from   itertools   import combinations

import numpy as np
from   scipy.spatial import KDTree

from   interp.grid         import grid
from   interp.grid         import cell

import logging
log = logging.getLogger('interp')



THREE_NODE_TRIANGLE = 2
FOUR_NODE_TET       = 4

EDGES_FOR_FACE_CONNECTIVITY   = 2
EDGES_FOR_VOLUME_CONNECTIVITY = 3



class ggrid(grid):

  def __init__(self, filename, dimension = 3):
    """
      construct an interp.grid.grid-compliant grid
      object out of a {2,3}D gmsh file
    """
    self.dim = dimension
    log.debug("dimension: %d", self.dim)

    gmsh_file = open(filename, 'r')


    gmsh_file.readline() # $MeshFormat
    gmsh_file.readline()
    gmsh_file.readline() # $EndMeshFormat

    gmsh_file.readline() # $Nodes

    node_count = int(gmsh_file.readline())

    self.verts = np.empty((node_count, dimension))
    self.q     = np.empty(node_count)

    for i in xrange(node_count):
      cur_line = gmsh_file.readline()
      (index, x,y,z) = cur_line.split()
      index = int(index) - 1

      self.verts[i][0] = float(x)
      self.verts[i][1] = float(y)

      if self.dim == 3:
        self.verts[i][2] = float(z)


    self.tree = KDTree(self.verts)

    # initialize rest of structures about to be populated (cells,
    # cells_for_vert)
    grid.__init__(self)

    gmsh_file.readline() # $EndNodes
    gmsh_file.readline() # $Elements

    # temporary dict used to compute cell connectivity
    neighbors = {}

    element_count = int(gmsh_file.readline())
    for i in xrange(element_count):
      cur_line = gmsh_file.readline()
      cur_line = cur_line.split()
      cur_cell_index, node_type, rest = (int(cur_line[0]),
                                         int(cur_line[1]),
                                         [int(j) for j in  cur_line[2:]])

      if    (node_type == THREE_NODE_TRIANGLE and self.dim == 2) \
         or (node_type == FOUR_NODE_TET       and self.dim == 3):
        points_for_cur_cell = [i-1 for i in rest[rest[0]+1:]]

        cur_cell = cell(cur_cell_index)

        for cur_point in points_for_cur_cell:
          self.cells_for_vert[cur_point].append(cur_cell)

        cur_cell.verts       = points_for_cur_cell

        self.cells[cur_cell_index] = cur_cell
        edges = [tuple(sorted(i)) for i in combinations(points_for_cur_cell, self.dim)]

        for edge in edges:
          if edge in neighbors:
            neighbors[edge].append(cur_cell_index)
          else:
            neighbors[edge] = [cur_cell_index]

    for k,v in neighbors.iteritems():
      if len(v) > 1:
        self.cells[v[0]].add_neighbor(self.cells[v[1]])
        self.cells[v[1]].add_neighbor(self.cells[v[0]])