return repo.scm_instance.get_changeset(rev)

        except EmptyRepositoryError, e:

            if not redirect_after:

                return None

            h.flash(h.literal(_('There are no changesets yet')),

                    category='warning')

            redirect(url('summary_home', repo_name=repo.repo_name))

        except RepositoryError, e:

            log.error(traceback.format_exc())

            h.flash(str(e), category='warning')

            if not partial:

                redirect(h.url('summary_home', repo_name=repo.repo_name))

            raise HTTPBadRequest()

    def index(self, org_ref_type, org_ref, other_ref_type, other_ref):

        # org_ref will be evaluated in org_repo

        org_repo = c.rhodecode_db_repo.repo_name

        org_ref = (org_ref_type, org_ref)

        # other_ref will be evaluated in other_repo

        other_ref = (other_ref_type, other_ref)

        other_repo = request.GET.get('other_repo', org_repo)

        # If merge is True:

        #   Show what org would get if merged with other:

        #   List changesets that are ancestors of other but not of org.

        #   New changesets in org is thus ignored.

        #   Diff will be from common ancestor, and merges of org to other will thus be ignored.

        # If merge is False:

        #   Make a raw diff from org to other, no matter if related or not.

        #   Changesets in one and not in the other will be ignored

        merge = bool(request.GET.get('merge'))

        # fulldiff disables cut_off_limit

        c.fulldiff = request.GET.get('fulldiff')

        # partial uses compare_cs.html template directly

        partial = request.environ.get('HTTP_X_PARTIAL_XHR')

        # as_form puts hidden input field with changeset revisions

        c.as_form = partial and request.GET.get('as_form')

        # swap url for compare_diff page - never partial and never as_form

        c.swap_url = h.url('compare_url',

            repo_name=other_repo,

            org_ref_type=other_ref[0], org_ref=other_ref[1],

            other_repo=org_repo,

            other_ref_type=org_ref[0], other_ref=org_ref[1],

            merge=merge or '')

        org_repo = Repository.get_by_repo_name(org_repo)

        other_repo = Repository.get_by_repo_name(other_repo)

        if org_repo is None:

            log.error('Could not find org repo %s' % org_repo)

            raise HTTPNotFound

        if other_repo is None:

            log.error('Could not find other repo %s' % other_repo)

            raise HTTPNotFound

        if org_repo != other_repo and h.is_git(org_repo):

            log.error('compare of two remote repos not available for GIT REPOS')

            raise HTTPNotFound

        if org_repo.scm_instance.alias != other_repo.scm_instance.alias:

            log.error('compare of two different kind of remote repos not available')

            raise HTTPNotFound

        c.org_repo = org_repo

        c.other_repo = other_repo

        c.org_ref = org_ref[1]

        c.other_ref = other_ref[1]

        c.org_ref_type = org_ref[0]

        c.other_ref_type = other_ref[0]

        c.cs_ranges, c.ancestor = PullRequestModel().get_compare_data(

            org_repo, org_ref, other_repo, other_ref, merge)

        c.statuses = c.rhodecode_db_repo.statuses([x.raw_id for x in

                                                   c.cs_ranges])

        if partial:

            assert c.ancestor

            return render('compare/compare_cs.html')

        if c.ancestor:

            assert merge

            # case we want a simple diff without incoming changesets,

            # previewing what will be merged.

            # Make the diff on the other repo (which is known to have other_ref)

            log.debug('Using ancestor %s as org_ref instead of %s'

                      % (c.ancestor, org_ref))

            org_ref = ('rev', c.ancestor)

            org_repo = other_repo

        diff_limit = self.cut_off_limit if not c.fulldiff else None

        _diff = diffs.differ(org_repo, org_ref, other_repo, other_ref)

        diff_processor = diffs.DiffProcessor(_diff or '', format='gitdiff',

                                             diff_limit=diff_limit)

        _parsed = diff_processor.prepare()

        c.limited_diff = False

        if isinstance(_parsed, LimitedDiffContainer):

            c.limited_diff = True

        c.files = []

        c.changes = {}

        c.lines_added = 0

        c.lines_deleted = 0

        for f in _parsed:

            st = f['stats']

            if st[0] != 'b':

                c.lines_added += st[0]

                c.lines_deleted += st[1]

            fid = h.FID('', f['filename'])