# Copyright (C) 2012, Ansgar Burchardt <ansgar@debian.org>
#
# Parts based on code that is
# Copyright (C) 2001-2006, James Troup <james@nocrew.org>
# Copyright (C) 2009-2010, Joerg Jaspert <joerg@debian.org>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

"""module provided pre-acceptance tests

Please read the documentation for the L{Check} class for the interface.
"""

from daklib.config import Config
from daklib.dbconn import *
import daklib.dbconn as dbconn
from daklib.regexes import *
from daklib.textutils import fix_maintainer, ParseMaintError
import daklib.lintian as lintian
import daklib.utils as utils
from daklib.upload import InvalidHashException

import apt_inst
import apt_pkg
from apt_pkg import version_compare
import errno
import os
import time
import yaml

# TODO: replace by subprocess
import commands

def check_fields_for_valid_utf8(filename, control):
    """Check all fields of a control file for valid UTF-8"""
    for field in control.keys():
        try:
            field.decode('utf-8')
            control[field].decode('utf-8')
        except UnicodeDecodeError:
            raise Reject('{0}: The {1} field is not valid UTF-8'.format(filename, field))

class Reject(Exception):
    """exception raised by failing checks"""
    pass

class RejectStupidMaintainerException(Exception):
    """exception raised by failing the external hashes check"""

    def __str__(self):
        return "'%s' has mismatching %s from the external files db ('%s' [current] vs '%s' [external])" % self.args[:4]

class RejectACL(Reject):
    """exception raise by failing ACL checks"""
    def __init__(self, acl, reason):
        self.acl = acl
        self.reason = reason

    def __str__(self):
        return "ACL {0}: {1}".format(self.acl.name, self.reason)

class Check(object):
    """base class for checks

    checks are called by L{daklib.archive.ArchiveUpload}. Failing tests should
    raise a L{daklib.checks.Reject} exception including a human-readable
    description why the upload should be rejected.
    """
    def check(self, upload):
        """do checks

        @type  upload: L{daklib.archive.ArchiveUpload}
        @param upload: upload to check

        @raise daklib.checks.Reject: upload should be rejected
        """
        raise NotImplemented
    def per_suite_check(self, upload, suite):
        """do per-suite checks

        @type  upload: L{daklib.archive.ArchiveUpload}
        @param upload: upload to check

        @type  suite: L{daklib.dbconn.Suite}
        @param suite: suite to check

        @raise daklib.checks.Reject: upload should be rejected
        """
        raise NotImplemented
    @property
    def forcable(self):
        """allow to force ignore failing test

        C{True} if it is acceptable to force ignoring a failing test,
        C{False} otherwise
        """
        return False

class SignatureAndHashesCheck(Check):
    """Check signature of changes and dsc file (if included in upload)

    Make sure the signature is valid and done by a known user.
    """
    def check(self, upload):
        changes = upload.changes
        if not changes.valid_signature:
            raise Reject("Signature for .changes not valid.")
        self._check_hashes(upload, changes.filename, changes.files.itervalues())

        source = None
        try:
            source = changes.source
        except Exception as e:
            raise Reject("Invalid dsc file: {0}".format(e))
        if source is not None:
            if not source.valid_signature:
                raise Reject("Signature for .dsc not valid.")
            if source.primary_fingerprint != changes.primary_fingerprint:
                raise Reject(".changes and .dsc not signed by the same key.")
            self._check_hashes(upload, source.filename, source.files.itervalues())

        if upload.fingerprint is None or upload.fingerprint.uid is None:
            raise Reject(".changes signed by unknown key.")

    """Make sure hashes match existing files

    @type  upload: L{daklib.archive.ArchiveUpload}
    @param upload: upload we are processing

    @type  filename: str
    @param filename: name of the file the expected hash values are taken from

    @type  files: sequence of L{daklib.upload.HashedFile}
    @param files: files to check the hashes for
    """
    def _check_hashes(self, upload, filename, files):
        try:
            for f in files:
                f.check(upload.directory)
        except IOError as e:
            if e.errno == errno.ENOENT:
                raise Reject('{0} refers to non-existing file: {1}\n'
                             'Perhaps you need to include it in your upload?'
                             .format(filename, os.path.basename(e.filename)))
            raise
        except InvalidHashException as e:
            raise Reject('{0}: {1}'.format(filename, unicode(e)))

class ChangesCheck(Check):
    """Check changes file for syntax errors."""
    def check(self, upload):
        changes = upload.changes
        control = changes.changes
        fn = changes.filename

        for field in ('Distribution', 'Source', 'Binary', 'Architecture', 'Version', 'Maintainer', 'Files', 'Changes', 'Description'):
            if field not in control:
                raise Reject('{0}: misses mandatory field {1}'.format(fn, field))

        check_fields_for_valid_utf8(fn, control)

        source_match = re_field_source.match(control['Source'])
        if not source_match:
            raise Reject('{0}: Invalid Source field'.format(fn))
        version_match = re_field_version.match(control['Version'])
        if not version_match:
            raise Reject('{0}: Invalid Version field'.format(fn))
        version_without_epoch = version_match.group('without_epoch')

        match = re_file_changes.match(fn)
        if not match:
            raise Reject('{0}: Does not match re_file_changes'.format(fn))
        if match.group('package') != source_match.group('package'):
            raise Reject('{0}: Filename does not match Source field'.format(fn))
        if match.group('version') != version_without_epoch:
            raise Reject('{0}: Filename does not match Version field'.format(fn))

        for bn in changes.binary_names:
            if not re_field_package.match(bn):
                raise Reject('{0}: Invalid binary package name {1}'.format(fn, bn))

        if 'source' in changes.architectures and changes.source is None:
            raise Reject("Changes has architecture source, but no source found.")
        if changes.source is not None and 'source' not in changes.architectures:
            raise Reject("Upload includes source, but changes does not say so.")

        try:
            fix_maintainer(changes.changes['Maintainer'])
        except ParseMaintError as e:
            raise Reject('{0}: Failed to parse Maintainer field: {1}'.format(changes.filename, e))

        try:
            changed_by = changes.changes.get('Changed-By')
            if changed_by is not None:
                fix_maintainer(changed_by)
        except ParseMaintError as e:
            raise Reject('{0}: Failed to parse Changed-By field: {1}'.format(changes.filename, e))

        if len(changes.files) == 0:
            raise Reject("Changes includes no files.")

        for bugnum in changes.closed_bugs:
            if not re_isanum.match(bugnum):
                raise Reject('{0}: "{1}" in Closes field is not a number'.format(changes.filename, bugnum))

        return True

class ExternalHashesCheck(Check):
    """Checks hashes in .changes and .dsc against an external database."""
    def check_single(self, session, f):
        q = session.execute("SELECT size, md5sum, sha1sum, sha256sum FROM external_files WHERE filename LIKE '%%/%s'" % f.filename)
        (ext_size, ext_md5sum, ext_sha1sum, ext_sha256sum) = q.fetchone() or (None, None, None, None)

        if not ext_size:
            return

        if ext_size != f.size:
            raise RejectStupidMaintainerException(f.filename, 'size', f.size, ext_size)

        if ext_md5sum != f.md5sum:
            raise RejectStupidMaintainerException(f.filename, 'md5sum', f.md5sum, ext_md5sum)

        if ext_sha1sum != f.sha1sum:
            raise RejectStupidMaintainerException(f.filename, 'sha1sum', f.sha1sum, ext_sha1sum)

        if ext_sha256sum != f.sha256sum:
            raise RejectStupidMaintainerException(f.filename, 'sha256sum', f.sha256sum, ext_sha256sum)

    def check(self, upload):
        cnf = Config()

        if not cnf.use_extfiles:
            return

        session = upload.session
        changes = upload.changes

        for f in changes.files.itervalues():
            self.check_single(session, f)
        source = changes.source
        if source is not None:
            for f in source.files.itervalues():
                self.check_single(session, f)

class BinaryCheck(Check):
    """Check binary packages for syntax errors."""
    def check(self, upload):
        for binary in upload.changes.binaries:
            self.check_binary(upload, binary)

        binary_names = set([ binary.control['Package'] for binary in upload.changes.binaries ])
        for bn in binary_names:
            if bn not in upload.changes.binary_names:
                raise Reject('Package {0} is not mentioned in Binary field in changes'.format(bn))

        return True

    def check_binary(self, upload, binary):
        fn = binary.hashed_file.filename
        control = binary.control

        for field in ('Package', 'Architecture', 'Version', 'Description'):
            if field not in control:
                raise Reject('{0}: Missing mandatory field {0}.'.format(fn, field))

        check_fields_for_valid_utf8(fn, control)

        # check fields

        package = control['Package']
        if not re_field_package.match(package):
            raise Reject('{0}: Invalid Package field'.format(fn))

        version = control['Version']
        version_match = re_field_version.match(version)
        if not version_match:
            raise Reject('{0}: Invalid Version field'.format(fn))
        version_without_epoch = version_match.group('without_epoch')

        architecture = control['Architecture']
        if architecture not in upload.changes.architectures:
            raise Reject('{0}: Architecture not in Architecture field in changes file'.format(fn))
        if architecture == 'source':
            raise Reject('{0}: Architecture "source" invalid for binary packages'.format(fn))

        source = control.get('Source')
        if source is not None and not re_field_source.match(source):
            raise Reject('{0}: Invalid Source field'.format(fn))

        # check filename

        match = re_file_binary.match(fn)
        if package != match.group('package'):
            raise Reject('{0}: filename does not match Package field'.format(fn))
        if version_without_epoch != match.group('version'):
            raise Reject('{0}: filename does not match Version field'.format(fn))
        if architecture != match.group('architecture'):
            raise Reject('{0}: filename does not match Architecture field'.format(fn))

        # check dependency field syntax

        for field in ('Breaks', 'Conflicts', 'Depends', 'Enhances', 'Pre-Depends',
                      'Provides', 'Recommends', 'Replaces', 'Suggests'):
            value = control.get(field)
            if value is not None:
                if value.strip() == '':
                    raise Reject('{0}: empty {1} field'.format(fn, field))
                try:
                    apt_pkg.parse_depends(value)
                except:
                    raise Reject('{0}: APT could not parse {1} field'.format(fn, field))

        for field in ('Built-Using',):
            value = control.get(field)
            if value is not None:
                if value.strip() == '':
                    raise Reject('{0}: empty {1} field'.format(fn, field))
                try:
                    apt_pkg.parse_src_depends(value)
                except:
                    raise Reject('{0}: APT could not parse {1} field'.format(fn, field))

class BinaryTimestampCheck(Check):
    """check timestamps of files in binary packages

    Files in the near future cause ugly warnings and extreme time travel
    can cause errors on extraction.
    """
    def check(self, upload):
        cnf = Config()
        future_cutoff = time.time() + cnf.find_i('Dinstall::FutureTimeTravelGrace', 24*3600)
        past_cutoff = time.mktime(time.strptime(cnf.find('Dinstall::PastCutoffYear', '1975'), '%Y'))

        class TarTime(object):
            def __init__(self):
                self.future_files = dict()
                self.past_files = dict()
            def callback(self, member, data):
                if member.mtime > future_cutoff:
                    self.future_files[member.name] = member.mtime
                elif member.mtime < past_cutoff:
                    self.past_files[member.name] = member.mtime

        def format_reason(filename, direction, files):
            reason = "{0}: has {1} file(s) with a timestamp too far in the {2}:\n".format(filename, len(files), direction)
            for fn, ts in files.iteritems():
                reason += "  {0} ({1})".format(fn, time.ctime(ts))
            return reason

        for binary in upload.changes.binaries:
            filename = binary.hashed_file.filename
            path = os.path.join(upload.directory, filename)
            deb = apt_inst.DebFile(path)
            tar = TarTime()
            deb.control.go(tar.callback)
            if tar.future_files:
                raise Reject(format_reason(filename, 'future', tar.future_files))
            if tar.past_files:
                raise Reject(format_reason(filename, 'past', tar.past_files))

class SourceCheck(Check):
    """Check source package for syntax errors."""
    def check_filename(self, control, filename, regex):
        # In case we have an .orig.tar.*, we have to strip the Debian revison
        # from the version number. So handle this special case first.
        is_orig = True
        match = re_file_orig.match(filename)
        if not match:
            is_orig = False
            match = regex.match(filename)

        if not match:
            raise Reject('{0}: does not match regular expression for source filenames'.format(filename))
        if match.group('package') != control['Source']:
            raise Reject('{0}: filename does not match Source field'.format(filename))

        version = control['Version']
        if is_orig:
            upstream_match = re_field_version_upstream.match(version)
            if not upstream_match:
                raise Reject('{0}: Source package includes upstream tarball, but {0} has no Debian revision.'.format(filename, version))
            version = upstream_match.group('upstream')
        version_match =  re_field_version.match(version)
        version_without_epoch = version_match.group('without_epoch')
        if match.group('version') != version_without_epoch:
            raise Reject('{0}: filename does not match Version field'.format(filename))

    def check(self, upload):
        if upload.changes.source is None:
            return True

        changes = upload.changes.changes
        source = upload.changes.source
        control = source.dsc
        dsc_fn = source._dsc_file.filename

        check_fields_for_valid_utf8(dsc_fn, control)

        # check fields
        if not re_field_package.match(control['Source']):
            raise Reject('{0}: Invalid Source field'.format(dsc_fn))
        if control['Source'] != changes['Source']:
            raise Reject('{0}: Source field does not match Source field in changes'.format(dsc_fn))
        if control['Version'] != changes['Version']:
            raise Reject('{0}: Version field does not match Version field in changes'.format(dsc_fn))

        # check filenames
        self.check_filename(control, dsc_fn, re_file_dsc)
        for f in source.files.itervalues():
            self.check_filename(control, f.filename, re_file_source)

        # check dependency field syntax
        for field in ('Build-Conflicts', 'Build-Conflicts-Indep', 'Build-Depends', 'Build-Depends-Arch', 'Build-Depends-Indep'):
            value = control.get(field)
            if value is not None:
                if value.strip() == '':
                    raise Reject('{0}: empty {1} field'.format(dsc_fn, field))
                try:
                    apt_pkg.parse_src_depends(value)
                except Exception as e:
                    raise Reject('{0}: APT could not parse {1} field: {2}'.format(dsc_fn, field, e))

        rejects = utils.check_dsc_files(dsc_fn, control, source.files.keys())
        if len(rejects) > 0:
            raise Reject("\n".join(rejects))

        return True

class SingleDistributionCheck(Check):
    """Check that the .changes targets only a single distribution."""
    def check(self, upload):
        if len(upload.changes.distributions) != 1:
            raise Reject("Only uploads to a single distribution are allowed.")

class ACLCheck(Check):
    """Check the uploader is allowed to upload the packages in .changes"""

    def _does_hijack(self, session, upload, suite):
        # Try to catch hijacks.
        # This doesn't work correctly. Uploads to experimental can still
        # "hijack" binaries from unstable. Also one can hijack packages
        # via buildds (but people who try this should not be DMs).
        for binary_name in upload.changes.binary_names:
            binaries = session.query(DBBinary).join(DBBinary.source) \
                .filter(DBBinary.suites.contains(suite)) \
                .filter(DBBinary.package == binary_name)
            for binary in binaries:
                if binary.source.source != upload.changes.changes['Source']:
                    return True, binary.package, binary.source.source
        return False, None, None

    def _check_acl(self, session, upload, acl):
        source_name = upload.changes.source_name

        if acl.match_fingerprint and upload.fingerprint not in acl.fingerprints:
            return None, None
        if acl.match_keyring is not None and upload.fingerprint.keyring != acl.match_keyring:
            return None, None

        if not acl.allow_new:
            if upload.new:
                return False, "NEW uploads are not allowed"
            for f in upload.changes.files.itervalues():
                if f.section == 'byhand' or f.section.startswith("raw-"):
                    return False, "BYHAND uploads are not allowed"
        if not acl.allow_source and upload.changes.source is not None:
            return False, "sourceful uploads are not allowed"
        binaries = upload.changes.binaries
        if len(binaries) != 0:
            if not acl.allow_binary:
                return False, "binary uploads are not allowed"
            if upload.changes.source is None and not acl.allow_binary_only:
                return False, "binary-only uploads are not allowed"
            if not acl.allow_binary_all:
                uploaded_arches = set(upload.changes.architectures)
                uploaded_arches.discard('source')
                allowed_arches = set(a.arch_string for a in acl.architectures)
                forbidden_arches = uploaded_arches - allowed_arches
                if len(forbidden_arches) != 0:
                    return False, "uploads for architecture(s) {0} are not allowed".format(", ".join(forbidden_arches))
        if not acl.allow_hijack:
            for suite in upload.final_suites:
                does_hijack, hijacked_binary, hijacked_from = self._does_hijack(session, upload, suite)
                if does_hijack:
                    return False, "hijacks are not allowed (binary={0}, other-source={1})".format(hijacked_binary, hijacked_from)

        acl_per_source = session.query(ACLPerSource).filter_by(acl=acl, fingerprint=upload.fingerprint, source=source_name).first()
        if acl.allow_per_source:
            if acl_per_source is None:
                return False, "not allowed to upload source package '{0}'".format(source_name)
        if acl.deny_per_source and acl_per_source is not None:
            return False, acl_per_source.reason or "forbidden to upload source package '{0}'".format(source_name)

        return True, None

    def check(self, upload):
        session = upload.session
        fingerprint = upload.fingerprint
        keyring = fingerprint.keyring

        if keyring is None:
            raise Reject('No keyring for fingerprint {0}'.format(fingerprint.fingerprint))
        if not keyring.active:
            raise Reject('Keyring {0} is not active'.format(keyring.name))

        acl = fingerprint.acl or keyring.acl
        if acl is None:
            raise Reject('No ACL for fingerprint {0}'.format(fingerprint.fingerprint))
        result, reason = self._check_acl(session, upload, acl)
        if not result:
            raise RejectACL(acl, reason)

        for acl in session.query(ACL).filter_by(is_global=True):
            result, reason = self._check_acl(session, upload, acl)
            if result == False:
                raise RejectACL(acl, reason)

        return True

    def per_suite_check(self, upload, suite):
        acls = suite.acls
        if len(acls) != 0:
            accept = False
            for acl in acls:
                result, reason = self._check_acl(upload.session, upload, acl)
                if result == False:
                    raise Reject(reason)
                accept = accept or result
            if not accept:
                raise Reject('Not accepted by any per-suite acl (suite={0})'.format(suite.suite_name))
        return True

class TransitionCheck(Check):
    """check for a transition"""
    def check(self, upload):
        if 'source' not in upload.changes.architectures:
            return True

        transitions = self.get_transitions()
        if transitions is None:
            return True

        control = upload.changes.changes
        source = re_field_source.match(control['Source']).group('package')

        for trans in transitions:
            t = transitions[trans]
            source = t["source"]
            expected = t["new"]

            # Will be None if nothing is in testing.
            current = get_source_in_suite(source, "testing", session)
            if current is not None:
                compare = apt_pkg.version_compare(current.version, expected)

            if current is None or compare < 0:
                # This is still valid, the current version in testing is older than
                # the new version we wait for, or there is none in testing yet

                # Check if the source we look at is affected by this.
                if source in t['packages']:
                    # The source is affected, lets reject it.

                    rejectmsg = "{0}: part of the {1} transition.\n\n".format(source, trans)

                    if current is not None:
                        currentlymsg = "at version {0}".format(current.version)
                    else:
                        currentlymsg = "not present in testing"

                    rejectmsg += "Transition description: {0}\n\n".format(t["reason"])

                    rejectmsg += "\n".join(textwrap.wrap("""Your package
is part of a testing transition designed to get {0} migrated (it is
currently {1}, we need version {2}).  This transition is managed by the
Release Team, and {3} is the Release-Team member responsible for it.
Please mail debian-release@lists.debian.org or contact {3} directly if you
need further assistance.  You might want to upload to experimental until this
transition is done.""".format(source, currentlymsg, expected,t["rm"])))

                    raise Reject(rejectmsg)

        return True

    def get_transitions(self):
        cnf = Config()
        path = cnf.get('Dinstall::ReleaseTransitions', '')
        if path == '' or not os.path.exists(path):
            return None

        contents = file(path, 'r').read()
        try:
            transitions = yaml.safe_load(contents)
            return transitions
        except yaml.YAMLError as msg:
            utils.warn('Not checking transitions, the transitions file is broken: {0}'.format(msg))

        return None

class NoSourceOnlyCheck(Check):
    """Check for source-only upload

    Source-only uploads are only allowed if Dinstall::AllowSourceOnlyUploads is
    set. Otherwise they are rejected.
    """
    def check(self, upload):
        if Config().find_b("Dinstall::AllowSourceOnlyUploads"):
            return True
        changes = upload.changes
        if changes.source is not None and len(changes.binaries) == 0:
            raise Reject('Source-only uploads are not allowed.')
        return True

class LintianCheck(Check):
    """Check package using lintian"""
    def check(self, upload):
        changes = upload.changes

        # Only check sourceful uploads.
        if changes.source is None:
            return True
        # Only check uploads to unstable or experimental.
        if 'unstable' not in changes.distributions and 'experimental' not in changes.distributions:
            return True

        cnf = Config()
        if 'Dinstall::LintianTags' not in cnf:
            return True
        tagfile = cnf['Dinstall::LintianTags']

        with open(tagfile, 'r') as sourcefile:
            sourcecontent = sourcefile.read()
        try:
            lintiantags = yaml.safe_load(sourcecontent)['lintian']
        except yaml.YAMLError as msg:
            raise Exception('Could not read lintian tags file {0}, YAML error: {1}'.format(tagfile, msg))

        fd, temp_filename = utils.temp_filename(mode=0o644)
        temptagfile = os.fdopen(fd, 'w')
        for tags in lintiantags.itervalues():
            for tag in tags:
                print >>temptagfile, tag
        temptagfile.close()

        changespath = os.path.join(upload.directory, changes.filename)
        try:
            cmd = []

            user = cnf.get('Dinstall::UnprivUser') or None
            if user is not None:
                cmd.extend(['sudo', '-H', '-u', user])

            cmd.extend(['LINTIAN_COLL_UNPACKED_SKIP_SIG=1', '/usr/bin/lintian', '--show-overrides', '--tags-from-file', temp_filename, changespath])
            result, output = commands.getstatusoutput(" ".join(cmd))
        finally:
            os.unlink(temp_filename)

        if result == 2:
            utils.warn("lintian failed for %s [return code: %s]." % \
                (changespath, result))
            utils.warn(utils.prefix_multi_line_string(output, \
                " [possible output:] "))

        parsed_tags = lintian.parse_lintian_output(output)
        rejects = list(lintian.generate_reject_messages(parsed_tags, lintiantags))
        if len(rejects) != 0:
            raise Reject('\n'.join(rejects))

        return True

class SourceFormatCheck(Check):
    """Check source format is allowed in the target suite"""
    def per_suite_check(self, upload, suite):
        source = upload.changes.source
        session = upload.session
        if source is None:
            return True

        source_format = source.dsc['Format']
        query = session.query(SrcFormat).filter_by(format_name=source_format).filter(SrcFormat.suites.contains(suite))
        if query.first() is None:
            raise Reject('source format {0} is not allowed in suite {1}'.format(source_format, suite.suite_name))

class SuiteArchitectureCheck(Check):
    def per_suite_check(self, upload, suite):
        session = upload.session
        for arch in upload.changes.architectures:
            query = session.query(Architecture).filter_by(arch_string=arch).filter(Architecture.suites.contains(suite))
            if query.first() is None:
                raise Reject('Architecture {0} is not allowed in suite {1}'.format(arch, suite.suite_name))

        return True

class VersionCheck(Check):
    """Check version constraints"""
    def _highest_source_version(self, session, source_name, suite):
        db_source = session.query(DBSource).filter_by(source=source_name) \
            .filter(DBSource.suites.contains(suite)).order_by(DBSource.version.desc()).first()
        if db_source is None:
            return None
        else:
            return db_source.version

    def _highest_binary_version(self, session, binary_name, suite, architecture):
        db_binary = session.query(DBBinary).filter_by(package=binary_name) \
            .filter(DBBinary.suites.contains(suite)) \
            .join(DBBinary.architecture) \
            .filter(Architecture.arch_string.in_(['all', architecture])) \
            .order_by(DBBinary.version.desc()).first()
        if db_binary is None:
            return None
        else:
            return db_binary.version

    def _version_checks(self, upload, suite, other_suite, op, op_name):
        session = upload.session

        if upload.changes.source is not None:
            source_name = upload.changes.source.dsc['Source']
            source_version = upload.changes.source.dsc['Version']
            v = self._highest_source_version(session, source_name, other_suite)
            if v is not None and not op(version_compare(source_version, v)):
                raise Reject("Version check failed:\n"
                             "Your upload included the source package {0}, version {1},\n"
                             "however {3} already has version {2}.\n"
                             "Uploads to {5} must have a {4} version than present in {3}."
                             .format(source_name, source_version, v, other_suite.suite_name, op_name, suite.suite_name))

        for binary in upload.changes.binaries:
            binary_name = binary.control['Package']
            binary_version = binary.control['Version']
            architecture = binary.control['Architecture']
            v = self._highest_binary_version(session, binary_name, other_suite, architecture)
            if v is not None and not op(version_compare(binary_version, v)):
                raise Reject("Version check failed:\n"
                             "Your upload included the binary package {0}, version {1}, for {2},\n"
                             "however {4} already has version {3}.\n"
                             "Uploads to {6} must have a {5} version than present in {4}."
                             .format(binary_name, binary_version, architecture, v, other_suite.suite_name, op_name, suite.suite_name))

    def per_suite_check(self, upload, suite):
        session = upload.session

        vc_newer = session.query(dbconn.VersionCheck).filter_by(suite=suite) \
            .filter(dbconn.VersionCheck.check.in_(['MustBeNewerThan', 'Enhances']))
        must_be_newer_than = [ vc.reference for vc in vc_newer ]
        # Must be newer than old versions in `suite`
        must_be_newer_than.append(suite)

        for s in must_be_newer_than:
            self._version_checks(upload, suite, s, lambda result: result > 0, 'higher')

        vc_older = session.query(dbconn.VersionCheck).filter_by(suite=suite, check='MustBeOlderThan')
        must_be_older_than = [ vc.reference for vc in vc_older ]

        for s in must_be_older_than:
            self._version_checks(upload, suite, s, lambda result: result < 0, 'lower')

        return True

    @property
    def forcable(self):
        return True