/** Calculates the accumulated PRE value shifts for all updates on the list. */
private void accumulatePreValueShifts() {
if (!dirty) return;
int s = 0;
for (int i = updStructural.size() - 1; i >= 0; i--) {
final BasicUpdate t = updStructural.get(i);
s += t.shifts;
t.accumulatedShifts = s;
}
dirty = false;
}
/**
* Resolves unwanted text node adjacency which can result from structural changes in the database.
* Adjacent text nodes are two text nodes A and B, where PRE(B)=PRE(A)+1 and PARENT(A)=PARENT(B).
*/
private void resolveTextAdjacency() {
// Text node merges are also gathered on a separate list to leverage optimizations.
final AtomicUpdateList allMerges = new AtomicUpdateList(data);
// keep track of the visited locations to avoid superfluous checks
final IntSet s = new IntSet();
// Text nodes have to be merged from the highest to the lowest pre value
for (int i = 0; i < updStructural.size(); i++) {
final BasicUpdate u = updStructural.get(i);
final Data insseq = u.getInsertionData();
// calculate the new location of the update, here we have to check for adjacency
final int newLocation = u.location + u.accumulatedShifts - u.shifts;
final int beforeNewLocation = newLocation - 1;
// check surroundings of this location for adjacent text nodes depending on the
// kind of update, first the one with higher PRE values (due to shifts!)
// ... for insert/replace ...
if (insseq != null) {
// calculate the current following node
final int followingNode = newLocation + insseq.meta.size;
final int beforeFollowingNode = followingNode - 1;
// check the nodes at the end of/after the insertion sequence
if (!s.contains(beforeFollowingNode)) {
final AtomicUpdateList merges = necessaryMerges(beforeFollowingNode, allMerges.data);
mergeNodes(merges);
allMerges.merge(merges);
s.add(beforeFollowingNode);
}
}
// check nodes for delete and for insert before the updated location
if (!s.contains(beforeNewLocation)) {
final AtomicUpdateList merges = necessaryMerges(beforeNewLocation, allMerges.data);
mergeNodes(merges);
allMerges.merge(merges);
s.add(beforeNewLocation);
}
}
allMerges.updateDistances();
allMerges.clear();
}
/**
* Checks the list of updates for violations. Updates must be ordered strictly from the highest to
* the lowest PRE value.
*
* <p>A single node must not be affected by more than one {@link Rename}, {@link UpdateValue}
* operation.
*
* <p>A single node must not be affected by more than one destructive operation. These operations
* include {@link Replace}, {@link Delete}.
*/
public void check() {
if (ok || updStructural.size() < 2 && updValue.size() < 2) return;
int i = 0;
while (i + 1 < updStructural.size()) {
final BasicUpdate current = updStructural.get(i);
final BasicUpdate next = updStructural.get(++i);
// check order of location PRE
if (current.location < next.location)
Util.notexpected("Invalid order at location " + current.location);
if (current.location == next.location) {
// check multiple {@link Delete}, {@link Replace}
if (current.destructive() && next.destructive())
Util.notexpected("Multiple deletes/replaces on node " + current.location);
}
}
i = 0;
while (i + 1 < updValue.size()) {
final BasicUpdate current = updValue.get(i++);
final BasicUpdate next = updValue.get(i);
// check order of location PRE
if (current.location < next.location)
Util.notexpected("Invalid order at location " + current.location);
if (current.location == next.location) {
// check multiple {@link Rename}
if (current instanceof Rename && next instanceof Rename)
Util.notexpected("Multiple renames on node " + current.location);
// check multiple {@link UpdateValue}
if (current instanceof UpdateValue && next instanceof UpdateValue)
Util.notexpected("Multiple updates on node " + current.location);
}
}
ok = true;
}
/**
* Removes superfluous update operations. If a node T is deleted or replaced, all updates on the
* descendant axis of T can be left out as they won't affect the database after all.
*
* <p>Superfluous updates can have a minimum PRE value of pre(T)+1 and a maximum PRE value of
* pre(T)+size(T).
*
* <p>An update with location pre(T)+size(T) can only be removed if the update is an atomic insert
* and the inserted node is then part of the subtree of T.
*/
public void optimize() {
if (opt) return;
check();
// traverse from lowest to highest PRE value
int i = updStructural.size() - 1;
while (i >= 0) {
final BasicUpdate u = updStructural.get(i);
// If this update can lead to superfluous updates ...
if (u.destructive()) {
// we determine the lowest and highest PRE values of a superfluous update
final int pre = u.location;
final int fol = pre + data.size(pre, data.kind(pre));
i--;
// and have a look at the next candidate
while (i >= 0) {
final BasicUpdate desc = updStructural.get(i);
final int descpre = desc.location;
// if the candidate operates on the subtree of T and inserts a node ...
if (descpre <= fol
&& (desc instanceof Insert || desc instanceof InsertAttr)
&& desc.parent() >= pre
&& desc.parent() < fol) {
// it is removed.
updStructural.remove(i--);
// Other updates (not inserting a node) that operate on the subtree of T can
// only have a PRE value that is smaller than the following PRE of T
} else if (descpre < fol) {
// these we delete.
updStructural.remove(i--);
// Else there's nothing to delete
} else break;
}
} else i--;
}
opt = true;
}
/** Carries out value updates. */
public void applyValueUpdates() {
for (final BasicUpdate t : updValue) t.apply(data);
}
/** Carries out structural updates. */
public void applyStructuralUpdates() {
accumulatePreValueShifts();
for (final BasicUpdate t : updStructural) t.apply(data);
}
