class CompareController(BaseRepoController):

    def __before__(self):

        super(CompareController, self).__before__()

    def __get_cs_or_redirect(self, rev, repo, redirect_after=True,

                             partial=False):

        """

        Safe way to get changeset if error occur it redirects to changeset with

        proper message. If partial is set then don't do redirect raise Exception

        instead

        :param rev: revision to fetch

        :param repo: repo instance

        """

        try:

            type_, rev = rev

            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 _get_changesets(self, alias, org_repo, org_ref, other_repo, other_ref, merge):

        """

        Returns a list of changesets that can be merged from org_repo@org_ref

        to other_repo@other_ref ... and the ancestor that would be used for merge

        :param org_repo:

        :param org_ref:

        :param other_repo:

        :param other_ref:

        :param tmp:

        """

        ancestor = None

        if alias == 'hg':

            # lookup up the exact node id

            _revset_predicates = {

                    'branch': 'branch',

                    'book': 'bookmark',

                    'tag': 'tag',

                    'rev': 'id',

                }

            org_rev_spec = "max(%s('%s'))" % (_revset_predicates[org_ref[0]],

                                              safe_str(org_ref[1]))

            org_revs = scmutil.revrange(org_repo._repo, [org_rev_spec])

            org_rev = org_repo._repo[org_revs[-1] if org_revs else -1].hex()

            other_rev_spec = "max(%s('%s'))" % (_revset_predicates[other_ref[0]],

                                                safe_str(other_ref[1]))

            other_revs = scmutil.revrange(other_repo._repo, [other_rev_spec])

            other_rev = other_repo._repo[other_revs[-1] if other_revs else -1].hex()

            #case two independent repos

            if org_repo != other_repo:

                hgrepo = unionrepo.unionrepository(other_repo.baseui,

                                                   other_repo.path,

                                                   org_repo.path)

                # all the changesets we are looking for will be in other_repo,

                # so rev numbers from hgrepo can be used in other_repo

            #no remote compare do it on the same repository

            else:

                hgrepo = other_repo._repo

            if merge:

                revs = ["ancestors(id('%s')) and not ancestors(id('%s')) and not id('%s')" %

                        (other_rev, org_rev, org_rev)]

                ancestors = scmutil.revrange(hgrepo,

                     ["ancestor(id('%s'), id('%s'))" % (org_rev, other_rev)])

                if ancestors:

                    # pick arbitrary ancestor - but there is usually only one

                    ancestor = hgrepo[ancestors[0]].hex()

            else:

                # TODO: have both + and - changesets

                revs = ["id('%s') :: id('%s') - id('%s')" %

                        (org_rev, other_rev, org_rev)]

            changesets = [other_repo.get_changeset(cs)

                          for cs in scmutil.revrange(hgrepo, revs)]

        elif alias == 'git':

            so, se = org_repo.run_git_command(

                'log --reverse --pretty="format: %%H" -s -p %s..%s'

                    % (org_ref[1], other_ref[1])

            )

            changesets = [org_repo.get_changeset(cs)

                          for cs in re.findall(r'[0-9a-fA-F]{40}', so)]

        return changesets, ancestor

    @LoginRequired()

    @HasRepoPermissionAnyDecorator('repository.read', 'repository.write',

                                   'repository.admin')

    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

        self.__get_cs_or_redirect(rev=org_ref, repo=org_repo, partial=partial)

        self.__get_cs_or_redirect(rev=other_ref, repo=other_repo, partial=partial)

        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 = self._get_changesets(org_repo.scm_instance.alias,

                                                       org_repo.scm_instance, org_ref,

                                                       other_repo.scm_instance, other_ref,

                                                       merge)

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

                                                   c.cs_ranges])

        if not c.ancestor:

            log.warning('Unable to find ancestor revision')

        if partial:

            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

        log.debug('running diff between %s@%s and %s@%s'