@staticmethod

    def _get_changesets(alias, org_repo, org_rev, other_repo, other_rev):

        """

        Returns lists of changesets that can be merged from org_repo@org_rev

        to other_repo@other_rev

        ... and the other way

        ... and the ancestors that would be used for merge

        :param org_repo: repo object, that is most likely the original repo we forked from

        :param org_rev: the revision we want our compare to be made

        :param other_repo: repo object, most likely the fork of org_repo. It has

            all changesets that we need to obtain

        :param other_rev: revision we want out compare to be made on other_repo

        """

        ancestors = None

        if org_rev == other_rev:

            org_changesets = []

            other_changesets = []

        elif alias == 'hg':

            #case two independent repos

            if org_repo != other_repo:

                hgrepo = unionrepo.unionrepository(other_repo.baseui,

                                                   other_repo.path,

                                                   org_repo.path)

                # all ancestors of other_rev will be in other_repo and

                # rev numbers from hgrepo can be used in other_repo - org_rev ancestors cannot

            #no remote compare do it on the same repository

            else:

                hgrepo = other_repo._repo

            ancestors = [hgrepo[ancestor].hex() for ancestor in

                         hgrepo.revs("id(%s) & ::id(%s)", other_rev, org_rev)]

            if ancestors:

                log.debug("shortcut found: %s is already an ancestor of %s", other_rev, org_rev)

            else:

                log.debug("no shortcut found: %s is not an ancestor of %s", other_rev, org_rev)

                ancestors = [hgrepo[ancestor].hex() for ancestor in

                             hgrepo.revs("heads(::id(%s) & ::id(%s))", org_rev, other_rev)] # FIXME: expensive!

            other_revs = hgrepo.revs("ancestors(id(%s)) and not ancestors(id(%s)) and not id(%s)",

                                     other_rev, org_rev, org_rev)

            other_changesets = [other_repo.get_changeset(rev) for rev in other_revs]

            org_revs = hgrepo.revs("ancestors(id(%s)) and not ancestors(id(%s)) and not id(%s)",

                                   org_rev, other_rev, other_rev)

            org_changesets = [org_repo.get_changeset(hgrepo[rev].hex()) for rev in org_revs]

        elif alias == 'git':

            if org_repo != other_repo:

                from dulwich.repo import Repo

                from dulwich.client import SubprocessGitClient

                gitrepo = Repo(org_repo.path)

                SubprocessGitClient(thin_packs=False).fetch(safe_str(other_repo.path), gitrepo)

                gitrepo_remote = Repo(other_repo.path)

                SubprocessGitClient(thin_packs=False).fetch(safe_str(org_repo.path), gitrepo_remote)

                revs = [

                    x.commit.id

                    for x in gitrepo_remote.get_walker(include=[other_rev],

                                                       exclude=[org_rev])

                ]

                other_changesets = [other_repo.get_changeset(rev) for rev in reversed(revs)]

                if other_changesets:

                    ancestors = [other_changesets[0].parents[0].raw_id]

                else:

                    # no changesets from other repo, ancestor is the other_rev

                    ancestors = [other_rev]

                gitrepo.close()

                gitrepo_remote.close()

            else:

                so, se = org_repo.run_git_command(

                    ['log', '--reverse', '--pretty=format:%H',

                     '-s', '%s..%s' % (org_rev, other_rev)]

                )

                other_changesets = [org_repo.get_changeset(cs)

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

                so, se = org_repo.run_git_command(

                    ['merge-base', org_rev, other_rev]

                )

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

            org_changesets = []

        else:

            raise Exception('Bad alias only git and hg is allowed')

        return other_changesets, org_changesets, ancestors

    @LoginRequired()

    @HasRepoPermissionLevelDecorator('read')

    def index(self, repo_name):

        c.compare_home = True

        return render('compare/compare_diff.html')

    @LoginRequired()

    @HasRepoPermissionLevelDecorator('read')

    def compare(self, repo_name, org_ref_type, org_ref_name, other_ref_type, other_ref_name):

        org_ref_name = org_ref_name.strip()

        other_ref_name = other_ref_name.strip()

        # 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')

        # is_ajax_preview puts hidden input field with changeset revisions

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

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

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

            repo_name=c.cs_repo.repo_name,

            org_ref_type=other_ref_type, org_ref_name=other_ref_name,

            other_repo=c.a_repo.repo_name,

            other_ref_type=org_ref_type, other_ref_name=org_ref_name,

            merge=merge or '')

        # set callbacks for generating markup for icons

        c.ignorews_url = _ignorews_url

        c.context_url = _context_url

        ignore_whitespace = request.GET.get('ignorews') == '1'

        line_context = safe_int(request.GET.get('context'), 3)

        c.a_rev = self._get_ref_rev(c.a_repo, org_ref_type, org_ref_name,

            returnempty=True)

        c.cs_rev = self._get_ref_rev(c.cs_repo, other_ref_type, other_ref_name)

        c.compare_home = False

        c.a_ref_name = org_ref_name

        c.a_ref_type = org_ref_type

        c.cs_ref_name = other_ref_name

        c.cs_ref_type = other_ref_type

        c.cs_ranges, c.cs_ranges_org, c.ancestors = self._get_changesets(

            c.a_repo.scm_instance.alias, c.a_repo.scm_instance, c.a_rev,

            c.cs_repo.scm_instance, c.cs_rev)

        raw_ids = [x.raw_id for x in c.cs_ranges]

        c.cs_comments = c.cs_repo.get_comments(raw_ids)

        c.statuses = c.cs_repo.statuses(raw_ids)

        revs = [ctx.revision for ctx in reversed(c.cs_ranges)]

        c.jsdata = graph_data(c.cs_repo.scm_instance, revs)

        if partial:

            return render('compare/compare_cs.html')

        org_repo = c.a_repo

        other_repo = c.cs_repo

        if merge:

            rev1 = msg = None

            if not c.cs_ranges:

                msg = _('Cannot show empty diff')

            elif not c.ancestors:

                msg = _('No ancestor found for merge diff')

            elif len(c.ancestors) == 1:

                rev1 = c.ancestors[0]

            else:

                msg = _('Multiple merge ancestors found for merge compare')

            if rev1 is None:

                h.flash(msg, category='error')

                log.error(msg)

                raise HTTPNotFound

            # 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_rev)

            log.debug('Using ancestor %s as rev1 instead of %s',

                      rev1, c.a_rev)

            org_repo = other_repo

        else: # comparing tips, not necessarily linearly related

            if org_repo != other_repo:

                # TODO: we could do this by using hg unionrepo

                log.error('cannot compare across repos %s and %s', org_repo, other_repo)

                h.flash(_('Cannot compare repositories without using common ancestor'), category='error')

                raise HTTPBadRequest

            rev1 = c.a_rev

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

        log.debug('running diff between %s and %s in %s',

                  rev1, c.cs_rev, org_repo.scm_instance.path)

        ${_('%s Compare') % c.repo_name} - ${'%s@%s' % (c.a_repo.repo_name, c.a_ref_name)} > ${'%s@%s' % (c.cs_repo.repo_name, c.cs_ref_name)}

    %endif

</%block>

<%def name="breadcrumbs_links()">

  ${_('Compare Revisions')}

</%def>

<%block name="header_menu">

    ${self.menu('repositories')}

</%block>

<%def name="main()">

${self.repo_context_bar('changelog')}

<div class="panel panel-primary">

    <div class="panel-heading clearfix">

        ${self.breadcrumbs()}

    </div>

    <div class="panel-body">

      <div>

        <div id="body" class="diffblock">

            <div class="compare-revision-selector">

                ## divs are "inline-block" and cannot have whitespace between them.

                <div>

                    ${h.hidden('compare_org')}

                </div><div>

                    <i class="icon-right"></i>

                </div><div>

                    ${h.hidden('compare_other')}

                </div><div>

                    %if not c.compare_home:

                        <a class="btn btn-default btn-sm" href="${c.swap_url}"><i class="icon-arrows-cw"></i> ${_('Swap')}</a>

                    %endif

                    <div id="compare_revs" class="btn btn-default btn-sm"><i class="icon-git-compare"></i> ${_('Compare Revisions')}</div>

                </div>

            </div>

        </div>

    %if c.compare_home:

        <div id="changeset_compare_view_content">

         <h4 class="text-muted">${_('Compare revisions, branches, bookmarks, or tags.')}</h4>

        </div>

    %else:

        <div id="changeset_compare_view_content">

                ##CS

                <h5>${ungettext('Showing %s commit','Showing %s commits', len(c.cs_ranges)) % len(c.cs_ranges)}</h5>

                <%include file="compare_cs.html" />

                ## FILES

                <h5>

                % if c.limited_diff:

                    ${ungettext('%s file changed', '%s files changed', len(c.file_diff_data)) % len(c.file_diff_data)}:

                % else:

                    ${ungettext('%s file changed with %s insertions and %s deletions','%s files changed with %s insertions and %s deletions', len(c.file_diff_data)) % (len(c.file_diff_data),c.lines_added,c.lines_deleted)}:

                %endif

                ${c.ignorews_url(request.GET)}

                ${c.context_url(request.GET)}

                </h5>

                <div class="cs_files">

                  %if not c.file_diff_data:

                     <span class="empty_data">${_('No files')}</span>

                  %endif

                  %for fid, url_fid, op, a_path, path, diff, stats in c.file_diff_data:

                    <div class="cs_${op}">

                      <div class="node">

                          <i class="icon-diff-${op}"></i>

                          ${h.link_to(h.safe_unicode(path), '#%s' % fid)}

                      </div>

                      <div class="changes">${h.fancy_file_stats(stats)}</div>

                    </div>

                  %endfor

                  %if c.limited_diff:

                    <h5>${_('Changeset was too big and was cut off...')} <a href="${h.url.current(fulldiff=1, **request.GET.mixed())}">${_('Show full diff anyway')}</a></h5>

                  %endif

                </div>

        </div>

        ## diff block

        <%namespace name="diff_block" file="/changeset/diff_block.html"/>

        ${diff_block.diff_block_js()}

        ${diff_block.diff_block(c.a_repo.repo_name, c.a_ref_type, c.a_ref_name, c.a_rev,

                                c.cs_repo.repo_name, c.cs_ref_type, c.cs_ref_name, c.cs_rev, c.file_diff_data)}

        % if c.limited_diff:

          <h4>${_('Changeset was too big and was cut off...')} <a href="${h.url.current(fulldiff=1, **request.GET.mixed())}">${_('Show full diff')}</a></h4>

        % endif

      </div>

    %endif

    </div>

</div>

    <script type="text/javascript">

   $(document).ready(function(){

    var cache = {};

      $(css_selector).select2({

        formatSelection: function(obj){

            return '{0}@{1}'.format(repo_name, obj.text);

        },

        dropdownAutoWidth: true,

        maxResults: 50,

        query: function(query){

          var key = cache_key;

          var cached = cache[key] ;

          if(cached) {

            var data = {results: []};

            var queryLower = query.term.toLowerCase();

            //filter results

            $.each(cached.results, function(){

                var section = this.text;

                var children = [];

                $.each(this.children, function(){

                    if(children.length < 50 ?

                       ((queryLower.length == 0) || (this.text.toLowerCase().indexOf(queryLower) >= 0)) :

                       ((queryLower.length != 0) && (this.text.toLowerCase().indexOf(queryLower) == 0))) {

                        children.push(this);

                    }

                });

                children = branchSort(children, undefined, query)

                data.results.push({'text': section, 'children': children});

            });

            //push the typed in changeset

            data.results.push({'text':_TM['Specify changeset'],

                               'children': [{'id': query.term, 'text': query.term, 'type': 'rev'}]});

            query.callback(data);

          }else{

              $.ajax({

                url: pyroutes.url('repo_refs_data', {'repo_name': repo_name}),

                data: {},

                dataType: 'json',

                type: 'GET',

                success: function(data) {

                  cache[key] = data;

                  query.callback(data);

                }

              });

          }

        }

    });

    }

    var values_changed = function() {

        var values = $('#compare_org').select2('data') && $('#compare_other').select2('data');

        if (values) {

             $('#compare_revs').removeClass("disabled");

             // TODO: the swap button ... if any

        } else {

             $('#compare_revs').addClass("disabled");

             // TODO: the swap button ... if any

        }

    }

    values_changed();

    $('#compare_org').change(values_changed);

    $('#compare_other').change(values_changed);

    $('#compare_revs').on('click', function(e){

        var org = $('#compare_org').select2('data');

        var other = $('#compare_other').select2('data');

        if (!org || !other) {

            return;

        }

        var compare_url = ${h.js(h.url('compare_url',repo_name=c.repo_name,org_ref_type='__other_ref_type__',org_ref_name='__org__',other_ref_type='__org_ref_type__',other_ref_name='__other__', other_repo=c.cs_repo.repo_name))};

        var u = compare_url.replace('__other_ref_type__',org.type)

                           .replace('__org__',org.text)

                           .replace('__org_ref_type__',other.type)

                           .replace('__other__',other.text);

        window.location = u;

    });

   });

    </script>

</%def>