XMLElement.hh

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#ifndef XMLELEMENT_HH
#define XMLELEMENT_HH
 
#include "MemBuffer.hh"
#include "monotonic_allocator.hh"
#include "serialize_meta.hh"
#include <cassert>
#include <cstddef>
#include <iterator>
//#include <memory_resource>
#include <string>
#include <string_view>
#include <vector>
 
namespace openmsx {
 
struct OldXMLElement; // for backwards compatible savestates
 
// The classes XMLDocument, XMLElement and XMLAttribute together form an
// in-memory representation of XML files (or at least the subset of the features
// needed for openMSX).
//
// This representation is optimized for fast parsing and to be compact in
// memory. This is achieved by:
// - Keeping a buffer to the actual xml file, and modifying that buffer.
//   For example the strings are modified in place (resolve escape sequences
//   and add zero-terminators) and the actual XML classes refer to this buffer.
// - The 'XMLElement' and 'XMLAttribute' objects are allocated from a monotonic
//   allocator.
// - Both the file buffer and the monotonic allocator are owned by the
//   XMLDocument class.
 
// Modifying the information (e.g. after it has been parsed from a file) is
// possible. But this is not the main intended use-case. For example it is
// possible to assign a new value-string to an attribute or an xml element. That
// string will be allocated from the monotonic allocator, but the memory for the
// old string will not be freed. So it's probably not a good idea to use these
// classes in a heavy-modification scenario.
 
 
// XMLAttribute is a name-value pair. This class only refers to the name and
// value strings, it does not own these strings. The owner could be either
// XMLDocument (in the file buffer or in the monotonic allocator) or it could
// be a string with static lifetime (e.g. a string-literal).
//
// XMLAttributes are organized in a (single-)linked list. So this class also
// contains a pointer to the next element in the list. The last element in the
// list contains a nullptr.
class XMLAttribute
{
public:
        XMLAttribute(const char* name_, const char* value_)
                : name(name_), value(value_) {}
        [[nodiscard]] std::string_view getName() const { return name; }
        [[nodiscard]] std::string_view getValue() const { return value; }
        void setValue(const char* value_) { value = value_; }
 
        XMLAttribute* setNextAttribute(XMLAttribute* attribute) {
                assert(!nextAttribute);
                nextAttribute = attribute;
                return attribute;
        }
 
private:
        const char* name;
        const char* value;
        XMLAttribute* nextAttribute = nullptr;
 
        friend class XMLElement;
        friend class XMLDocument;
        friend class XMLDocumentHandler;
};
 
// This XMLElement class represents a single XML-element (or XML-node). It has a
// name, attributes, a value (could be empty) and zero or more children. The
// value and the children are mutually exclusive, in other words: elements with
// children cannot have a non-empty value.
//
// String-ownership is the same as with XMLAttribute.
//
// Attributes are organized in a (single-)linked list. This class points to the
// first attribute (possibly nullptr when there are no attributes) and that
// attribute points to the next and so on.
//
// Hierarchy is achieved via two pointers. This class has a pointer to its first
// child and to its next sibling. Thus getting all children of a specfic
// elements requires to first follow the 'firstChild' pointer, and from there on
// follow the 'nextSibling' pointers (and stop when any of these pointers in
// nullptr). XMLElement objects do not have a pointer to their parent.
class XMLElement
{
        // iterator classes for children and attributes
        // TODO c++20: use iterator + sentinel instead of 2 x iterator
        struct ChildIterator {
                using difference_type = ptrdiff_t;
                using value_type = const XMLElement;
                using pointer = value_type*;
                using reference = value_type&;
                using iterator_category = std::forward_iterator_tag;
 
                const XMLElement* elem;
 
                const XMLElement& operator*() const { return *elem; }
                ChildIterator operator++() { elem = elem->nextSibling; return *this; }
                [[nodiscard]] bool operator==(const ChildIterator& i) const { return elem == i.elem; }
        };
        struct ChildRange {
                const XMLElement* elem;
                ChildIterator begin() const { return {elem->firstChild}; }
                ChildIterator end()   const { return {nullptr}; }
        };
 
        struct NamedChildIterator {
                using difference_type = ptrdiff_t;
                using value_type = const XMLElement*;
                using pointer = value_type*;
                using reference = value_type&;
                using iterator_category = std::forward_iterator_tag;
 
                const XMLElement* elem;
                const std::string_view name;
 
                NamedChildIterator(const XMLElement* elem_, std::string_view name_)
                        : elem(elem_), name(name_)
                {
                        while (elem && elem->getName() != name) {
                                elem = elem->nextSibling;
                        }
                }
 
                const XMLElement* operator*() const { return elem; }
                NamedChildIterator operator++() {
                        do {
                                elem = elem->nextSibling;
                        } while (elem && elem->getName() != name);
                        return *this;
                }
                [[nodiscard]] bool operator==(const NamedChildIterator& i) const { return elem == i.elem; }
        };
        struct NamedChildRange {
                const XMLElement* elem;
                std::string_view name;
                NamedChildIterator begin() const { return {elem->firstChild, name}; }
                NamedChildIterator end()   const { return {nullptr, std::string_view{}}; }
        };
 
        struct AttributeIterator {
                using difference_type = ptrdiff_t;
                using value_type = const XMLAttribute;
                using pointer = value_type*;
                using reference = value_type&;
                using iterator_category = std::forward_iterator_tag;
 
                const XMLAttribute* attr;
 
                const XMLAttribute& operator*() const { return *attr; }
                AttributeIterator operator++() { attr = attr->nextAttribute; return *this; }
                [[nodiscard]] bool operator==(const AttributeIterator& i) const { return attr == i.attr; }
        };
        struct AttributeRange {
                const XMLElement* elem;
                AttributeIterator begin() const { return {elem->firstAttribute}; }
                AttributeIterator end()   const { return {nullptr}; }
        };
 
public:
        XMLElement(const char* name_) : name(name_) {}
        XMLElement(const char* name_, const char* data_) : name(name_), data(data_) {}
 
        [[nodiscard]] std::string_view getName() const { return name; }
        void clearName() { name = ""; } // hack to 'remove' child from findChild()
 
        [[nodiscard]] std::string_view getData() const {
                return data ? std::string_view(data) : std::string_view();
        }
        XMLElement* setData(const char* data_) {
                data = data_;
                return this;
        }
 
        [[nodiscard]] bool hasChildren() const { return firstChild; }
        [[nodiscard]] const XMLElement* getFirstChild() const { return firstChild; }
        [[nodiscard]] const XMLElement* findChild(std::string_view childName) const;
        [[nodiscard]] const XMLElement* findChild(std::string_view childName, const XMLElement*& hint) const;
        [[nodiscard]] const XMLElement& getChild(std::string_view childName) const;
 
        [[nodiscard]] std::string_view getChildData(std::string_view childName) const;
        [[nodiscard]] std::string_view getChildData(std::string_view childName,
                                                    std::string_view defaultValue) const;
        [[nodiscard]] bool getChildDataAsBool(std::string_view childName, bool defaultValue) const;
        [[nodiscard]] int getChildDataAsInt(std::string_view childName, int defaultValue) const;
 
        [[nodiscard]] size_t numChildren() const;
        ChildRange getChildren() const { return {this}; }
        NamedChildRange getChildren(std::string_view childName) const { return {this, childName}; }
 
        [[nodiscard]] const XMLAttribute* findAttribute(std::string_view attrName) const;
        [[nodiscard]] const XMLAttribute& getAttribute(std::string_view attrName) const;
        [[nodiscard]] std::string_view getAttributeValue(std::string_view attrName) const;
        [[nodiscard]] std::string_view getAttributeValue(std::string_view attrName,
                                                         std::string_view defaultValue) const;
        [[nodiscard]] bool getAttributeValueAsBool(std::string_view attrName,
                                                   bool defaultValue) const;
        [[nodiscard]] int getAttributeValueAsInt(std::string_view attrName,
                                                 int defaultValue) const;
        [[nodiscard]] XMLAttribute** findAttributePointer(std::string_view attrName);
        static void removeAttribute(XMLAttribute** attrPtr);
        [[nodiscard]] size_t numAttributes() const;
        AttributeRange getAttributes() const { return {this}; }
 
        XMLElement* setFirstChild(XMLElement* child) {
                assert(!firstChild);
                firstChild = child;
                return child;
        }
        XMLElement* setNextSibling(XMLElement* sibling) {
                assert(!nextSibling);
                nextSibling = sibling;
                return sibling;
        }
        XMLAttribute* setFirstAttribute(XMLAttribute* attribute) {
                assert(!firstAttribute);
                firstAttribute = attribute;
                return attribute;
        }
 
private:
        const char* name;
        const char* data = nullptr;
        XMLElement* firstChild = nullptr;
        XMLElement* nextSibling = nullptr;
        XMLAttribute* firstAttribute = nullptr;
 
        friend class XMLDocument;
        friend class XMLDocumentHandler;
};
 
// This class mainly exists to manage ownership over the objects involved in a
// full XML document. These are the XMLElement and XMLAttribute objects but also
// the name/value/attribute strings. This class also has a pointer to the root
// element.
//
// Because of the way how ownership is handled, most modifying operations are
// part of this class API. For example there's a method 'setChildData()' which
// searches for a child with a specific name, if not found such a child is
// created, then the child-data is set to a new value. Because this operation
// possibly requires to allocate a new XMLElement (and the allocator is part of
// this class) this method is part of this class rather than the XMLElement
// class.
class XMLDocument
{
public:
        // singleton-like document, mainly used as owner for static XML snippets
        // (so with lifetime the whole openMSX session)
        static XMLDocument& getStaticDocument() {
                static XMLDocument doc;
                return doc;
        }
 
        // Create an empty XMLDocument (root == nullptr).  All constructor
        // arguments are delegated to the monotonic allocator constructor.
        template<typename ...Args>
        XMLDocument(Args&& ...args)
                : allocator(std::forward<Args>(args)...) {}
 
        // Load/parse an xml file. Requires that the document is still empty.
        void load(const std::string& filename, std::string_view systemID);
 
        [[nodiscard]] const XMLElement* getRoot() const { return root; }
        void setRoot(XMLElement* root_) { assert(!root); root = root_; }
 
        [[nodiscard]] XMLElement* allocateElement(const char* name);
        [[nodiscard]] XMLElement* allocateElement(const char* name, const char* data);
        [[nodiscard]] XMLAttribute* allocateAttribute(const char* name, const char* value);
        [[nodiscard]] const char* allocateString(std::string_view str);
 
        [[nodiscard]] XMLElement* getOrCreateChild(XMLElement& parent, const char* childName, const char* childData);
        XMLElement* setChildData(XMLElement& parent, const char* childName, const char* childData);
        void setAttribute(XMLElement& elem, const char* attrName, const char* attrValue);
 
        template<typename Range, typename UnaryOp>
        void generateList(XMLElement& parent, const char* itemName, Range&& range, UnaryOp op) {
                XMLElement** next = &parent.firstChild;
                assert(!*next);
                for (auto& r : range) {
                        auto* elem = allocateElement(itemName);
                        op(elem, r);
                        *next = elem;
                        next = &elem->nextSibling;
                }
        }
 
        void load(OldXMLElement& elem); // bw compat
 
        void serialize(MemInputArchive&  ar, unsigned version);
        void serialize(MemOutputArchive& ar, unsigned version);
        void serialize(XmlInputArchive&  ar, unsigned version);
        void serialize(XmlOutputArchive& ar, unsigned version);
 
private:
        XMLElement* loadElement(MemInputArchive& ar);
        XMLElement* clone(const XMLElement& inElem);
        XMLElement* clone(const OldXMLElement& elem);
 
private:
        XMLElement* root = nullptr;
        MemBuffer<char> buf;
        // part of c++17, but not yet implemented in libc++
        //    std::pmr::monotonic_buffer_resource allocator;
        monotonic_allocator allocator;
 
        friend class XMLDocumentHandler;
};
 
 
// For backwards-compatibility with old savestates
//   needed with HardwareConfig-version <= 5.
class FileContext;
struct OldXMLElement
{
        template<typename Archive>
        void serialize(Archive& ar, unsigned version);
 
        // For backwards compatibility with version=1 savestates
        static std::unique_ptr<FileContext> getLastSerializedFileContext();
 
        std::string name;
        std::string data;
        std::vector<OldXMLElement> children;
        std::vector<std::pair<std::string, std::string>> attributes;
};
SERIALIZE_CLASS_VERSION(OldXMLElement, 2);
 
} // namespace openmsx
 
#endif