/*
 * Copyright(C) 1999-2020 National Technology & Engineering Solutions
 * of Sandia, LLC (NTESS).  Under the terms of Contract DE-NA0003525 with
 * NTESS, the U.S. Government retains certain rights in this software.
 *
 * See packages/seacas/LICENSE for details
 */

#include "smalloc.h" // for smalloc, srealloc, sfree
#include "structs.h" // for vtx_data
#include <stdio.h>   // for NULL, printf

void makecgraph2(struct vtx_data ** graph,       /* array of vtx data for graph */
                 int                nvtxs,       /* number of vertices in graph */
                 int                nedges,      /* number of edges in graph */
                 struct vtx_data ***pcgraph,     /* coarsened version of graph */
                 int *              pcnvtxs,     /* number of vtxs in coarsened graph */
                 int *              pcnedges,    /* number of edges in coarsened graph */
                 int *              mflag,       /* flag indicating vtx matched or not */
                 int *              v2cv,        /* mapping from vtxs to coarsened vtxs */
                 int                nmerged,     /* number of merged vertices */
                 int                using_ewgts, /* are edge weights being used? */
                 int                igeom,       /* dimensions of geometric data */
                 float **           coords,      /* coordinates for vertices */
                 float **           ccoords      /* coordinates for coarsened vertices */
)
{
  extern double     make_cgraph_time;
  extern int        DEBUG_COARSEN;   /* debug flag for coarsening output */
  extern int        COARSEN_VWGTS;   /* turn off vertex weights in coarse graph? */
  extern int        COARSEN_EWGTS;   /* turn off edge weights in coarse graph? */
  struct vtx_data **cgraph;          /* coarsened version of graph */
  struct vtx_data * links    = NULL; /* space for all the vertex data */
  struct vtx_data **gptr     = NULL; /* loops through cgraph */
  struct vtx_data * cgptr    = NULL; /* loops through cgraph */
  int *             iptr     = NULL; /* loops through integer arrays */
  int *             seenflag = NULL; /* flags for vtxs already put in edge list */
  int *             sptr     = NULL; /* loops through seenflags */
  float *           eweights = NULL; /* space for edge weights in coarsened graph */
  float *           ewptr    = NULL; /* loops through eweights */
  float *           fptr     = NULL; /* loops through eweights */
  float             ewgt;            /* edge weight */
  double            ewgt_sum;        /* sum of edge weights */
  double            time;            /* timing parameters */
  int               nseen;           /* number of edges of coarse graph seen so far */
  int               cnvtxs;          /* number of vtxs in coarsened graph */
  int               cnedges;         /* twice number of edges in coarsened graph */
  int               neighbor;        /* neighboring vertex */
  int               size;            /* space needed for coarsened graph */
  int *             edges = NULL;    /* space for edges in coarsened graph */
  int *             eptr  = NULL;    /* loops through edges data structure */
  int               cvtx;            /* vertex number in coarsened graph */
  int               cneighbor;       /* neighboring vertex number in coarsened graph */
  double            m1, m2;          /* vertex weights of vertices being merged */
  int               v1, v2;          /* vertices being merged */
  int               i, j;            /* loop counters */
  double            seconds();
  void              makev2cv();

  /* Compute the number of vertices and edges in the coarsened graph, */
  /* and construct start pointers into coarsened edge array. */
  time = seconds();

  *pcnvtxs = cnvtxs = nvtxs - nmerged;

  /* Construct mapping from original graph vtxs to coarsened graph vtxs. */
  makev2cv(mflag, nvtxs, v2cv);

  /* Compute an upper bound on the number of coarse graph edges. */
  cnedges = nedges - nmerged;

  /* Now allocate space for the new graph. */
  *pcgraph = cgraph = smalloc((cnvtxs + 1) * sizeof(struct vtx_data *));
  links             = smalloc(cnvtxs * sizeof(struct vtx_data));

  size  = 2 * cnedges + cnvtxs;
  edges = smalloc(size * sizeof(int));
  if (COARSEN_EWGTS) {
    ewptr = eweights = smalloc(size * sizeof(float));
  }

  /* Zero all the seen flags. */
  seenflag = smalloc((cnvtxs + 1) * sizeof(int));
  sptr     = seenflag;
  for (i = cnvtxs; i; i--) {
    *(++sptr) = 0;
  }

  /* Use the renumbering to fill in the edge lists for the new graph. */
  /* Note: This assumes coarse graph vertices are encountered in order. */
  cnedges = 0;
  eptr    = edges;
  ewgt    = 1;
  sptr    = seenflag;

  for (i = 1; i <= nvtxs; i++) {
    if (mflag[i] > i || mflag[i] == 0) {
      /* Unmatched edge, or first appearance of matched edge. */
      nseen = 1;
      cvtx  = v2cv[i];
      cgptr = cgraph[cvtx] = links++;

      if (COARSEN_VWGTS) {
        cgptr->vwgt = 0;
      }
      else {
        cgptr->vwgt = 1;
      }

      eptr[0]      = cvtx;
      cgptr->edges = eptr;
      if (COARSEN_EWGTS) {
        cgptr->ewgts = ewptr;
      }
      else {
        cgptr->ewgts = NULL;
      }
      *(++sptr) = 0;

      ewgt_sum = 0;

      iptr = graph[i]->edges;
      if (using_ewgts) {
        fptr = graph[i]->ewgts;
      }
      for (j = graph[i]->nedges - 1; j; j--) {
        neighbor  = *(++iptr);
        cneighbor = v2cv[neighbor];
        if (cneighbor != cvtx) {
          if (using_ewgts) {
            ewgt = *(++fptr);
          }
          ewgt_sum += ewgt;

          /* Seenflags being used as map from cvtx to index. */
          if (seenflag[cneighbor] == 0) { /* New neighbor. */
            cgptr->edges[nseen] = cneighbor;
            if (COARSEN_EWGTS) {
              cgptr->ewgts[nseen] = ewgt;
            }
            seenflag[cneighbor] = nseen++;
          }
          else { /* Already seen neighbor. */
            if (COARSEN_EWGTS) {
              cgptr->ewgts[seenflag[cneighbor]] += ewgt;
            }
          }
        }
        else if (using_ewgts) {
          ++fptr;
        }
      }

      if (mflag[i] > i) { /* Now handle the matched vertex. */
        iptr = graph[mflag[i]]->edges;
        if (using_ewgts) {
          fptr = graph[mflag[i]]->ewgts;
        }
        for (j = graph[mflag[i]]->nedges - 1; j; j--) {
          neighbor  = *(++iptr);
          cneighbor = v2cv[neighbor];
          if (cneighbor != cvtx) {
            if (using_ewgts) {
              ewgt = *(++fptr);
            }
            ewgt_sum += ewgt;

            if (seenflag[cneighbor] == 0) { /* New neighbor. */
              cgptr->edges[nseen] = cneighbor;
              if (COARSEN_EWGTS) {
                cgptr->ewgts[nseen] = ewgt;
              }
              seenflag[cneighbor] = nseen++;
            }
            else { /* Already seen neighbor. */
              if (COARSEN_EWGTS) {
                cgptr->ewgts[seenflag[cneighbor]] += ewgt;
              }
            }
          }
          else if (using_ewgts) {
            ++fptr;
          }
        }
      }
      if (COARSEN_EWGTS) {
        cgptr->ewgts[0] = -ewgt_sum;
      }
      /* Increment pointers into edges list. */
      cgptr->nedges = nseen;
      eptr += nseen;
      if (COARSEN_EWGTS) {
        ewptr += nseen;
      }

      /* Now clear the seenflag values. */
      iptr = cgptr->edges;
      for (j = nseen - 1; j; j--) {
        seenflag[*(++iptr)] = 0;
      }

      cnedges += nseen - 1;
    }
  }

  sfree(seenflag);

  /* Form new vertex weights by adding those from contracted edges. */
  if (COARSEN_VWGTS) {
    gptr = graph;
    for (i = 1; i <= nvtxs; i++) {
      cgraph[v2cv[i]]->vwgt += (*(++gptr))->vwgt;
    }
  }

  /* If desired, make new vtx coordinates = center-of-mass of their parents. */
  if (coords != NULL && ccoords != NULL && igeom > 0) {
    for (i = 0; i < igeom; i++) {
      ccoords[i] = smalloc((cnvtxs + 1) * sizeof(float));
    }
    for (j = 1; j <= nvtxs; j++) {
      if (mflag[j] == 0) { /* If unmatched, leave it alone. */
        for (i = 0; i < igeom; i++) {
          ccoords[i][v2cv[j]] = coords[i][j];
        }
      }
      else if (j < mflag[j]) { /* If matched, use center of mass. */
        v1 = j;
        v2 = mflag[j];
        m1 = graph[v1]->vwgt;
        m2 = graph[v2]->vwgt;
        for (i = 0; i < igeom; i++) {
          ccoords[i][v2cv[j]] = (m1 * coords[i][v1] + m2 * coords[i][v2]) / (m1 + m2);
        }
      }
    }
  }

  cnedges /= 2;
  *pcnedges = cnedges;
  size      = 2 * cnedges + cnvtxs;
  edges     = srealloc(edges, size * sizeof(int));
  if (COARSEN_EWGTS) {
    eweights = srealloc(eweights, size * sizeof(float));
  }

  if (DEBUG_COARSEN > 0) {
    printf(" Coarse graph has %d vertices and %d edges\n", cnvtxs, cnedges);
  }

  make_cgraph_time += seconds() - time;
  sfree(links);
  sfree(eweights);
  sfree(edges);
}
