__docformat__ = 'restructuredtext'

from fipy.tools import numerix

from fipy.boundaryConditions.boundaryCondition import BoundaryCondition
from fipy.boundaryConditions.fixedValue import FixedValue
from fipy.tools import vector

__all__ = ["FixedFlux"]

class FixedFlux(BoundaryCondition):
    r"""

    The `FixedFlux` boundary condition adds a contribution, equivalent to a
    fixed flux (Neumann condition), to the equation's RHS vector.  The
    contribution, given by `value`, is only added to entries corresponding to
    the specified `faces`, and is weighted by the face areas.

    """

    def __init__(self,faces,value):
        """
        Creates a `FixedFlux` object.

        :Parameters:
            - `faces`: A `list` or `tuple` of `Face` objects to which this condition applies.
            - `value`: The value to impose.

        """
        BoundaryCondition.__init__(self,faces,value)
        ## The extra index [self.faces.value] makes self.contribution the same length as self.adjacentCellIDs
        self.contribution = (self.value * self.faces.mesh._faceAreas)[self.faces.value]

    def _buildMatrix(self, SparseMatrix, Ncells, MaxFaces, coeff):
        """Leave **L** unchanged and add gradient to **b**

        :Parameters:
          - `SparseMatrix`: *unused* (empty matrix)
          - `Ncells`:       Size of **b**-vector
          - `MaxFaces`:     *unused*
          - `coeff`:        *unused*
        """

        bb = numerix.zeros((Ncells,),'d')

        if not self.boundaryConditionApplied:
            vector.putAdd(bb, self.adjacentCellIDs, -self.contribution)
            self.boundaryConditionApplied = True

        return (0, bb)

    def _getDerivative(self, order):
        if order == 1:
            return FixedValue(self.faces, self.value)
        else:
            return BoundaryCondition._getDerivative(self, order)

    def _test(self):
        """
        The following tests check that self.contributions is the same length as
        self.adjacentCellIDs.

           >>> from fipy import *
           >>> m = Grid1D(nx = 10)
           >>> v = FaceVariable(mesh=m)
           >>> bc = FixedFlux(value=v.globalValue[-1], faces=m.facesRight)
           >>> len(bc.contribution) == len(bc.adjacentCellIDs)
           True
           >>> bc = FixedFlux(value=v, faces=m.facesRight)
           >>> len(bc.contribution) == len(bc.adjacentCellIDs)
           True
        """

def _test():
    import fipy.tests.doctestPlus
    return fipy.tests.doctestPlus.testmod()

if __name__ == "__main__":
    _test()
