feat(commit): add ability to create commit

lib/src/commit.dart

@@ -1,8 +1,11 @@
 import 'dart:ffi';
+
 import 'bindings/libgit2_bindings.dart';
 import 'bindings/commit.dart' as bindings;
+import 'repository.dart';
 import 'oid.dart';
 import 'signature.dart';
+import 'tree.dart';
 import 'util.dart';
 
 class Commit {
@@ -26,6 +29,58 @@ class Commit {
   /// Pointer to memory address for allocated commit object.
   late final Pointer<git_commit> _commitPointer;
 
+  /// Creates new commit in the repository.
+  ///
+  /// Throws a [LibGit2Error] if error occured.
+  static Oid create({
+    required Repository repo,
+    required String message,
+    required Signature author,
+    required Signature commiter,
+    required String treeSHA,
+    required List<String> parentsSHA,
+    String? updateRef,
+    String? messageEncoding,
+  }) {
+    libgit2.git_libgit2_init();
+
+    final parentCount = parentsSHA.length;
+    late final Tree tree;
+
+    if (treeSHA.length == 40) {
+      final treeOid = Oid.fromSHA(treeSHA);
+      tree = Tree.lookup(
+        repo.pointer,
+        treeOid.pointer,
+      );
+    } else {
+      final odb = repo.odb;
+      final treeOid = Oid.fromShortSHA(treeSHA, odb);
+      tree = Tree.lookup(
+        repo.pointer,
+        treeOid.pointer,
+      );
+      odb.free();
+    }
+
+    final result = Oid(bindings.create(
+      repo.pointer,
+      updateRef,
+      author.pointer,
+      commiter.pointer,
+      messageEncoding,
+      message,
+      tree.pointer,
+      parentCount,
+      parentsSHA,
+    ));
+
+    tree.free();
+    libgit2.git_libgit2_init();
+
+    return result;
+  }
+
   /// Returns the encoding for the message of a commit, as a string
   /// representing a standard encoding name.
   String get messageEncoding => bindings.messageEncoding(_commitPointer);