path: root/src/mongo/bson/mutable/algorithm.h

/**
 *    Copyright (C) 2018-present MongoDB, Inc.
 *
 *    This program is free software: you can redistribute it and/or modify
 *    it under the terms of the Server Side Public License, version 1,
 *    as published by MongoDB, Inc.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    Server Side Public License for more details.
 *
 *    You should have received a copy of the Server Side Public License
 *    along with this program. If not, see
 *    <http://www.mongodb.com/licensing/server-side-public-license>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the Server Side Public License in all respects for
 *    all of the code used other than as permitted herein. If you modify file(s)
 *    with this exception, you may extend this exception to your version of the
 *    file(s), but you are not obligated to do so. If you do not wish to do so,
 *    delete this exception statement from your version. If you delete this
 *    exception statement from all source files in the program, then also delete
 *    it in the license file.
 */

#pragma once

#include <algorithm>
#include <cstddef>
#include <vector>

#include "mongo/base/string_data_comparator_interface.h"
#include "mongo/bson/mutable/const_element.h"
#include "mongo/bson/mutable/element.h"
#include "mongo/util/mongoutils/str.h"

namespace mongo {
namespace mutablebson {

/** For an overview of mutable BSON, please see the file document.h in this directory.
 *
 *  This file defines, in analogy with <algorithm>, a collection of useful algorithms for
 *  use with mutable BSON classes. In particular, algorithms for searching, sorting,
 *  indexed access, and counting are included.
 */

/** 'findElement' searches rightward among the sibiling Elements of 'first', returning an
 *  Element representing the first item matching the predicate 'predicate'. If no Element
 *  matches, then the 'ok' method on the returned Element will return false.
 */
template <typename ElementType, typename Predicate>
inline ElementType findElement(ElementType first, Predicate predicate) {
    while (first.ok() && !predicate(first))
        first = first.rightSibling();
    return first;
}

/** A predicate for findElement that matches on the field name of Elements. */
struct FieldNameEquals {
    // The lifetime of this object must be a subset of the lifetime of 'fieldName'.
    explicit FieldNameEquals(StringData fieldName) : fieldName(fieldName) {}

    bool operator()(const ConstElement& element) const {
        return (fieldName == element.getFieldName());
    }

    StringData fieldName;
};

/** An overload of findElement that delegates to the special implementation
 *  Element::findElementNamed to reduce traffic across the Element API.
 */
template <typename ElementType>
inline ElementType findElement(ElementType first, FieldNameEquals predicate) {
    return first.ok() ? first.findElementNamed(predicate.fieldName) : first;
}

/** A convenience wrapper around findElement<ElementType, FieldNameEquals>. */
template <typename ElementType>
inline ElementType findElementNamed(ElementType first, StringData fieldName) {
    return findElement(first, FieldNameEquals(fieldName));
}

/** Finds the first child under 'parent' that matches the given predicate. If no such child
 *  Element is found, the returned Element's 'ok' method will return false.
 */
template <typename ElementType, typename Predicate>
inline ElementType findFirstChild(ElementType parent, Predicate predicate) {
    return findElement(parent.leftchild(), predicate);
}

/** An overload of findFirstChild that delegates to the special implementation
 *  Element::findFirstChildNamed to reduce traffic across the Element API.
 */
template <typename ElementType>
inline ElementType findFirstChild(ElementType parent, FieldNameEquals predicate) {
    return parent.ok() ? parent.findFirstChildNamed(predicate.fieldName) : parent;
}

/** Finds the first child under 'parent' that matches the given field name. If no such child
 *  Element is found, the returned Element's 'ok' method will return false.
 */
template <typename ElementType>
inline ElementType findFirstChildNamed(ElementType parent, StringData fieldName) {
    return findFirstChild(parent, FieldNameEquals(fieldName));
}

/** A less-than ordering for Elements that compares based on the Element field names. */
class FieldNameLessThan {
    // TODO: This should possibly derive from std::binary_function.
public:
    inline bool operator()(const ConstElement& left, const ConstElement& right) const {
        return left.getFieldName() < right.getFieldName();
    }
};

/** Sort any children of Element 'parent' by way of Comparator 'comp', which should provide
 *  an operator() that takes two const Element&'s and implements a strict weak ordering.
 */
template <typename Comparator>
void sortChildren(Element parent, Comparator comp) {
    // TODO: The following works, but obviously is not ideal.

    // First, build a vector of the children.
    std::vector<Element> children;
    Element current = parent.leftChild();
    while (current.ok()) {
        children.push_back(current);
        current = current.rightSibling();
    }

    // Then, sort the child vector with our comparator.
    std::sort(children.begin(), children.end(), comp);

    // Finally, reorder the children of parent according to the ordering established in
    // 'children'.
    std::vector<Element>::iterator where = children.begin();
    const std::vector<Element>::iterator end = children.end();
    for (; where != end; ++where) {
        // Detach from its current location.
        where->remove().transitional_ignore();
        // Make it the new rightmost element.
        parent.pushBack(*where).transitional_ignore();
    }
}

/** Remove any consecutive children that compare as identical according to 'comp'. The
 *  children must be sorted (see sortChildren, above), and the equality comparator here
 *  must be compatible with the comparator used for the sort.
 */
template <typename EqualityComparator>
void deduplicateChildren(Element parent, EqualityComparator equal) {
    Element current = parent.leftChild();
    while (current.ok()) {
        Element next = current.rightSibling();
        if (next.ok() && equal(current, next)) {
            next.remove().transitional_ignore();
        } else {
            current = next;
        }
    }
}

/** A less-than ordering for Elements that compares based on woCompare */
class woLess {
    // TODO: This should possibly derive from std::binary_function.
public:
    woLess(const StringData::ComparatorInterface* comparator, bool considerFieldName = true)
        : _comp(comparator), _considerFieldName(considerFieldName) {}

    inline bool operator()(const ConstElement& left, const ConstElement& right) const {
        return left.compareWithElement(right, _comp, _considerFieldName) < 0;
    }

private:
    const StringData::ComparatorInterface* _comp = nullptr;
    const bool _considerFieldName;
};

/** A greater-than ordering for Elements that compares based on woCompare */
class woGreater {
    // TODO: This should possibly derive from std::binary_function.
public:
    woGreater(const StringData::ComparatorInterface* comparator, bool considerFieldName = true)
        : _comp(comparator), _considerFieldName(considerFieldName) {}

    inline bool operator()(const ConstElement& left, const ConstElement& right) const {
        return left.compareWithElement(right, _comp, _considerFieldName) > 0;
    }

private:
    const StringData::ComparatorInterface* _comp = nullptr;
    const bool _considerFieldName;
};

/** An equality predicate for elements that compares based on woCompare */
class woEqual {
    // TODO: This should possibly derive from std::binary_function.
public:
    woEqual(const StringData::ComparatorInterface* comparator, bool considerFieldName = true)
        : _comp(comparator), _considerFieldName(considerFieldName) {}

    inline bool operator()(const ConstElement& left, const ConstElement& right) const {
        return left.compareWithElement(right, _comp, _considerFieldName) == 0;
    }

private:
    const StringData::ComparatorInterface* _comp = nullptr;
    const bool _considerFieldName;
};

/** An equality predicate for elements that compares based on woCompare */
class woEqualTo {
    // TODO: This should possibly derive from std::binary_function.
public:
    woEqualTo(const ConstElement& value,
              const StringData::ComparatorInterface* comparator,
              bool considerFieldName = true)
        : _value(value), _comp(comparator), _considerFieldName(considerFieldName) {}

    inline bool operator()(const ConstElement& elt) const {
        return _value.compareWithElement(elt, _comp, _considerFieldName) == 0;
    }

private:
    const ConstElement _value;
    const StringData::ComparatorInterface* _comp = nullptr;
    const bool _considerFieldName;
};

// NOTE: Originally, these truly were algorithms, in that they executed the loop over a
// generic ElementType. However, these operations were later made intrinsic to
// Element/Document for performance reasons. These functions hare here for backward
// compatibility, and just delegate to the appropriate Element or ConstElement method of
// the same name.

/** Return the element that is 'n' Elements to the left in the sibling chain of 'element'. */
template <typename ElementType>
ElementType getNthLeftSibling(ElementType element, std::size_t n) {
    return element.leftSibling(n);
}

/** Return the element that is 'n' Elements to the right in the sibling chain of 'element'. */
template <typename ElementType>
ElementType getNthRightSibling(ElementType element, std::size_t n) {
    return element.rightSibling(n);
}

/** Move 'n' Elements left or right in the sibling chain of 'element' */
template <typename ElementType>
ElementType getNthSibling(ElementType element, int n) {
    return (n < 0) ? getNthLeftSibling(element, -n) : getNthRightSibling(element, n);
}

/** Get the child that is 'n' Elements to the right of 'element's left child. */
template <typename ElementType>
ElementType getNthChild(ElementType element, std::size_t n) {
    return element.findNthChild(n);
}

/** Returns the number of valid siblings to the left of 'element'. */
template <typename ElementType>
std::size_t countSiblingsLeft(ElementType element) {
    return element.countSiblingsLeft();
}

/** Returns the number of valid siblings to the right of 'element'. */
template <typename ElementType>
std::size_t countSiblingsRight(ElementType element) {
    return element.countSiblingsRight();
}

/** Return the number of children of 'element'. */
template <typename ElementType>
std::size_t countChildren(ElementType element) {
    return element.countChildren();
}

/** Return the full (path) name of this element separating each name with the delim string. */
template <typename ElementType>
std::string getFullName(ElementType element, char delim = '.') {
    std::vector<StringData> names;
    ElementType curr = element;
    while (curr.ok() && curr.parent().ok()) {
        names.push_back(curr.getFieldName());
        curr = curr.parent();
    }

    mongoutils::str::stream name;
    bool first = true;
    for (std::vector<StringData>::reverse_iterator it = names.rbegin(); it != names.rend(); ++it) {
        if (!first)
            name << delim;
        name << *it;
        first = false;
    }
    return name;
}
}  // namespace mutablebson
}  // namespace mongo