import collections
from sympy.core.expr import Expr
from sympy.core import sympify, S, preorder_traversal
from sympy.vector.coordsysrect import CoordSys3D
from sympy.vector.vector import Vector, VectorMul, VectorAdd, Cross, Dot, dot
from sympy.vector.scalar import BaseScalar
from sympy.utilities.exceptions import SymPyDeprecationWarning
from sympy.core.function import Derivative
from sympy import Add, Mul


def _get_coord_systems(expr):
    g = preorder_traversal(expr)
    ret = set([])
    for i in g:
        if isinstance(i, CoordSys3D):
            ret.add(i)
            g.skip()
    return frozenset(ret)


def _get_coord_sys_from_expr(expr, coord_sys=None):
    """
    expr : expression
        The coordinate system is extracted from this parameter.
    """

    # TODO: Remove this line when warning from issue #12884 will be removed
    if coord_sys is not None:
        SymPyDeprecationWarning(
            feature="coord_sys parameter",
            useinstead="do not use it",
            deprecated_since_version="1.1",
            issue=12884,
        ).warn()

    return _get_coord_systems(expr)


def _split_mul_args_wrt_coordsys(expr):
    d = collections.defaultdict(lambda: S.One)
    for i in expr.args:
        d[_get_coord_systems(i)] *= i
    return list(d.values())


class Gradient(Expr):
    """
    Represents unevaluated Gradient.

    Examples
    ========

    >>> from sympy.vector import CoordSys3D, Gradient
    >>> R = CoordSys3D('R')
    >>> s = R.x*R.y*R.z
    >>> Gradient(s)
    Gradient(R.x*R.y*R.z)

    """

    def __new__(cls, expr):
        expr = sympify(expr)
        obj = Expr.__new__(cls, expr)
        obj._expr = expr
        return obj

    def doit(self, **kwargs):
        return gradient(self._expr, doit=True)


class Divergence(Expr):
    """
    Represents unevaluated Divergence.

    Examples
    ========

    >>> from sympy.vector import CoordSys3D, Divergence
    >>> R = CoordSys3D('R')
    >>> v = R.y*R.z*R.i + R.x*R.z*R.j + R.x*R.y*R.k
    >>> Divergence(v)
    Divergence(R.y*R.z*R.i + R.x*R.z*R.j + R.x*R.y*R.k)

    """

    def __new__(cls, expr):
        expr = sympify(expr)
        obj = Expr.__new__(cls, expr)
        obj._expr = expr
        return obj

    def doit(self, **kwargs):
        return divergence(self._expr, doit=True)


class Curl(Expr):
    """
    Represents unevaluated Curl.

    Examples
    ========

    >>> from sympy.vector import CoordSys3D, Curl
    >>> R = CoordSys3D('R')
    >>> v = R.y*R.z*R.i + R.x*R.z*R.j + R.x*R.y*R.k
    >>> Curl(v)
    Curl(R.y*R.z*R.i + R.x*R.z*R.j + R.x*R.y*R.k)

    """

    def __new__(cls, expr):
        expr = sympify(expr)
        obj = Expr.__new__(cls, expr)
        obj._expr = expr
        return obj

    def doit(self, **kwargs):
        return curl(self._expr, doit=True)


def curl(vect, coord_sys=None, doit=True):
    """
    Returns the curl of a vector field computed wrt the base scalars
    of the given coordinate system.

    Parameters
    ==========

    vect : Vector
        The vector operand

    coord_sys : CoordSys3D
        The coordinate system to calculate the gradient in.
        Deprecated since version 1.1

    doit : bool
        If True, the result is returned after calling .doit() on
        each component. Else, the returned expression contains
        Derivative instances

    Examples
    ========

    >>> from sympy.vector import CoordSys3D, curl
    >>> R = CoordSys3D('R')
    >>> v1 = R.y*R.z*R.i + R.x*R.z*R.j + R.x*R.y*R.k
    >>> curl(v1)
    0
    >>> v2 = R.x*R.y*R.z*R.i
    >>> curl(v2)
    R.x*R.y*R.j + (-R.x*R.z)*R.k

    """

    coord_sys = _get_coord_sys_from_expr(vect, coord_sys)

    if len(coord_sys) == 0:
        return Vector.zero
    elif len(coord_sys) == 1:
        coord_sys = next(iter(coord_sys))
        i, j, k = coord_sys.base_vectors()
        x, y, z = coord_sys.base_scalars()
        h1, h2, h3 = coord_sys.lame_coefficients()
        vectx = vect.dot(i)
        vecty = vect.dot(j)
        vectz = vect.dot(k)
        outvec = Vector.zero
        outvec += (Derivative(vectz * h3, y) -
                   Derivative(vecty * h2, z)) * i / (h2 * h3)
        outvec += (Derivative(vectx * h1, z) -
                   Derivative(vectz * h3, x)) * j / (h1 * h3)
        outvec += (Derivative(vecty * h2, x) -
                   Derivative(vectx * h1, y)) * k / (h2 * h1)

        if doit:
            return outvec.doit()
        return outvec
    else:
        if isinstance(vect, (Add, VectorAdd)):
            from sympy.vector import express
            try:
                cs = next(iter(coord_sys))
                args = [express(i, cs, variables=True) for i in vect.args]
            except ValueError:
                args = vect.args
            return VectorAdd.fromiter(curl(i, doit=doit) for i in args)
        elif isinstance(vect, (Mul, VectorMul)):
            vector = [i for i in vect.args if isinstance(i, (Vector, Cross, Gradient))][0]
            scalar = Mul.fromiter(i for i in vect.args if not isinstance(i, (Vector, Cross, Gradient)))
            res = Cross(gradient(scalar), vector).doit() + scalar*curl(vector, doit=doit)
            if doit:
                return res.doit()
            return res
        elif isinstance(vect, (Cross, Curl, Gradient)):
            return Curl(vect)
        else:
            raise Curl(vect)


def divergence(vect, coord_sys=None, doit=True):
    """
    Returns the divergence of a vector field computed wrt the base
    scalars of the given coordinate system.

    Parameters
    ==========

    vector : Vector
        The vector operand

    coord_sys : CoordSys3D
        The coordinate system to calculate the gradient in
        Deprecated since version 1.1

    doit : bool
        If True, the result is returned after calling .doit() on
        each component. Else, the returned expression contains
        Derivative instances

    Examples
    ========

    >>> from sympy.vector import CoordSys3D, divergence
    >>> R = CoordSys3D('R')
    >>> v1 = R.x*R.y*R.z * (R.i+R.j+R.k)

    >>> divergence(v1)
    R.x*R.y + R.x*R.z + R.y*R.z
    >>> v2 = 2*R.y*R.z*R.j
    >>> divergence(v2)
    2*R.z

    """
    coord_sys = _get_coord_sys_from_expr(vect, coord_sys)
    if len(coord_sys) == 0:
        return S.Zero
    elif len(coord_sys) == 1:
        if isinstance(vect, (Cross, Curl, Gradient)):
            return Divergence(vect)
        # TODO: is case of many coord systems, this gets a random one:
        coord_sys = next(iter(coord_sys))
        i, j, k = coord_sys.base_vectors()
        x, y, z = coord_sys.base_scalars()
        h1, h2, h3 = coord_sys.lame_coefficients()
        vx = _diff_conditional(vect.dot(i), x, h2, h3) \
             / (h1 * h2 * h3)
        vy = _diff_conditional(vect.dot(j), y, h3, h1) \
             / (h1 * h2 * h3)
        vz = _diff_conditional(vect.dot(k), z, h1, h2) \
             / (h1 * h2 * h3)
        res = vx + vy + vz
        if doit:
            return res.doit()
        return res
    else:
        if isinstance(vect, (Add, VectorAdd)):
            return Add.fromiter(divergence(i, doit=doit) for i in vect.args)
        elif isinstance(vect, (Mul, VectorMul)):
            vector = [i for i in vect.args if isinstance(i, (Vector, Cross, Gradient))][0]
            scalar = Mul.fromiter(i for i in vect.args if not isinstance(i, (Vector, Cross, Gradient)))
            res = Dot(vector, gradient(scalar)) + scalar*divergence(vector, doit=doit)
            if doit:
                return res.doit()
            return res
        elif isinstance(vect, (Cross, Curl, Gradient)):
            return Divergence(vect)
        else:
            raise Divergence(vect)


def gradient(scalar_field, coord_sys=None, doit=True):
    """
    Returns the vector gradient of a scalar field computed wrt the
    base scalars of the given coordinate system.

    Parameters
    ==========

    scalar_field : SymPy Expr
        The scalar field to compute the gradient of

    coord_sys : CoordSys3D
        The coordinate system to calculate the gradient in
        Deprecated since version 1.1

    doit : bool
        If True, the result is returned after calling .doit() on
        each component. Else, the returned expression contains
        Derivative instances

    Examples
    ========

    >>> from sympy.vector import CoordSys3D, gradient
    >>> R = CoordSys3D('R')
    >>> s1 = R.x*R.y*R.z
    >>> gradient(s1)
    R.y*R.z*R.i + R.x*R.z*R.j + R.x*R.y*R.k
    >>> s2 = 5*R.x**2*R.z
    >>> gradient(s2)
    10*R.x*R.z*R.i + 5*R.x**2*R.k

    """
    coord_sys = _get_coord_sys_from_expr(scalar_field, coord_sys)

    if len(coord_sys) == 0:
        return Vector.zero
    elif len(coord_sys) == 1:
        coord_sys = next(iter(coord_sys))
        h1, h2, h3 = coord_sys.lame_coefficients()
        i, j, k = coord_sys.base_vectors()
        x, y, z = coord_sys.base_scalars()
        vx = Derivative(scalar_field, x) / h1
        vy = Derivative(scalar_field, y) / h2
        vz = Derivative(scalar_field, z) / h3

        if doit:
            return (vx * i + vy * j + vz * k).doit()
        return vx * i + vy * j + vz * k
    else:
        if isinstance(scalar_field, (Add, VectorAdd)):
            return VectorAdd.fromiter(gradient(i) for i in scalar_field.args)
        if isinstance(scalar_field, (Mul, VectorMul)):
            s = _split_mul_args_wrt_coordsys(scalar_field)
            return VectorAdd.fromiter(scalar_field / i * gradient(i) for i in s)
        return Gradient(scalar_field)


def _diff_conditional(expr, base_scalar, coeff_1, coeff_2):
    """
    First re-expresses expr in the system that base_scalar belongs to.
    If base_scalar appears in the re-expressed form, differentiates
    it wrt base_scalar.
    Else, returns S(0)
    """
    from sympy.vector.functions import express
    new_expr = express(expr, base_scalar.system, variables=True)
    if base_scalar in new_expr.atoms(BaseScalar):
        return Derivative(coeff_1 * coeff_2 * new_expr, base_scalar)
    return S(0)
