws IOException {
			if(ptr >= length)
				return -1;
			int x = f.read();
			if(x != -1)
				ptr++;
			return x;
		}

		@Override
		public int read(byte[] buf, int offset, int len) throws IOException {
			if(ptr >= length)
				return -1;
			len = (int) Math.min(len, length - ptr);
			int x = f.read(buf, offset, len);
			ptr += x;
			return x;
		}

		@Override
		public int read(byte[] buf) throws IOException {
			return read(buf, 0, buf.length);
		}

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

	public static class ReadOnlyFileSliceBucketException extends IOException {

		private static final long serialVersionUID = -1;

		public ReadOnlyFileSliceBucketException(FileNotFoundException e) {
			super("File not found: " + e.getMessage());
			initCause(e);
		}

		public ReadOnlyFileSliceBucketException(String string) {
			super(string);
		}
	}

	@Override
	public void free() {
	}

	@Override
	public Bucket createShadow() {
		String fnam = file.getPath();
		File newFile = new File(fnam);
		return new ReadOnlyFileSliceBucket(newFile, startAt, length);
	}

    @Override
    public void onResume(ClientContext context) {
        // Do nothing.
    }
    
    static final int MAGIC = 0x99e54c4;
    static final int VERSION = 1;

    @Override
    public void storeTo(DataOutputStream dos) throws IOException {
        dos.writeInt(MAGIC);
        dos.writeInt(VERSION);
        dos.writeUTF(file.toString());
        dos.writeLong(startAt);
        dos.writeLong(length);
    }

    protected ReadOnlyFileSliceBucket(DataInputStream dis) throws StorageFormatException, IOException {
        int version = dis.readInt();
        if(version != VERSION) throw new StorageFormatException("Bad version");
        file = new File(dis.readUTF());
        startAt = dis.readLong();
        if(startAt < 0) throw new StorageFormatException("Bad start at");
        length = dis.readLong();
        if(length < 0) throw new StorageFormatException("Bad length");
        if(!file.exists()) throw new StorageFormatException("File does not exist any more");
        if(file.length() < startAt+length) throw new StorageFormatException("Slice does not fit in file");
    }

}
