#!/opt/cloudlinux/venv/bin/python3 -sbb
# coding=utf-8
#
# Copyright © Cloud Linux GmbH & Cloud Linux Software, Inc 2010-2020 All Rights Reserved
#
# Licensed under CLOUD LINUX LICENSE AGREEMENT
# http://cloudlinux.com/docs/LICENCE.TXT
#

import os
import contextlib
import sqlite3

from datetime import datetime, timedelta
from sqlalchemy import (
    Column,
    Boolean,
    DateTime,
    Integer,
    String,
    create_engine,
    event, func, text
)
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.engine.reflection import Inspector
from sqlalchemy.orm import Session
from sqlalchemy.orm.session import close_all_sessions
from sqlalchemy.exc import DatabaseError

SSA_DB = '/var/lve/ssa.db'
OLD_SSA_DB = SSA_DB + '.old'
RETENTION_TIME_DAYS = 1

Base = declarative_base()


class RequestResult(Base):
    """
    Describes processed request stored in database file.

    E.g.
    {
        "timestamp": "1650008727",
        "url": "http://mydomain.com/index.php",
        "duration": 162077,
        "hitting_limits": false,
        "throttled_time": 0,
        "io_throttled_time": 0,
        "wordpress": true
    }

    Note: created_at, updated_at is saved in local TZ format
    """
    __tablename__ = 'scrape_result'

    id = Column(Integer, primary_key=True)

    domain = Column(String, index=True, nullable=False)
    path = Column(String, index=True, nullable=False)

    timestamp = Column(Integer, nullable=False)

    duration = Column(Integer, nullable=False)
    is_slow_request = Column(Boolean, nullable=False)
    hitting_limits = Column(Boolean, nullable=False)
    throttled_time = Column(Integer, nullable=False)
    io_throttled_time = Column(Integer, nullable=False)
    wordpress = Column(Boolean, nullable=False)

    created_at = Column(DateTime(timezone=True), server_default=func.now())
    updated_at = Column(DateTime(timezone=True), onupdate=func.now(), server_default=func.now())


def cleanup_old_data(engine):
    """
    Removes outdated records from database, saving disk space.
    """
    n_days_ago = datetime.today() - timedelta(days=RETENTION_TIME_DAYS)
    with session_scope(engine) as session:
        session.query(RequestResult)\
            .filter(RequestResult.created_at < n_days_ago)\
            .delete()


def create_db_if_not_exist(engine):
    if not is_db_present(engine):
        Base.metadata.create_all(engine)


def is_db_present(engine):
    if not os.path.isfile(SSA_DB):
        return False
    database_inspection = Inspector.from_engine(engine)
    tables = [table for table in database_inspection.get_table_names()]
    return len(tables) > 0


def setup_wal_mode(dbapi_con, con_record):
    dbapi_con.execute('PRAGMA journal_mode = WAL')


def _setup_database(readonly):
    connection_string = f'file:{SSA_DB}'
    if readonly:
        connection_string = f'{connection_string}?mode=ro'
    creator = lambda: sqlite3.connect(connection_string, uri=True)
    engine = create_engine(
        'sqlite:////', creator=creator, echo=False,
    )
    event.listen(engine, 'connect', setup_wal_mode)
    create_db_if_not_exist(engine)
    return engine


def setup_database(readonly=False):
    return _setup_database(readonly)


def restore_database(engine):
    """
    Restore database by establish connections to old and new databases,
    merge data to new one if possible and delete old one.
    """
    if os.path.exists(SSA_DB):
        # Closing all sessions to ensure that no sessions is using database during replacing
        close_all_sessions()
        os.replace(SSA_DB, OLD_SSA_DB)

    new_engine = setup_database()
    # Dispose of the existing engine to close and refresh all connections, ensuring it connects to the new database
    engine.dispose()
    old_engine = create_engine(f'sqlite:////{OLD_SSA_DB}')

    try:
        with session_scope(old_engine) as session_old, session_scope(new_engine) as session_new:
            # Check if old database is able to read and it make sense to try save unharmed data
            session_old.query(RequestResult).first()
            merge_unharmed_data_from_database(session_old, session_new)
    except DatabaseError:
        pass

    for path in (OLD_SSA_DB, SSA_DB + "-wal", SSA_DB + "-shm"):
        if os.path.exists(path):
            os.remove(path)


def merge_unharmed_data_from_database(session_old, session_new):
    """
    Scrape all unharmed records from malformed database and merge them into new database.
    """
    offset = 0
    batch_size = 10
    while True:
        query = session_old.query(RequestResult).offset(offset).limit(batch_size)
        try:
            records_to_save = query.all()
            if not records_to_save:
                break
            for record in records_to_save:
                session_new.merge(record)
        except DatabaseError:
            for pos_in_batch in range(batch_size):
                try:
                    record_to_save = query.offset(offset + pos_in_batch).first()
                    if not record_to_save:
                        break
                    session_new.merge(record_to_save)
                except DatabaseError:
                    pass
        session_new.commit()
        offset += batch_size


def is_malformed_database(engine):
    """
    Try integrity check of database file to see if it is malformed.
    If database unable to execute it, will also count as malformed.
    """
    if os.path.exists(OLD_SSA_DB) and os.path.exists(SSA_DB):
        os.remove(OLD_SSA_DB)
    try:
        with session_scope(engine) as db:
            result = db.execute(text("PRAGMA integrity_check"))
            errors = result.fetchall()
            return errors[0][0] != 'ok'
    except DatabaseError:
        return True


@contextlib.contextmanager
def session_scope(engine) -> Session:
    """
    Provide a transactional scope around a series of operations.
    """
    session = Session(bind=engine)
    try:
        yield session
        session.commit()
    except:
        session.rollback()
        raise
    finally:
        session.close()