#!/usr/bin/env python

#############################################################################
##
# This file is part of Taurus
##
# http://taurus-scada.org
##
# Copyright 2011 CELLS / ALBA Synchrotron, Bellaterra, Spain
##
# Taurus is free software: you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
##
# Taurus is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Lesser General Public License for more details.
##
# You should have received a copy of the GNU Lesser General Public License
# along with Taurus.  If not, see <http://www.gnu.org/licenses/>.
##
#############################################################################

"""
safeeval.py: Safe eval replacement with whitelist support
"""

__all__ = ["SafeEvaluator"]

__docformat__ = "restructuredtext"


class SafeEvaluator(object):
    """This class provides a safe eval replacement.

    The method eval() will only evaluate the expressions considered safe (whitelisted).
    By default it has a whitelist of mathematical expressions that can be turn off using defaultSafe=False at init

    The user can add more safe functions passing a safedict to the addSafe() or init methods.

    Functions can be removed by name using removeSafe()

    Note: In order to use variables defined outside, the user must explicitly declare them safe.
    """

    def __init__(self, safedict=None, defaultSafe=True):
        self._default_numpy = ('abs', 'array', 'arange', 'arccos', 'arcsin', 'arctan', 'arctan2', 'average',
                               'ceil', 'cos', 'cosh', 'degrees', 'dot', 'e', 'exp', 'fabs', 'floor', 'fmod',
                               'frexp', 'hypot', 'ldexp', 'linspace', 'log', 'log10', 'logspace',
                               'modf', 'ones', 'pi', 'radians', 'shape', 'sin', 'sinh', 'sqrt', 'sum', 'tan',
                               'tanh', 'zeros')
        self._default_numpy_random = ('randn', 'rand', 'randint')

        if safedict is None:
            safedict = {}
        self.safe_dict = safedict
        if defaultSafe:
            import numpy
            from taurus.external.pint import Quantity
            self.safe_dict['pow'] = pow
            self.safe_dict['len'] = len
            self.safe_dict['int'] = int
            self.safe_dict['float'] = float
            self.safe_dict['bool'] = bool
            self.safe_dict['str'] = str
            self.safe_dict['bytes'] = bytes
            self.safe_dict['list'] = list
            self.safe_dict['range'] = range
            self.safe_dict['True'] = True
            self.safe_dict['False'] = False
            self.safe_dict['None'] = None
            for n in self._default_numpy:
                self.safe_dict[n] = getattr(numpy, n)
            for n in self._default_numpy_random:
                self.safe_dict[n] = getattr(numpy.random, n)
            self.safe_dict['Quantity'] = Quantity
            self.safe_dict['Q'] = Quantity  # Q() is an alias for Quantity()

        self._originalSafeDict = self.safe_dict.copy()

    def eval(self, expr):
        """safe eval"""
        return eval(expr, {"__builtins__": None}, self.safe_dict)

    def addSafe(self, safedict, permanent=False):
        """The values in safedict will be evaluable (whitelisted)
        The safedict is as follows: {"eval_name":object, ...}. The evaluator will interpret eval_name as object.
        """
        self.safe_dict.update(safedict)
        if permanent:
            self._originalSafeDict.update(safedict)

    def removeSafe(self, name, permanent=False):
        """Removes an object from the whitelist"""
        self.safe_dict.pop(name)
        if permanent:
            try:
                self._originalSafeDict.pop(name)
            except KeyError:
                pass

    def resetSafe(self):
        """restores the safe dict with wich the evaluator was instantiated"""
        self.safe_dict = self._originalSafeDict.copy()

    def getSafe(self):
        """returns the currently whitelisted expressions"""
        return self.safe_dict


##-----------------------------------------------##
# A demo of use

if __name__ == '__main__':

    x = range(6)
    sev = SafeEvaluator()
    print "trying to evaluate a variable that has not been registered"
    try:
        # This will fail because 'x' is not registered in sev
        print sev.safeEval('x+2')
    except:
        print "failed!!"

    sev.addSafe({'x': x})  # After registering x, we can use it...
    f0 = 'x'
    f1 = 'sqrt(x)'
    f2 = 'pow(2,8)'
    f3 = 'ceil(array(x)/2.)'
    f4 = 'x[3]*2'
    # This is something we do not want to be evaluated
    f5 = 'open("/etc/passwd")'

    for f in [f0, f1, f2, f3, f4, f5]:
        print 'Evaluating "%s":' % f
        try:
            print sev.eval(f)
        except:
            print 'ERROR: %s cannot be evaluated' % f

    vector = numpy.arange(6)
    # Another way of registering a variable is using the init method...
    sev2 = SafeEvaluator({'x': x, 'y': vector}, defaultSafe=False)
    print 'x*y=', sev2.eval('x*y')
    y = 0  # note that the registered variable is local to the evaluator!!
    # here, y still has the previously registered value instead of 0
    print 'x*y=', sev2.eval('x*y')
