// File: DataBlock.java
//
// Author: Andrew H. Fagg
// 11/15/2
//
// Represents the contents of a data block.  The
//  buffer[] component occupies the entire block.
//
// To Do: nothing
//



import java.util.*;
import java.lang.*;
import java.io.*;


class DataBlock extends Block {

    // Buffer of bytes that will be written to the first disk block
    public byte buffer[];

    // Allocate a new DataBlock

    public DataBlock(Disk dsk) {
	disk = dsk;
	buffer = new byte[disk.blockSize - 2];	// (vs)
    };

    // public void write(int block)
    //  Write this FreeBlock to disk block <block>
    //
    //  Effects:
    //  1.  Change the state of the specified block on the disk.
    //  2.  Leaves the write head at the end of the block
    //
    // Return = nothing
    //
    // Throws FileSystemException if:
    //  1.  There is an i/o error
    //   

    public void write(int block) throws FileSystemException {
	try{
	    // Move the write head to the correct location on the disk
	    disk.fp.seek(block * disk.blockSize);

	    disk.fp.writeShort(nextBlkPtr);	// (vs)
	    // Write out the data
	    disk.fp.write(buffer);
	}catch(IOException e){
	    // Translate the exception
	    throw new FileSystemException("DataBlock::write() error: " + e);
	};
    };

    
    // public void read(int block)
    //  Read disk block <block> into this DataBlock
    //
    // Effects:
    //   1. Changes the state of this DirectoryBlock to that stored
    //       on the disk
    //   2. Leaves the read head at the end of the block
    //   3. Remembers the originating block (stored in block_num)
    //
    // Throws FileSystemException if:
    //   1. There is an i/o error
    //
    

    public void read(int block) throws FileSystemException {
	try{
	    // Move the read head to the correct location on the disk
	    disk.fp.seek(block * disk.blockSize);

	    nextBlkPtr = disk.fp.readShort();	// (vs)
	    // Read in the buffer of bytes
	    disk.fp.read(buffer);

	    // Remember the original block number
	    block_num = block;
	}catch(IOException e){
	    // Translate exceptions
	    throw new FileSystemException("DataBlock::read() error: " + e);
	};
    };
};