Raw File
# Copyright (C) 2015-2016  The Software Heritage developers
# See the AUTHORS file at the top-level directory of this distribution
# License: GNU General Public License version 3, or any later version
# See top-level LICENSE file for more information

import binascii
import datetime
import functools
import json
import psycopg2
import psycopg2.extras
import select
import tempfile
import time

from contextlib import contextmanager

TMP_CONTENT_TABLE = 'tmp_content'


psycopg2.extras.register_uuid()


def stored_procedure(stored_proc):
    """decorator to execute remote stored procedure, specified as argument

    Generally, the body of the decorated function should be empty. If it is
    not, the stored procedure will be executed first; the function body then.

    """
    def wrap(meth):
        @functools.wraps(meth)
        def _meth(self, *args, **kwargs):
            cur = kwargs.get('cur', None)
            self._cursor(cur).execute('SELECT %s()' % stored_proc)
            meth(self, *args, **kwargs)
        return _meth
    return wrap


def jsonize(value):
    """Convert a value to a psycopg2 JSON object if necessary"""
    if isinstance(value, dict):
        return psycopg2.extras.Json(value)

    return value


def entry_to_bytes(entry):
    """Convert an entry coming from the database to bytes"""
    if isinstance(entry, memoryview):
        return entry.tobytes()
    if isinstance(entry, list):
        return [entry_to_bytes(value) for value in entry]
    return entry


def line_to_bytes(line):
    """Convert a line coming from the database to bytes"""
    if isinstance(line, dict):
        return {k: entry_to_bytes(v) for k, v in line.items()}
    return line.__class__(entry_to_bytes(entry) for entry in line)


def cursor_to_bytes(cursor):
    """Yield all the data from a cursor as bytes"""
    yield from (line_to_bytes(line) for line in cursor)


class Db:
    """Proxy to the SWH DB, with wrappers around stored procedures

    """

    @classmethod
    def connect(cls, *args, **kwargs):
        """factory method to create a DB proxy

        Accepts all arguments of psycopg2.connect; only some specific
        possibilities are reported below.

        Args:
            connstring: libpq2 connection string

        """
        conn = psycopg2.connect(*args, **kwargs)
        return cls(conn)

    def _cursor(self, cur_arg):
        """get a cursor: from cur_arg if given, or a fresh one otherwise

        meant to avoid boilerplate if/then/else in methods that proxy stored
        procedures

        """
        if cur_arg is not None:
            return cur_arg
        # elif self.cur is not None:
        #     return self.cur
        else:
            return self.conn.cursor()

    def __init__(self, conn):
        """create a DB proxy

        Args:
            conn: psycopg2 connection to the SWH DB

        """
        self.conn = conn

    @contextmanager
    def transaction(self):
        """context manager to execute within a DB transaction

        Yields:
            a psycopg2 cursor

        """
        with self.conn.cursor() as cur:
            try:
                yield cur
                self.conn.commit()
            except:
                if not self.conn.closed:
                    self.conn.rollback()
                raise

    def mktemp(self, tblname, cur=None):
        self._cursor(cur).execute('SELECT swh_mktemp(%s)', (tblname,))

    def mktemp_dir_entry(self, entry_type, cur=None):
        self._cursor(cur).execute('SELECT swh_mktemp_dir_entry(%s)',
                                  (('directory_entry_%s' % entry_type),))

    @stored_procedure('swh_mktemp_revision')
    def mktemp_revision(self, cur=None): pass

    @stored_procedure('swh_mktemp_release')
    def mktemp_release(self, cur=None): pass

    @stored_procedure('swh_mktemp_occurrence_history')
    def mktemp_occurrence_history(self, cur=None): pass

    @stored_procedure('swh_mktemp_entity_lister')
    def mktemp_entity_lister(self, cur=None): pass

    @stored_procedure('swh_mktemp_entity_history')
    def mktemp_entity_history(self, cur=None): pass

    @stored_procedure('swh_mktemp_bytea')
    def mktemp_bytea(self, cur=None): pass

    def copy_to(self, items, tblname, columns, cur=None, item_cb=None):
        def escape(data):
            if data is None:
                return ''
            if isinstance(data, bytes):
                return '\\x%s' % binascii.hexlify(data).decode('ascii')
            elif isinstance(data, str):
                return '"%s"' % data.replace('"', '""')
            elif isinstance(data, datetime.datetime):
                # We escape twice to make sure the string generated by
                # isoformat gets escaped
                return escape(data.isoformat())
            elif isinstance(data, dict):
                return escape(json.dumps(data))
            elif isinstance(data, list):
                return escape("{%s}" % ','.join(escape(d) for d in data))
            elif isinstance(data, psycopg2.extras.Range):
                # We escape twice here too, so that we make sure
                # everything gets passed to copy properly
                return escape(
                    '%s%s,%s%s' % (
                        '[' if data.lower_inc else '(',
                        '-infinity' if data.lower_inf else escape(data.lower),
                        'infinity' if data.upper_inf else escape(data.upper),
                        ']' if data.upper_inc else ')',
                    )
                )
            else:
                # We don't escape here to make sure we pass literals properly
                return str(data)
        with tempfile.TemporaryFile('w+') as f:
            for d in items:
                if item_cb is not None:
                    item_cb(d)
                line = [escape(d.get(k)) for k in columns]
                f.write(','.join(line))
                f.write('\n')
            f.seek(0)
            self._cursor(cur).copy_expert('COPY %s (%s) FROM STDIN CSV' % (
                tblname, ', '.join(columns)), f)

    def register_listener(self, notify_queue, cur=None):
        """Register a listener for NOTIFY queue `notify_queue`"""
        self._cursor(cur).execute("LISTEN %s" % notify_queue)

    def listen_notifies(self, timeout):
        """Listen to notifications for `timeout` seconds"""
        if select.select([self.conn], [], [], timeout) == ([], [], []):
            return
        else:
            self.conn.poll()
            while self.conn.notifies:
                yield self.conn.notifies.pop(0)

    @stored_procedure('swh_content_add')
    def content_add_from_temp(self, cur=None): pass

    @stored_procedure('swh_directory_add')
    def directory_add_from_temp(self, cur=None): pass

    @stored_procedure('swh_skipped_content_add')
    def skipped_content_add_from_temp(self, cur=None): pass

    @stored_procedure('swh_revision_add')
    def revision_add_from_temp(self, cur=None): pass

    @stored_procedure('swh_release_add')
    def release_add_from_temp(self, cur=None): pass

    @stored_procedure('swh_occurrence_history_add')
    def occurrence_history_add_from_temp(self, cur=None): pass

    @stored_procedure('swh_entity_history_add')
    def entity_history_add_from_temp(self, cur=None): pass

    def store_tmp_bytea(self, ids, cur=None):
        """Store the given identifiers in a new tmp_bytea table"""
        cur = self._cursor(cur)

        self.mktemp_bytea(cur)
        self.copy_to(({'id': elem} for elem in ids), 'tmp_bytea',
                     ['id'], cur)

    content_get_metadata_keys = ['sha1', 'sha1_git', 'sha256', 'length',
                                 'status']

    def content_get_metadata_from_temp(self, cur=None):
        cur = self._cursor(cur)
        cur.execute("""select t.id as sha1, %s from tmp_bytea t
                       left join content on t.id = content.sha1
                    """ % ', '.join(self.content_get_metadata_keys[1:]))

        yield from cursor_to_bytes(cur)

    def content_missing_from_temp(self, cur=None):
        cur = self._cursor(cur)

        cur.execute("""SELECT sha1, sha1_git, sha256
                       FROM swh_content_missing()""")

        yield from cursor_to_bytes(cur)

    def content_missing_per_sha1_from_temp(self, cur=None):
        cur = self._cursor(cur)

        cur.execute("""SELECT *
                       FROM swh_content_missing_per_sha1()""")

        yield from cursor_to_bytes(cur)

    def skipped_content_missing_from_temp(self, cur=None):
        cur = self._cursor(cur)

        cur.execute("""SELECT sha1, sha1_git, sha256
                       FROM swh_skipped_content_missing()""")

        yield from cursor_to_bytes(cur)

    def occurrence_get(self, origin_id, cur=None):
        """Retrieve latest occurrence's information by origin_id.

        """
        cur = self._cursor(cur)

        cur.execute("""SELECT origin, branch, target, target_type,
                              (select max(date) from origin_visit
                               where origin=%s) as date
                       FROM occurrence
                       WHERE origin=%s
                    """,
                    (origin_id, origin_id))

        yield from cursor_to_bytes(cur)

    def content_find(self, sha1=None, sha1_git=None, sha256=None, cur=None):
        """Find the content optionally on a combination of the following
        checksums sha1, sha1_git or sha256.

        Args:
            sha1: sha1 content
            git_sha1: the sha1 computed `a la git` sha1 of the content
            sha256: sha256 content

        Returns:
            The triplet (sha1, sha1_git, sha256) if found or None.

        """
        cur = self._cursor(cur)

        cur.execute("""SELECT sha1, sha1_git, sha256, length, ctime, status
                       FROM swh_content_find(%s, %s, %s)
                       LIMIT 1""", (sha1, sha1_git, sha256))

        content = line_to_bytes(cur.fetchone())
        if set(content) == {None}:
            return None
        else:
            return content

    def content_find_occurrence(self, sha1, cur=None):
        """Find one content's occurrence.

        Args:
            sha1: sha1 content
            cur: cursor to use

        Returns:
            One occurrence for that particular sha1

        """
        cur = self._cursor(cur)

        cur.execute("""SELECT origin_type, origin_url, branch, target, target_type, path
                       FROM swh_content_find_occurrence(%s)
                       LIMIT 1""",
                    (sha1, ))

        return line_to_bytes(cur.fetchone())

    def directory_get_from_temp(self, cur=None):
        cur = self._cursor(cur)
        cur.execute('''SELECT id, file_entries, dir_entries, rev_entries
                       FROM swh_directory_get()''')
        yield from cursor_to_bytes(cur)

    def directory_missing_from_temp(self, cur=None):
        cur = self._cursor(cur)
        cur.execute('SELECT * FROM swh_directory_missing()')
        yield from cursor_to_bytes(cur)

    def directory_walk_one(self, directory, cur=None):
        cur = self._cursor(cur)
        cur.execute('SELECT * FROM swh_directory_walk_one(%s)', (directory,))
        yield from cursor_to_bytes(cur)

    def directory_walk(self, directory, cur=None):
        cur = self._cursor(cur)
        cur.execute('SELECT * FROM swh_directory_walk(%s)', (directory,))
        yield from cursor_to_bytes(cur)

    def revision_missing_from_temp(self, cur=None):
        cur = self._cursor(cur)

        cur.execute('SELECT id FROM swh_revision_missing() as r(id)')

        yield from cursor_to_bytes(cur)

    revision_add_cols = [
        'id', 'date', 'date_offset', 'date_neg_utc_offset', 'committer_date',
        'committer_date_offset', 'committer_date_neg_utc_offset', 'type',
        'directory', 'message', 'author_fullname', 'author_name',
        'author_email', 'committer_fullname', 'committer_name',
        'committer_email', 'metadata', 'synthetic',
    ]

    revision_get_cols = revision_add_cols + [
        'author_id', 'committer_id', 'parents']

    def origin_visit_add(self, origin, ts, cur=None):
        """Add a new origin_visit for origin origin at timestamp ts with
        status 'ongoing'.

        Args:
            origin: origin concerned by the visit
            ts: the date of the visit

        Returns:
            The new visit index step for that origin

        """
        cur = self._cursor(cur)
        self._cursor(cur).execute('SELECT swh_origin_visit_add(%s, %s)',
                                  (origin, ts))
        return cur.fetchone()[0]

    def origin_visit_update(self, origin, visit_id, status,
                            metadata, cur=None):
        """Update origin_visit's status."""
        cur = self._cursor(cur)
        update = """UPDATE origin_visit
                    SET status=%s, metadata=%s
                    WHERE origin=%s AND visit=%s"""
        cur.execute(update, (status, jsonize(metadata), origin, visit_id))

    origin_visit_get_cols = [
        'origin', 'visit', 'date', 'status', 'metadata',
    ]

    def origin_visit_get(self, origin_id, cur=None):
        """Retrieve all visits for origin with id origin_id.

        Args:
            origin_id: The occurrence's origin

        Yields:
            The occurrence's history visits

        """
        cur = self._cursor(cur)

        query = """\
        SELECT %s
        FROM origin_visit
        WHERE origin=%%s""" % (', '.join(self.origin_visit_get_cols))

        cur.execute(query, (origin_id, ))

        yield from cursor_to_bytes(cur)

    def revision_get_from_temp(self, cur=None):
        cur = self._cursor(cur)
        query = 'SELECT %s FROM swh_revision_get()' % (
            ', '.join(self.revision_get_cols))
        cur.execute(query)
        yield from cursor_to_bytes(cur)

    def revision_log(self, root_revisions, limit=None, cur=None):
        cur = self._cursor(cur)

        query = """SELECT %s
                   FROM swh_revision_log(%%s, %%s)
                """ % ', '.join(self.revision_get_cols)

        cur.execute(query, (root_revisions, limit))
        yield from cursor_to_bytes(cur)

    revision_shortlog_cols = ['id', 'parents']

    def revision_shortlog(self, root_revisions, limit=None, cur=None):
        cur = self._cursor(cur)

        query = """SELECT %s
                   FROM swh_revision_list(%%s, %%s)
                """ % ', '.join(self.revision_shortlog_cols)

        cur.execute(query, (root_revisions, limit))
        yield from cursor_to_bytes(cur)

    def release_missing_from_temp(self, cur=None):
        cur = self._cursor(cur)
        cur.execute('SELECT id FROM swh_release_missing() as r(id)')
        yield from cursor_to_bytes(cur)

    object_find_by_sha1_git_cols = ['sha1_git', 'type', 'id', 'object_id']

    def object_find_by_sha1_git(self, ids, cur=None):
        cur = self._cursor(cur)

        self.store_tmp_bytea(ids, cur)
        query = 'select %s from swh_object_find_by_sha1_git()' % (
            ', '.join(self.object_find_by_sha1_git_cols)
        )
        cur.execute(query)

        yield from cursor_to_bytes(cur)

    def stat_counters(self, cur=None):
        cur = self._cursor(cur)
        cur.execute('SELECT * FROM swh_stat_counters()')
        yield from cur

    fetch_history_cols = ['origin', 'date', 'status', 'result', 'stdout',
                          'stderr', 'duration']

    def create_fetch_history(self, fetch_history, cur=None):
        """Create a fetch_history entry with the data in fetch_history"""
        cur = self._cursor(cur)
        query = '''INSERT INTO fetch_history (%s)
                   VALUES (%s) RETURNING id''' % (
            ','.join(self.fetch_history_cols),
            ','.join(['%s'] * len(self.fetch_history_cols))
        )
        cur.execute(query, [fetch_history.get(col) for col in
                            self.fetch_history_cols])

        return cur.fetchone()[0]

    def get_fetch_history(self, fetch_history_id, cur=None):
        """Get a fetch_history entry with the given id"""
        cur = self._cursor(cur)
        query = '''SELECT %s FROM fetch_history WHERE id=%%s''' % (
            ', '.join(self.fetch_history_cols),
        )
        cur.execute(query, (fetch_history_id,))

        data = cur.fetchone()

        if not data:
            return None

        ret = {'id': fetch_history_id}
        for i, col in enumerate(self.fetch_history_cols):
            ret[col] = data[i]

        return ret

    def update_fetch_history(self, fetch_history, cur=None):
        """Update the fetch_history entry from the data in fetch_history"""
        cur = self._cursor(cur)
        query = '''UPDATE fetch_history
                   SET %s
                   WHERE id=%%s''' % (
            ','.join('%s=%%s' % col for col in self.fetch_history_cols)
        )
        cur.execute(query, [jsonize(fetch_history.get(col)) for col in
                            self.fetch_history_cols + ['id']])

    base_entity_cols = ['uuid', 'parent', 'name', 'type',
                        'description', 'homepage', 'active',
                        'generated', 'lister_metadata',
                        'metadata']

    entity_cols = base_entity_cols + ['last_seen', 'last_id']
    entity_history_cols = base_entity_cols + ['id', 'validity']

    def origin_add(self, type, url, cur=None):
        """Insert a new origin and return the new identifier."""
        insert = """INSERT INTO origin (type, url) values (%s, %s)
                    RETURNING id"""

        cur.execute(insert, (type, url))
        return cur.fetchone()[0]

    def origin_get_with(self, type, url, cur=None):
        """Retrieve the origin id from its type and url if found."""
        cur = self._cursor(cur)

        query = """SELECT id, type, url, lister, project
                   FROM origin
                   WHERE type=%s AND url=%s"""

        cur.execute(query, (type, url))
        data = cur.fetchone()
        if data:
            return line_to_bytes(data)
        return None

    def origin_get(self, id, cur=None):
        """Retrieve the origin per its identifier.

        """
        cur = self._cursor(cur)

        query = "SELECT id, type, url, lister, project FROM origin WHERE id=%s"

        cur.execute(query, (id,))
        data = cur.fetchone()
        if data:
            return line_to_bytes(data)
        return None

    person_cols = ['fullname', 'name', 'email']
    person_get_cols = person_cols + ['id']

    def person_add(self, person, cur=None):
        """Add a person identified by its name and email.

        Returns:
            The new person's id

        """
        cur = self._cursor(cur)

        query_new_person = '''\
        INSERT INTO person(%s)
        VALUES (%s)
        RETURNING id''' % (
            ', '.join(self.person_cols),
            ', '.join('%s' for i in range(len(self.person_cols)))
        )
        cur.execute(query_new_person,
                    [person[col] for col in self.person_cols])
        return cur.fetchone()[0]

    def person_get(self, ids, cur=None):
        """Retrieve the persons identified by the list of ids.

        """
        cur = self._cursor(cur)

        query = """SELECT %s
                   FROM person
                   WHERE id IN %%s""" % ', '.join(self.person_get_cols)

        cur.execute(query, (tuple(ids),))
        yield from cursor_to_bytes(cur)

    release_add_cols = [
        'id', 'target', 'target_type', 'date', 'date_offset',
        'date_neg_utc_offset', 'name', 'comment', 'synthetic',
        'author_fullname', 'author_name', 'author_email',
    ]
    release_get_cols = release_add_cols + ['author_id']

    def release_get_from_temp(self, cur=None):
        cur = self._cursor(cur)
        query = '''
        SELECT %s
            FROM swh_release_get()
        ''' % ', '.join(self.release_get_cols)
        cur.execute(query)
        yield from cursor_to_bytes(cur)

    def release_get_by(self,
                       origin_id,
                       limit=None,
                       cur=None):
        """Retrieve a release by occurrence criterion (only origin right now)

        Args:
            - origin_id: The origin to look for.

        """
        cur = self._cursor(cur)
        query = """
        SELECT %s
            FROM swh_release_get_by(%%s)
            LIMIT %%s
        """ % ', '.join(self.release_get_cols)
        cur.execute(query, (origin_id, limit))
        yield from cursor_to_bytes(cur)

    def revision_get_by(self,
                        origin_id,
                        branch_name,
                        datetime,
                        limit=None,
                        cur=None):
        """Retrieve a revision by occurrence criterion.

        Args:
            - origin_id: The origin to look for
            - branch_name: the branch name to look for
            - datetime: the lower bound of timerange to look for.
            - limit: limit number of results to return
            The upper bound being now.
        """
        cur = self._cursor(cur)
        if branch_name and isinstance(branch_name, str):
            branch_name = branch_name.encode('utf-8')

        query = '''
        SELECT %s
            FROM swh_revision_get_by(%%s, %%s, %%s)
            LIMIT %%s
        ''' % ', '.join(self.revision_get_cols)

        cur.execute(query, (origin_id, branch_name, datetime, limit))
        yield from cursor_to_bytes(cur)

    def directory_entry_get_by_path(self, directory, paths, cur=None):
        """Retrieve a directory entry by path.

        """
        cur = self._cursor(cur)
        cur.execute("""SELECT dir_id, type, target, name, perms, status, sha1,
                       sha1_git, sha256
                       FROM swh_find_directory_entry_by_path(%s, %s)""",
                    (directory, paths))

        data = cur.fetchone()
        if set(data) == {None}:
            return None
        return line_to_bytes(data)

    def entity_get(self, uuid, cur=None):
        """Retrieve the entity and its parent hierarchy chain per uuid.

        """
        cur = self._cursor(cur)
        cur.execute("""SELECT %s
                       FROM swh_entity_get(%%s)""" % (
                           ', '.join(self.entity_cols)),
                    (uuid, ))
        yield from cursor_to_bytes(cur)

    def entity_get_one(self, uuid, cur=None):
        """Retrieve a single entity given its uuid.

        """
        cur = self._cursor(cur)
        cur.execute("""SELECT %s
                       FROM entity
                       WHERE uuid = %%s""" % (
                           ', '.join(self.entity_cols)),
                    (uuid, ))
        data = cur.fetchone()
        if not data:
            return None
        return line_to_bytes(data)

    def archive_ls(self, cur=None):
        """ Get all the archives registered on the server.

        Yields:
            a tuple (server_id, server_url) for each archive server.
        """
        cur = self._cursor(cur)
        cur.execute("""SELECT id, url
                    FROM archive
                    """)
        yield from cursor_to_bytes(cur)

    def content_archive_get(self, content_id, cur=None):
        """ Get the archival status of a content in a specific server.

        Retrieve from the database the archival status of the given content
        in the given archive server.

        Args:
            content_id: the sha1 of the content.

        Yields:
            A tuple (content_id, present_copies, ongoing_copies), where
            ongoing_copies is a dict mapping copy to mtime.
        """
        query = """SELECT content_id,
                          array(
                            SELECT key
                            FROM jsonb_each(copies)
                            WHERE value->>'status' = 'present'
                            ORDER BY key
                          ) AS present,
                          array(
                            SELECT key
                            FROM jsonb_each(copies)
                            WHERE value->>'status' = 'ongoing'
                            ORDER BY key
                          ) AS ongoing,
                          array(
                            SELECT value->'mtime'
                            FROM jsonb_each(copies)
                            WHERE value->>'status' = 'ongoing'
                            ORDER BY key
                          ) AS ongoing_mtime
                   FROM content_archive
                   WHERE content_id = %s
                   ORDER BY content_id
        """

        cur = self._cursor(cur)
        cur.execute(query, (content_id,))
        content_id, present, ongoing, mtimes = cur.fetchone()
        return (content_id, present, dict(zip(ongoing, mtimes)))

    def content_archive_get_copies(self, last_content=None, limit=1000,
                                   cur=None):
        """Get the list of copies for `limit` contents starting after
           `last_content`.

        Args:
            last_content: sha1 of the last content retrieved. May be None
                              to start at the beginning.
            limit: number of contents to retrieve. Can be None to retrieve all
                   objects (will be slow).

        Yields:
            A tuple (content_id, present_copies, ongoing_copies), where
            ongoing_copies is a dict mapping copy to mtime.

        """

        query = """SELECT content_id,
                          array(
                            SELECT key
                            FROM jsonb_each(copies)
                            WHERE value->>'status' = 'present'
                            ORDER BY key
                          ) AS present,
                          array(
                            SELECT key
                            FROM jsonb_each(copies)
                            WHERE value->>'status' = 'ongoing'
                            ORDER BY key
                          ) AS ongoing,
                          array(
                            SELECT value->'mtime'
                            FROM jsonb_each(copies)
                            WHERE value->>'status' = 'ongoing'
                            ORDER BY key
                          ) AS ongoing_mtime
                   FROM content_archive
                   WHERE content_id > %s
                   ORDER BY content_id
                   LIMIT %s
        """

        if last_content is None:
            last_content = b''

        cur = self._cursor(cur)
        cur.execute(query, (last_content, limit))
        for content_id, present, ongoing, mtimes in cursor_to_bytes(cur):
            yield (content_id, present, dict(zip(ongoing, mtimes)))

    def content_archive_get_unarchived_copies(
            self, retention_policy, last_content=None,
            limit=1000, cur=None):
        """ Get the list of copies for `limit` contents starting after
            `last_content`. Yields only copies with number of present
            smaller than `retention policy`.

        Args:
            last_content: sha1 of the last content retrieved. May be None
                              to start at the beginning.
            retention_policy: number of presentcopies required.
            limit: number of contents to retrieve. Can be None to retrieve all
                   objects (will be slow).

        Yields:
            A tuple (content_id, present_copies, ongoing_copies), where
            ongoing_copies is a dict mapping copy to mtime.

        """

        query = """SELECT content_id,
                          array(
                            SELECT key
                            FROM jsonb_each(copies)
                            WHERE value->>'status' = 'present'
                            ORDER BY key
                          ) AS present,
                          array(
                            SELECT key
                            FROM jsonb_each(copies)
                            WHERE value->>'status' = 'ongoing'
                            ORDER BY key
                          ) AS ongoing,
                          array(
                            SELECT value->'mtime'
                            FROM jsonb_each(copies)
                            WHERE value->>'status' = 'ongoing'
                            ORDER BY key
                          ) AS ongoing_mtime
                   FROM content_archive
                   WHERE content_id > %s AND num_present < %s
                   ORDER BY content_id
                   LIMIT %s
        """

        if last_content is None:
            last_content = b''

        cur = self._cursor(cur)
        cur.execute(query, (last_content, retention_policy, limit))
        for content_id, present, ongoing, mtimes in cursor_to_bytes(cur):
            yield (content_id, present, dict(zip(ongoing, mtimes)))

    def content_archive_update(self, content_id, archive_id,
                               new_status=None, cur=None):
        """ Update the status of an archive content and set its mtime to

        Change the mtime of an archived content for the given archive and set
        it's mtime to the current time.

        Args:
            content_id (str): content sha1
            archive_id (str): name of the archive
            new_status (str): one of 'missing', 'present' or 'ongoing'.
                this status will replace the previous one. If not given,
                the function only change the mtime of the content for the
                given archive.
        """
        if new_status is not None:
            query = """UPDATE content_archive
                    SET copies=jsonb_set(
                        copies, '{%s}',
                        '{"status":"%s", "mtime":%d}'
                    )
                    WHERE content_id='%s'
                    """ % (archive_id,
                           new_status, int(time.time()),
                           content_id)
        else:
            query = """ UPDATE content_archive
                    SET copies=jsonb_set(copies, '{%s,mtime}', '%d')
                    WHERE content_id='%s'
                    """ % (archive_id, int(time.time()))

        cur = self._cursor(cur)
        cur.execute(query)
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