ytil_git/

branch.rs

//! Branch operations for Git repositories.
//!
//! Provides functions for retrieving default and current branch names, creating new branches,
//! switching branches, fetching branches from remotes, and listing all branches with metadata.

use std::collections::HashSet;
use std::path::Path;
use std::process::Command;

use git2::BranchType;
use git2::Cred;
use git2::RemoteCallbacks;
use git2::Repository;
use jiff::Timestamp;
use rootcause::bail;
use rootcause::prelude::ResultExt;
use rootcause::report;
use ytil_cmd::CmdError;
use ytil_cmd::CmdExt;

/// Retrieves the default branch name from the Git repository.
///
/// Iterates over all configured remotes and returns the branch name pointed to by the first valid
/// `refs/remotes/{remote}/HEAD` reference.
///
/// # Errors
/// - If the repository cannot be opened.
/// - If no remote has a valid `HEAD` reference.
/// - If the branch name cannot be extracted from the reference target.
pub fn get_default() -> rootcause::Result<String> {
    let repo_path = Path::new(".");
    let repo = crate::repo::discover(repo_path)
        .context("error getting repo for getting default branch")
        .attach_with(|| format!("path={}", repo_path.display()))?;

    let default_remote_ref = crate::remote::get_default(&repo)?;

    let Some(target) = default_remote_ref
        .symbolic_target()
        .context("error reading default remote symbolic target")?
    else {
        bail!("error missing default branch");
    };

    Ok(target
        .split('/')
        .next_back()
        .ok_or_else(|| report!("error extracting default branch_name from target"))
        .attach_with(|| format!("target={target:?}"))?
        .to_string())
}

/// Get current branch name (fails if HEAD detached).
///
/// # Errors
/// - Repository discovery fails or HEAD is detached.
pub fn get_current() -> rootcause::Result<String> {
    let repo_path = Path::new(".");
    let repo = crate::repo::discover(repo_path)
        .context("error getting repo for getting current branch")
        .attach_with(|| format!("path={}", repo_path.display()))?;

    if repo
        .head_detached()
        .context("error checking if head is detached")
        .attach_with(|| format!("path={}", repo_path.display()))?
    {
        Err(report!("error head is detached")).attach_with(|| format!("path={}", repo_path.display()))?;
    }

    let head = repo
        .head()
        .context("error getting head")
        .attach_with(|| format!("path={}", repo_path.display()))?;
    let branch_name = head
        .shorthand()
        .context("error invalid branch shorthand UTF-8")
        .attach_with(|| format!("path={}", repo_path.display()))?;
    Ok(branch_name.to_string())
}

/// Returns the branch checked out at or before `timestamp`, inferred from `HEAD` reflog.
///
/// Returns [`None`] when `path` is not in a repository, `HEAD` has no usable
/// reflog, or no checkout/switch entry exists before the timestamp.
pub fn get_at(path: &Path, timestamp: Timestamp) -> Option<String> {
    let repo = crate::repo::discover(path).ok()?;
    let reflog = repo.reflog("HEAD").ok()?;
    let timestamp = timestamp.as_second();
    reflog
        .iter()
        .filter_map(|entry| {
            // git2 decodes reflog messages lazily; unreadable or missing messages cannot
            // prove branch history, so this lookup skips only that entry.
            let message = entry.message().ok()??;
            Some((entry.committer().when().seconds(), branch_from_reflog_message(message)?))
        })
        .filter(|(entry_timestamp, _)| *entry_timestamp <= timestamp)
        .max_by_key(|(entry_timestamp, _)| *entry_timestamp)
        .map(|(_, branch)| branch)
}

/// Create a new local branch at current HEAD (no checkout).
///
/// # Errors
/// - Repository discovery, HEAD resolution, or branch creation fails.
pub fn create_from_default_branch(branch_name: &str, repo: Option<&Repository>) -> rootcause::Result<()> {
    let repo = if let Some(repo) = repo {
        repo
    } else {
        let path = Path::new(".");
        &crate::repo::discover(path)
            .context("error getting repo for creating new branch")
            .attach_with(|| format!("path={} branch={branch_name:?}", path.display()))?
    };

    let commit = repo
        .head()
        .context("error getting head")
        .attach_with(|| format!("branch_name={branch_name:?}"))?
        .peel_to_commit()
        .context("error peeling head to commit")
        .attach_with(|| format!("branch_name={branch_name:?}"))?;

    repo.branch(branch_name, &commit, false)
        .context("error creating branch")
        .attach_with(|| format!("branch_name={branch_name:?}"))?;

    Ok(())
}

/// Rename the current local branch.
///
/// Mirrors `git branch -m <branch_name>` semantics: the rename is not forced,
/// so it fails when the target branch already exists.
///
/// # Errors
/// - Repository discovery fails.
/// - HEAD is detached or the current branch cannot be resolved.
/// - The current local branch cannot be found.
/// - The branch rename fails.
pub fn rename_current(branch_name: &str, repo: Option<&Repository>) -> rootcause::Result<()> {
    let repo = if let Some(repo) = repo {
        repo
    } else {
        let path = Path::new(".");
        &crate::repo::discover(path)
            .context("error getting repo for renaming current branch")
            .attach_with(|| format!("path={} branch={branch_name:?}", path.display()))?
    };

    let head = repo
        .head()
        .context("error getting repo head")
        .attach_with(|| format!("repo_path={}", repo.path().display()))
        .attach_with(|| format!("branch_name={branch_name:?}"))?;
    let current_branch_name = head
        .shorthand()
        .context("error invalid current branch shorthand UTF-8")
        .attach_with(|| format!("repo_path={}", repo.path().display()))
        .attach_with(|| format!("branch_name={branch_name:?}"))?;
    let mut branch = repo
        .find_branch(current_branch_name, BranchType::Local)
        .context("error finding current branch")
        .attach_with(|| format!("repo_path={}", repo.path().display()))
        .attach_with(|| format!("current_branch_name={current_branch_name:?} branch_name={branch_name:?}"))?;

    branch
        .rename(branch_name, false)
        .context("error renaming current branch")
        .attach_with(|| format!("repo_path={}", repo.path().display()))
        .attach_with(|| format!("current_branch_name={current_branch_name:?} branch_name={branch_name:?}"))?;

    Ok(())
}

/// Pushes a branch to the default remote.
///
/// Uses the default remote (determined by the first valid `refs/remotes/{remote}/HEAD` reference)
/// to push the specified branch.
///
/// # Errors
/// - Repository discovery fails.
/// - No default remote can be determined.
/// - The default remote cannot be found.
/// - Pushing the branch fails.
pub fn push(branch_name: &str, repo: Option<&Repository>) -> rootcause::Result<()> {
    let repo = if let Some(repo) = repo {
        repo
    } else {
        let path = Path::new(".");
        &crate::repo::discover(path)
            .context("error getting repo for pushing new branch")
            .attach_with(|| format!("path={} branch={branch_name:?}", path.display()))?
    };

    let default_remote = crate::remote::get_default(repo)?;

    let default_remote_name = default_remote
        .name()
        .context("error reading name of default remote")?
        .trim_start_matches("refs/remotes/")
        .trim_end_matches("/HEAD");

    let mut remote = repo.find_remote(default_remote_name)?;

    let mut callbacks = RemoteCallbacks::new();
    callbacks.credentials(|_url, username_from_url, _allowed_types| {
        Cred::ssh_key_from_agent(username_from_url.unwrap_or("git"))
    });

    let mut push_opts = git2::PushOptions::new();
    push_opts.remote_callbacks(callbacks);

    let branch_refspec = format!("refs/heads/{branch_name}");
    remote
        .push(&[&branch_refspec], Some(&mut push_opts))
        .context("error pushing branch to remote")
        .attach_with(|| format!("branch_refspec={branch_refspec:?} default_remote_name={default_remote_name:?}"))?;

    Ok(())
}

/// Returns the name of the previously checked-out branch (`@{-1}`), if any.
///
/// Walks the HEAD reflog looking for the most recent checkout/switch entry and
/// extracts the source branch name from the message.
///
/// Returns [`None`] when there is no recorded previous branch (e.g. fresh clone)
/// or the reflog cannot be read.
pub fn get_previous(repo: &Repository) -> Option<String> {
    let reflog = repo.reflog("HEAD").ok()?;
    reflog.iter().find_map(|entry| {
        let msg = entry.message().ok()??;
        let rest = msg
            .strip_prefix("checkout: moving from ")
            .or_else(|| msg.strip_prefix("switch: moving from "))?;
        Some(rest.rsplit_once(" to ")?.0.to_string())
    })
}

/// Returns the configured Git user email for the repository, if present.
///
/// Looks up `user.email` using the repository's config resolution order.
///
/// # Errors
/// - Reading repository configuration fails.
pub fn get_user_email(repo: &Repository) -> rootcause::Result<Option<String>> {
    let config = repo.config().context("error opening repo config")?;
    match config.get_string("user.email") {
        Ok(email) => Ok(Some(email)),
        Err(err) if err.code() == git2::ErrorCode::NotFound => Ok(None),
        Err(err) => Err(report!("error reading user.email from repo config").attach(err.to_string())),
    }
}

/// Checkout a branch or detach HEAD.
///
/// # Errors
/// - `git switch` command fails.
pub fn switch(branch_name: &str) -> Result<(), Box<CmdError>> {
    Command::new("git")
        .args(["switch", branch_name, "--guess"])
        .exec()
        .map_err(Box::new)?;
    Ok(())
}

/// Fetches all branches from the 'origin' remote and returns all local and remote [`Branch`]es
/// sorted by last committer date (most recent first).
///
/// # Errors
/// - The 'origin' remote cannot be found.
/// - Performing `git fetch` for all branches fails.
/// - Enumerating branches fails.
/// - A branch name is not valid UTF-8.
/// - Resolving the branch tip commit fails.
/// - Converting the committer timestamp into a [`Timestamp`] fails.
pub fn get_all(repo: &Repository) -> rootcause::Result<Vec<Branch>> {
    fetch_with_repo(repo, &[]).context("error fetching branches")?;

    let mut out = vec![];
    for branch_res in repo.branches(None).context("error enumerating branches")? {
        let branch = branch_res.context("error getting branch result")?;
        out.push(Branch::try_from(branch).context("error creating branch from result")?);
    }

    out.sort_unstable_by(|a, b| b.committer_date_time().cmp(a.committer_date_time()));

    Ok(out)
}

/// Retrieves all branches without redundant remote duplicates.
///
/// # Errors
/// - The 'origin' remote cannot be found.
/// - Performing `git fetch` for all branches fails.
/// - Enumerating branches fails.
/// - A branch name is not valid UTF-8.
/// - Resolving the branch tip commit fails.
/// - Converting the committer timestamp into a [`Timestamp`] fails.
pub fn get_all_no_redundant(repo: &Repository) -> rootcause::Result<Vec<Branch>> {
    let mut branches = get_all(repo)?;
    remove_redundant_remotes(&mut branches);
    Ok(branches)
}

/// Fetches the specified branch names from the `origin` remote.
///
/// Used before switching to a branch that may only exist remotely
/// (e.g. derived from a GitHub PR URL).
///
/// # Errors
/// - The repository cannot be discovered.
/// - The `origin` remote cannot be found.
/// - Performing `git fetch` for the requested branches fails.
pub fn fetch(branches: &[&str]) -> rootcause::Result<()> {
    let repo_path = Path::new(".");
    let repo = crate::repo::discover(repo_path)
        .context("error getting repo for fetching branches")
        .attach_with(|| format!("path={} branches={branches:?}", repo_path.display()))?;
    fetch_with_repo(&repo, branches)
}

/// Removes remote branches that have a corresponding local branch of the same
/// shortened name.
///
/// A remote branch is considered redundant if its name after the first `/`
/// (e.g. `origin/feature-x` -> `feature-x`) matches a local branch name.
///
/// After this function returns, each remaining [`Branch::Remote`] has no local
/// counterpart with the same short name.
pub fn remove_redundant_remotes(branches: &mut Vec<Branch>) {
    // Collect local branch names as owned `String`s. An owned `HashSet` is required because
    // `retain` takes `&mut self`, which conflicts with any `&str` borrows into the same vec.
    let local_names: HashSet<String> = branches
        .iter()
        .filter_map(|b| {
            if let Branch::Local { name, .. } = b {
                Some(name.clone())
            } else {
                None
            }
        })
        .collect();

    branches.retain(|b| match b {
        Branch::Local { .. } => true,
        Branch::Remote { name, .. } => {
            let short = name.split_once('/').map_or(name.as_str(), |(_, rest)| rest);
            !local_names.contains(short)
        }
    });
}

/// Local or remote branch with metadata about the last commit.
#[derive(Clone, Debug)]
#[cfg_attr(any(test, feature = "test-utils"), derive(Eq, PartialEq))]
pub enum Branch {
    /// Local branch (under `refs/heads/`).
    Local {
        /// The name of the branch (without refs/heads/ or refs/remotes/ prefix).
        name: String,
        /// The email address of the last committer.
        committer_email: String,
        /// The date and time when the last commit was made.
        committer_date_time: Timestamp,
    },
    /// Remote tracking branch (under `refs/remotes/`).
    Remote {
        /// The name of the branch (without refs/heads/ or refs/remotes/ prefix).
        name: String,
        /// The email address of the last committer.
        committer_email: String,
        /// The date and time when the last commit was made.
        committer_date_time: Timestamp,
    },
}

impl Branch {
    /// Returns the branch name (no "refs/" prefix).
    pub fn name(&self) -> &str {
        match self {
            Self::Local { name, .. } | Self::Remote { name, .. } => name,
        }
    }

    /// Returns the branch name with the "origin/" prefix removed if present.
    pub fn name_no_origin(&self) -> &str {
        self.name().trim_start_matches("origin/")
    }

    /// Returns the email address of the last committer on this branch.
    pub fn committer_email(&self) -> &str {
        match self {
            Self::Local { committer_email, .. } | Self::Remote { committer_email, .. } => committer_email,
        }
    }

    /// Returns the timestamp of the last commit on this branch.
    pub const fn committer_date_time(&self) -> &Timestamp {
        match self {
            Self::Local {
                committer_date_time, ..
            }
            | Self::Remote {
                committer_date_time, ..
            } => committer_date_time,
        }
    }
}

/// Attempts to convert a libgit2 branch and its type into our [`Branch`] enum.
///
/// Extracts the branch name, last committer email and date from the raw branch.
///
/// # Errors
/// - Branch name is not valid UTF-8.
/// - Resolving the branch tip commit fails.
/// - Committer email is not valid UTF-8.
/// - Converting the committer timestamp into a [`Timestamp`] fails.
impl<'a> TryFrom<(git2::Branch<'a>, git2::BranchType)> for Branch {
    type Error = rootcause::Report;

    fn try_from((raw_branch, branch_type): (git2::Branch<'a>, git2::BranchType)) -> Result<Self, Self::Error> {
        let branch_name = raw_branch
            .name()?
            .ok_or_else(|| report!("error invalid branch name UTF-8"))
            .attach_with(|| format!("branch_name={:?}", raw_branch.name()))?;
        let committer = raw_branch.get().peel_to_commit()?.committer().to_owned();
        let committer_email = committer
            .email()
            .context("error invalid committer email UTF-8")
            .attach_with(|| format!("branch_name={branch_name:?}"))?
            .to_string();
        let committer_date_time = Timestamp::from_second(committer.when().seconds())
            .map_err(|_| report!("error invalid commit timestamp"))
            .attach_with(|| format!("seconds={}", committer.when().seconds()))?;

        Ok(match branch_type {
            git2::BranchType::Local => Self::Local {
                name: branch_name.to_string(),
                committer_email,
                committer_date_time,
            },
            git2::BranchType::Remote => Self::Remote {
                name: branch_name.to_string(),
                committer_email,
                committer_date_time,
            },
        })
    }
}

/// Fetches branches using a pre-discovered repository, avoiding redundant filesystem walks.
fn fetch_with_repo(repo: &Repository, branches: &[&str]) -> rootcause::Result<()> {
    let mut callbacks = RemoteCallbacks::new();
    callbacks.credentials(|_url, username_from_url, _allowed_types| {
        Cred::ssh_key_from_agent(username_from_url.unwrap_or("git"))
    });

    let mut fetch_opts = git2::FetchOptions::new();
    fetch_opts.remote_callbacks(callbacks);

    repo.find_remote("origin")
        .context("error finding origin remote")?
        .fetch(branches, Some(&mut fetch_opts), None)
        .context("error performing fetch from origin remote")
        .attach_with(|| format!("branches={branches:?}"))?;

    Ok(())
}

fn branch_from_reflog_message(message: &str) -> Option<String> {
    let rest = message
        .strip_prefix("checkout: moving from ")
        .or_else(|| message.strip_prefix("switch: moving from "))?;
    let (_, branch) = rest.rsplit_once(" to ")?;
    let branch = branch.trim();
    (!branch.is_empty()).then(|| branch.to_string())
}

#[cfg(test)]
mod tests {
    use git2::Signature;
    use git2::Time;
    use rstest::rstest;
    use test_that::prelude::*;

    use super::*;

    #[rstest]
    #[case::remote_same_short_name(
        vec![local("feature-x"), remote("origin/feature-x")],
        vec![local("feature-x")]
    )]
    #[case::no_redundant(
        vec![local("feature-x"), remote("origin/feature-y")],
        vec![local("feature-x"), remote("origin/feature-y")]
    )]
    #[case::multiple_mixed(
        vec![
            local("feature-x"),
            remote("origin/feature-x"),
            remote("origin/feature-y"),
            local("main"),
            remote("upstream/main")
        ],
        vec![local("feature-x"), remote("origin/feature-y"), local("main")]
    )]
    #[case::different_remote_prefix(
        vec![local("feature-x"), remote("upstream/feature-x")],
        vec![local("feature-x")]
    )]
    fn remove_redundant_remotes_cases(#[case] mut input: Vec<Branch>, #[case] expected: Vec<Branch>) {
        remove_redundant_remotes(&mut input);
        assert_eq!(input, expected);
    }

    #[test]
    fn test_branch_try_from_converts_local_branch_successfully() {
        let (_temp_dir, repo) = crate::tests::init_test_repo(Some(Time::new(42, 3)));

        let head_commit = repo.head().unwrap().peel_to_commit().unwrap();
        let branch = repo.branch("test-branch", &head_commit, false).unwrap();

        let branch_result = Branch::try_from((branch, git2::BranchType::Local));
        assert_that!(branch_result, ok(anything()));
        let result = branch_result.expect("local branch should convert");

        assert_that!(
            result,
            eq(Branch::Local {
                name: "test-branch".to_string(),
                committer_email: "test@example.com".to_string(),
                committer_date_time: Timestamp::from_second(42).unwrap(),
            })
        );
    }

    #[test]
    fn test_rename_current_renames_the_current_branch() {
        let (_temp_dir, repo) = crate::tests::init_test_repo(None);

        assert_that!(rename_current("renamed", Some(&repo)), ok(eq(())));

        assert_that!(repo.head().unwrap().shorthand().unwrap(), eq("renamed"));
        repo.find_branch("renamed", git2::BranchType::Local).unwrap();
        assert_that!(
            repo.find_branch("master", git2::BranchType::Local).map(|_| ()),
            err(anything())
        );
    }

    #[test]
    fn test_rename_current_fails_when_target_branch_already_exists() {
        let (_temp_dir, repo) = crate::tests::init_test_repo(None);
        let head_commit = repo.head().unwrap().peel_to_commit().unwrap();
        repo.branch("existing", &head_commit, false).unwrap();

        let rename_result = rename_current("existing", Some(&repo));
        assert_that!(rename_result.as_ref(), err(anything()));
        let err = rename_result.expect_err("renaming over existing branch should fail");

        assert_that!(err.to_string(), contains_substring("error renaming current branch"));
    }

    #[test]
    fn test_get_at_when_path_is_not_git_repo_returns_none() {
        let temp_dir = tempfile::TempDir::new().unwrap();
        let timestamp = Timestamp::from_second(10).unwrap();

        let actual = get_at(temp_dir.path(), timestamp);

        assert_that!(actual, eq(None));
    }

    #[test]
    fn test_get_at_when_checkout_reflog_exists_returns_destination_branch_before_timestamp() {
        let (_temp_dir, repo) = crate::tests::init_test_repo(None);
        append_head_reflog(&repo, 10, "checkout: moving from master to feature/a");
        append_head_reflog(&repo, 20, "checkout: moving from feature/a to feature/b");
        append_head_reflog(&repo, 30, "checkout: moving from feature/b to feature/c");

        let actual = get_at(repo.workdir().unwrap(), Timestamp::from_second(25).unwrap());

        assert_that!(actual, eq(Some("feature/b".to_string())));
    }

    #[test]
    fn test_get_at_when_switch_reflog_exists_returns_destination_branch() {
        let (_temp_dir, repo) = crate::tests::init_test_repo(None);
        append_head_reflog(&repo, 10, "switch: moving from feature/a to main");

        let actual = get_at(repo.workdir().unwrap(), Timestamp::from_second(10).unwrap());

        assert_that!(actual, eq(Some("main".to_string())));
    }

    #[test]
    fn test_get_at_when_reflog_has_no_checkout_or_switch_before_timestamp_returns_none() {
        let (_temp_dir, repo) = crate::tests::init_test_repo(None);
        append_head_reflog(&repo, 10, "commit: message");
        append_head_reflog(&repo, 20, "checkout: moving from main");
        append_head_reflog(&repo, 30, "switch: moving from main to ");

        let actual = get_at(repo.workdir().unwrap(), Timestamp::from_second(30).unwrap());

        assert_that!(actual, eq(None));
    }

    #[rstest]
    #[case::local_variant(local("main"), "main")]
    #[case::remote_variant(remote("origin/feature"), "origin/feature")]
    fn test_branch_name_when_variant_returns_name(#[case] branch: Branch, #[case] expected: &str) {
        assert_that!(branch.name(), eq(expected));
    }

    #[rstest]
    #[case::local_no_origin(local("main"), "main")]
    #[case::remote_origin_prefix(remote("origin/main"), "main")]
    #[case::remote_other_prefix(remote("upstream/feature"), "upstream/feature")]
    fn test_branch_name_no_origin_when_name_returns_trimmed(#[case] branch: Branch, #[case] expected: &str) {
        assert_that!(branch.name_no_origin(), eq(expected));
    }

    #[rstest]
    #[case::local_variant(
        Branch::Local {
            name: "test".to_string(),
            committer_email: "a@b.com".to_string(),
            committer_date_time: Timestamp::from_second(123_456).unwrap(),
        },
        Timestamp::from_second(123_456).unwrap()
    )]
    #[case::remote_variant(
        Branch::Remote {
            name: "origin/test".to_string(),
            committer_email: "a@b.com".to_string(),
            committer_date_time: Timestamp::from_second(654_321).unwrap(),
        },
        Timestamp::from_second(654_321).unwrap()
    )]
    fn branch_committer_date_time_when_variant_returns_date_time(#[case] branch: Branch, #[case] expected: Timestamp) {
        assert_that!(branch.committer_date_time(), eq(&expected));
    }

    fn local(name: &str) -> Branch {
        Branch::Local {
            name: name.into(),
            committer_email: String::new(),
            committer_date_time: Timestamp::from_second(0).unwrap(),
        }
    }

    fn remote(name: &str) -> Branch {
        Branch::Remote {
            name: name.into(),
            committer_email: String::new(),
            committer_date_time: Timestamp::from_second(0).unwrap(),
        }
    }

    fn append_head_reflog(repo: &Repository, timestamp: i64, message: &str) {
        let oid = repo.head().unwrap().target().unwrap();
        let sig = Signature::new("test", "test@example.com", &Time::new(timestamp, 0)).unwrap();
        let mut reflog = repo.reflog("HEAD").unwrap();
        reflog.append(oid, &sig, Some(message)).unwrap();
        reflog.write().unwrap();
    }
}