/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.commons.jxpath.ri.axes;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.apache.commons.jxpath.JXPathException;
import org.apache.commons.jxpath.ri.Compiler;
import org.apache.commons.jxpath.ri.EvalContext;
import org.apache.commons.jxpath.ri.InfoSetUtil;
import org.apache.commons.jxpath.ri.QName;
import org.apache.commons.jxpath.ri.compiler.Expression;
import org.apache.commons.jxpath.ri.compiler.NameAttributeTest;
import org.apache.commons.jxpath.ri.compiler.NodeNameTest;
import org.apache.commons.jxpath.ri.compiler.NodeTest;
import org.apache.commons.jxpath.ri.compiler.Step;
import org.apache.commons.jxpath.ri.model.NodeIterator;
import org.apache.commons.jxpath.ri.model.NodePointer;
import org.apache.commons.jxpath.ri.model.beans.LangAttributePointer;
import org.apache.commons.jxpath.ri.model.beans.NullElementPointer;
import org.apache.commons.jxpath.ri.model.beans.NullPropertyPointer;
import org.apache.commons.jxpath.ri.model.beans.PropertyOwnerPointer;
import org.apache.commons.jxpath.ri.model.beans.PropertyPointer;

/**
 * An evaluation mechanism for simple XPaths, which is much faster than the usual process. It is only used for xpaths which have no context-dependent parts,
 * consist entirely of {@code child::name} and {@code self::node()} steps with predicates that either integer or have the form {@code [@name = ...]}.
 */
public class SimplePathInterpreter {
    // Because of the complexity caused by the variety of situations
    // that need to be addressed by this class, we attempt to break up
    // the class into individual methods addressing those situations
    // individually. The names of the methods are supposed to
    // give brief descriptions of those situations.

    private static final QName QNAME_NAME = new QName(null, "name");
    private static final int PERFECT_MATCH = 1000;
    // Uncomment this variable and the PATH = ... lines in
    // the two following methods in order to be able to print the
    // currently evaluated path for debugging of this class
//    private static String PATH;       // Debugging

    /**
     * For a pointer that matches an actual node, returns 0. For a pointer that does not match an actual node, but whose parent pointer does returns -1, etc.
     *
     * @param pointer input pointer
     * @return int match quality code
     */
    private static int computeQuality(NodePointer pointer) {
        int quality = PERFECT_MATCH;
        while (pointer != null && !pointer.isActual()) {
            quality--;
            pointer = pointer.getImmediateParentPointer();
        }
        return quality;
    }

    /**
     * Create the child pointer for a given step.
     *
     * @param parentPointer parent pointer
     * @param step          associated step
     * @return NodePointer
     */
    private static NodePointer createChildPointerForStep(final PropertyOwnerPointer parentPointer, final Step step) {
        final int axis = step.getAxis();
        if (axis == Compiler.AXIS_CHILD || axis == Compiler.AXIS_ATTRIBUTE) {
            final QName qName = ((NodeNameTest) step.getNodeTest()).getNodeName();
            if (axis == Compiler.AXIS_ATTRIBUTE && isLangAttribute(qName)) {
                return new LangAttributePointer(parentPointer);
            }
            if (parentPointer.isValidProperty(qName)) {
                final NodePointer childPointer = parentPointer.getPropertyPointer();
                ((PropertyPointer) childPointer).setPropertyName(qName.toString());
                childPointer.setAttribute(axis == Compiler.AXIS_ATTRIBUTE);
                return childPointer;
            }
            // invalid property gets nothing, not even a NullPointer
            return null;
        }
        return parentPointer;
    }

    /**
     * Creates a "null pointer" that a) represents the requested path and b) can be used for creation of missing nodes in the path.
     *
     * @param context     evaluation context
     * @param parent      parent pointer
     * @param steps       path steps
     * @param currentStep step number
     * @return NodePointer
     */
    public static NodePointer createNullPointer(final EvalContext context, NodePointer parent, final Step[] steps, final int currentStep) {
        if (currentStep == steps.length) {
            return parent;
        }
        parent = valuePointer(parent);
        final Step step = steps[currentStep];
        final int axis = step.getAxis();
        if (axis == Compiler.AXIS_CHILD || axis == Compiler.AXIS_ATTRIBUTE) {
            final NullPropertyPointer pointer = new NullPropertyPointer(parent);
            final QName qName = ((NodeNameTest) step.getNodeTest()).getNodeName();
            pointer.setPropertyName(qName.toString());
            pointer.setAttribute(axis == Compiler.AXIS_ATTRIBUTE);
            parent = pointer;
        }
        // else { it is self::node() }
        final Expression[] predicates = step.getPredicates();
        return createNullPointerForPredicates(context, parent, steps, currentStep, predicates, 0);
    }

    /**
     * Creates a "null pointer" that starts with predicates.
     *
     * @param context          evaluation context
     * @param parent           parent pointer
     * @param steps            path steps
     * @param currentStep      step number
     * @param predicates       predicates
     * @param currentPredicate int predicate number
     * @return NodePointer
     */
    private static NodePointer createNullPointerForPredicates(final EvalContext context, NodePointer parent, final Step[] steps, final int currentStep,
            final Expression[] predicates, final int currentPredicate) {
        for (int i = currentPredicate; i < predicates.length; i++) {
            final Expression predicate = predicates[i];
            if (predicate instanceof NameAttributeTest) {
                final String key = keyFromPredicate(context, predicate);
                parent = valuePointer(parent);
                final NullPropertyPointer pointer = new NullPropertyPointer(parent);
                pointer.setNameAttributeValue(key);
                parent = pointer;
            } else {
                final int index = indexFromPredicate(context, predicate);
                if (parent instanceof NullPropertyPointer) {
                    parent.setIndex(index);
                } else {
                    parent = new NullElementPointer(parent, index);
                }
            }
        }
        // Proceed with the remaining steps
        return createNullPointer(context, parent, steps, currentStep + 1);
    }

    /**
     * Evaluates predicates and proceeds with the subsequent steps of the path.
     *
     * @param context          evaluation context
     * @param parent           parent pointer
     * @param steps            path steps
     * @param currentStep      step number
     * @param predicates       predicate expressions
     * @param currentPredicate int predicate number
     * @return NodePointer
     */
    private static NodePointer doPredicate(final EvalContext context, final NodePointer parent, final Step[] steps, final int currentStep,
            final Expression[] predicates, final int currentPredicate) {
        if (currentPredicate == predicates.length) {
            return doStep(context, parent, steps, currentStep + 1);
        }
        final Expression predicate = predicates[currentPredicate];
        if (predicate instanceof NameAttributeTest) { // [@name = key1]
            return doPredicateName(context, parent, steps, currentStep, predicates, currentPredicate);
        }
        // else [index]
        return doPredicateIndex(context, parent, steps, currentStep, predicates, currentPredicate);
    }

    /**
     * Evaluate a subscript predicate: see if the node is a collection and if the index is inside the collection.
     *
     * @param context          evaluation context
     * @param parent           parent pointer
     * @param steps            path steps
     * @param currentStep      step number
     * @param predicates       predicates
     * @param currentPredicate int predicate number
     * @return NodePointer
     */
    private static NodePointer doPredicateIndex(final EvalContext context, final NodePointer parent, final Step[] steps, final int currentStep,
            final Expression[] predicates, final int currentPredicate) {
        final Expression predicate = predicates[currentPredicate];
        final int index = indexFromPredicate(context, predicate);
        NodePointer pointer = parent;
        if (isCollectionElement(pointer, index)) {
            pointer = (NodePointer) pointer.clone();
            pointer.setIndex(index);
            return doPredicate(context, pointer, steps, currentStep, predicates, currentPredicate + 1);
        }
        return createNullPointerForPredicates(context, parent, steps, currentStep, predicates, currentPredicate);
    }

    /**
     * Execute a NameAttributeTest predicate
     *
     * @param context          evaluation context
     * @param parent           parent pointer
     * @param steps            path steps
     * @param currentStep      int step number
     * @param predicates       predicates
     * @param currentPredicate int predicate number
     * @return NodePointer
     */
    private static NodePointer doPredicateName(final EvalContext context, final NodePointer parent, final Step[] steps, final int currentStep,
            final Expression[] predicates, final int currentPredicate) {
        final Expression predicate = predicates[currentPredicate];
        final String key = keyFromPredicate(context, predicate);
        NodePointer child = valuePointer(parent);
        if (child instanceof PropertyOwnerPointer) {
            final PropertyPointer pointer = ((PropertyOwnerPointer) child).getPropertyPointer();
            pointer.setPropertyName(key);
            if (pointer.isActual()) {
                return doPredicate(context, pointer, steps, currentStep, predicates, currentPredicate + 1);
            }
        } else if (child.isCollection()) {
            // For each node in the collection, perform the following:
            // if the node is a property owner, apply this predicate to it;
            // if the node is a collection, apply this predicate to each elem.;
            // if the node is not a prop owner or a collection,
            // see if it has the attribute "name" with the right value,
            // if so - proceed to the next predicate
            NodePointer bestMatch = null;
            int bestQuality = 0;
            child = (NodePointer) child.clone();
            final int count = child.getLength();
            for (int i = 0; i < count; i++) {
                child.setIndex(i);
                final NodePointer valuePointer = valuePointer(child);
                NodePointer pointer;
                if (valuePointer instanceof PropertyOwnerPointer || valuePointer.isCollection()) {
                    pointer = doPredicateName(context, valuePointer, steps, currentStep, predicates, currentPredicate);
                } else if (isNameAttributeEqual(valuePointer, key)) {
                    pointer = doPredicate(context, valuePointer, steps, currentStep, predicates, currentPredicate + 1);
                } else {
                    pointer = null;
                }
                if (pointer != null) {
                    final int quality = computeQuality(pointer);
                    if (quality == PERFECT_MATCH) {
                        return pointer;
                    }
                    if (quality > bestQuality) {
                        bestMatch = (NodePointer) pointer.clone();
                        bestQuality = quality;
                    }
                }
            }
            if (bestMatch != null) {
                return bestMatch;
            }
        } else {
            // If the node is a standard InfoSet node (e.g. DOM Node),
            // employ doPredicates_standard, which will iterate through
            // the node's children and apply all predicates
            final NodePointer found = doPredicatesStandard(context, Collections.singletonList(child), steps, currentStep, predicates, currentPredicate);
            if (found != null) {
                return found;
            }
        }
        // If nothing worked - return a null pointer
        return createNullPointerForPredicates(context, child, steps, currentStep, predicates, currentPredicate);
    }

    /**
     * Called exclusively for standard InfoSet nodes, e.g. DOM nodes to evaluate predicate sequences like [@name=...][@name=...][index].
     *
     * @param context          evaluation context
     * @param parents          List of parent pointers
     * @param steps            path steps
     * @param currentStep      step number
     * @param predicates       predicates
     * @param currentPredicate int predicate number
     * @return NodePointer
     */
    private static NodePointer doPredicatesStandard(final EvalContext context, final List<NodePointer> parents, final Step[] steps, final int currentStep,
            final Expression[] predicates, final int currentPredicate) {
        if (parents.isEmpty()) {
            return null;
        }
        // If all predicates have been processed, take the first
        // element from the list of results and proceed to the
        // remaining steps with that element.
        if (currentPredicate == predicates.length) {
            final NodePointer pointer = parents.get(0);
            return doStep(context, pointer, steps, currentStep + 1);
        }
        final Expression predicate = predicates[currentPredicate];
        if (predicate instanceof NameAttributeTest) {
            final String key = keyFromPredicate(context, predicate);
            final List<NodePointer> newList = new ArrayList<>();
            for (int i = 0; i < parents.size(); i++) {
                final NodePointer pointer = parents.get(i);
                if (isNameAttributeEqual(pointer, key)) {
                    newList.add(pointer);
                }
            }
            if (newList.isEmpty()) {
                return null;
            }
            return doPredicatesStandard(context, newList, steps, currentStep, predicates, currentPredicate + 1);
        }
        // For a subscript, simply take the corresponding
        // element from the list of results and
        // proceed to the remaining predicates with that element
        final int index = indexFromPredicate(context, predicate);
        if (index < 0 || index >= parents.size()) {
            return null;
        }
        final NodePointer ptr = parents.get(index);
        return doPredicate(context, ptr, steps, currentStep, predicates, currentPredicate + 1);
    }

    /**
     * Recursive evaluation of a path. The general plan is: Look at the current step, find nodes that match it, iterate over those nodes and for each of them
     * call doStep again for subsequent steps.
     *
     * @param context     evaluation context
     * @param parent      parent pointer
     * @param steps       path steps
     * @param currentStep step number
     * @return NodePointer
     */
    private static NodePointer doStep(final EvalContext context, NodePointer parent, final Step[] steps, final int currentStep) {
        if (parent == null) {
            return null;
        }
        if (currentStep == steps.length) {
            // We have reached the end of the list of steps
            return parent;
        }
        // Open all containers
        parent = valuePointer(parent);
        final Step step = steps[currentStep];
        final Expression[] predicates = step.getPredicates();
        // Divide and conquer: the process is broken out into
        // four major use cases.
        // 1. Current step has no predicates and
        // the root is a property owner (e.g. bean or map)
        // 2. Current step has predicates and
        // the root is a property owner (e.g. bean or map)
        // 3. Current step has no predicates and
        // the root is an InfoSet standard node (e.g. DOM Node)
        // 4. Current step has predicates and
        // the root is an InfoSet standard node (e.g. DOM Node)
        if (parent instanceof PropertyOwnerPointer) {
            if (predicates == null || predicates.length == 0) {
                return doStepNoPredicatesPropertyOwner(context, (PropertyOwnerPointer) parent, steps, currentStep);
            }
            return doStepPredicatesPropertyOwner(context, (PropertyOwnerPointer) parent, steps, currentStep);
        }
        if (predicates == null || predicates.length == 0) {
            return doStepNoPredicatesStandard(context, parent, steps, currentStep);
        }
        return doStepPredicatesStandard(context, parent, steps, currentStep);
    }

    /**
     * We have a step that starts with a property owner (bean, map, etc) and has no predicates. The name test of the step may map to a scalar property or to a
     * collection. If it is a collection, we should apply the tail of the path to each element until we find a match. If we don't find a perfect match, we
     * should return the "best quality" pointer, which has the longest chain of steps mapping to existing nodes and the shortes tail of Null* pointers.
     *
     * @param context       evaluation context
     * @param parentPointer property owner pointer
     * @param steps         path steps
     * @param currentStep   step number
     * @return NodePointer
     */
    private static NodePointer doStepNoPredicatesPropertyOwner(final EvalContext context, final PropertyOwnerPointer parentPointer, final Step[] steps,
            final int currentStep) {
        final Step step = steps[currentStep];
        NodePointer childPointer = createChildPointerForStep(parentPointer, step);
        if (childPointer == null) {
            return null;
        }
        if (!childPointer.isActual()) {
            // The property does not exist - create a null pointer.
            return createNullPointer(context, parentPointer, steps, currentStep);
        }
        if (currentStep == steps.length - 1) {
            // If this is the last step - we are done, we found it
            return childPointer;
        }
        if (childPointer.isCollection()) {
            // Iterate over all values and
            // execute remaining steps for each node,
            // looking for the best quality match
            int bestQuality = 0;
            childPointer = (NodePointer) childPointer.clone();
            NodePointer bestMatch = null;
            final int count = childPointer.getLength();
            for (int i = 0; i < count; i++) {
                childPointer.setIndex(i);
                final NodePointer pointer = doStep(context, childPointer, steps, currentStep + 1);
                final int quality = computeQuality(pointer);
                if (quality == PERFECT_MATCH) {
                    return pointer;
                }
                if (quality > bestQuality) {
                    bestQuality = quality;
                    bestMatch = (NodePointer) pointer.clone();
                }
            }
            if (bestMatch != null) {
                return bestMatch;
            }
            // This step did not find anything - return a null pointer
            return createNullPointer(context, childPointer, steps, currentStep);
        }
        // Evaluate subsequent steps
        return doStep(context, childPointer, steps, currentStep + 1);
    }

    /**
     * A path that starts with a standard InfoSet node (e.g. DOM Node) and has no predicates. Get a child iterator and apply the tail of the path to each
     * element until we find a match. If we don't find a perfect match, we should return the "best quality" pointer, which has the longest chain of steps
     * mapping to existing nodes and the shortes tail of Null* pointers.
     *
     * @param context       evaluation context
     * @param parentPointer parent pointer
     * @param steps         path steps
     * @param currentStep   step number
     * @return NodePointer
     */
    private static NodePointer doStepNoPredicatesStandard(final EvalContext context, final NodePointer parentPointer, final Step[] steps,
            final int currentStep) {
        final Step step = steps[currentStep];
        if (step.getAxis() == Compiler.AXIS_SELF) {
            return doStep(context, parentPointer, steps, currentStep + 1);
        }
        int bestQuality = 0;
        NodePointer bestMatch = null;
        final NodeIterator it = getNodeIterator(context, parentPointer, step);
        if (it != null) {
            for (int i = 1; it.setPosition(i); i++) {
                final NodePointer childPointer = it.getNodePointer();
                if (steps.length == currentStep + 1) {
                    // If this is the last step - we are done, we found it
                    return childPointer;
                }
                final NodePointer pointer = doStep(context, childPointer, steps, currentStep + 1);
                final int quality = computeQuality(pointer);
                if (quality == PERFECT_MATCH) {
                    return pointer;
                }
                if (quality > bestQuality) {
                    bestQuality = quality;
                    bestMatch = (NodePointer) pointer.clone();
                }
            }
        }
        return bestMatch != null ? bestMatch : createNullPointer(context, parentPointer, steps, currentStep);
    }

    /**
     * A path that starts with a property owner. The method evaluates the first predicate in a special way and then forwards to a general predicate processing
     * method.
     *
     * @param context       evaluation context
     * @param parentPointer parent pointer
     * @param steps         path steps
     * @param currentStep   step number
     * @return NodePointer
     */
    private static NodePointer doStepPredicatesPropertyOwner(final EvalContext context, final PropertyOwnerPointer parentPointer, final Step[] steps,
            final int currentStep) {
        final Step step = steps[currentStep];
        final Expression[] predicates = step.getPredicates();
        final NodePointer childPointer = createChildPointerForStep(parentPointer, step);
        if (!childPointer.isActual()) {
            // Property does not exist - return a null pointer
            return createNullPointer(context, parentPointer, steps, currentStep);
        }
        // Evaluate predicates
        return doPredicate(context, childPointer, steps, currentStep, predicates, 0);
    }

    /**
     * A path that starts with a standard InfoSet node, e.g. a DOM Node. The method evaluates the first predicate in a special way and then forwards to a
     * general predicate processing method.
     *
     * @param context     evaluation context
     * @param parent      parent pointer
     * @param steps       path steps
     * @param currentStep step number
     * @return NodePointer
     */
    private static NodePointer doStepPredicatesStandard(final EvalContext context, final NodePointer parent, final Step[] steps, final int currentStep) {
        final Step step = steps[currentStep];
        final Expression[] predicates = step.getPredicates();
        final int axis = step.getAxis();
        if (axis == Compiler.AXIS_SELF) {
            return doPredicate(context, parent, steps, currentStep, predicates, 0);
        }
        final Expression predicate = predicates[0];
        // Optimize for a single predicate to avoid building a list
        // and to allow the direct access to the index'th element
        // in the case of a simple subscript predecate
        // It is a very common use case, so it deserves individual
        // attention
        if (predicates.length == 1) {
            final NodeIterator it = getNodeIterator(context, parent, step);
            NodePointer pointer = null;
            if (it != null) {
                if (predicate instanceof NameAttributeTest) { // [@name = key]
                    final String key = keyFromPredicate(context, predicate);
                    for (int i = 1; it.setPosition(i); i++) {
                        final NodePointer ptr = it.getNodePointer();
                        if (isNameAttributeEqual(ptr, key)) {
                            pointer = ptr;
                            break;
                        }
                    }
                } else {
                    final int index = indexFromPredicate(context, predicate);
                    if (it.setPosition(index + 1)) {
                        pointer = it.getNodePointer();
                    }
                }
            }
            if (pointer != null) {
                return doStep(context, pointer, steps, currentStep + 1);
            }
        } else {
            final NodeIterator it = getNodeIterator(context, parent, step);
            if (it != null) {
                final List<NodePointer> list = new ArrayList<>();
                for (int i = 1; it.setPosition(i); i++) {
                    list.add(it.getNodePointer());
                }
                final NodePointer pointer = doPredicatesStandard(context, list, steps, currentStep, predicates, 0);
                if (pointer != null) {
                    return pointer;
                }
            }
        }
        return createNullPointer(context, parent, steps, currentStep);
    }

    /**
     * Gets a NodeIterator.
     *
     * @param context evaluation context
     * @param pointer owning pointer
     * @param step    triggering step
     * @return NodeIterator
     */
    private static NodeIterator getNodeIterator(final EvalContext context, final NodePointer pointer, final Step step) {
        if (step.getAxis() == Compiler.AXIS_CHILD) {
            NodeTest nodeTest = step.getNodeTest();
            final QName qname = ((NodeNameTest) nodeTest).getNodeName();
            final String prefix = qname.getPrefix();
            if (prefix != null) {
                final String namespaceURI = context.getJXPathContext().getNamespaceURI(prefix);
                nodeTest = new NodeNameTest(qname, namespaceURI);
            }
            return pointer.childIterator(nodeTest, false, null);
        }
        // else Compiler.AXIS_ATTRIBUTE
        if (!(step.getNodeTest() instanceof NodeNameTest)) {
            throw new UnsupportedOperationException("Not supported node test for attributes: " + step.getNodeTest());
        }
        return pointer.attributeIterator(((NodeNameTest) step.getNodeTest()).getNodeName());
    }

    /**
     * Extract an integer from a subscript predicate. The returned index starts with 0, even though the subscript starts with 1.
     *
     * @param context   evaluation context
     * @param predicate to evaluate
     * @return calculated index
     */
    private static int indexFromPredicate(final EvalContext context, final Expression predicate) {
        Object value = predicate.computeValue(context);
        if (value instanceof EvalContext) {
            value = ((EvalContext) value).getSingleNodePointer();
        }
        if (value instanceof NodePointer) {
            value = ((NodePointer) value).getValue();
        }
        if (value == null) {
            throw new JXPathException("Predicate value is null: " + predicate);
        }
        if (value instanceof Number) {
            final double round = 0.5;
            return (int) (InfoSetUtil.doubleValue(value) + round) - 1;
        }
        return InfoSetUtil.booleanValue(value) ? 0 : -1;
    }

    /**
     * Interpret the steps of a simple expression path that starts with the given root, which is the result of evaluation of the root expression of the
     * expression path, applies the given predicates to it and then follows the given steps. All steps must have the axis "child::" or "attribute::" and a name
     * test. They can also optionally have predicates of type [@name=...] or simply [...] interpreted as an index.
     *
     * @param context    evaluation context
     * @param root       root pointer
     * @param predicates predicates corresponding to {@code steps}
     * @param steps      path steps
     * @return NodePointer
     */
    public static NodePointer interpretSimpleExpressionPath(final EvalContext context, final NodePointer root, final Expression[] predicates,
            final Step[] steps) {
//        PATH = createNullPointerForPredicates(context, root,
//                    steps, -1, predicates, 0).toString();  // Debugging
        final NodePointer pointer = doPredicate(context, root, steps, -1, predicates, 0);
//        return valuePointer(pointer);
        return pointer;
    }

    /**
     * Interpret a simple path that starts with the given root and follows the given steps. All steps must have the axis "child::" and a name test. They can
     * also optionally have predicates of type [@name=expression] or simply [expression] interpreted as an index.
     *
     * @param context evaluation context
     * @param root    root pointer
     * @param steps   path steps
     * @return NodePointer
     */
    public static NodePointer interpretSimpleLocationPath(final EvalContext context, final NodePointer root, final Step[] steps) {
//        PATH = createNullPointer(context, root, steps, 0).toString();  // Dbg
        final NodePointer pointer = doStep(context, root, steps, 0);
//        return valuePointer(pointer);
        return pointer;
    }

    /**
     * Returns true if the pointer is a collection and the index is withing the bounds of the collection.
     *
     * @param pointer input pointer
     * @param index   to check
     * @return boolean
     */
    private static boolean isCollectionElement(final NodePointer pointer, final int index) {
        return pointer.isActual() && (index == 0 || pointer.isCollection() && index >= 0 && index < pointer.getLength());
    }

    /**
     * Tests whether {@code name} is a lang attribute.
     *
     * @param qName to compare
     * @return boolean
     */
    private static boolean isLangAttribute(final QName qName) {
        return qName.getPrefix() != null && qName.getPrefix().equals("xml") && qName.getName().equals("lang");
    }

    /**
     * Returns true if the pointer has an attribute called "name" and its value is equal to the supplied string.
     *
     * @param pointer input pointer
     * @param name    name to check
     * @return boolean
     */
    private static boolean isNameAttributeEqual(final NodePointer pointer, final String name) {
        final NodeIterator it = pointer.attributeIterator(QNAME_NAME);
        return it != null && it.setPosition(1) && name.equals(it.getNodePointer().getValue());
    }

    /**
     * Extracts the string value of the expression from a predicate like [@name=expression].
     *
     * @param context   evaluation context
     * @param predicate predicate to evaluate
     * @return String key extracted
     */
    private static String keyFromPredicate(final EvalContext context, final Expression predicate) {
        final Expression expr = ((NameAttributeTest) predicate).getNameTestExpression();
        return InfoSetUtil.stringValue(expr.computeValue(context));
    }

    /**
     * For an intermediate pointer (e.g. PropertyPointer, ContainerPointer) returns a pointer for the contained value.
     *
     * @param pointer input pointer
     * @return NodePointer
     */
    private static NodePointer valuePointer(final NodePointer pointer) {
        return pointer == null ? null : pointer.getValuePointer();
    }

    /**
     * Constructs a new instance.
     *
     * @deprecated Will be private in the next major version.
     */
    @Deprecated
    public SimplePathInterpreter() {
        // empty
    }
}