GitWrapper.java

import java.io.File;
import java.io.IOException;

public class GitWrapper {

    /**
     * Initializes a new Git repository.
     * This method creates the necessary directory structure
     * and initial files (index, HEAD) required for a Git repository.
     */
    public void init() {
        Git.deleteIfExists(Git.git);
        Git.git    = Git.makeFolder("git");
        Git.objects = Git.makeFolder("objects", Git.git);
        try {
            Git.index = Git.makeFile("index", Git.git);
            Git.HEAD  = Git.makeFile("HEAD", Git.git);
        } catch (IOException e) {
            throw new RuntimeException("Failed to initialize Git repository", e);
        }
    };

    /**
     * Stages a file for the next commit.
     * This method adds a file to the index file.
     * If the file does not exist, it throws an IOException.
     * If the file is a directory, it throws an IOException.
     * If the file is already in the index, it does nothing.
     * If the file is successfully staged, it creates a blob for the file.
     * @param filePath The path to the file to be staged.
     */
    public void add(String filePath) {
        File f = new File(filePath);
        if (!f.exists() || !f.isFile()) throw new IllegalArgumentException("File has to exist and be a file " + filePath);
        try {
            Git.addToIndex(f);
        } catch (IOException e) {
            throw new RuntimeException("Failed add file to index " + filePath, e);
        }
    };

    /**
     * Creates a commit with the given author and message.
     * It should capture the current state of the repository by building trees based on the index file,
     * writing the tree to the objects directory,
     * writing the commit to the objects directory,
     * updating the HEAD file,
     * and returning the commit hash.
     * 
     * The commit should be formatted as follows:
     * tree: <tree_sha>
     * parent: <parent_sha>
     * author: <author>
     * date: <date>
     * summary: <summary>
     *
     * @param author  The name of the author making the commit.
     * @param message The commit message describing the changes.
     * @return The SHA1 hash of the new commit.
     */
    public String commit(String author, String message) {
        try {
            return Git.commit(author, message);
        } catch (IOException e) {
            throw new RuntimeException("Failed to create commit", e);
        }
    };

     /**
     * EXTRA CREDIT:
     * Checks out a specific commit given its hash.
     * This method should read the HEAD file to determine the "checked out" commit.
     * Then it should update the working directory to match the
     * state of the repository at that commit by tracing through the root tree and
     * all its children.
     *
     * @param commitHash The SHA1 hash of the commit to check out.
     */
    public void checkout(String commitHash) {
        // to-do: implement functionality here

    };
}