// This example is from the book _Java in a Nutshell_ by David Flanagan.
// Written by David Flanagan.  Copyright (c) 1996 O'Reilly & Associates.
// You may study, use, modify, and distribute this example for any purpose.
// This example is provided WITHOUT WARRANTY either expressed or implied.

import java.io.*;

public class FileCopy {
    public static void copy(String source_name, String dest_name) 
        throws IOException
    {
        File source_file = new File(source_name);
        File destination_file = new File(dest_name);
        FileInputStream source = null;
        FileOutputStream destination = null;
        byte[] buffer;
        int bytes_read;
        
        try {
            // First make sure the specified source file 
            // exists, is a file, and is readable.
            if (!source_file.exists() || !source_file.isFile())
                throw new FileCopyException("FileCopy: no such source file: " +
                                source_name);
            if (!source_file.canRead())
                throw new FileCopyException("FileCopy: source file " + 
                                "is unreadable: " + source_name);
            
            // If the destination exists, make sure it is a writeable file
            // and ask before overwriting it.  If the destination doesn't
            // exist, make sure the directory exists and is writeable.
            if (destination_file.exists()) {
                if (destination_file.isFile()) {
                    DataInputStream in = new DataInputStream(System.in);
                    String response;
                    
                    if (!destination_file.canWrite())
                        throw new FileCopyException("FileCopy: destination " +
                                        "file is unwriteable: " + dest_name);
                    
                    System.out.print("File " + dest_name + 
                             " already exists.  Overwrite? (Y/N): ");
                    System.out.flush();
                    response = in.readLine();
                    if (!response.equals("Y") && !response.equals("y"))
                        throw new FileCopyException("FileCopy: copy cancelled.");
                }
                else
                    throw new FileCopyException("FileCopy: destination "
                                    + "is not a file: " +  dest_name);
            }
            else {
                File parentdir = parent(destination_file);
                if (!parentdir.exists())
                    throw new FileCopyException("FileCopy: destination "
                                    + "directory doesn't exist: " + dest_name);
                if (!parentdir.canWrite())
                    throw new FileCopyException("FileCopy: destination "
                                    + "directory is unwriteable: " + dest_name);
            }
            
            // If we've gotten this far, then everything is okay; we can
            // copy the file.
            source = new FileInputStream(source_file);
            destination = new FileOutputStream(destination_file);
            buffer = new byte[1024];
            while(true) {
                bytes_read = source.read(buffer);
                if (bytes_read == -1) break;
                destination.write(buffer, 0, bytes_read);
            }
        }
        // No matter what happens, always close any streams we've opened.
        finally {
            if (source != null) 
                try { source.close(); } catch (IOException e) { ; }
            if (destination != null) 
                try { destination.close(); } catch (IOException e) { ; }
        }
    }
    
    // File.getParent() can return null when the file is specified without
    // a directory or is in the root directory.  
    // This method handles those cases.
    private static File parent(File f) {
        String dirname = f.getParent();
        if (dirname == null) {
            if (f.isAbsolute()) return new File(File.separator);
            else return new File(System.getProperty("user.dir"));
        }
        return new File(dirname);
    }
    
    public static void main(String[] args) {
        if (args.length != 2)
            System.err.println("Usage: java FileCopy " + 
                       "<source file> <destination file>");
        else {
            try { copy(args[0], args[1]); }
            catch (IOException e) { System.err.println(e.getMessage()); }
        }
    }
}

class FileCopyException extends IOException { 
    public FileCopyException(String msg) { super(msg); }
}