# GNU MediaGoblin -- federated, autonomous media hosting
# Copyright (C) 2011, 2012 MediaGoblin contributors.  See AUTHORS.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as published by
# the Free Software Foundation, either version 3 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 Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

import datetime
import uuid

from sqlalchemy import (MetaData, Table, Column, Boolean, SmallInteger,
                        Integer, Unicode, UnicodeText, DateTime,
                        ForeignKey, Date, Index)
from sqlalchemy.exc import ProgrammingError
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.sql import and_
from migrate.changeset.constraint import UniqueConstraint

from mediagoblin.db.extratypes import JSONEncoded, MutationDict
from mediagoblin.db.migration_tools import (
    RegisterMigration, inspect_table, replace_table_hack)
from mediagoblin.db.models import (MediaEntry, Collection, MediaComment, User,
        create_uuid, Privilege)
from mediagoblin.db.extratypes import JSONEncoded, MutationDict

MIGRATIONS = {}


@RegisterMigration(1, MIGRATIONS)
def ogg_to_webm_audio(db_conn):
    metadata = MetaData(bind=db_conn.bind)

    file_keynames = Table('core__file_keynames', metadata, autoload=True,
                          autoload_with=db_conn.bind)

    db_conn.execute(
        file_keynames.update().where(file_keynames.c.name == 'ogg').
            values(name='webm_audio')
    )
    db_conn.commit()


@RegisterMigration(2, MIGRATIONS)
def add_wants_notification_column(db_conn):
    metadata = MetaData(bind=db_conn.bind)

    users = Table('core__users', metadata, autoload=True,
            autoload_with=db_conn.bind)

    col = Column('wants_comment_notification', Boolean,
            default=True, nullable=True)
    col.create(users, populate_defaults=True)
    db_conn.commit()


@RegisterMigration(3, MIGRATIONS)
def add_transcoding_progress(db_conn):
    metadata = MetaData(bind=db_conn.bind)

    media_entry = inspect_table(metadata, 'core__media_entries')

    col = Column('transcoding_progress', SmallInteger)
    col.create(media_entry)
    db_conn.commit()


class Collection_v0(declarative_base()):
    __tablename__ = "core__collections"

    id = Column(Integer, primary_key=True)
    title = Column(Unicode, nullable=False)
    slug = Column(Unicode)
    created = Column(DateTime, nullable=False, default=datetime.datetime.now,
        index=True)
    description = Column(UnicodeText)
    creator = Column(Integer, ForeignKey(User.id), nullable=False)
    items = Column(Integer, default=0)

class CollectionItem_v0(declarative_base()):
    __tablename__ = "core__collection_items"

    id = Column(Integer, primary_key=True)
    media_entry = Column(
        Integer, ForeignKey(MediaEntry.id), nullable=False, index=True)
    collection = Column(Integer, ForeignKey(Collection.id), nullable=False)
    note = Column(UnicodeText, nullable=True)
    added = Column(DateTime, nullable=False, default=datetime.datetime.now)
    position = Column(Integer)

    ## This should be activated, normally.
    ## But this would change the way the next migration used to work.
    ## So it's commented for now.
    __table_args__ = (
        UniqueConstraint('collection', 'media_entry'),
        {})

collectionitem_unique_constraint_done = False

@RegisterMigration(4, MIGRATIONS)
def add_collection_tables(db_conn):
    Collection_v0.__table__.create(db_conn.bind)
    CollectionItem_v0.__table__.create(db_conn.bind)

    global collectionitem_unique_constraint_done
    collectionitem_unique_constraint_done = True

    db_conn.commit()


@RegisterMigration(5, MIGRATIONS)
def add_mediaentry_collected(db_conn):
    metadata = MetaData(bind=db_conn.bind)

    media_entry = inspect_table(metadata, 'core__media_entries')

    col = Column('collected', Integer, default=0)
    col.create(media_entry)
    db_conn.commit()


class ProcessingMetaData_v0(declarative_base()):
    __tablename__ = 'core__processing_metadata'

    id = Column(Integer, primary_key=True)
    media_entry_id = Column(Integer, ForeignKey(MediaEntry.id), nullable=False,
            index=True)
    callback_url = Column(Unicode)

@RegisterMigration(6, MIGRATIONS)
def create_processing_metadata_table(db):
    ProcessingMetaData_v0.__table__.create(db.bind)
    db.commit()


# Okay, problem being:
#  Migration #4 forgot to add the uniqueconstraint for the
#  new tables. While creating the tables from scratch had
#  the constraint enabled.
#
# So we have four situations that should end up at the same
# db layout:
#
# 1. Fresh install.
#    Well, easy. Just uses the tables in models.py
# 2. Fresh install using a git version just before this migration
#    The tables are all there, the unique constraint is also there.
#    This migration should do nothing.
#    But as we can't detect the uniqueconstraint easily,
#    this migration just adds the constraint again.
#    And possibly fails very loud. But ignores the failure.
# 3. old install, not using git, just releases.
#    This one will get the new tables in #4 (now with constraint!)
#    And this migration is just skipped silently.
# 4. old install, always on latest git.
#    This one has the tables, but lacks the constraint.
#    So this migration adds the constraint.
@RegisterMigration(7, MIGRATIONS)
def fix_CollectionItem_v0_constraint(db_conn):
    """Add the forgotten Constraint on CollectionItem"""

    global collectionitem_unique_constraint_done
    if collectionitem_unique_constraint_done:
        # Reset it. Maybe the whole thing gets run again
        # For a different db?
        collectionitem_unique_constraint_done = False
        return

    metadata = MetaData(bind=db_conn.bind)

    CollectionItem_table = inspect_table(metadata, 'core__collection_items')

    constraint = UniqueConstraint('collection', 'media_entry',
        name='core__collection_items_collection_media_entry_key',
        table=CollectionItem_table)

    try:
        constraint.create()
    except ProgrammingError:
        # User probably has an install that was run since the
        # collection tables were added, so we don't need to run this migration.
        pass

    db_conn.commit()


@RegisterMigration(8, MIGRATIONS)
def add_license_preference(db):
    metadata = MetaData(bind=db.bind)

    user_table = inspect_table(metadata, 'core__users')

    col = Column('license_preference', Unicode)
    col.create(user_table)
    db.commit()


@RegisterMigration(9, MIGRATIONS)
def mediaentry_new_slug_era(db):
    """
    Update for the new era for media type slugs.

    Entries without slugs now display differently in the url like:
      /u/cwebber/m/id=251/

    ... because of this, we should back-convert:
     - entries without slugs should be converted to use the id, if possible, to
       make old urls still work
     - slugs with = (or also : which is now also not allowed) to have those
       stripped out (small possibility of breakage here sadly)
    """

    def slug_and_user_combo_exists(slug, uploader):
        return db.execute(
            media_table.select(
                and_(media_table.c.uploader==uploader,
                     media_table.c.slug==slug))).first() is not None

    def append_garbage_till_unique(row, new_slug):
        """
        Attach junk to this row until it's unique, then save it
        """
        if slug_and_user_combo_exists(new_slug, row.uploader):
            # okay, still no success;
            # let's whack junk on there till it's unique.
            new_slug += '-' + uuid.uuid4().hex[:4]
            # keep going if necessary!
            while slug_and_user_combo_exists(new_slug, row.uploader):
                new_slug += uuid.uuid4().hex[:4]

        db.execute(
            media_table.update(). \
            where(media_table.c.id==row.id). \
            values(slug=new_slug))

    metadata = MetaData(bind=db.bind)

    media_table = inspect_table(metadata, 'core__media_entries')

    for row in db.execute(media_table.select()):
        # no slug, try setting to an id
        if not row.slug:
            append_garbage_till_unique(row, unicode(row.id))
        # has "=" or ":" in it... we're getting rid of those
        elif u"=" in row.slug or u":" in row.slug:
            append_garbage_till_unique(
                row, row.slug.replace(u"=", u"-").replace(u":", u"-"))

    db.commit()


@RegisterMigration(10, MIGRATIONS)
def unique_collections_slug(db):
    """Add unique constraint to collection slug"""
    metadata = MetaData(bind=db.bind)
    collection_table = inspect_table(metadata, "core__collections")
    existing_slugs = {}
    slugs_to_change = []

    for row in db.execute(collection_table.select()):
        # if duplicate slug, generate a unique slug
        if row.creator in existing_slugs and row.slug in \
           existing_slugs[row.creator]:
            slugs_to_change.append(row.id)
        else:
            if not row.creator in existing_slugs:
                existing_slugs[row.creator] = [row.slug]
            else:
                existing_slugs[row.creator].append(row.slug)

    for row_id in slugs_to_change:
        new_slug = unicode(uuid.uuid4())
        db.execute(collection_table.update().
                   where(collection_table.c.id == row_id).
                   values(slug=new_slug))
    # sqlite does not like to change the schema when a transaction(update) is
    # not yet completed
    db.commit()

    constraint = UniqueConstraint('creator', 'slug',
                                  name='core__collection_creator_slug_key',
                                  table=collection_table)
    constraint.create()

    db.commit()

@RegisterMigration(11, MIGRATIONS)
def drop_token_related_User_columns(db):
    """
    Drop unneeded columns from the User table after switching to using
    itsdangerous tokens for email and forgot password verification.
    """
    metadata = MetaData(bind=db.bind)
    user_table = inspect_table(metadata, 'core__users')

    verification_key = user_table.columns['verification_key']
    fp_verification_key = user_table.columns['fp_verification_key']
    fp_token_expire = user_table.columns['fp_token_expire']

    verification_key.drop()
    fp_verification_key.drop()
    fp_token_expire.drop()

    db.commit()


class CommentSubscription_v0(declarative_base()):
    __tablename__ = 'core__comment_subscriptions'
    id = Column(Integer, primary_key=True)

    created = Column(DateTime, nullable=False, default=datetime.datetime.now)

    media_entry_id = Column(Integer, ForeignKey(MediaEntry.id), nullable=False)

    user_id = Column(Integer, ForeignKey(User.id), nullable=False)

    notify = Column(Boolean, nullable=False, default=True)
    send_email = Column(Boolean, nullable=False, default=True)


class Notification_v0(declarative_base()):
    __tablename__ = 'core__notifications'
    id = Column(Integer, primary_key=True)
    type = Column(Unicode)

    created = Column(DateTime, nullable=False, default=datetime.datetime.now)

    user_id = Column(Integer, ForeignKey(User.id), nullable=False,
                     index=True)
    seen = Column(Boolean, default=lambda: False, index=True)


class CommentNotification_v0(Notification_v0):
    __tablename__ = 'core__comment_notifications'
    id = Column(Integer, ForeignKey(Notification_v0.id), primary_key=True)

    subject_id = Column(Integer, ForeignKey(MediaComment.id))


class ProcessingNotification_v0(Notification_v0):
    __tablename__ = 'core__processing_notifications'

    id = Column(Integer, ForeignKey(Notification_v0.id), primary_key=True)

    subject_id = Column(Integer, ForeignKey(MediaEntry.id))


@RegisterMigration(12, MIGRATIONS)
def add_new_notification_tables(db):
    metadata = MetaData(bind=db.bind)

    user_table = inspect_table(metadata, 'core__users')
    mediaentry_table = inspect_table(metadata, 'core__media_entries')
    mediacomment_table = inspect_table(metadata, 'core__media_comments')

    CommentSubscription_v0.__table__.create(db.bind)

    Notification_v0.__table__.create(db.bind)
    CommentNotification_v0.__table__.create(db.bind)
    ProcessingNotification_v0.__table__.create(db.bind)

    db.commit()


@RegisterMigration(13, MIGRATIONS)
def pw_hash_nullable(db):
    """Make pw_hash column nullable"""
    metadata = MetaData(bind=db.bind)
    user_table = inspect_table(metadata, "core__users")

    user_table.c.pw_hash.alter(nullable=True)

    # sqlite+sqlalchemy seems to drop this constraint during the
    # migration, so we add it back here for now a bit manually.
    if db.bind.url.drivername == 'sqlite':
        constraint = UniqueConstraint('username', table=user_table)
        constraint.create()

    db.commit()


# oauth1 migrations
class Client_v0(declarative_base()):
    """
        Model representing a client - Used for API Auth
    """
    __tablename__ = "core__clients"

    id = Column(Unicode, nullable=True, primary_key=True)
    secret = Column(Unicode, nullable=False)
    expirey = Column(DateTime, nullable=True)
    application_type = Column(Unicode, nullable=False)
    created = Column(DateTime, nullable=False, default=datetime.datetime.now)
    updated = Column(DateTime, nullable=False, default=datetime.datetime.now)

    # optional stuff
    redirect_uri = Column(JSONEncoded, nullable=True)
    logo_url = Column(Unicode, nullable=True)
    application_name = Column(Unicode, nullable=True)
    contacts = Column(JSONEncoded, nullable=True)

    def __repr__(self):
        if self.application_name:
            return "<Client {0} - {1}>".format(self.application_name, self.id)
        else:
            return "<Client {0}>".format(self.id)

class RequestToken_v0(declarative_base()):
    """
        Model for representing the request tokens
    """
    __tablename__ = "core__request_tokens"

    token = Column(Unicode, primary_key=True)
    secret = Column(Unicode, nullable=False)
    client = Column(Unicode, ForeignKey(Client_v0.id))
    user = Column(Integer, ForeignKey(User.id), nullable=True)
    used = Column(Boolean, default=False)
    authenticated = Column(Boolean, default=False)
    verifier = Column(Unicode, nullable=True)
    callback = Column(Unicode, nullable=False, default=u"oob")
    created = Column(DateTime, nullable=False, default=datetime.datetime.now)
    updated = Column(DateTime, nullable=False, default=datetime.datetime.now)

class AccessToken_v0(declarative_base()):
    """
        Model for representing the access tokens
    """
    __tablename__ = "core__access_tokens"

    token = Column(Unicode, nullable=False, primary_key=True)
    secret = Column(Unicode, nullable=False)
    user = Column(Integer, ForeignKey(User.id))
    request_token = Column(Unicode, ForeignKey(RequestToken_v0.token))
    created = Column(DateTime, nullable=False, default=datetime.datetime.now)
    updated = Column(DateTime, nullable=False, default=datetime.datetime.now)


class NonceTimestamp_v0(declarative_base()):
    """
        A place the timestamp and nonce can be stored - this is for OAuth1
    """
    __tablename__ = "core__nonce_timestamps"

    nonce = Column(Unicode, nullable=False, primary_key=True)
    timestamp = Column(DateTime, nullable=False, primary_key=True)


@RegisterMigration(14, MIGRATIONS)
def create_oauth1_tables(db):
    """ Creates the OAuth1 tables """

    Client_v0.__table__.create(db.bind)
    RequestToken_v0.__table__.create(db.bind)
    AccessToken_v0.__table__.create(db.bind)
    NonceTimestamp_v0.__table__.create(db.bind)

    db.commit()

@RegisterMigration(15, MIGRATIONS)
def wants_notifications(db):
    """Add a wants_notifications field to User model"""
    metadata = MetaData(bind=db.bind)
    user_table = inspect_table(metadata, "core__users")
    col = Column('wants_notifications', Boolean, default=True)
    col.create(user_table)
    db.commit()



@RegisterMigration(16, MIGRATIONS)
def upload_limits(db):
    """Add user upload limit columns"""
    metadata = MetaData(bind=db.bind)

    user_table = inspect_table(metadata, 'core__users')
    media_entry_table = inspect_table(metadata, 'core__media_entries')

    col = Column('uploaded', Integer, default=0)
    col.create(user_table)

    col = Column('upload_limit', Integer)
    col.create(user_table)

    col = Column('file_size', Integer, default=0)
    col.create(media_entry_table)

    db.commit()


@RegisterMigration(17, MIGRATIONS)
def add_file_metadata(db):
    """Add file_metadata to MediaFile"""
    metadata = MetaData(bind=db.bind)
    media_file_table = inspect_table(metadata, "core__mediafiles")

    col = Column('file_metadata', MutationDict.as_mutable(JSONEncoded))
    col.create(media_file_table)

    db.commit()

###################
# Moderation tables
###################

class ReportBase_v0(declarative_base()):
    __tablename__ = 'core__reports'
    id = Column(Integer, primary_key=True)
    reporter_id = Column(Integer, ForeignKey(User.id), nullable=False)
    report_content = Column(UnicodeText)
    reported_user_id = Column(Integer, ForeignKey(User.id), nullable=False)
    created = Column(DateTime, nullable=False, default=datetime.datetime.now)
    discriminator = Column('type', Unicode(50))
    resolver_id = Column(Integer, ForeignKey(User.id))
    resolved = Column(DateTime)
    result = Column(UnicodeText)
    __mapper_args__ = {'polymorphic_on': discriminator}


class CommentReport_v0(ReportBase_v0):
    __tablename__ = 'core__reports_on_comments'
    __mapper_args__ = {'polymorphic_identity': 'comment_report'}

    id = Column('id',Integer, ForeignKey('core__reports.id'),
                                                primary_key=True)
    comment_id = Column(Integer, ForeignKey(MediaComment.id), nullable=True)


class MediaReport_v0(ReportBase_v0):
    __tablename__ = 'core__reports_on_media'
    __mapper_args__ = {'polymorphic_identity': 'media_report'}

    id = Column('id',Integer, ForeignKey('core__reports.id'), primary_key=True)
    media_entry_id = Column(Integer, ForeignKey(MediaEntry.id), nullable=True)


class UserBan_v0(declarative_base()):
    __tablename__ = 'core__user_bans'
    user_id = Column(Integer, ForeignKey(User.id), nullable=False,
                                         primary_key=True)
    expiration_date = Column(Date)
    reason = Column(UnicodeText, nullable=False)


class Privilege_v0(declarative_base()):
    __tablename__ = 'core__privileges'
    id = Column(Integer, nullable=False, primary_key=True, unique=True)
    privilege_name = Column(Unicode, nullable=False, unique=True)


class PrivilegeUserAssociation_v0(declarative_base()):
    __tablename__ = 'core__privileges_users'
    privilege_id = Column(
        'core__privilege_id',
        Integer,
        ForeignKey(User.id),
        primary_key=True)
    user_id = Column(
        'core__user_id',
        Integer,
        ForeignKey(Privilege.id),
        primary_key=True)


PRIVILEGE_FOUNDATIONS_v0 = [{'privilege_name':u'admin'},
                            {'privilege_name':u'moderator'},
                            {'privilege_name':u'uploader'},
                            {'privilege_name':u'reporter'},
                            {'privilege_name':u'commenter'},
                            {'privilege_name':u'active'}]


# vR1 stands for "version Rename 1".  This only exists because we need
# to deal with dropping some booleans and it's otherwise impossible
# with sqlite.

class User_vR1(declarative_base()):
    __tablename__ = 'rename__users'
    id = Column(Integer, primary_key=True)
    username = Column(Unicode, nullable=False, unique=True)
    email = Column(Unicode, nullable=False)
    pw_hash = Column(Unicode)
    created = Column(DateTime, nullable=False, default=datetime.datetime.now)
    wants_comment_notification = Column(Boolean, default=True)
    wants_notifications = Column(Boolean, default=True)
    license_preference = Column(Unicode)
    url = Column(Unicode)
    bio = Column(UnicodeText)  # ??
    uploaded = Column(Integer, default=0)
    upload_limit = Column(Integer)


@RegisterMigration(18, MIGRATIONS)
def create_moderation_tables(db):

    # First, we will create the new tables in the database.
    #--------------------------------------------------------------------------
    ReportBase_v0.__table__.create(db.bind)
    CommentReport_v0.__table__.create(db.bind)
    MediaReport_v0.__table__.create(db.bind)
    UserBan_v0.__table__.create(db.bind)
    Privilege_v0.__table__.create(db.bind)
    PrivilegeUserAssociation_v0.__table__.create(db.bind)

    db.commit()

    # Then initialize the tables that we will later use
    #--------------------------------------------------------------------------
    metadata = MetaData(bind=db.bind)
    privileges_table= inspect_table(metadata, "core__privileges")
    user_table = inspect_table(metadata, 'core__users')
    user_privilege_assoc = inspect_table(
        metadata, 'core__privileges_users')

    # This section initializes the default Privilege foundations, that
    # would be created through the FOUNDATIONS system in a new instance
    #--------------------------------------------------------------------------
    for parameters in PRIVILEGE_FOUNDATIONS_v0:
        db.execute(privileges_table.insert().values(**parameters))

    db.commit()

    # This next section takes the information from the old is_admin and status
    # columns and converts those to the new privilege system
    #--------------------------------------------------------------------------
    admin_users_ids, active_users_ids, inactive_users_ids = (
        db.execute(
            user_table.select().where(
                user_table.c.is_admin==True)).fetchall(),
        db.execute(
            user_table.select().where(
                user_table.c.is_admin==False).where(
                user_table.c.status==u"active")).fetchall(),
        db.execute(
            user_table.select().where(
                user_table.c.is_admin==False).where(
                user_table.c.status!=u"active")).fetchall())

    # Get the ids for each of the privileges so we can reference them ~~~~~~~~~
    (admin_privilege_id, uploader_privilege_id,
     reporter_privilege_id, commenter_privilege_id,
     active_privilege_id) = [
        db.execute(privileges_table.select().where(
            privileges_table.c.privilege_name==privilege_name)).first()['id']
        for privilege_name in
            [u"admin",u"uploader",u"reporter",u"commenter",u"active"]
    ]

    # Give each user the appopriate privileges depending whether they are an
    # admin, an active user or an inactive user ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    for admin_user in admin_users_ids:
        admin_user_id = admin_user['id']
        for privilege_id in [admin_privilege_id, uploader_privilege_id,
                            reporter_privilege_id, commenter_privilege_id,
                            active_privilege_id]:
            db.execute(user_privilege_assoc.insert().values(
                core__privilege_id=admin_user_id,
                core__user_id=privilege_id))

    for active_user in active_users_ids:
        active_user_id = active_user['id']
        for privilege_id in [uploader_privilege_id, reporter_privilege_id,
                            commenter_privilege_id, active_privilege_id]:
            db.execute(user_privilege_assoc.insert().values(
                core__privilege_id=active_user_id,
                core__user_id=privilege_id))

    for inactive_user in inactive_users_ids:
        inactive_user_id = inactive_user['id']
        for privilege_id in [uploader_privilege_id, reporter_privilege_id,
                             commenter_privilege_id]:
            db.execute(user_privilege_assoc.insert().values(
                core__privilege_id=inactive_user_id,
                core__user_id=privilege_id))

    db.commit()

    # And then, once the information is taken from is_admin & status columns
    # we drop all of the vestigial columns from the User table.
    #--------------------------------------------------------------------------
    if db.bind.url.drivername == 'sqlite':
        # SQLite has some issues that make it *impossible* to drop boolean
        # columns. So, the following code is a very hacky workaround which
        # makes it possible. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

        User_vR1.__table__.create(db.bind)
        db.commit()
        new_user_table = inspect_table(metadata, 'rename__users')
        replace_table_hack(db, user_table, new_user_table)
    else:
        # If the db is not run using SQLite, this process is much simpler ~~~~~

        status = user_table.columns['status']
        email_verified = user_table.columns['email_verified']
        is_admin = user_table.columns['is_admin']
        status.drop()
        email_verified.drop()
        is_admin.drop()

    db.commit()


@RegisterMigration(19, MIGRATIONS)
def drop_MediaEntry_collected(db):
    """
    Drop unused MediaEntry.collected column
    """
    metadata = MetaData(bind=db.bind)

    media_collected= inspect_table(metadata, 'core__media_entries')
    media_collected = media_collected.columns['collected']

    media_collected.drop()

    db.commit()


@RegisterMigration(20, MIGRATIONS)
def add_metadata_column(db):
    metadata = MetaData(bind=db.bind)

    media_entry = inspect_table(metadata, 'core__media_entries')

    col = Column('media_metadata', MutationDict.as_mutable(JSONEncoded),
        default=MutationDict())
    col.create(media_entry)

    db.commit()


class PrivilegeUserAssociation_R1(declarative_base()):
    __tablename__ = 'rename__privileges_users'
    user = Column(
        "user",
        Integer,
        ForeignKey(User.id),
        primary_key=True)
    privilege = Column(
        "privilege",
        Integer,
        ForeignKey(Privilege.id),
        primary_key=True)

@RegisterMigration(21, MIGRATIONS)
def fix_privilege_user_association_table(db):
    """
    There was an error in the PrivilegeUserAssociation table that allowed for a
    dangerous sql error. We need to the change the name of the columns to be
    unique, and properly referenced.
    """
    metadata = MetaData(bind=db.bind)

    privilege_user_assoc = inspect_table(
        metadata, 'core__privileges_users')

    # This whole process is more complex if we're dealing with sqlite
    if db.bind.url.drivername == 'sqlite':
        PrivilegeUserAssociation_R1.__table__.create(db.bind)
        db.commit()

        new_privilege_user_assoc = inspect_table(
            metadata, 'rename__privileges_users')
        result = db.execute(privilege_user_assoc.select())
        for row in result:
            # The columns were improperly named before, so we switch the columns
            user_id, priv_id = row['core__privilege_id'], row['core__user_id']
            db.execute(new_privilege_user_assoc.insert().values(
                user=user_id,
                privilege=priv_id))

        db.commit()

        privilege_user_assoc.drop()
        new_privilege_user_assoc.rename('core__privileges_users')

    # much simpler if postgres though!
    else:
        privilege_user_assoc.c.core__user_id.alter(name="privilege")
        privilege_user_assoc.c.core__privilege_id.alter(name="user")

    db.commit()

@RegisterMigration(22, MIGRATIONS)
def add_index_username_field(db):
    """
    This indexes the User.username field which is frequently queried
    for example a user logging in. This solves the issue #894
    """
    metadata = MetaData(bind=db.bind)
    user_table = inspect_table(metadata, "core__users")

    new_index = Index("ix_core__users_uploader", user_table.c.username)
    new_index.create()

    db.commit()
