Sample.java

import java.io.File;

public class Sample extends Utility {

    public Sample(Editor e) {
        super(e);
        set_username_password();
    }

    @Override
    public void create(String file_name, String user_name, String password) throws Exception {
        dir = new File(file_name);

        dir.mkdirs();
        File meta = new File(dir, "0");
        String toWrite = "";
        toWrite = "0\n";  //length of the file
        toWrite += user_name;   //add username

        //padding
        while (toWrite.length() < Config.BLOCK_SIZE) {
            toWrite += '\0';
        }

        save_to_file(toWrite.getBytes(), meta);
        return;
    }

    @Override
    public String findUser(String file_name) throws Exception {
        File file = new File(file_name);
        File meta = new File(file, "0");
        String s = byteArray2String(read_from_file(meta));
        String[] strs = s.split("\n");
        return strs[1];
    }

    @Override
    public int length(String file_name, String password) throws Exception {
        File file = new File(file_name);
        File meta = new File(file, "0");
        String s = byteArray2String(read_from_file(meta));
        String[] strs = s.split("\n");
        return Integer.parseInt(strs[0]);
    }

    @Override
    public byte[] read(String file_name, int starting_position, int len, String password) throws Exception {
        File root = new File(file_name);
        int file_length = length(file_name, password);
        if (starting_position + len > file_length) {
            throw new Exception();
        }

        int start_block = starting_position / Config.BLOCK_SIZE;

        int end_block = (starting_position + len) / Config.BLOCK_SIZE;

        String toReturn = "";

        for (int i = start_block + 1; i <= end_block + 1; i++) {
            String temp = byteArray2String(read_from_file(new File(root, Integer.toString(i))));
            if (i == end_block + 1) {
                temp = temp.substring(0, starting_position + len - end_block * Config.BLOCK_SIZE);
            }
            if (i == start_block + 1) {
                temp = temp.substring(starting_position - start_block * Config.BLOCK_SIZE);
            }
            toReturn += temp;
        }

        return toReturn.getBytes("UTF-8");

    }

    @Override
    public void write(String file_name, int starting_position, byte[] content, String password) throws Exception {
        String str_content = byteArray2String(content);
        File root = new File(file_name);
        int file_length = length(file_name, password);

        if (starting_position > file_length) {
            throw new Exception();
        }


        int len = str_content.length();
        int start_block = starting_position / Config.BLOCK_SIZE;
        int end_block = (starting_position + len) / Config.BLOCK_SIZE;
        for (int i = start_block + 1; i <= end_block + 1; i++) {
            int sp = (i - 1) * Config.BLOCK_SIZE - starting_position;
            int ep = (i) * Config.BLOCK_SIZE - starting_position;
            String prefix = "";
            String postfix = "";
            if (i == start_block + 1 && starting_position != start_block * Config.BLOCK_SIZE) {

                prefix = byteArray2String(read_from_file(new File(root, Integer.toString(i))));
                prefix = prefix.substring(0, starting_position - start_block * Config.BLOCK_SIZE);
                sp = Math.max(sp, 0);
            }

            if (i == end_block + 1) {
                File end = new File(root, Integer.toString(i));
                if (end.exists()) {

                    postfix = byteArray2String(read_from_file(new File(root, Integer.toString(i))));

                    if (postfix.length() > starting_position + len - end_block * Config.BLOCK_SIZE) {
                        postfix = postfix.substring(starting_position + len - end_block * Config.BLOCK_SIZE);
                    } else {
                        postfix = "";
                    }
                }
                ep = Math.min(ep, len);
            }

            String toWrite = prefix + str_content.substring(sp, ep) + postfix;

            while (toWrite.length() < Config.BLOCK_SIZE) {
                toWrite += '\0';
            }

            save_to_file(toWrite.getBytes(), new File(root, Integer.toString(i)));
        }


        //update meta data

        if (content.length + starting_position > length(file_name, password)) {
            String s = byteArray2String(read_from_file(new File(root, "0")));
            String[] strs = s.split("\n");
            strs[0] = Integer.toString(content.length + starting_position);
            String toWrite = "";
            for (String t : strs) {
                toWrite += t + "\n";
            }
            while (toWrite.length() < Config.BLOCK_SIZE) {
                toWrite += '\0';
            }
            save_to_file(toWrite.getBytes(), new File(root, "0"));

        }

    }

    @Override
    public boolean check_integrity(String file_name, String password) {
        return false;
    }

    @Override
    public void cut(String file_name, int len, String password) throws Exception {

        File root = new File(file_name);
        int file_length = length(file_name, password);

        if (len > file_length) {
            throw new Exception();
        }
        int end_block = (len) / Config.BLOCK_SIZE;

        File file = new File(root, Integer.toString(end_block + 1));
        String str = byteArray2String(read_from_file(file));
        str = str.substring(0, len - end_block * Config.BLOCK_SIZE);
        while (str.length() < Config.BLOCK_SIZE) {
            str += '\0';
        }

        save_to_file(str.getBytes(), file);

        int cur = end_block + 2;
        file = new File(root, Integer.toString(cur));
        while (file.exists()) {
            file.delete();
            cur++;
        }

        //update meta data
        String s = byteArray2String(read_from_file(new File(root, "0")));
        String[] strs = s.split("\n");
        strs[0] = Integer.toString(len);
        String toWrite = "";
        for (String t : strs) {
            toWrite += t + "\n";
        }
        while (toWrite.length() < Config.BLOCK_SIZE) {
            toWrite += '\0';
        }
        save_to_file(toWrite.getBytes(), new File(root, "0"));
    }
}