From f7f4a395c091fdd9d858f0fa9a8fc95215a5cd58 Mon Sep 17 00:00:00 2001
From: Aleksey Kulikov <skinny.mind@gmail.com>
Date: Wed, 15 Sep 2021 15:18:27 +0300
Subject: [PATCH] feat(diff): add ability to get patchid

---
 lib/src/bindings/diff.dart | 21 +++++++++++++++++++++
 lib/src/diff.dart          | 12 ++++++++++++
 test/diff_test.dart        |  1 +
 3 files changed, 34 insertions(+)

diff --git a/lib/src/bindings/diff.dart b/lib/src/bindings/diff.dart
index da8f34f..a7425fc 100644
--- a/lib/src/bindings/diff.dart
+++ b/lib/src/bindings/diff.dart
@@ -199,6 +199,27 @@ void findSimilar(
   calloc.free(opts);
 }
 
+/// Calculate the patch ID for the given patch.
+///
+/// Calculate a stable patch ID for the given patch by summing the hash of the file diffs,
+/// ignoring whitespace and line numbers. This can be used to derive whether two diffs are
+/// the same with a high probability.
+///
+/// Currently, this function only calculates stable patch IDs, as defined in `git-patch-id(1)`,
+/// and should in fact generate the same IDs as the upstream git project does.
+///
+/// Throws a [LibGit2Error] if error occured.
+Pointer<git_oid> patchId(Pointer<git_diff> diff) {
+  final out = calloc<git_oid>();
+  final error = libgit2.git_diff_patchid(out, diff, nullptr);
+
+  if (error < 0) {
+    throw LibGit2Error(libgit2.git_error_last());
+  } else {
+    return out;
+  }
+}
+
 /// Return the diff delta for an entry in the diff list.
 ///
 /// Throws [RangeError] if index out of range.
diff --git a/lib/src/diff.dart b/lib/src/diff.dart
index e363e63..261f8f0 100644
--- a/lib/src/diff.dart
+++ b/lib/src/diff.dart
@@ -75,6 +75,18 @@ class Diff {
     );
   }
 
+  /// Calculate the patch ID for the given patch.
+  ///
+  /// Calculate a stable patch ID for the given patch by summing the hash of the file diffs,
+  /// ignoring whitespace and line numbers. This can be used to derive whether two diffs are
+  /// the same with a high probability.
+  ///
+  /// Currently, this function only calculates stable patch IDs, as defined in `git-patch-id(1)`,
+  /// and should in fact generate the same IDs as the upstream git project does.
+  ///
+  /// Throws a [LibGit2Error] if error occured.
+  Oid get patchId => Oid(bindings.patchId(_diffPointer));
+
   /// Releases memory allocated for diff object.
   void free() => bindings.free(_diffPointer);
 }
diff --git a/test/diff_test.dart b/test/diff_test.dart
index dca6b65..54bff98 100644
--- a/test/diff_test.dart
+++ b/test/diff_test.dart
@@ -188,6 +188,7 @@ index e69de29..c217c63 100644
       expect(diff.length, 1);
       expect(stats.filesChanged, 1);
       expect(stats.insertions, 1);
+      expect(diff.patchId.sha, '699556913185bc38632ae20a49d5c18b9233335e');
 
       stats.free();
       diff.free();