XMBData.h

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/* Copyright (C) 2021 Wildfire Games.
 * This file is part of 0 A.D.
 *
 * 0 A.D. is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * 0 A.D. 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
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
 */

/*
    Xeromyces - XMB reading library

Brief outline:

XMB originated as a binary representation of XML, with some limitations
but much more efficiency (particularly for loading simple data
classes that don't need much initialisation).

Theoretical file structure:

XMB_File {
    char Header[4]; // because everyone has one; currently "XMB0"
    u32 Version;

    int OffsetFromStartToElementNames;
    int ElementNameCount;

    int OffsetFromStartToAttributeNames;
    int AttributeNameCount;

    XMB_Node Root;

    ZStr8 ElementNames[];
    ZStr8 AttributeNames[];

}

XMB_Node {
0)  int Length; // of entire struct, so it can be skipped over

4)  int ElementName;

8)  int AttributeCount;
12) int ChildCount;

16) int ChildrenOffset; // == sizeof(Text)+sizeof(Attributes)
20) XMB_Text Text;
    XMB_Attribute Attributes[];
    XMB_Node Children[];

}

XMB_Attribute {
    int Name;
    ZStr8 Value;
}

ZStr8 {
    int Length; // in bytes
    char* Text; // null-terminated UTF8
}

XMB_Text {
20) int Length; // 0 if there's no text, else 4+sizeof(Text) in bytes including terminator
    // If Length != 0:
24) int LineNumber; // for e.g. debugging scripts
28) char* Text; // null-terminated UTF8
}

*/

#ifndef INCLUDED_XEROXMB
#define INCLUDED_XEROXMB

#include "ps/CStr.h"

#include <string>
#include <string_view>

class XMBStorage;

class XMBElement;
class XMBElementList;
class XMBAttributeList;


class XMBData
{
public:

    XMBData() : m_Pointer(nullptr) {}

    /*
    * Initialise from the contents of an XMBStorage.
    * @param doc must remain allocated and unchanged while
    * the XMBData is being used.
    * @return indication of success; main cause for failure is attempting to
    * load a partially valid XMB file (e.g. if the game was interrupted
    * while writing it), which we detect by checking the magic string.
    * It also fails when trying to load an XMB file with a different version.
    */
    bool Initialise(const XMBStorage& doc);

    // Returns the root element
    XMBElement GetRoot() const;

    // Returns internal ID for a given element/attribute string.
    int GetElementID(const char* Name) const;
    int GetAttributeID(const char* Name) const;

    // Returns element/attribute string for a given internal ID.
    const char* GetElementString(const int ID) const;
    const char* GetAttributeString(const int ID) const;

    std::string_view GetElementStringView(const int ID) const;
    std::string_view GetAttributeStringView(const int ID) const;

private:
    const char* m_Pointer;

    int m_ElementNameCount;
    int m_AttributeNameCount;
    const char* m_ElementPointer;
    const char* m_AttributePointer;
};

class XMBElement
{
public:
    XMBElement()
        : m_Pointer(0) {}

    XMBElement(const char* offset)
        : m_Pointer(offset) {}

    int GetNodeName() const;
    XMBElementList GetChildNodes() const;
    XMBAttributeList GetAttributes() const;
    CStr8 GetText() const;
    // Returns the line number of the text within this element,
    // or -1 if there is no text
    int GetLineNumber() const;

private:
    // Pointer to the start of the node
    const char* m_Pointer;
};

class XMBElementList
{
public:
    XMBElementList(const char* offset, size_t count, const char* endoffset)
        : m_Size(count), m_Pointer(offset), m_CurItemID(0), m_CurPointer(offset), m_EndPointer(endoffset) {}

    // Get first element in list with the given name.
    // Performance is linear in the number of elements in the list.
    XMBElement GetFirstNamedItem(const int ElementName) const;

    // Linear in the number of elements in the list
    XMBElement operator[](size_t id); // returns Children[id]

    class iterator
    {
    public:
        typedef ptrdiff_t difference_type;
        typedef XMBElement value_type;
        typedef XMBElement reference; // Because we need to construct the object
        typedef XMBElement pointer; // Because we need to construct the object
        typedef std::forward_iterator_tag iterator_category;

        iterator(size_t size, const char* ptr, const char* endptr = NULL)
            : m_Size(size), m_CurItemID(endptr ? size : 0), m_CurPointer(endptr ? endptr : ptr) {}
        XMBElement operator*() const { return XMBElement(m_CurPointer); }
        XMBElement operator->() const { return **this; }
        iterator& operator++();

        bool operator==(const iterator& rhs) const
        {
            return m_Size == rhs.m_Size &&
                   m_CurItemID == rhs.m_CurItemID &&
                   m_CurPointer == rhs.m_CurPointer;
        }
        bool operator!=(const iterator& rhs) const { return !(*this == rhs); }
    private:
        size_t m_Size;
        size_t m_CurItemID;
        const char* m_CurPointer;
    };
    iterator begin() { return iterator(m_Size, m_Pointer); }
    iterator end() { return iterator(m_Size, m_Pointer, m_EndPointer); }

    size_t size() const { return m_Size; }
    bool empty() const { return m_Size == 0; }

private:
    size_t m_Size;

    const char* m_Pointer;

    // For optimised sequential access:
    size_t m_CurItemID;
    const char* m_CurPointer;

    const char* m_EndPointer;
};


struct XMBAttribute
{
    XMBAttribute() {}
    XMBAttribute(int name, const CStr8& value)
        : Name(name), Value(value) {};

    int Name;
    CStr8 Value; // UTF-8 encoded
};

class XMBAttributeList
{
public:
    XMBAttributeList(const char* offset, size_t count, const char* endoffset)
        : m_Size(count), m_Pointer(offset), m_CurItemID(0), m_CurPointer(offset), m_EndPointer(endoffset) {}

    // Get the attribute value directly
    CStr8 GetNamedItem(const int AttributeName) const;

    // Linear in the number of elements in the list
    XMBAttribute operator[](size_t id); // returns Children[id]

    class iterator
    {
    public:
        typedef ptrdiff_t difference_type;
        typedef XMBAttribute value_type;
        typedef XMBAttribute reference; // Because we need to construct the object
        typedef XMBAttribute pointer; // Because we need to construct the object
        typedef std::forward_iterator_tag iterator_category;

        iterator(size_t size, const char* ptr, const char* endptr = NULL)
            : m_Size(size), m_CurItemID(endptr ? size : 0), m_CurPointer(endptr ? endptr : ptr) {}
        XMBAttribute operator*() const;
        XMBAttribute operator->() const { return **this; }
        iterator& operator++();

        bool operator==(const iterator& rhs) const
        {
            return m_Size == rhs.m_Size &&
                   m_CurItemID == rhs.m_CurItemID &&
                   m_CurPointer == rhs.m_CurPointer;
        }
        bool operator!=(const iterator& rhs) const { return !(*this == rhs); }
    private:
        size_t m_Size;
        size_t m_CurItemID;
        const char* m_CurPointer;
    };
    iterator begin() const { return iterator(m_Size, m_Pointer); }
    iterator end() const { return iterator(m_Size, m_Pointer, m_EndPointer); }

    size_t size() const { return m_Size; }
    bool empty() const { return m_Size == 0; }

private:
    size_t m_Size;

    // Pointer to start of attribute list
    const char* m_Pointer;

    // For optimised sequential access:
    size_t m_CurItemID;
    const char* m_CurPointer;

    const char* m_EndPointer;
};

#endif // INCLUDED_XEROXMB