global _urlify_issues_f

    if _urlify_issues_f is None:

        from kallithea import CONFIG

        from kallithea.model.db import URL_SEP

        assert CONFIG['sqlalchemy.url'] # make sure config has been loaded

        # Build chain of urlify functions, starting with not doing any transformation

        def tmp_urlify_issues_f(s):

            return s

        issue_pat_re = re.compile(r'issue_pat(.*)')

        for k in CONFIG:

            # Find all issue_pat* settings that also have corresponding server_link and prefix configuration

            m = issue_pat_re.match(k)

            if m is None:

                continue

            suffix = m.group(1)

            issue_pat = CONFIG.get(k)

            issue_server_link = CONFIG.get('issue_server_link%s' % suffix)

            issue_sub = CONFIG.get('issue_sub%s' % suffix)

            issue_prefix = CONFIG.get('issue_prefix%s' % suffix)

            if issue_prefix:

                log.error('found unsupported issue_prefix%s = %r - use issue_sub%s instead', suffix, issue_prefix, suffix)

            if not issue_pat or not issue_server_link or issue_sub is None: # issue_sub can be empty but should be present

                continue

            # Wrap tmp_urlify_issues_f with substitution of this pattern, while making sure all loop variables (and compiled regexpes) are bound

            try:

                issue_re = re.compile(issue_pat)

            except re.error as e:

                continue

            def issues_replace(match_obj,

                               issue_server_link=issue_server_link, issue_sub=issue_sub):

                try:

                    issue_url = match_obj.expand(issue_server_link)

                except (IndexError, re.error) as e:

                    log.error('invalid issue_url setting %r -> %r %r. Error: %s', issue_pat, issue_server_link, issue_sub, str(e))

                    issue_url = issue_server_link

                issue_url = issue_url.replace('{repo}', repo_name)

                issue_url = issue_url.replace('{repo_name}', repo_name.split(URL_SEP)[-1])

                # if issue_sub is empty use the matched issue reference verbatim

                if not issue_sub:

                    issue_text = match_obj.group()

                else:

                    try:

                        issue_text = match_obj.expand(issue_sub)

                    except (IndexError, re.error) as e:

                        log.error('invalid issue_sub setting %r -> %r %r. Error: %s', issue_pat, issue_server_link, issue_sub, str(e))

                        issue_text = match_obj.group()

                return (

                    '<a class="issue-tracker-link" href="%(url)s">'

                    '%(text)s'

                    '</a>'