from SimPEG.Utils.sputils import kron3, speye, sdiag
import numpy as np
import scipy.sparse as sp
def ddxFaceDivBC(n, bc):

  ij   = (np.array([0, n-1]),np.array([0, 1]))
  vals = np.zeros(2)

  # Set the first side
  if(bc[0] == 'dirichlet'):
    vals[0] = 0
  elif(bc[0] == 'neumann'):
    vals[0] = -1
  # Set the second side
  if(bc[1] == 'dirichlet'):
    vals[1] = 0
  elif(bc[1] == 'neumann'):
    vals[1] = 1
  D = sp.csr_matrix((vals, ij), shape=(n,2))
  return D


def faceDivBC(mesh, BC, ind):
  """
  The facd divergence boundary condtion matrix

  """
  # The number of cell centers in each direction
  n = mesh.nCv
  # Compute faceDivergence operator on faces
  if(mesh.dim == 1):
    D = ddxFaceDivBC(n[0], BC[0])
  elif(mesh.dim == 2):
    D1 = sp.kron(speye(n[1]), ddxFaceDivBC(n[0]), BC[0])
    D2 = sp.kron(ddxFaceDivBC(n[1], BC[1]), speye(n[0]))
    D = sp.hstack((D1, D2), format="csr")
  elif(mesh.dim == 3):
    D1 = kron3(speye(n[2]), speye(n[1]), ddxFaceDivBC(n[0], BC[0]))
    D2 = kron3(speye(n[2]), ddxFaceDivBC(n[1], BC[1]), speye(n[0]))
    D3 = kron3(ddxFaceDivBC(n[2], BC[2]), speye(n[1]), speye(n[0]))
  D = sp.hstack((D1, D2, D3), format="csr")
  # Compute areas of cell faces & volumes
  S = mesh.area[ind]
  V = mesh.vol
  mesh._faceDiv = sdiag(1/V)*D*sdiag(S)

  return mesh._faceDiv


def faceBCind(mesh):
  """
  Find indices of boundary faces in each direction

  """
  if(mesh.dim==1):
    indxd = (mesh.gridFx[:,0]==min(mesh.gridFx[:,0]))
    indxu = (mesh.gridFx[:,0]==max(mesh.gridFx[:,0]))
    return indxd, indxu
  elif(mesh.dim==1):
    indxd = (mesh.gridFx[:,0]==min(mesh.gridFx[:,0]))
    indxu = (mesh.gridFx[:,0]==max(mesh.gridFx[:,0]))
    indyd = (mesh.gridFy[:,1]==min(mesh.gridFy[:,1]))
    indyu = (mesh.gridFy[:,1]==max(mesh.gridFy[:,1]))
    return indxd, indxu, indyd, indyu
  elif(mesh.dim==3):
    indxd = (mesh.gridFx[:,0]==min(mesh.gridFx[:,0]))
    indxu = (mesh.gridFx[:,0]==max(mesh.gridFx[:,0]))
    indyd = (mesh.gridFy[:,1]==min(mesh.gridFy[:,1]))
    indyu = (mesh.gridFy[:,1]==max(mesh.gridFy[:,1]))
    indzd = (mesh.gridFz[:,2]==min(mesh.gridFz[:,2]))
    indzu = (mesh.gridFz[:,2]==max(mesh.gridFz[:,2]))
    return indxd, indxu, indyd, indyu, indzd, indzu