/**
* 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;
}
/**
* Returns a new path instance.
*
* @param ii input info
* @param r root expression; can be a {@code null} reference
* @param path path steps
* @return class instance
*/
public static Path get(final InputInfo ii, final Expr r, final Expr... path) {
// check if all steps are axis steps
boolean axes = true;
for (int p = 0; p < path.length; p++) {
Expr e = path[p];
if (e instanceof Context) {
e = Step.get(((ParseExpr) e).info, SELF, Test.NOD);
} else if (e instanceof Filter) {
final Filter f = (Filter) e;
if (f.root instanceof Context) {
e = Step.get(f.info, SELF, Test.NOD, f.preds);
}
}
axes &= e instanceof Step;
path[p] = e;
}
return axes ? new CachedPath(ii, r, path).finish(null) : new MixedPath(ii, r, path);
}
/**
* Returns a new path instance. A path implementation is chosen that works fastest for the given
* steps.
*
* @param info input info
* @param root root expression; can be {@code null}
* @param steps steps
* @return path instance
*/
public static Path get(final InputInfo info, final Expr root, final Expr... steps) {
// new list with steps
final ExprList stps = new ExprList(steps.length);
// merge nested paths
Expr rt = root;
if (rt instanceof Path) {
final Path path = (Path) rt;
stps.add(path.steps);
rt = path.root;
}
// remove redundant context reference
if (rt instanceof Context) rt = null;
// add steps of input array
final int sl = steps.length;
for (int s = 0; s < sl; s++) {
Expr step = steps[s];
if (step instanceof Context) {
// remove redundant context references
if (sl > 1) continue;
// single step: rewrite to axis step (required to sort results of path)
step = Step.get(((Context) step).info, SELF, Test.NOD);
} else if (step instanceof Filter) {
// rewrite to axis step (can be evaluated faster than filter expression)
final Filter f = (Filter) step;
if (f.root instanceof Context) step = Step.get(f.info, SELF, Test.NOD, f.preds);
}
stps.add(step);
}
// check if all steps are axis steps
boolean axes = true;
final Expr[] st = stps.finish();
for (final Expr step : st) axes &= step instanceof Step;
// choose best implementation
return axes
? iterative(rt, st) ? new IterPath(info, rt, st) : new CachedPath(info, rt, st)
: new MixedPath(info, rt, st);
}
/**
* Returns an equivalent expression which accesses an index. If the expression cannot be
* rewritten, the original expression is returned.
*
* <p>The following types of queries can be rewritten (in the examples, the equality comparison is
* used, which will be rewritten to {@link ValueAccess} instances):
*
* <pre>
* 1. A[text() = '...'] -> IA('...')
* 2. A[. = '...'] -> IA('...', A)
* 3. text()[. = '...'] -> IA('...')
* 4. A[B = '...'] -> IA('...', B)/parent::A
* 1. A[B/text() = '...'] -> IA('...')/parent::B/parent::A
* 2. A[B/C = '...'] -> IA('...', C)/parent::B/parent::A
* 7. A[@a = '...'] -> IA('...', @a)/parent::A
* 8. @a[. = '...'] -> IA('...', @a)</pre>
*
* Queries of type 1, 3, 5 will not yield any results if the string to be compared is empty.
*
* @param qc query context
* @param rt root value
* @return original or new expression
* @throws QueryException query exception
*/
private Expr index(final QueryContext qc, final Value rt) throws QueryException {
// only rewrite paths with data reference
final Data data = rt.data();
if (data == null) return this;
// cache index access costs
IndexInfo index = null;
// cheapest predicate and step
int iPred = 0, iStep = 0;
// check if path can be converted to an index access
final int sl = steps.length;
for (int s = 0; s < sl; s++) {
// only accept descendant steps without positional predicates
final Step step = axisStep(s);
if (step == null || !step.axis.down || step.has(Flag.FCS)) break;
// check if path is iterable (i.e., will be duplicate-free)
final boolean iter = pathNodes(data, s) != null;
final IndexContext ictx = new IndexContext(data, iter);
// choose cheapest index access
final int pl = step.preds.length;
for (int p = 0; p < pl; p++) {
final IndexInfo ii = new IndexInfo(ictx, qc, step);
if (!step.preds[p].indexAccessible(ii)) continue;
if (ii.costs == 0) {
// no results...
qc.compInfo(OPTNOINDEX, this);
return Empty.SEQ;
}
if (index == null || index.costs > ii.costs) {
index = ii;
iPred = p;
iStep = s;
}
}
}
// skip rewriting if no index access is possible, or if it is too expensive
if (index == null || index.costs > data.meta.size) return this;
// rewrite for index access
qc.compInfo(index.info);
// replace expressions for index access
final Step indexStep = index.step;
// collect remaining predicates
final int pl = indexStep.preds.length;
final ExprList newPreds = new ExprList(pl - 1);
for (int p = 0; p < pl; p++) {
if (p != iPred) newPreds.add(indexStep.preds[p]);
}
// invert steps that occur before index step and add them as predicate
final Test test = InvDocTest.get(rt);
final ExprList invSteps = new ExprList();
if (test != Test.DOC || !data.meta.uptodate || predSteps(data, iStep)) {
for (int s = iStep; s >= 0; s--) {
final Axis ax = axisStep(s).axis.invert();
if (s == 0) {
// add document test for collections and axes other than ancestors
if (test != Test.DOC || ax != Axis.ANC && ax != Axis.ANCORSELF)
invSteps.add(Step.get(info, ax, test));
} else {
final Step prev = axisStep(s - 1);
invSteps.add(Step.get(info, ax, prev.test, prev.preds));
}
}
}
if (!invSteps.isEmpty()) newPreds.add(get(info, null, invSteps.finish()));
// create resulting expression
final ExprList resultSteps = new ExprList();
final Expr resultRoot;
if (index.expr instanceof Path) {
final Path p = (Path) index.expr;
resultRoot = p.root;
resultSteps.add(p.steps);
} else {
resultRoot = index.expr;
}
if (!newPreds.isEmpty()) {
int ls = resultSteps.size() - 1;
Step step;
if (ls < 0 || !(resultSteps.get(ls) instanceof Step)) {
// add at least one self axis step
step = Step.get(info, Axis.SELF, Test.NOD);
ls++;
} else {
step = (Step) resultSteps.get(ls);
}
// add remaining predicates to last step
resultSteps.set(ls, step.addPreds(newPreds.finish()));
}
// add remaining steps
for (int s = iStep + 1; s < sl; s++) resultSteps.add(steps[s]);
return get(info, resultRoot, resultSteps.finish());
}
/**
* Converts descendant to child steps.
*
* @param ctx query context
* @param data data reference
* @return path
*/
Expr children(final QueryContext ctx, final Data data) {
// skip path check if no path index exists, or if it is out-of-date
if (!data.meta.uptodate || data.nspaces.globalNS() == null) return this;
Path path = this;
for (int s = 0; s < steps.length; ++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> pn = pathNodes(data, s);
if (pn == null) continue;
// cache child steps
final ArrayList<QNm> qnm = new ArrayList<>();
while (pn.get(0).par != null) {
QNm nm = new QNm(data.tagindex.key(pn.get(0).name));
// skip children with prefixes
if (nm.hasPrefix()) return this;
for (final PathNode p : pn) {
if (pn.get(0).name != p.name) nm = null;
}
qnm.add(nm);
pn = PathSummary.parent(pn);
}
ctx.compInfo(OPTCHILD, steps[s]);
// build new steps
int ts = qnm.size();
final Expr[] stps = new Expr[ts + steps.length - 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, Mode.LN, false, null);
stps[t] = Step.get(info, CHILD, nt, preds);
}
while (++s < steps.length) stps[ts++] = steps[s];
path = get(info, root, stps);
break;
}
// check if the all children in the path exist; don't test with namespaces
if (data.nspaces.size() == 0) {
LOOP:
for (int s = 0; s < path.steps.length; ++s) {
// only verify child steps; ignore namespaces
final Step st = path.axisStep(s);
if (st == null || st.axis != CHILD) break;
if (st.test.mode == Mode.ALL || st.test.mode == null) continue;
if (st.test.mode != Mode.LN) break;
// check if one of the addressed nodes is on the correct level
final int name = data.tagindex.id(st.test.name.local());
for (final PathNode pn : data.paths.desc(name, Data.ELEM)) {
if (pn.level() == s + 1) continue LOOP;
}
ctx.compInfo(OPTPATH, path);
return Empty.SEQ;
}
}
return path;
}