# SPDX-License-Identifier: AGPL-3.0-or-later
"""Calculate mathematical expressions using :py:obj:`ast.parse` (mode="eval").
"""

from __future__ import annotations
import typing

import ast
import re
import operator
import multiprocessing

import babel
import babel.numbers
from flask_babel import gettext

from searx.result_types import EngineResults
from searx.plugins import Plugin, PluginInfo

if typing.TYPE_CHECKING:
    from searx.search import SearchWithPlugins
    from searx.extended_types import SXNG_Request
    from searx.plugins import PluginCfg


class SXNGPlugin(Plugin):
    """Plugin converts strings to different hash digests.  The results are
    displayed in area for the "answers".
    """

    id = "calculator"

    def __init__(self, plg_cfg: "PluginCfg") -> None:
        super().__init__(plg_cfg)

        self.info = PluginInfo(
            id=self.id,
            name=gettext("Basic Calculator"),
            description=gettext("Calculate mathematical expressions via the search bar"),
            preference_section="general",
        )

    def post_search(self, request: "SXNG_Request", search: "SearchWithPlugins") -> EngineResults:
        results = EngineResults()

        # only show the result of the expression on the first page
        if search.search_query.pageno > 1:
            return results

        query = search.search_query.query
        # in order to avoid DoS attacks with long expressions, ignore long expressions
        if len(query) > 100:
            return results

        # replace commonly used math operators with their proper Python operator
        query = query.replace("x", "*").replace(":", "/")

        # use UI language
        ui_locale = babel.Locale.parse(request.preferences.get_value("locale"), sep="-")

        # parse the number system in a localized way
        def _decimal(match: re.Match) -> str:
            val = match.string[match.start() : match.end()]
            val = babel.numbers.parse_decimal(val, ui_locale, numbering_system="latn")
            return str(val)

        decimal = ui_locale.number_symbols["latn"]["decimal"]
        group = ui_locale.number_symbols["latn"]["group"]
        query = re.sub(f"[0-9]+[{decimal}|{group}][0-9]+[{decimal}|{group}]?[0-9]?", _decimal, query)

        # only numbers and math operators are accepted
        if any(str.isalpha(c) for c in query):
            return results

        # in python, powers are calculated via **
        query_py_formatted = query.replace("^", "**")

        # Prevent the runtime from being longer than 50 ms
        res = timeout_func(0.05, _eval_expr, query_py_formatted)
        if res is None or res == "":
            return results

        res = babel.numbers.format_decimal(res, locale=ui_locale)
        results.add(results.types.Answer(answer=f"{search.search_query.query} = {res}"))

        return results


operators: dict[type, typing.Callable] = {
    ast.Add: operator.add,
    ast.Sub: operator.sub,
    ast.Mult: operator.mul,
    ast.Div: operator.truediv,
    ast.Pow: operator.pow,
    ast.BitXor: operator.xor,
    ast.USub: operator.neg,
}

# with multiprocessing.get_context("fork") we are ready for Py3.14 (by emulating
# the old behavior "fork") but it will not solve the core problem of fork, nor
# will it remove the deprecation warnings in py3.12 & py3.13.  Issue is
# ddiscussed here: https://github.com/searxng/searxng/issues/4159
mp_fork = multiprocessing.get_context("fork")


def _eval_expr(expr):
    """
    >>> _eval_expr('2^6')
    64
    >>> _eval_expr('2**6')
    64
    >>> _eval_expr('1 + 2*3**(4^5) / (6 + -7)')
    -5.0
    """
    try:
        return _eval(ast.parse(expr, mode='eval').body)
    except ZeroDivisionError:
        # This is undefined
        return ""


def _eval(node):
    if isinstance(node, ast.Constant) and isinstance(node.value, (int, float)):
        return node.value

    if isinstance(node, ast.BinOp):
        return operators[type(node.op)](_eval(node.left), _eval(node.right))

    if isinstance(node, ast.UnaryOp):
        return operators[type(node.op)](_eval(node.operand))

    raise TypeError(node)


def handler(q: multiprocessing.Queue, func, args, **kwargs):  # pylint:disable=invalid-name
    try:
        q.put(func(*args, **kwargs))
    except:
        q.put(None)
        raise


def timeout_func(timeout, func, *args, **kwargs):

    que = mp_fork.Queue()
    p = mp_fork.Process(target=handler, args=(que, func, args), kwargs=kwargs)
    p.start()
    p.join(timeout=timeout)
    ret_val = None
    # pylint: disable=used-before-assignment,undefined-variable
    if not p.is_alive():
        ret_val = que.get()
    else:
        logger.debug("terminate function after timeout is exceeded")  # type: ignore
        p.terminate()
    p.join()
    p.close()
    return ret_val