# Source code for searx.sqlitedb

    # SPDX-License-Identifier: AGPL-3.0-or-later
    """Implementations to make access to SQLite databases a little more convenient.

    :py:obj:`SQLiteAppl`
      Abstract class with which DB applications can be implemented.

    :py:obj:`SQLiteProperties`:
      Class to manage properties stored in a database.

    ----

    """
    from __future__ import annotations

    import sys
    import re
    import sqlite3
    import threading
    import abc

    from searx import logger

    logger = logger.getChild('sqlitedb')

    class SQLiteAppl(abc.ABC):
        """Abstract base class for implementing convenient DB access in SQLite
        applications.  In the constructor, a :py:obj:`SQLiteProperties` instance is
        already aggregated under ``self.properties``."""

        DDL_CREATE_TABLES: dict[str, str] = {}

        DB_SCHEMA: int = 1
        """As soon as changes are made to the DB schema, the version number must be
        increased.  Changes to the version number require the DB to be recreated (or
        migrated / if an migration path exists and is implemented)."""

        SQLITE_THREADING_MODE = {
            0: "single-thread",
            1: "multi-thread",
            3: "serialized"}[sqlite3.threadsafety]  # fmt:skip
        """Threading mode of the SQLite library.  Depends on the options used at
        compile time and is different for different distributions and architectures.

        Possible values are 0:``single-thread``, 1:``multi-thread``,
        3:``serialized`` (see :py:obj:`sqlite3.threadsafety`).  Pre- Python 3.11
        this value was hard coded to 1.

        Depending on this value, optimizations are made, e.g. in “serialized” mode
        it is not necessary to create a separate DB connector for each thread.
        """

        SQLITE_JOURNAL_MODE = "WAL"
        SQLITE_CONNECT_ARGS = {
            # "timeout": 5.0,
            # "detect_types": 0,
            "check_same_thread": bool(SQLITE_THREADING_MODE != "serialized"),
            "cached_statements": 0,  # https://github.com/python/cpython/issues/118172
            # "uri": False,
            "autocommit": False,
        }  # fmt:skip
        """Connection arguments (:py:obj:`sqlite3.connect`)

        ``check_same_thread``:
          Is disabled by default when :py:obj:`SQLITE_THREADING_MODE` is
          ``serialized``.  The check is more of a hindrance in this case because it
          would prevent a DB connector from being used in multiple threads.

        ``autocommit``:
          Is disabled by default.  Note: autocommit option has been added in Python
          3.12.

        ``cached_statements``:
          Is set to ``0`` by default.  Note: Python 3.12+ fetch result are not
          consistent in multi-threading application and causing an API misuse error.

          The multithreading use in SQLiteAppl is intended and supported if
          threadsafety is set to 3 (aka "serialized"). CPython supports “serialized”
          from version 3.12 on, but unfortunately only with errors:

          - https://github.com/python/cpython/issues/118172
          - https://github.com/python/cpython/issues/123873

          The workaround for SQLite3 multithreading cache inconsistency ist to set
          option ``cached_statements`` to ``0`` by default.
        """

        def __init__(self, db_url):

            self.db_url = db_url
            self.properties = SQLiteProperties(db_url)
            self.thread_local = threading.local()
            self._init_done = False
            self._compatibility()

        def _compatibility(self):

            if self.SQLITE_THREADING_MODE == "serialized":
                self._DB = None
            else:
                msg = (
                    f"SQLite library is compiled with {self.SQLITE_THREADING_MODE} mode,"
                    " read https://docs.python.org/3/library/sqlite3.html#sqlite3.threadsafety"
                )
                if threading.active_count() > 1:
                    logger.error(msg)
                else:
                    logger.warning(msg)

            if sqlite3.sqlite_version_info <= (3, 35):
                # See "Generalize UPSERT:" in https://sqlite.org/releaselog/3_35_0.html
                logger.critical(
                    "SQLite runtime library version %s is not supported (require >= 3.35)", sqlite3.sqlite_version
                )

        def connect(self) -> sqlite3.Connection:
            """Creates a new DB connection (:py:obj:`SQLITE_CONNECT_ARGS`).  If not
            already done, the DB schema is set up
            """
            if sys.version_info < (3, 12):
                # Prior Python 3.12 there is no "autocommit" option
                self.SQLITE_CONNECT_ARGS.pop("autocommit", None)

            self.init()
            logger.debug("%s: connect to DB: %s // %s", self.__class__.__name__, self.db_url, self.SQLITE_CONNECT_ARGS)
            conn = sqlite3.Connection(self.db_url, **self.SQLITE_CONNECT_ARGS)  # type: ignore
            conn.execute(f"PRAGMA journal_mode={self.SQLITE_JOURNAL_MODE}")
            self.register_functions(conn)
            return conn

        def register_functions(self, conn):
            """Create user-defined_ SQL functions.

            ``REGEXP(<pattern>, <field>)`` : 0 | 1
               `re.search`_ returns (int) 1 for a match and 0 for none match of
               ``<pattern>`` in ``<field>``.

               .. code:: sql

                  SELECT '12' AS field WHERE REGEXP('^[0-9][0-9]$', field)
                  -- 12

                  SELECT REGEXP('[0-9][0-9]', 'X12Y')
                  -- 1
                  SELECT REGEXP('[0-9][0-9]', 'X1Y')
                  -- 0

            .. _user-defined: https://docs.python.org/3/library/sqlite3.html#sqlite3.Connection.create_function
            .. _deterministic: https://sqlite.org/deterministic.html
            .. _re.search: https://docs.python.org/3/library/re.html#re.search
            """

            conn.create_function('regexp', 2, lambda x, y: 1 if re.search(x, y) else 0, deterministic=True)

        @property
        def DB(self) -> sqlite3.Connection:
            """Provides a DB connection.  The connection is a *singleton* and
            therefore well suited for read access.  If
            :py:obj:`SQLITE_THREADING_MODE` is ``serialized`` only one DB connection
            is created for all threads.

            .. note::

               For dedicated `transaction control`_, it is recommended to create a
               new connection (:py:obj:`SQLiteAppl.connect`).

            .. _transaction control:
                https://docs.python.org/3/library/sqlite3.html#sqlite3-controlling-transactions
            """

            if getattr(self.thread_local, 'DB', None) is None:
                self.thread_local.DB = self.connect()

            # Theoretically it is possible to reuse the DB cursor across threads as
            # of Python 3.12, in practice the threading of the cursor seems to me to
            # be so faulty that I prefer to establish one connection per thread

            self.thread_local.DB.commit()
            return self.thread_local.DB

            # In "serialized" mode, SQLite can be safely used by multiple threads
            # with no restriction.
            #
            # if self.SQLITE_THREADING_MODE != "serialized":
            #     if getattr(self.thread_local, 'DB', None) is None:
            #         self.thread_local.DB = self.connect()
            #     return self.thread_local.DB
            #
            # if self._DB is None:
            #     self._DB = self.connect()  # pylint: disable=attribute-defined-outside-init
            # return self._DB

        def init(self):
            """Initializes the DB schema and properties, is only executed once even
            if called several times."""

            if self._init_done:
                return
            self._init_done = True

            logger.debug("init DB: %s", self.db_url)
            self.properties.init()
            ver = self.properties("DB_SCHEMA")
            if ver is None:
                with self.properties.DB:
                    self.create_schema(self.properties.DB)
            else:
                ver = int(ver)
                if ver != self.DB_SCHEMA:
                    raise sqlite3.DatabaseError("Expected DB schema v%s, DB schema is v%s" % (self.DB_SCHEMA, ver))
                logger.debug("DB_SCHEMA = %s", ver)

        def create_schema(self, conn):

            logger.debug("create schema ..")
            with conn:
                for table_name, sql in self.DDL_CREATE_TABLES.items():
                    conn.execute(sql)
                    self.properties.set(f"Table {table_name} created", table_name)
                    self.properties.set("DB_SCHEMA", self.DB_SCHEMA)
                    self.properties.set("LAST_MAINTENANCE", "")

    class SQLiteProperties(SQLiteAppl):
        """Simple class to manage properties of a DB application in the DB.  The
        object has its own DB connection and transaction area.

        .. code:: sql

           CREATE TABLE IF NOT EXISTS properties (
             name       TEXT,
             value      TEXT,
             m_time     INTEGER DEFAULT (strftime('%s', 'now')),
             PRIMARY KEY (name))

        """

        SQLITE_JOURNAL_MODE = "WAL"

        DDL_PROPERTIES = """\
    CREATE TABLE IF NOT EXISTS properties (
      name       TEXT,
      value      TEXT,
      m_time     INTEGER DEFAULT (strftime('%s', 'now')),  -- last modified (unix epoch) time in sec.
      PRIMARY KEY (name))"""

        """Table to store properties of the DB application"""

        SQL_GET = "SELECT value FROM properties WHERE name = ?"
        SQL_M_TIME = "SELECT m_time FROM properties WHERE name = ?"
        SQL_SET = (
            "INSERT INTO properties (name, value) VALUES (?, ?)"
            "    ON CONFLICT(name) DO UPDATE"
            "   SET value=excluded.value, m_time=strftime('%s', 'now')"
        )
        SQL_TABLE_EXISTS = (
            "SELECT name FROM sqlite_master"
            " WHERE type='table' AND name='properties'"
        )  # fmt:skip
        SQLITE_CONNECT_ARGS = dict(SQLiteAppl.SQLITE_CONNECT_ARGS)
        SQLITE_CONNECT_ARGS["autocommit"] = True  # This option has no effect before Python 3.12

        def __init__(self, db_url: str):  # pylint: disable=super-init-not-called

            self.db_url = db_url
            self.thread_local = threading.local()
            self._init_done = False
            self._compatibility()

        def init(self):
            """Initializes DB schema of the properties in the DB."""

            if self._init_done:
                return
            self._init_done = True
            logger.debug("init properties of DB: %s", self.db_url)
            with self.DB as conn:
                res = conn.execute(self.SQL_TABLE_EXISTS)
                if res.fetchone() is None:  # DB schema needs to be be created
                    self.create_schema(conn)

        def __call__(self, name, default=None):
            """Returns the value of the property ``name`` or ``default`` if property
            not exists in DB."""

            res = self.DB.execute(self.SQL_GET, (name,)).fetchone()
            if res is None:
                return default
            return res[0]

        def set(self, name, value):
            """Set ``value`` of property ``name`` in DB.  If property already
            exists, update the ``m_time`` (and the value)."""

            self.DB.execute(self.SQL_SET, (name, value))

            if sys.version_info <= (3, 12):
                # Prior Python 3.12 there is no "autocommit" option / lets commit
                # explicitely.
                self.DB.commit()

        def row(self, name, default=None):
            """Returns the DB row of property ``name`` or ``default`` if property
            not exists in DB."""

            cur = self.DB.cursor()
            cur.execute("SELECT * FROM properties WHERE name = ?", (name,))
            res = cur.fetchone()
            if res is None:
                return default
            col_names = [column[0] for column in cur.description]
            return dict(zip(col_names, res))

        def m_time(self, name, default: int = 0) -> int:
            """Last modification time of this property."""
            res = self.DB.execute(self.SQL_M_TIME, (name,)).fetchone()
            if res is None:
                return default
            return int(res[0])

        def create_schema(self, conn):
            with conn:
                conn.execute(self.DDL_PROPERTIES)