Graphviz - a program to swap head & tail of edges

swapTailHead.gvpr

/****************************************************************
  swapHeadTail.gvpr  -  swap tail & head of edge(s)

  (only seems to have "real" effect when using dot)

  replaces edges with tail & head swapped
    and (unless using -a0 option) "fixes" all the attribures that are associated with head or tail

  to swap ALL edges, either add
   - edge [swap=1] to your myFile.gv, then
     gvpr -cf swapTailHead.gvpr myFile.gv | dot -T...
   or
   - gvpr -a1 -cf swapTailHead.gvpr myFile.gv | dot -T...

*****************************************************************/
BEG_G {
  string  att, val, tailHeadAtt[], swapAtt[];
  string  swappedAtt, swappedVal, tmpS, swapStyle, thisSwapStyle[], help;
  int     a, i,  Delete[];
  edge_t  anEdge, newEdge;

help='
 swapHeadTail.gvpr  -  swap tail & head of edge(s)
  (only seems to have "real" effect when using dot)

  replaces edges with tail & head swapped
    and (unless using -a0 option) "fixes" all the attribures that are associated with head or tail

  to swap ALL edges, either add
   - edge [swap=1] to your myFile.gv, then
     gvpr -cf swapTailHead.gvpr myFile.gv | dot -T...
   or
   - gvpr -a1 -cf swapTailHead.gvpr myFile.gv | dot -T...
';

  swapStyle="";
  i=0;
  while (i<ARGC) {
    if (ARGV[i]=="0|1") {
      swapStyle=ARGV[i];
    } else {
      printf(2,help);
      exit(0);
    }
    i++;
  }
  
  print("//  FILENAME: ",$F);
  a=0;
  unset(tailHeadAtt);
  for (att = fstAttr($G,"E"); att != ""; att = nxtAttr($G,"E",att)) {
    //print("//   att: ", att);
    if (att=="*@(head|tail)*" || att=="dir") {
      tailHeadAtt[++a]=att;
      //print("// ATT: ", att);
    }
  }
}
E{
  if (swapStyle!="" || (hasAttr($, "swap") && $.swap!="")) {
    Delete[$]=1;
    if (swapStyle!="")
      thisSwapStyle[$]=swapStyle;
    else  //  if (hasAttr($, "swap") && $.swap!="")
      thisSwapStyle[$]=$.swap;
  }
}
END_G{
  for (Delete[anEdge]) {
    // do we swap attributes also?
    if (thisSwapStyle[anEdge]!="0") {
      unset(swapAtt);
      for (tailHeadAtt[i]) {
        att=tailHeadAtt[i];
        if (hasAttr(anEdge, att)) {
          val=aget(anEdge, att);
          tmpS="_Original_"+(string)att;
          aset(anEdge, tmpS, val);  // for debugging, keep original
          //print("// ATT & VAL:  >", att, "<     >", val, "<");
          if (att=="dir" && val=="")
            val="forward";
          if (val!="" ) {
            swappedVal=val;
            if (att=="*head*")
              swappedAtt=sub(att,"head","tail");
            else if (att=="*tail*")
              swappedAtt=sub(att,"tail","head");
            else {  // att==dir
              swappedAtt=att;
              if (val=="forward")
                swappedVal="back";
              else if (val=="back")
                swappedVal="forward";
            }
          }
          print("//  swap ", anEdge.name, "    ", att, "  ", val);
          swapAtt[swappedAtt]=swappedVal;
          aset(anEdge, att, "");  // as close to erase/delete as possible
        }
      }
    }
    //print("//    old: ", anEdge.name,"  ",anEdge.tail.name, " :: ", anEdge.head.name);
    newEdge=edge(anEdge.head, anEdge.tail, "");
    //print("//  new: ", newEdge.name);
    copyA(anEdge, newEdge);  // copy all the rest of the attributes
    for (swapAtt[att]) {
      aset(newEdge, att, swapAtt[att]);
    }
    delete($G, anEdge);
  }
}