import logging

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

from shutil import copy
from sqlite3 import connect, DatabaseError

from playhouse.sqlite_ext import SqliteExtDatabase

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() -> None:
    simplification.instance.db.init(Model.PATH)

    logger.info("Recreating schema for linked DBs...")
    attached_schemas = []
    for db_path, schema in app.MIGRATIONS_ATTACHED_DBS:
        logger.info("Attach db: %s", db_path)
        simplification.instance.db.execute_sql(
            "ATTACH ? AS ?", (db_path, schema)
        )
        attached_schemas.append(schema)

    recreate_schema_models(simplification.instance.db, attached_schemas)
    logger.info("Schema recreated successfully.")


def recreate_schema_models(
    db: SqliteExtDatabase, target_schemas: list[str]
) -> None:
    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 target_schemas
    ]
    logger.info("%r", models_to_create)

    # bind models to the db to avoid issues related to initialization order
    db.bind(models_to_create)

    db.create_tables(models_to_create)
    logger.info("Schema models recreated successfully.")