How to Revert a Commit and Create a New Revert Commit in Python

class GitCommit:
    """Minimal mock of a git commit for demonstrating revert behavior."""
    def __init__(self, sha, message):
        self.sha = sha
        self.message = message
        self.parent = None


class GitRepository:
    """Mock repository tracking a simple commit chain."""
    def __init__(self):
        self.head = None
        self.commits = {}

    def commit(self, message):
        sha = f"sha{len(self.commits) + 1}"
        new_commit = GitCommit(sha, message)
        new_commit.parent = self.head
        self.head = new_commit
        self.commits[sha] = new_commit
        return new_commit

    def revert_commit(self, sha):
        """Create a new commit that reverses the changes of an existing commit."""
        if sha not in self.commits:
            raise ValueError("Commit not found")
        original = self.commits[sha]
        revert_message = f"Revert \"{original.message}\""
        revert_commit = self.commit(revert_message)
        return revert_commit


if __name__ == "__main__":
    repo = GitRepository()
    c1 = repo.commit("add feature A")
    c2 = repo.commit("fix bug in B")
    c3 = repo.commit("refactor C")

    # Revert the first commit; creates a new revert commit on top
    revert = repo.revert_commit(c1.sha)

    print(f"Original commit: {c1.sha} - '{c1.message}'")
    print(f"New revert commit: {revert.sha} - '{revert.message}'")
    print(f"Current head: {repo.head.sha} - '{repo.head.message}'")

    # Demonstrate the linear chain
    chain = []
    current = repo.head
    while current:
        chain.append(current.sha)
        current = current.parent
    print("Commit chain (newest -> oldest):", " -> ".join(chain))