sclass WebNode {

  Web web;

  new L<Lisp> labels;

  O visInfo; // visualisation info

  *() {}

  *(Web *web) { web.fireNewNode(this); }

  void addLabel(S label) { addLabel(web.parseLabel(label)); }

  void addLabel(Lisp label) {

    if (setAdd(labels, label) && web != null) {

      web.index(label, this);

      ++web.size;

    }

  }

  void addLabels(Collection<Lisp> l) { for (Lisp lbl : l) addLabel(lbl); }

  void addStrings(Collection<S> l) { for (S lbl : l) addLabel(lbl); }

  bool hasLabel(Lisp label) { ret labels.contains(label); }

  bool hasLabel(S label) { ret labels.contains(web.parseLabel(label)); }

  toString { ret l(labels) == 1 ? str(first(labels)) : str(labels); }

  int count() { ret 1 + l(labels); }

  S text() { ret web.unparseLabel(first(labels)); }

  L<S> texts() { ret web.unparseLabels(labels); }

  void relation(S arrow, S b) {

    web.getRelation(this, web.node(b)).addLabel(arrow);

  }

  Lisp parseLabel(S l) { ret web.parseLabel(l); }

  S unparseLabel(Lisp l) { ret web.unparseLabel(l); }

}

sclass WebRelation extends WebNode {

  WebNode a, b;

  *() {}

  *(Web web, WebNode a, WebNode b) { super(web); this.a = a; this.b = b; }

}

sclass Web {

  new L<WebNode> nodes; // Relations are also nodes

  Map<Pair<WebNode>, WebRelation> relations = new HashMap;

  new MultiMap<Lisp, WebNode> index; // label -> node

  //Map<S, L<WebNode>> pots = new Map;

  transient Lock lock = reentrantLock(true);

  int size;

  //int flags; // TODO

  bool useCLParse = true;

  bool labelsToUpper;

  S title, globalID = aGlobalID();

  S source;

  bool unverified;

  long created = nowUnlessLoading();

  static new L onNewNode; // L<voidfunc(WebNode)>

  static new L onNewLabel; // L<voidfunc(WebNode, Lisp)>

  static int F_useCLParse = 1;

  static int F_labelsToupper = 2;

  static int F_unverified = 3;

  /*bool potNotEmpty(S pot) { ret nempty(getPot(pot)); }

  L<WebNode> clearPot(S pot) {

    L<WebNode> l = getPot(pot);

    L<WebNode> l2 = cloneList(l);

    l.clear();

    ret l2;

  }*/

  /*L<WebNode> getPot(S pot) {

    L<WebNode> l = pots.get(pot);

    if (l == null)

      pots.put(pot, l = cloneList(nodes));

    ret l;

  }*/

  void relation(WebNode a, S arrow, WebNode b) {

    getRelation(a, b).addLabel(arrow);

  }

  Pair<WebNode> relation(S a, S arrow, S b) {

    ret relation(lisp(arrow, a, b));

  }

  Pair<WebNode> relation(Lisp l) {

    if (l(l) == 1) {

      findNode(l.get(0)).addLabel(lisp("wvuyakuvuelmxpwp", l.head));

      null;

    } else if (l(l) == 2) {

      S a = lisp2label(l.get(0)), b = lisp2label(l.get(1));

      if (l.is("fgvvrzypbkqomktd")) { // X is Y.

        findNode(a).addLabel(b);

        findNode(b).addLabel(a);

      }

      WebNode na = findNode(a), nb = findNode(b);

      getRelation(na, nb).addLabel(l.head);

      ret pair(na, nb);

    }

    null;

  }

  void relations(L<Lisp> l) {

    for (Lisp li : l) relation(li);

  }

  WebRelation getRelation(S a, S b) {

    ret getRelation(findNode(a), findNode(b));

  }

  WebRelation getRelation(WebNode a, WebNode b) {

    ret getRelation(pair(a, b));

  }

  WebRelation relation(WebNode a, WebNode b) { ret getRelation(a, b); }

  WebRelation relation(Pair<WebNode> p) { ret getRelation(p); }

  WebRelation getRelationOpt(WebNode a, WebNode b) {

    ret relations.get(pair(a, b));

  }

  WebRelation getRelation(Pair<WebNode> p) {

    WebRelation r = relations.get(p);

    if (r == null) relations.put(p, r = _newRelation(p.a, p.b));

    ret r;

  }

  WebRelation _newRelation(WebNode a, WebNode b) {

    WebRelation r = new WebRelation(this, a, b);

    nodes.add(r); ++size;

    //for (L<WebNode> l : values(pots)) l.add(r);

    ret r;

  }

  WebNode newNode() {

    WebNode node = new WebNode(this);

    nodes.add(node); ++size;

    //for (L<WebNode> l : values(pots)) l.add(node);

    ret node;

  }

  WebNode newNode(S s) {

    WebNode node = newNode();

    node.addLabel(parseLabel(s));

    ret node;

  }

  WebNode node(S s) { ret findNode(s); }

  WebNode node(Lisp l) { ret findNode(l); }

  WebNode findNode(S s) {

    ret findNode(parseLabel(s));

  }

  WebNode findNode(Lisp l) {

    WebNode n = findNodeOpt(l);

    ret n != null ? n : newNode(l);

  }

  WebNode findNodeOpt(Lisp l) {

    ret first(index.get(l));

    /*for (WebNode n : nodes)

      if (n.labels.contains(l))

        ret n;

    null;*/

  }

  WebNode newNode(S... labels) {

    WebNode n = newNode();

    for (S label : labels) n.addLabel(label);

    ret n;

  }

  WebNode newNode(Lisp... labels) {

    WebNode n = newNode();

    for (Lisp label : labels) n.addLabel(label);

    ret n;

  }

  toString { ret webToString(this); }

  int count() {

    ret size;

    /*int count = 0;

    for (WebNode n : nodes) count += n.count();

    for (WebNode n : values(relations)) count += n.count();

    ret count;*/

  }

  void index(Lisp label, WebNode n) {

    index.put(label, n);

    fireNewLabel(n, label);

  }

  void clear {

    size = 0;

    clearAll(nodes, relations, index/*, pots*/);

  }

  Lisp parseLabel(S s) {

    if (useCLParse) ret clParse(s);

    ret lisp(labelsToUpper ? upper(s) : s);

  }

  S unparseLabel(Lisp l) {

    ret useCLParse ? clUnparse(l) : lispHead(l);

  }

  L<Lisp> parseLabels(L<S> l) {

    ret map(func(S s) { parseLabel(s) }, l);

  }

  L<S> unparseLabels(L<Lisp> l) {

    ret map(func(Lisp l) { unparseLabel(l) }, l);

  }

  void fireNewNode(WebNode node) { for (O f : onNewNode) pcallF(f, node); }

  void fireNewLabel(WebNode node, Lisp label) { for (O f : onNewLabel) pcallF(f, node, label); }

  void removeNode(WebNode n) {

    if (n == null || !nodes.contains(n)) ret;

    n.web = null;

    L<Pair<WebNode>> relationsToDelete = pairList_lookupAnySide(keys(relations), n);

    for (Lisp label : n.labels)

      index.remove(label, n);

    nodes.remove(n);

    for (Pair<WebNode> p : relationsToDelete)

      removeRelation(p.a, p.b);

  }

  void removeRelation(WebNode a, WebNode b) {

    Pair<WebNode> p = pair(a, b);

    WebNode r = relations.get(p);

    if (r == null) ret;

    relations.remove(p);

    removeNode(r);

  }

}