add name_to_id binding and headCommit to repo

- implemented git_reference_name_to_id binding
- created repository.headCommit getter

lib/src/bindings/reference.dart

@@ -449,5 +449,31 @@ Pointer<git_reference> duplicate(Pointer<git_reference> source) {
   return result;
 }
 
+/// Lookup a reference by name and resolve immediately to OID.
+///
+/// This function provides a quick way to resolve a reference name straight
+/// through to the object id that it refers to.  This avoids having to
+/// allocate or free any `git_reference` objects for simple situations.
+///
+/// The name will be checked for validity.
+/// See [createSymbolic] for rules about valid names.
+///
+/// Throws a [LibGit2Error] if error occured.
+Pointer<git_oid> nameToId({
+  required Pointer<git_repository> repoPointer,
+  required String refName,
+}) {
+  final result = calloc<git_oid>();
+  final nameC = refName.toChar();
+
+  final error = libgit2.git_reference_name_to_id(result, repoPointer, nameC);
+
+  if (error < 0) {
+    throw LibGit2Error(libgit2.git_error_last());
+  } else {
+    return result;
+  }
+}
+
 /// Free the given reference.
 void free(Pointer<git_reference> ref) => libgit2.git_reference_free(ref);

lib/src/reference.dart

@@ -191,6 +191,24 @@ class Reference extends Equatable {
     bindings.ensureLog(repoPointer: repo.pointer, refName: refName);
   }
 
+  /// Lookup a reference by name and resolve immediately to OID.
+  ///
+  /// This function provides a quick way to resolve a reference name straight
+  /// through to the object id that it refers to.  This avoids having to
+  /// allocate or free any `git_reference` objects for simple situations.
+  ///
+  /// The name will be checked for validity.
+  /// See [createSymbolic] for rules about valid names.
+  ///
+  /// Throws a [LibGit2Error] if error occured.
+  static Oid nameToId({
+    required Repository repo,
+    required String refName,
+  }) {
+    final res = bindings.nameToId(repoPointer: repo.pointer, refName: refName);
+    return Oid(res);
+  }
+
   /// Creates a copy of an existing reference.
   Reference duplicate() => Reference(bindings.duplicate(_refPointer));
 

lib/src/repository.dart

@@ -339,6 +339,11 @@ class Repository extends Equatable {
     );
   }
 
+  /// Retrieve the commit that HEAD is currently pointing to
+  Commit get headCommit {
+    return Commit.lookup(repo: this, oid: head.target);
+  }
+
   /// Removes all the metadata associated with an ongoing command like
   /// merge, revert, cherry-pick, etc. For example: MERGE_HEAD, MERGE_MSG, etc.
   ///

test/reference_test.dart

@@ -530,6 +530,11 @@ void main() {
       );
     });
 
+    test('get oid by name', () {
+      final oid = Reference.nameToId(repo: repo, refName: 'HEAD');
+      expect(oid, repo.head.target);
+    });
+
     test('manually releases allocated memory', () {
       final ref = Reference.lookup(repo: repo, name: 'refs/heads/master');
       expect(() => ref.free(), returnsNormally);

test/repository_test.dart

@@ -246,6 +246,10 @@ void main() {
       expect(() => repo.free(), returnsNormally);
     });
 
+    test('get head commit', () {
+      expect(repo.headCommit.oid.sha, lastCommit);
+    });
+
     test('returns string representation of Repository object', () {
       expect(repo.toString(), contains('Repository{'));
     });