# orm/evaluator.py
# Copyright (C) 2005-2016 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php

import operator
from ..sql import operators


class UnevaluatableError(Exception):
    pass

_straight_ops = set(getattr(operators, op)
                    for op in ('add', 'mul', 'sub',
                               'div',
                               'mod', 'truediv',
                               'lt', 'le', 'ne', 'gt', 'ge', 'eq'))


_notimplemented_ops = set(getattr(operators, op)
                          for op in ('like_op', 'notlike_op', 'ilike_op',
                                     'notilike_op', 'between_op', 'in_op',
                                     'notin_op', 'endswith_op', 'concat_op'))


class EvaluatorCompiler(object):
    def __init__(self, target_cls=None):
        self.target_cls = target_cls

    def process(self, clause):
        meth = getattr(self, "visit_%s" % clause.__visit_name__, None)
        if not meth:
            raise UnevaluatableError(
                "Cannot evaluate %s" % type(clause).__name__)
        return meth(clause)

    def visit_grouping(self, clause):
        return self.process(clause.element)

    def visit_null(self, clause):
        return lambda obj: None

    def visit_false(self, clause):
        return lambda obj: False

    def visit_true(self, clause):
        return lambda obj: True

    def visit_column(self, clause):
        if 'parentmapper' in clause._annotations:
            parentmapper = clause._annotations['parentmapper']
            if self.target_cls and not issubclass(
                    self.target_cls, parentmapper.class_):
                raise UnevaluatableError(
                    "Can't evaluate criteria against alternate class %s" %
                    parentmapper.class_
                )
            key = parentmapper._columntoproperty[clause].key
        else:
            key = clause.key

        get_corresponding_attr = operator.attrgetter(key)
        return lambda obj: get_corresponding_attr(obj)

    def visit_clauselist(self, clause):
        evaluators = list(map(self.process, clause.clauses))
        if clause.operator is operators.or_:
            def evaluate(obj):
                has_null = False
                for sub_evaluate in evaluators:
                    value = sub_evaluate(obj)
                    if value:
                        return True
                    has_null = has_null or value is None
                if has_null:
                    return None
                return False
        elif clause.operator is operators.and_:
            def evaluate(obj):
                for sub_evaluate in evaluators:
                    value = sub_evaluate(obj)
                    if not value:
                        if value is None:
                            return None
                        return False
                return True
        else:
            raise UnevaluatableError(
                "Cannot evaluate clauselist with operator %s" %
                clause.operator)

        return evaluate

    def visit_binary(self, clause):
        eval_left, eval_right = list(map(self.process,
                                         [clause.left, clause.right]))
        operator = clause.operator
        if operator is operators.is_:
            def evaluate(obj):
                return eval_left(obj) == eval_right(obj)
        elif operator is operators.isnot:
            def evaluate(obj):
                return eval_left(obj) != eval_right(obj)
        elif operator in _straight_ops:
            def evaluate(obj):
                left_val = eval_left(obj)
                right_val = eval_right(obj)
                if left_val is None or right_val is None:
                    return None
                return operator(eval_left(obj), eval_right(obj))
        else:
            raise UnevaluatableError(
                "Cannot evaluate %s with operator %s" %
                (type(clause).__name__, clause.operator))
        return evaluate

    def visit_unary(self, clause):
        eval_inner = self.process(clause.element)
        if clause.operator is operators.inv:
            def evaluate(obj):
                value = eval_inner(obj)
                if value is None:
                    return None
                return not value
            return evaluate
        raise UnevaluatableError(
            "Cannot evaluate %s with operator %s" %
            (type(clause).__name__, clause.operator))

    def visit_bindparam(self, clause):
        if clause.callable:
            val = clause.callable()
        else:
            val = clause.value
        return lambda obj: val
