/**
* Returns all summary path nodes for the specified location step or {@code null} if nodes cannot
* be retrieved or are found on different levels.
*
* @param data data reference
* @param last last step to be checked
* @return path nodes
*/
private ArrayList<PathNode> pathNodes(final Data data, final int last) {
// skip request if no path index exists or might be out-of-date
if (!data.meta.uptodate) return null;
ArrayList<PathNode> nodes = data.paths.root();
for (int s = 0; s <= last; s++) {
// only follow axis steps
final Step curr = axisStep(s);
if (curr == null) return null;
final boolean desc = curr.axis == DESC;
if (!desc && curr.axis != CHILD || curr.test.kind != Kind.NAME) return null;
final int name = data.elemNames.id(curr.test.name.local());
final ArrayList<PathNode> tmp = new ArrayList<>();
for (final PathNode node : PathSummary.desc(nodes, desc)) {
if (node.kind == Data.ELEM && name == node.name) {
// skip test if an element name occurs on different levels
if (!tmp.isEmpty() && tmp.get(0).level() != node.level()) return null;
tmp.add(node);
}
}
if (tmp.isEmpty()) return null;
nodes = tmp;
}
return nodes;
}
/**
* Returns all summary path nodes for the specified location step or {@code null} if nodes cannot
* be retrieved or are found on different levels.
*
* @param data data reference
* @param l last step to be checked
* @return path nodes
*/
ArrayList<PathNode> pathNodes(final Data data, final int l) {
// skip request if no path index exists or might be out-of-date
if (!data.meta.uptodate) return null;
ArrayList<PathNode> in = data.paths.root();
for (int s = 0; s <= l; ++s) {
final Step curr = axisStep(s);
if (curr == null) return null;
final boolean desc = curr.axis == DESC;
if (!desc && curr.axis != CHILD || curr.test.mode != Mode.LN) return null;
final int name = data.tagindex.id(curr.test.name.local());
final ArrayList<PathNode> al = new ArrayList<>();
for (final PathNode pn : PathSummary.desc(in, desc)) {
if (pn.kind == Data.ELEM && name == pn.name) {
// skip test if a tag is found on different levels
if (!al.isEmpty() && al.get(0).level() != pn.level()) return null;
al.add(pn);
}
}
if (al.isEmpty()) return null;
in = al;
}
return in;
}
/**
* Converts descendant to child steps.
*
* @param qc query context
* @param rt root value
* @return original or new expression
*/
private Expr children(final QueryContext qc, final Value rt) {
// skip if index does not exist or is out-dated, or if several namespaces occur in the input
final Data data = rt.data();
if (data == null || !data.meta.uptodate || data.nspaces.globalNS() == null) return this;
Path path = this;
final int sl = steps.length;
for (int s = 0; s < sl; s++) {
// don't allow predicates in preceding location steps
final Step prev = s > 0 ? axisStep(s - 1) : null;
if (prev != null && prev.preds.length != 0) break;
// ignore axes other than descendant, or numeric predicates
final Step curr = axisStep(s);
if (curr == null || curr.axis != DESC || curr.has(Flag.FCS)) continue;
// check if child steps can be retrieved for current step
ArrayList<PathNode> nodes = pathNodes(data, s);
if (nodes == null) continue;
// cache child steps
final ArrayList<QNm> qnm = new ArrayList<>();
while (nodes.get(0).parent != null) {
QNm nm = new QNm(data.elemNames.key(nodes.get(0).name));
// skip children with prefixes
if (nm.hasPrefix()) return this;
for (final PathNode p : nodes) {
if (nodes.get(0).name != p.name) nm = null;
}
qnm.add(nm);
nodes = PathSummary.parent(nodes);
}
qc.compInfo(OPTCHILD, steps[s]);
// build new steps
int ts = qnm.size();
final Expr[] stps = new Expr[ts + sl - s - 1];
for (int t = 0; t < ts; t++) {
final Expr[] preds = t == ts - 1 ? ((Preds) steps[s]).preds : new Expr[0];
final QNm nm = qnm.get(ts - t - 1);
final NameTest nt =
nm == null ? new NameTest(false) : new NameTest(nm, Kind.NAME, false, null);
stps[t] = Step.get(info, CHILD, nt, preds);
}
while (++s < sl) stps[ts++] = steps[s];
path = get(info, root, stps);
break;
}
// check if all steps yield results; if not, return empty sequence
final ArrayList<PathNode> nodes = pathNodes(qc);
if (nodes != null && nodes.isEmpty()) {
qc.compInfo(OPTPATH, path);
return Empty.SEQ;
}
return path;
}