1 files changed, 109 insertions, 0 deletions
diff --git a/crates/git-tracker/src/tracker.rs b/crates/git-tracker/src/tracker.rs
new file mode 100644
index 0000000..e26f82d
--- /dev/null
+++ b/crates/git-tracker/src/tracker.rs
@@ -0,0 +1,109 @@
+use std::path::Path;
+
+use git2::{Branch, BranchType, Commit, ErrorCode, Oid, Reference, Repository};
+
+#[derive(Debug, thiserror::Error)]
+pub enum Error {
+	#[error("libgit2 error")]
+	Git(#[from] git2::Error),
+	#[error("Repository path not found at `{0}`")]
+	RepositoryPathNotFound(String),
+}
+
+/// Helper struct for tracking Git objects
+pub struct Tracker {
+	repository: Repository,
+}
+
+impl Tracker {
+	/// Create a new [`Tracker`] using the repository at [`path`]
+	///
+	/// # Errors
+	///
+	/// Will return [`Err`] if the repository can not be opened
+	pub fn from_path(path: &str) -> Result<Self, Error> {
+		let repository_path = Path::new(path);
+		if repository_path.exists() {
+			let repository = Repository::open(repository_path)?;
+			Ok(Self { repository })
+		} else {
+			Err(Error::RepositoryPathNotFound(path.to_string()))
+		}
+	}
+
+	/// Finds a branch of name [`name`]
+	///
+	/// # Errors
+	///
+	/// Will return [`Err`] if the branch cannot be found locally
+	pub fn branch_by_name(&self, name: &str) -> Result<Branch, Error> {
+		Ok(self.repository.find_branch(name, BranchType::Remote)?)
+	}
+
+	/// Finds a commit with a SHA match [`sha`]
+	///
+	/// # Errors
+	///
+	/// Will return [`Err`] if [`sha`] cannot be converted an [`Oid`] or
+	/// a commit matching it cannot be found
+	pub fn commit_by_sha(&self, sha: &str) -> Result<Commit, Error> {
+		let oid = Oid::from_str(sha)?;
+		let commit = self.repository.find_commit(oid)?;
+
+		Ok(commit)
+	}
+
+	/// Check if [`Reference`] [`ref`] contains [`Commit`] [`commit`]
+	///
+	/// # Errors
+	///
+	/// Will return [`Err`] if the reference cannot be resolved to a commit or the descendants
+	/// of the reference cannot be resolved
+	pub fn ref_contains_commit(
+		&self,
+		reference: &Reference,
+		commit: &Commit,
+	) -> Result<bool, Error> {
+		let head = reference.peel_to_commit()?;
+
+		// NOTE: we have to check this as `Repository::graph_descendant_of()` (like the name says)
+		// only finds *descendants* of it's parent commit, and will not tell us if the parent commit
+		// *is* the child commit. i have no idea why i didn't think of this, but that's why this
+		// comment is here now
+		let is_head = head.id() == commit.id();
+
+		let has_commit = self
+			.repository
+			.graph_descendant_of(head.id(), commit.id())?;
+
+		Ok(has_commit || is_head)
+	}
+
+	/// Check if a [`Branch`] named [`branch_name`] has a commit with the SHA [`commit_sha`]
+	///
+	/// # Errors
+	///
+	/// Will return [`Err`] if the commit SHA cannot be resolved to an object id, the branch name cannot
+	/// be resolved to a branch, or the descendants of the resolved branch cannot be resolved
+	pub fn branch_contains_sha(&self, branch_name: &str, commit_sha: &str) -> Result<bool, Error> {
+		let commit = match self.commit_by_sha(commit_sha) {
+			Ok(commit) => commit,
+			Err(why) => {
+				// NOTE: we assume commits not found are just not in the branch *yet*, not an error
+				// this is because github decides to report merge commit shas for unmerged PRs...yeah
+				if let Error::Git(git_error) = &why {
+					if git_error.code() == ErrorCode::NotFound {
+						return Ok(false);
+					}
+				}
+
+				return Err(why);
+			}
+		};
+
+		let branch = self.branch_by_name(branch_name)?;
+		let has_pr = self.ref_contains_commit(&branch.into_reference(), &commit)?;
+
+		Ok(has_pr)
+	}
+}