// modifyChange returns a Change representing a modification to a known file
// in the go-git fixture, suitable for exercising filePatchWithContext.
func (s *ChangeSuite) modifyChange() *Change {
	path := "utils/difftree/difftree.go"
	name := "difftree.go"
	mode := filemode.Regular
	fromBlob := plumbing.NewHash("05f583ace3a9a078d8150905a53a4d82567f125f")
	fromTree := plumbing.NewHash("b1f01b730b855c82431918cb338ad47ed558999b")
	toBlob := plumbing.NewHash("de927fad935d172929aacf20e71f3bf0b91dd6f9")
	toTree := plumbing.NewHash("8b0af31d2544acb5c4f3816a602f11418cbd126e")
	return &Change{
		From: ChangeEntry{
			Name:      path,
			Tree:      s.tree(fromTree),
			TreeEntry: TreeEntry{Name: name, Mode: mode, Hash: fromBlob},
		},
		To: ChangeEntry{
			Name:      path,
			Tree:      s.tree(toTree),
			TreeEntry: TreeEntry{Name: name, Mode: mode, Hash: toBlob},
		},
	}
}

// TestPatchContextDeadlineExpired verifies that filePatchWithContext returns
// ErrCanceled when the context deadline has already expired before the call.
func (s *ChangeSuite) TestPatchContextDeadlineExpired() {
	change := s.modifyChange()

	// Deadline already in the past — filePatchWithContext must detect this
	// immediately and return ErrCanceled without performing any diff work.
	ctx, cancel := context.WithDeadline(context.Background(), time.Now().Add(-time.Second))
	defer cancel()

	fp, err := filePatchWithContext(ctx, change)
	s.Nil(fp)
	s.ErrorIs(err, ErrCanceled)
}

// TestPatchContextWithActiveDeadline verifies that filePatchWithContext
// succeeds and returns a non-empty patch when given a context with ample time
// remaining, exercising the diff.DoWithTimeout code path.
func (s *ChangeSuite) TestPatchContextWithActiveDeadline() {
	change := s.modifyChange()

	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
	defer cancel()

	fp, err := filePatchWithContext(ctx, change)
	s.NoError(err)
	s.NotNil(fp)
	s.NotEmpty(fp.Chunks())
}