# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php

"""Defines operators used in SQL expressions."""

from operator import (
    and_, or_, inv, add, mul, sub, mod, truediv, lt, le, ne, gt, ge, eq, neg
    )
    
# Py2K
from operator import (div,)
# end Py2K

from sqlalchemy.util import symbol


def from_():
    raise NotImplementedError()

def as_():
    raise NotImplementedError()

def exists():
    raise NotImplementedError()

def is_():
    raise NotImplementedError()

def isnot():
    raise NotImplementedError()

def collate():
    raise NotImplementedError()

def op(a, opstring, b):
    return a.op(opstring)(b)

def like_op(a, b, escape=None):
    return a.like(b, escape=escape)

def notlike_op(a, b, escape=None):
    raise NotImplementedError()

def ilike_op(a, b, escape=None):
    return a.ilike(b, escape=escape)

def notilike_op(a, b, escape=None):
    raise NotImplementedError()

def between_op(a, b, c):
    return a.between(b, c)

def in_op(a, b):
    return a.in_(b)

def notin_op(a, b):
    raise NotImplementedError()

def distinct_op(a):
    return a.distinct()

def startswith_op(a, b, escape=None):
    return a.startswith(b, escape=escape)

def endswith_op(a, b, escape=None):
    return a.endswith(b, escape=escape)

def contains_op(a, b, escape=None):
    return a.contains(b, escape=escape)

def match_op(a, b):
    return a.match(b)

def comma_op(a, b):
    raise NotImplementedError()

def concat_op(a, b):
    return a.concat(b)

def desc_op(a):
    return a.desc()

def asc_op(a):
    return a.asc()

_commutative = set([eq, ne, add, mul])
def is_commutative(op):
    return op in _commutative

_smallest = symbol('_smallest')
_largest = symbol('_largest')

_PRECEDENCE = {
    from_: 15,
    mul: 7,
    truediv: 7,
    # Py2K
    div: 7,
    # end Py2K
    mod: 7,
    neg: 7,
    add: 6,
    sub: 6,
    concat_op: 6,
    match_op: 6,
    ilike_op: 5,
    notilike_op: 5,
    like_op: 5,
    notlike_op: 5,
    in_op: 5,
    notin_op: 5,
    is_: 5,
    isnot: 5,
    eq: 5,
    ne: 5,
    gt: 5,
    lt: 5,
    ge: 5,
    le: 5,
    between_op: 5,
    distinct_op: 5,
    inv: 5,
    and_: 3,
    or_: 2,
    comma_op: -1,
    collate: 7,
    as_: -1,
    exists: 0,
    _smallest: -1000,
    _largest: 1000
}

def is_precedent(operator, against):
    return (_PRECEDENCE.get(operator, _PRECEDENCE[_smallest]) <=
            _PRECEDENCE.get(against, _PRECEDENCE[_largest]))