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import logging

import itertools
import os
from contextlib import suppress
from datetime import datetime

from shutil import copy
from sqlite3 import connect, DatabaseError

from defence360agent.application import app
from defence360agent import simple_rpc
from defence360agent.contracts.config import Model
from defence360agent.model import simplification

logger = logging.getLogger(__name__)


class OperationError(Exception):
    pass


WORKAROUND_MSG = "Blank database will be created on agent start "


def check_and_repair():
    base = Model.PATH
    if simple_rpc.is_running():
        raise OperationError(
            "Cannot perform database check and backup while agent is running. "
            "Please, stop the imunify360 agent with `service imunify360 stop`"
        )
    elif not os.path.isfile(base):
        raise OperationError(
            "DB %s is not exists. %s" % (base, WORKAROUND_MSG)
        )
    else:
        if is_db_corrupted(base):
            backup = make_backup(base)
            if not backup:
                raise OperationError(
                    "Cannot proceed without backup copy of the database."
                    "Please contact imunify360 support team at "
                    "https://cloudlinux.zendesk.com"
                )
            dump = dump_to_sql(base)
            logger.info("Removing original corrupted database at %s" % base)
            # TODO: Notify user in UI that original DB was dropped
            os.remove(base)
            if not dump:
                raise OperationError(
                    "Cannot dump database to sql. Old DB backuped at %s. %s"
                    % (backup, WORKAROUND_MSG)
                )
            else:
                restored = load_from_sql(base, dump)
                if not restored:
                    raise OperationError(
                        "Loading dump to new database failed. Database will "
                        "be recreated during migrations."
                    )

                if is_db_corrupted(restored):
                    os.remove(restored)
                    raise OperationError(
                        "Restored database is still corrupt. Removing "
                        "restored database. %s" % WORKAROUND_MSG
                    )

                logger.info(
                    "Database restored successfully. Removing dump %s" % dump
                )
                os.remove(dump)
                try:
                    logger.info("Performing migrations on restored database")
                    simplification.migrate()
                except Exception as e:
                    os.remove(base)
                    raise OperationError(
                        "Migrations on restored database failed: %s. %s"
                        % (e, WORKAROUND_MSG)
                    )
                else:
                    if not all_tables_are_present():
                        os.remove(base)
                        raise OperationError(
                            "Restored database does not "
                            "contain all necessary tables. "
                            "%s" % WORKAROUND_MSG
                        )


def mark_with_timestamp(filename, extension=None):
    """
    >>> mark_with_timestamp('/var/imunify360/imunify360.db')
    '/var/imunify360/imunify360.db_2017-09-26_03:33:44.705967'
    >>> mark_with_timestamp('/var/imunify360/imunify360.db', extension='sql')
    '/var/imunify360/imunify360.db_2017-09-26_03:34:01.098544.sql'
    """
    instant = datetime.now()
    basename = "{}_{}".format(filename, instant.isoformat("_"))
    if extension:
        return basename + ".%s" % extension
    else:
        return basename


def is_db_corrupted(db_path):
    logger.info("Database %s integrity check..." % db_path)
    is_corrupted = True
    with connect(db_path) as connection:
        try:
            cursor = connection.execute("PRAGMA INTEGRITY_CHECK;")
            result = next(cursor)
            if "ok" in result:
                logger.info("Database integrity check succeeded.")
                is_corrupted = False
        except DatabaseError as e:
            logger.warning("DatabaseError detected: %s", e)
        return is_corrupted


def dump_to_sql(db_path):
    dumpfile = mark_with_timestamp(db_path, extension="sql")
    logger.info("Dumping imunify360 database to %s" % dumpfile)
    try:
        with open(dumpfile, "w") as dump, connect(db_path) as connection:
            for row in connection.iterdump():
                dump.write(row)
    except (DatabaseError, OSError) as e:
        logger.error("Error during dump: %s. Operation aborted" % e)
        with suppress(OSError):
            os.remove(dumpfile)
        dumpfile = None
    return dumpfile


def load_from_sql(db_path, dumpfile):
    # This is unlikely to happen because we delete the original file
    # but to be defensive here won't hurt in case of reuse in other places.
    if os.path.exists(db_path):
        logger.warning(
            "Database already exists. Loading dump to existing "
            "database may cause errors. Operation aborted"
        )
        return None
    logger.info(
        "Reading dump %s into new database %s..." % (dumpfile, db_path)
    )
    with open(dumpfile, "r") as dump, connect(db_path) as connection:
        # We cannot read line by line because SQL statements are dumped
        # not in a statement-per-line way
        try:
            sql = dump.read()
            connection.executescript(sql)
        except MemoryError as e:
            logger.error(e)
            with suppress(OSError):
                os.remove(db_path)
            db_path = None
    return db_path


def make_backup(db_path):
    logger.info("Making backup of the %s..." % db_path)
    backup_filename = mark_with_timestamp(db_path, "backup")
    try:
        copy(db_path, backup_filename)
        logger.info("Database copied successfully to: %s " % backup_filename)
    except Exception as e:
        logger.error("Making backup failed: %s", e)
        with suppress(OSError):
            os.remove(backup_filename)
        backup_filename = None
    return backup_filename


def all_tables_are_present():
    logger.info(
        "Verifying that db schema is up-to-date and all tables are present..."
    )
    models = itertools.chain(
        *[
            simplification.get_models(module)
            for module in app.MODULES_WITH_MODELS
        ]
    )
    if all(model.table_exists() for model in models):
        logger.info("All tables are present")
        return True
    else:
        logger.error("Some tables are missing in db.")
        return False


def recreate_schema():
    simplification.instance.db.init(Model.PATH)

    logger.info("Recreating schema for linked DBs...")
    linked_dbs = []
    for db_path, schema in app.MIGRATIONS_ATTACHED_DBS:
        logger.info("Attach db: %s", db_path)
        simplification.instance.db.execute_sql(
            "ATTACH '{}' AS {}".format(db_path, schema)
        )
        linked_dbs.append(schema)
    models_to_create = [
        model
        for model in itertools.chain(
            *[
                simplification.get_models(module)
                for module in app.MODULES_WITH_MODELS
            ]
        )
        if model._meta.schema in linked_dbs
    ]
    logger.info("%r", models_to_create)
    simplification.instance.db.create_tables(models_to_create)
    logger.info("Schema recreated successfully.")