Git.java

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.zip.DeflaterOutputStream;

public class Git {
    File gitDirectory = new File ("git");
    File objectsDirectory = new File ("git/objects");
    String indexFileName = "index";
    File indexFile = new File (gitDirectory, indexFileName);
    boolean toZip;

    public Git (boolean toZip) throws IOException {
        this.toZip = toZip;
        if (!gitDirectory.exists()) {
            gitDirectory.mkdir();
            objectsDirectory.mkdirs();
            indexFile.createNewFile();
        }
        else if (objectsDirectory.exists() && !indexFile.exists()){
            indexFile.createNewFile();
        }
        else if (indexFile.exists() && !objectsDirectory.exists()) {
            objectsDirectory.mkdirs();
        }
        else if (!indexFile.exists() && !objectsDirectory.exists()) {
            indexFile.createNewFile();
            objectsDirectory.mkdirs();
        }
        else {
            System.out.println("Git Repository already exists");
        }

    }

    public void compressData (String fileName) throws IOException {
        FileInputStream fis = new FileInputStream(fileName);
        FileOutputStream fos = new FileOutputStream("compressedFile.zip");
        DeflaterOutputStream dos = new DeflaterOutputStream(fos);
        int data; 
        while ((data=fis.read())!=-1) 
        { 
            dos.write(data); 
        } 
        fis.close(); 
        dos.close(); 
    }

    public String hashingFunction(String fileName) throws FileNotFoundException, NoSuchAlgorithmException, IOException {
        if (toZip) {
            compressData(fileName);
            fileName = "compressedFile.zip";
        }
        File file = new File(fileName);
        MessageDigest digest = MessageDigest.getInstance("SHA-1");

        try (FileInputStream fis = new FileInputStream(file)) {
            byte[] byteArray = new byte[1024];
            int bytesRead;
            while ((bytesRead = fis.read(byteArray)) != -1) {
                digest.update(byteArray, 0, bytesRead);
            }
        }
        
        byte[] hash = digest.digest();
        StringBuilder hexString = new StringBuilder();
        for (byte b : hash) {
            String hex = Integer.toHexString(0xff & b);
            if (hex.length() == 1) {
                hexString.append('0');
            }
            hexString.append(hex);
        }
        return hexString.toString();
    }

    public void fileWriter (String toRead, File toWrite) throws IOException {
        BufferedWriter bw = new BufferedWriter (new FileWriter (toWrite));
        BufferedReader br = new BufferedReader(new FileReader(toRead));
        while (br.ready()) {
            bw.append((char) br.read());
        }
        br.close();
        bw.close(); 
    }

    public void makeBLOB(String fileName) throws IOException, NoSuchAlgorithmException {
        String hash = hashingFunction(fileName);
        File file = new File("git/objects", hash);
        file.createNewFile();
        fileWriter(fileName, file);
        String toAppend = hash + " " + new File(fileName).getName();
        try (BufferedWriter bw = new BufferedWriter(new FileWriter(indexFile, true))) {
            bw.append(toAppend);
            bw.newLine(); 
        }
    }

}