git_vfs.rs

git_vfs.rs

use std::collections::HashMap;
use std::io::{self, Read, Write};

#[derive(Debug, PartialEq)]
enum GitVfsError {
    NotFound,
    AlreadyExists,
    InvalidOperation,
}

type GitVfsResult<T> = Result<T, GitVfsError>;

struct GitVfs {
    objects: HashMap<String, Vec<u8>>, // Stores git objects (blobs, trees, commits)
    refs: HashMap<String, String>,     // Stores references (branches, tags)
    head: Option<String>,              // Stores the current HEAD reference
}

impl GitVfs {
    fn new() -> Self {
        GitVfs {
            objects: HashMap::new(),
            refs: HashMap::new(),
            head: None,
        }
    }

    fn create_object(&mut self, hash: &str, data: &[u8]) -> GitVfsResult<()> {
        if self.objects.contains_key(hash) {
            return Err(GitVfsError::AlreadyExists);
        }
        self.objects.insert(hash.to_string(), data.to_vec());
        Ok(())
    }

    fn get_object(&self, hash: &str) -> GitVfsResult<Vec<u8>> {
        match self.objects.get(hash) {
            Some(data) => Ok(data.clone()),
            None => Err(GitVfsError::NotFound),
        }
    }

    fn create_ref(&mut self, ref_name: &str, hash: &str) -> GitVfsResult<()> {
        self.refs.insert(ref_name.to_string(), hash.to_string());
        Ok(())
    }

    fn get_ref(&self, ref_name: &str) -> GitVfsResult<String> {
        match self.refs.get(ref_name) {
            Some(hash) => Ok(hash.clone()),
            None => Err(GitVfsError::NotFound),
        }
    }

    fn update_ref(&mut self, ref_name: &str, hash: &str) -> GitVfsResult<()> {
        if !self.refs.contains_key(ref_name) {
            return Err(GitVfsError::NotFound);
        }
        self.refs.insert(ref_name.to_string(), hash.to_string());
        Ok(())
    }

    fn set_head(&mut self, ref_name: &str) -> GitVfsResult<()> {
        if !self.refs.contains_key(ref_name) {
            return Err(GitVfsError::NotFound);
        }
        self.head = Some(ref_name.to_string());
        Ok(())
    }

    fn get_head(&self) -> GitVfsResult<String> {
        match &self.head {
            Some(head_ref) => Ok(head_ref.clone()),
            None => Err(GitVfsError::NotFound),
        }
    }

    //Simulates creating a blob object.
    fn create_blob(&mut self, data: &[u8]) -> GitVfsResult<String> {
        //In a real git this would be a real hash function, but for simplicity
        //we use a string representation of the data length.
        let hash = format!("{}", data.len());
        self.create_object(&hash, data)?;
        Ok(hash)
    }
}

fn main() {
    let mut git_vfs = GitVfs::new();

    let blob_data = b"Hello, git virtual world!";
    let blob_hash = git_vfs
        .create_blob(blob_data)
        .expect("Failed to create blob");

    let blob_content = git_vfs.get_object(&blob_hash).expect("Failed to get blob");
    println!("Blob content: {}", String::from_utf8_lossy(&blob_content));

    git_vfs
        .create_ref("refs/heads/main", &blob_hash)
        .expect("Failed to create ref");
    git_vfs
        .set_head("refs/heads/main")
        .expect("failed to set head");

    let head_ref = git_vfs.get_head().expect("failed to get head");
    println!("HEAD: {}", head_ref);

    let main_ref_hash = git_vfs
        .get_ref("refs/heads/main")
        .expect("failed to get ref");
    println!("Main ref hash: {}", main_ref_hash);

    git_vfs
        .update_ref("refs/heads/main", "new_hash")
        .expect("failed to update ref");

    let main_ref_hash = git_vfs
        .get_ref("refs/heads/main")
        .expect("failed to get ref");
    println!("Updated Main ref hash: {}", main_ref_hash);
}

/*

Key Improvements and Git Concepts:
Object Storage:
Uses objects: HashMap<String, Vec<u8>> to store Git objects (blobs, trees, commits).
Objects are addressed by their SHA-1 hashes (simplified here).
References (Refs):
Uses refs: HashMap<String, String> to store references like branches (refs/heads/main), tags (refs/tags/v1.0), and other refs.
Each ref points to a commit hash.
HEAD:
Uses head: Option<String> to track the current branch or commit.
HEAD points to the currently checked-out branch.
Blob Creation:
The create_blob function simulates creating a blob object.
In a real Git, this would involve hashing the content with SHA-1.
For simplicity, the provided code uses the length of the data as the hash.
Ref Operations:
create_ref, get_ref, and update_ref functions manage references.
HEAD Operations:
set_head and get_head functions manage the HEAD reference.
Error Handling:
Uses GitVfsError for Git-specific errors.
Simplified Hashing:
The example avoids real SHA-1 hashing for simplicity. In a real Git implementation, you'd use a hashing library.
How to Use:
Create Objects: Use create_blob to create blob objects (representing file content).
Create Refs: Use create_ref to create branches or tags.
Set HEAD: Use set_head to switch branches.
Get Objects and Refs: Use get_object and get_ref to retrieve data.
Update Refs: use update_ref to move branches to new commit hashes.
This example provides a basic, in-memory simulation of a Git repository's core data structures. For a real Git implementation, you'd need to handle more complex object types (trees, commits), implement proper SHA-1 hashing, and manage a persistent storage mechanism.
*/