"""Implementation of :class:`PolynomialRing` class. """

from __future__ import print_function, division

from sympy.core.compatibility import iterable, range
from sympy.polys.agca.modules import FreeModulePolyRing
from sympy.polys.domains.characteristiczero import CharacteristicZero
from sympy.polys.domains.compositedomain import CompositeDomain
from sympy.polys.domains.old_fractionfield import FractionField
from sympy.polys.domains.ring import Ring
from sympy.polys.orderings import monomial_key, build_product_order
from sympy.polys.polyclasses import DMP, DMF
from sympy.polys.polyerrors import (GeneratorsNeeded, PolynomialError,
        CoercionFailed, ExactQuotientFailed, NotReversible)
from sympy.polys.polyutils import dict_from_basic, basic_from_dict, _dict_reorder
from sympy.utilities import public

# XXX why does this derive from CharacteristicZero???

@public
class PolynomialRingBase(Ring, CharacteristicZero, CompositeDomain):
    """
    Base class for generalized polynomial rings.

    This base class should be used for uniform access to generalized polynomial
    rings. Subclasses only supply information about the element storage etc.

    Do not instantiate.
    """

    has_assoc_Ring = True
    has_assoc_Field = True

    default_order = "grevlex"

    def __init__(self, dom, *gens, **opts):
        if not gens:
            raise GeneratorsNeeded("generators not specified")

        lev = len(gens) - 1
        self.ngens = len(gens)

        self.zero = self.dtype.zero(lev, dom, ring=self)
        self.one = self.dtype.one(lev, dom, ring=self)

        self.domain = self.dom = dom
        self.symbols = self.gens = gens
        # NOTE 'order' may not be set if inject was called through CompositeDomain
        self.order = opts.get('order', monomial_key(self.default_order))

    def new(self, element):
        return self.dtype(element, self.dom, len(self.gens) - 1, ring=self)

    def __str__(self):
        s_order = str(self.order)
        orderstr = (
            " order=" + s_order) if s_order != self.default_order else ""
        return str(self.dom) + '[' + ','.join(map(str, self.gens)) + orderstr + ']'

    def __hash__(self):
        return hash((self.__class__.__name__, self.dtype, self.dom,
                     self.gens, self.order))

    def __eq__(self, other):
        """Returns `True` if two domains are equivalent. """
        return isinstance(other, PolynomialRingBase) and \
            self.dtype == other.dtype and self.dom == other.dom and \
            self.gens == other.gens and self.order == other.order

    def from_ZZ_python(K1, a, K0):
        """Convert a Python `int` object to `dtype`. """
        return K1(K1.dom.convert(a, K0))

    def from_QQ_python(K1, a, K0):
        """Convert a Python `Fraction` object to `dtype`. """
        return K1(K1.dom.convert(a, K0))

    def from_ZZ_gmpy(K1, a, K0):
        """Convert a GMPY `mpz` object to `dtype`. """
        return K1(K1.dom.convert(a, K0))

    def from_QQ_gmpy(K1, a, K0):
        """Convert a GMPY `mpq` object to `dtype`. """
        return K1(K1.dom.convert(a, K0))

    def from_RealField(K1, a, K0):
        """Convert a mpmath `mpf` object to `dtype`. """
        return K1(K1.dom.convert(a, K0))

    def from_AlgebraicField(K1, a, K0):
        """Convert a `ANP` object to `dtype`. """
        if K1.dom == K0:
            return K1(a)

    def from_GlobalPolynomialRing(K1, a, K0):
        """Convert a `DMP` object to `dtype`. """
        if K1.gens == K0.gens:
            if K1.dom == K0.dom:
                return K1(a.rep)  # set the correct ring
            else:
                return K1(a.convert(K1.dom).rep)
        else:
            monoms, coeffs = _dict_reorder(a.to_dict(), K0.gens, K1.gens)

            if K1.dom != K0.dom:
                coeffs = [ K1.dom.convert(c, K0.dom) for c in coeffs ]

            return K1(dict(zip(monoms, coeffs)))

    def get_field(self):
        """Returns a field associated with `self`. """
        return FractionField(self.dom, *self.gens)

    def poly_ring(self, *gens):
        """Returns a polynomial ring, i.e. `K[X]`. """
        raise NotImplementedError('nested domains not allowed')

    def frac_field(self, *gens):
        """Returns a fraction field, i.e. `K(X)`. """
        raise NotImplementedError('nested domains not allowed')

    def revert(self, a):
        try:
            return 1/a
        except (ExactQuotientFailed, ZeroDivisionError):
            raise NotReversible('%s is not a unit' % a)

    def gcdex(self, a, b):
        """Extended GCD of `a` and `b`. """
        return a.gcdex(b)

    def gcd(self, a, b):
        """Returns GCD of `a` and `b`. """
        return a.gcd(b)

    def lcm(self, a, b):
        """Returns LCM of `a` and `b`. """
        return a.lcm(b)

    def factorial(self, a):
        """Returns factorial of `a`. """
        return self.dtype(self.dom.factorial(a))

    def _vector_to_sdm(self, v, order):
        """
        For internal use by the modules class.

        Convert an iterable of elements of this ring into a sparse distributed
        module element.
        """
        raise NotImplementedError

    def _sdm_to_dics(self, s, n):
        """Helper for _sdm_to_vector."""
        from sympy.polys.distributedmodules import sdm_to_dict
        dic = sdm_to_dict(s)
        res = [{} for _ in range(n)]
        for k, v in dic.items():
            res[k[0]][k[1:]] = v
        return res

    def _sdm_to_vector(self, s, n):
        """
        For internal use by the modules class.

        Convert a sparse distributed module into a list of length ``n``.

        Examples
        ========

        >>> from sympy import QQ, ilex
        >>> from sympy.abc import x, y
        >>> R = QQ.old_poly_ring(x, y, order=ilex)
        >>> L = [((1, 1, 1), QQ(1)), ((0, 1, 0), QQ(1)), ((0, 0, 1), QQ(2))]
        >>> R._sdm_to_vector(L, 2)
        [x + 2*y, x*y]
        """
        dics = self._sdm_to_dics(s, n)
        # NOTE this works for global and local rings!
        return [self(x) for x in dics]

    def free_module(self, rank):
        """
        Generate a free module of rank ``rank`` over ``self``.

        Examples
        ========

        >>> from sympy.abc import x
        >>> from sympy import QQ
        >>> QQ.old_poly_ring(x).free_module(2)
        QQ[x]**2
        """
        return FreeModulePolyRing(self, rank)


def _vector_to_sdm_helper(v, order):
    """Helper method for common code in Global and Local poly rings."""
    from sympy.polys.distributedmodules import sdm_from_dict
    d = {}
    for i, e in enumerate(v):
        for key, value in e.to_dict().items():
            d[(i,) + key] = value
    return sdm_from_dict(d, order)


@public
class GlobalPolynomialRing(PolynomialRingBase):
    """A true polynomial ring, with objects DMP. """

    is_PolynomialRing = is_Poly = True
    dtype = DMP

    def from_FractionField(K1, a, K0):
        """
        Convert a ``DMF`` object to ``DMP``.

        Examples
        ========

        >>> from sympy.polys.polyclasses import DMP, DMF
        >>> from sympy.polys.domains import ZZ
        >>> from sympy.abc import x

        >>> f = DMF(([ZZ(1), ZZ(1)], [ZZ(1)]), ZZ)
        >>> K = ZZ.old_frac_field(x)

        >>> F = ZZ.old_poly_ring(x).from_FractionField(f, K)

        >>> F == DMP([ZZ(1), ZZ(1)], ZZ)
        True
        >>> type(F)
        <class 'sympy.polys.polyclasses.DMP'>

        """
        if a.denom().is_one:
            return K1.from_GlobalPolynomialRing(a.numer(), K0)

    def to_sympy(self, a):
        """Convert `a` to a SymPy object. """
        return basic_from_dict(a.to_sympy_dict(), *self.gens)

    def from_sympy(self, a):
        """Convert SymPy's expression to `dtype`. """
        try:
            rep, _ = dict_from_basic(a, gens=self.gens)
        except PolynomialError:
            raise CoercionFailed("can't convert %s to type %s" % (a, self))

        for k, v in rep.items():
            rep[k] = self.dom.from_sympy(v)

        return self(rep)

    def is_positive(self, a):
        """Returns True if `LC(a)` is positive. """
        return self.dom.is_positive(a.LC())

    def is_negative(self, a):
        """Returns True if `LC(a)` is negative. """
        return self.dom.is_negative(a.LC())

    def is_nonpositive(self, a):
        """Returns True if `LC(a)` is non-positive. """
        return self.dom.is_nonpositive(a.LC())

    def is_nonnegative(self, a):
        """Returns True if `LC(a)` is non-negative. """
        return self.dom.is_nonnegative(a.LC())

    def _vector_to_sdm(self, v, order):
        """
        Examples
        ========

        >>> from sympy import lex, QQ
        >>> from sympy.abc import x, y
        >>> R = QQ.old_poly_ring(x, y)
        >>> f = R.convert(x + 2*y)
        >>> g = R.convert(x * y)
        >>> R._vector_to_sdm([f, g], lex)
        [((1, 1, 1), 1), ((0, 1, 0), 1), ((0, 0, 1), 2)]
        """
        return _vector_to_sdm_helper(v, order)


class GeneralizedPolynomialRing(PolynomialRingBase):
    """A generalized polynomial ring, with objects DMF. """

    dtype = DMF

    def new(self, a):
        """Construct an element of `self` domain from `a`. """
        res = self.dtype(a, self.dom, len(self.gens) - 1, ring=self)

        # make sure res is actually in our ring
        if res.denom().terms(order=self.order)[0][0] != (0,)*len(self.gens):
            from sympy.printing.str import sstr
            raise CoercionFailed("denominator %s not allowed in %s"
                                 % (sstr(res), self))
        return res

    def __contains__(self, a):
        try:
            a = self.convert(a)
        except CoercionFailed:
            return False
        return a.denom().terms(order=self.order)[0][0] == (0,)*len(self.gens)

    def from_FractionField(K1, a, K0):
        dmf = K1.get_field().from_FractionField(a, K0)
        return K1((dmf.num, dmf.den))

    def to_sympy(self, a):
        """Convert `a` to a SymPy object. """
        return (basic_from_dict(a.numer().to_sympy_dict(), *self.gens) /
                basic_from_dict(a.denom().to_sympy_dict(), *self.gens))

    def from_sympy(self, a):
        """Convert SymPy's expression to `dtype`. """
        p, q = a.as_numer_denom()

        num, _ = dict_from_basic(p, gens=self.gens)
        den, _ = dict_from_basic(q, gens=self.gens)

        for k, v in num.items():
            num[k] = self.dom.from_sympy(v)

        for k, v in den.items():
            den[k] = self.dom.from_sympy(v)

        return self((num, den)).cancel()

    def _vector_to_sdm(self, v, order):
        """
        Turn an iterable into a sparse distributed module.

        Note that the vector is multiplied by a unit first to make all entries
        polynomials.

        Examples
        ========

        >>> from sympy import ilex, QQ
        >>> from sympy.abc import x, y
        >>> R = QQ.old_poly_ring(x, y, order=ilex)
        >>> f = R.convert((x + 2*y) / (1 + x))
        >>> g = R.convert(x * y)
        >>> R._vector_to_sdm([f, g], ilex)
        [((0, 0, 1), 2), ((0, 1, 0), 1), ((1, 1, 1), 1), ((1,
          2, 1), 1)]
        """
        # NOTE this is quite inefficient...
        u = self.one.numer()
        for x in v:
            u *= x.denom()
        return _vector_to_sdm_helper([x.numer()*u/x.denom() for x in v], order)


@public
def PolynomialRing(dom, *gens, **opts):
    r"""
    Create a generalized multivariate polynomial ring.

    A generalized polynomial ring is defined by a ground field `K`, a set
    of generators (typically `x_1, \ldots, x_n`) and a monomial order `<`.
    The monomial order can be global, local or mixed. In any case it induces
    a total ordering on the monomials, and there exists for every (non-zero)
    polynomial `f \in K[x_1, \ldots, x_n]` a well-defined "leading monomial"
    `LM(f) = LM(f, >)`. One can then define a multiplicative subset
    `S = S_> = \{f \in K[x_1, \ldots, x_n] | LM(f) = 1\}`. The generalized
    polynomial ring corresponding to the monomial order is
    `R = S^{-1}K[x_1, \ldots, x_n]`.

    If `>` is a so-called global order, that is `1` is the smallest monomial,
    then we just have `S = K` and `R = K[x_1, \ldots, x_n]`.

    Examples
    ========

    A few examples may make this clearer.

    >>> from sympy.abc import x, y
    >>> from sympy import QQ

    Our first ring uses global lexicographic order.

    >>> R1 = QQ.old_poly_ring(x, y, order=(("lex", x, y),))

    The second ring uses local lexicographic order. Note that when using a
    single (non-product) order, you can just specify the name and omit the
    variables:

    >>> R2 = QQ.old_poly_ring(x, y, order="ilex")

    The third and fourth rings use a mixed orders:

    >>> o1 = (("ilex", x), ("lex", y))
    >>> o2 = (("lex", x), ("ilex", y))
    >>> R3 = QQ.old_poly_ring(x, y, order=o1)
    >>> R4 = QQ.old_poly_ring(x, y, order=o2)

    We will investigate what elements of `K(x, y)` are contained in the various
    rings.

    >>> L = [x, 1/x, y/(1 + x), 1/(1 + y), 1/(1 + x*y)]
    >>> test = lambda R: [f in R for f in L]

    The first ring is just `K[x, y]`:

    >>> test(R1)
    [True, False, False, False, False]

    The second ring is R1 localised at the maximal ideal (x, y):

    >>> test(R2)
    [True, False, True, True, True]

    The third ring is R1 localised at the prime ideal (x):

    >>> test(R3)
    [True, False, True, False, True]

    Finally the fourth ring is R1 localised at `S = K[x, y] \setminus yK[y]`:

    >>> test(R4)
    [True, False, False, True, False]
    """

    order = opts.get("order", GeneralizedPolynomialRing.default_order)
    if iterable(order):
        order = build_product_order(order, gens)
    order = monomial_key(order)
    opts['order'] = order

    if order.is_global:
        return GlobalPolynomialRing(dom, *gens, **opts)
    else:
        return GeneralizedPolynomialRing(dom, *gens, **opts)
