    // Copyright (C) 2003  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #ifndef DLIB_XML_PARSER_KERNEl_1_
    #define DLIB_XML_PARSER_KERNEl_1_

    #include "xml_parser_kernel_abstract.h"

    #include <sstream>
    #include <string>
    #include <fstream>
    #include <iostream>
    #include "xml_parser_kernel_interfaces.h"
    #include "../algs.h"
    #include <cstdio>
    #include "../map.h"
    #include "../stack.h"
    #include "../sequence.h"
    #include "../memory_manager.h"

    namespace dlib
    {

        class xml_parser
        {
            typedef dlib::map<std::string,std::string,memory_manager<char>::kernel_2a>::kernel_1b map;
            typedef dlib::stack<std::string,memory_manager<char>::kernel_2a>::kernel_1a stack;
            typedef sequence<document_handler*>::kernel_2a seq_dh;
            typedef sequence<error_handler*>::kernel_2a seq_eh;

             /*!
                INITIAL VALUE
                    dh_list.size() == 0
                    eh_list.size() == 0

                CONVENTION
                    dh_list == a sequence of pointers to all the document_handlers that
                               have been added to the xml_parser
                    eh_list == a sequence of pointers to all the error_handlers that
                               have been added to the xml_parser

                    map is used to implement the attribute_list interface
                    stack is used just inside the parse function
                    seq_dh is used to make the dh_list member variable
                    seq_eh is used to make the eh_list member variable
            !*/

            public:

                // These typedefs are here for backwards compatibily with previous versions of
                // dlib.
                typedef xml_parser kernel_1a;
                typedef xml_parser kernel_1a_c;

                xml_parser(
                ) {}

                virtual ~xml_parser(
                ){}

                inline void clear(
                );

                inline void parse (
                    std::istream& in
                );

                inline void add_document_handler (
                    document_handler& item
                );

                inline void add_error_handler (
                    error_handler& item
                );

                inline void swap (
                    xml_parser& item
                );

            private:

                // -----------------------------------

                // attribute_list interface implementation
                class attrib_list : public attribute_list
                {
                public:
                    // the list of attribute name/value pairs
                    map list;

                    bool is_in_list (
                        const std::string& key
                    ) const
                    {
                        return list.is_in_domain(key);
                    }

                    const std::string& operator[] (
                        const std::string& key
                    ) const
                    {
                        return list[key];
                    }

                    bool at_start (
                    ) const { return list.at_start(); }

                    void reset (
                    ) const { return list.reset(); }

                    bool current_element_valid (
                    ) const { return list.current_element_valid(); }

                    const type& element (
                    ) const { return list.element(); }

                    type& element (
                    ) { return list.element(); }

                    bool move_next (
                    ) const { return list.move_next(); }

                    unsigned long size (
                    ) const { return list.size(); }
                };

                // -----------------------------------

                enum token_type
                {
                    element_start, // the first tag of an element
                    element_end,   // the last tag of an element
                    empty_element, // the singular tag of an empty element
                    pi,            // processing instruction
                    chars,         // the non-markup data between tags
                    chars_cdata,   // the data from a CDATA section
                    eof,           // this token is returned when we reach the end of input
                    error,         // this token indicates that the tokenizer couldn't
                                   // determine which category the next token fits into
                    dtd,           // this token is for an entire dtd
                    comment        // this is a token for comments
                };
                /*
                    notes about the tokens:
                        the tokenizer guarantees that the following tokens to not
                        contain the '<' character except as the first character of the token
                        element_start, element_end, empty_element, and pi.  they also only
                        contain the '>' characer as their last character.

                        it is also guaranteed that pi is at least of the form <??>.  that
                        is to say that it always always begins with <? and ends with ?>.

                        it is also guaranteed that all markup tokens will begin with the '<'
                        character and end with the '>'. there won't be any leading or
                        trailing whitespaces.   this whitespace is considered a chars token.
                */

                // private member functions
                inline void get_next_token(
                    std::istream& in,
                    std::string& token_text,
                    int& token_kind,
                    unsigned long& line_number
                );
                /*!
                    ensures
                        gets the next token from in and puts it in token_text and
                        token_kind == the kind of the token found and
                        line_number is incremented every time a '\n' is encountered and
                        entity references are translated into the characters they represent
                        only for chars tokens
                !*/

                inline int parse_element (
                    const std::string& token,
                    std::string& name,
                    attrib_list& atts
                );
                /*!
                    requires
                        token is a token of kind start_element or empty_element
                    ensures
                        gets the element name and puts it into the string name and
                        parses out the attributes and puts them into the attribute_list atts

                        return 0 upon success or
                        returns -1 if it failed to parse token
                !*/

                inline int parse_pi (
                    const std::string& token,
                    std::string& target,
                    std::string& data
                );
                /*!
                    requires
                        token is a token of kind pi
                    ensures
                        the target from the processing instruction is put into target and
                        the data from the processing instruction is put into data

                        return 0 upon success or
                        returns -1 if it failed to parse token
                !*/

                inline int parse_element_end (
                    const std::string& token,
                    std::string& name
                );
                /*!
                    requires
                        token is a token of kind element_end
                    ensures
                        the name from the ending element tag is put into the string name

                        return 0 upon success or
                        returns -1 if it failed to parse token
                !*/

                inline int change_entity (
                    std::istream& in
                );
                /*!
                    ensures
                        performs the following translations and returns the new character
                                    amp;   -> &
                                    lt;    -> <
                                    gt;    -> >
                                    apos;  -> '
                                    quot;  -> "

                        or returns -1 if we hit an undefined entity reference or EOF.
                                (i.e. it was not one of the entities listed above)

                !*/

                // -----------------------------------

                // private member data
                seq_dh dh_list;
                seq_eh eh_list;

                // -----------------------------------

                // restricted functions: assignment and copy construction
                xml_parser(xml_parser&);
                xml_parser& operator= (
                            xml_parser&
                            );

        };

        inline void swap (
            xml_parser& a,
            xml_parser& b
        ) { a.swap(b); }

    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------
        // member function definitions
    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------

        void xml_parser::
        clear(
        )
        {
            // unregister all event handlers
            eh_list.clear();
            dh_list.clear();
        }

    // ----------------------------------------------------------------------------------------

        void xml_parser::
        parse (
            std::istream& in
        )
        {
            DLIB_CASSERT ( in.fail() == false ,
                "\tvoid xml_parser::parse"
                << "\n\tthe input stream must not be in the fail state"
                << "\n\tthis: " << this
                );

            // save which exceptions in will throw and make it so it won't throw any
            // for the life of this function
            std::ios::iostate old_exceptions = in.exceptions();
            // set it to not throw anything
            in.exceptions(std::ios::goodbit);

            try
            {
                unsigned long line_number = 1;

                // skip any whitespace before the start of the document
                while (in.peek() == ' ' || in.peek() == '\t' || in.peek() == '\n' || in.peek() == '\r' )
                {
                    if (in.peek() == '\n')
                        ++line_number;
                    in.get();
                }

                stack tags; // this stack contains the last start tag seen
                bool seen_fatal_error = false;
                bool seen_root_tag = false;  // this is true after we have seen the root tag

                // notify all the document_handlers that we are about to being parsing
                for (unsigned long i = 0; i < dh_list.size(); ++i)
                {
                    dh_list[i]->start_document();
                }

                std::string chars_buf; // used to collect chars data between consecutive
                                    // chars and chars_cdata tokens so that
                                    // document_handlers receive all chars data between
                                    // tags in one call

                // variables to be used with the parsing functions
                attrib_list atts;
                std::string name;
                std::string target;
                std::string data;

                // variables to use with the get_next_token() function
                std::string token_text;
                int token_kind;

                get_next_token(in,token_text,token_kind,line_number);

                while (token_kind != eof)
                {
                    bool is_empty = false;  // this becomes true when this token is an empty_element

                    switch (token_kind)
                    {

                    case empty_element: is_empty = true;
                    case element_start:
                        {
                            seen_root_tag = true;

                            int status = parse_element(token_text,name,atts);
                            // if there was no error parsing the element
                            if (status == 0)
                            {
                                // notify all the document_handlers
                                for (unsigned long i = 0; i < dh_list.size(); ++i)
                                {
                                    dh_list[i]->start_element(line_number,name,atts);
                                    if (is_empty)
                                        dh_list[i]->end_element(line_number,name);
                                }
                            }
                            else
                            {
                                seen_fatal_error = true;
                            }

                            // if this is an element_start token then push the name of
                            // the element on to the stack
                            if (token_kind == element_start)
                            {
                                tags.push(name);
                            }

                        }break;

                    // ----------------------------------------

                    case element_end:
                        {

                            int status = parse_element_end (token_text,name);

                            // if there was no error parsing the element
                            if (status == 0)
                            {
                                // make sure this ending element tag matches the last start
                                // element tag we saw
                                if ( tags.size() == 0 || name != tags.current())
                                {
                                    // they don't match so signal a fatal error
                                    seen_fatal_error = true;
                                }
                                else
                                {
                                    // notify all the document_handlers
                                    for (unsigned long i = 0; i < dh_list.size(); ++i)
                                    {
                                        dh_list[i]->end_element(line_number,name);
                                    }

                                    // they match so throw away this element name
                                    tags.pop(name);
                                }
                            }
                            else
                            {
                                seen_fatal_error = true;
                            }

                        }break;

                    // ----------------------------------------

                    case pi:
                        {

                            int status = parse_pi (token_text,target,data);
                            // if there was no error parsing the element
                            if (status == 0)
                            {
                                // notify all the document_handlers
                                for (unsigned long i = 0; i < dh_list.size(); ++i)
                                {
                                    dh_list[i]->processing_instruction(line_number,target,data);
                                }
                            }
                            else
                            {
                                // notify all the error_handlers
                                for (unsigned long i = 0; i < eh_list.size(); ++i)
                                {
                                    eh_list[i]->error(line_number);
                                }
                            }
                            while (in.peek() == ' ' || in.peek() == '\t' || in.peek() == '\n' || in.peek() == '\r' )
                            {
                                if (in.peek() == '\n')
                                    ++line_number;
                                in.get();
                            }

                        }break;

                    // ----------------------------------------

                    case chars:
                        {
                            if (tags.size() != 0)
                            {
                                chars_buf += token_text;
                            }
                            else if (token_text.find_first_not_of(" \t\r\n") != std::string::npos)
                            {
                                // you can't have non whitespace chars data outside the root element
                                seen_fatal_error = true;
                            }
                        }break;

                    // ----------------------------------------

                    case chars_cdata:
                        {
                            if (tags.size() != 0)
                            {
                                chars_buf += token_text;
                            }
                            else
                            {
                                // you can't have chars_data outside the root element
                                seen_fatal_error = true;
                            }
                        }break;

                    // ----------------------------------------

                    case eof:
                        break;

                    // ----------------------------------------

                    case error:
                        {
                            seen_fatal_error = true;
                        }break;

                    // ----------------------------------------

                    case dtd:       // fall though
                    case comment:   // do nothing
                        break;

                    // ----------------------------------------

                    }

                    // if there was a fatal error then quit loop
                    if (seen_fatal_error)
                        break;

                    // if we have seen the last tag then quit the loop
                    if (tags.size() == 0 && seen_root_tag)
                        break;

                    get_next_token(in,token_text,token_kind,line_number);

                    // if the next token is not a chars or chars_cdata token then flush
                    // the chars_buf to the document_handlers
                    if ( (token_kind != chars) &&
                        (token_kind != chars_cdata) &&
                        (token_kind != dtd) &&
                        (token_kind != comment) &&
                        (chars_buf.size() != 0)
                        )
                    {
                        // notify all the document_handlers
                        for (unsigned long i = 0; i < dh_list.size(); ++i)
                        {
                            dh_list[i]->characters(chars_buf);
                        }
                        chars_buf.erase();
                    }

                } //while (token_kind != eof)

                // you can't have any unmatched tags or any fatal erros
                if (tags.size() != 0 || seen_fatal_error)
                {
                    // notify all the error_handlers
                    for (unsigned long i = 0; i < eh_list.size(); ++i)
                    {
                        eh_list[i]->fatal_error(line_number);
                    }

                }

                // notify all the document_handlers that we have ended parsing
                for (unsigned long i = 0; i < dh_list.size(); ++i)
                {
                    dh_list[i]->end_document();
                }

            }
            catch (...)
            {
                // notify all the document_handlers that we have ended parsing
                for (unsigned long i = 0; i < dh_list.size(); ++i)
                {
                    dh_list[i]->end_document();
                }

                // restore the old exception settings to in
                in.exceptions(old_exceptions);

                // don't forget to rethrow the exception
                throw;
            }

            // restore the old exception settings to in
            in.exceptions(old_exceptions);

        }

    // ----------------------------------------------------------------------------------------

        void xml_parser::
        add_document_handler (
            document_handler& item
        )
        {
            document_handler* temp = &item;
            dh_list.add(dh_list.size(),temp);
        }

    // ----------------------------------------------------------------------------------------

        void xml_parser::
        add_error_handler (
            error_handler& item
        )
        {
            error_handler* temp = &item;
            eh_list.add(eh_list.size(),temp);
        }

    // ----------------------------------------------------------------------------------------

        void xml_parser::
        swap (
            xml_parser& item
        )
        {
            dh_list.swap(item.dh_list);
            eh_list.swap(item.eh_list);
        }

    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------
        // private member function definitions
    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------

        void xml_parser::
        get_next_token(
            std::istream& in,
            std::string& token_text,
            int& token_kind,
            unsigned long& line_number
        )
        {

            token_text.erase();

            std::istream::int_type ch1 = in.get();
            std::istream::int_type ch2;

            switch (ch1)
            {

            // -----------------------------------------

                // this is the start of some kind of a tag
            case '<':
                {
                    ch2 = in.get();
                    switch (ch2)
                    {

                    // ---------------------------------

                        // this is a dtd, comment, or chars_cdata token
                    case '!':
                        {
                            // if this is a CDATA section *******************************
                            if ( in.peek() == '[')
                            {
                                token_kind = chars_cdata;

                                // throw away the '['
                                in.get();

                                // make sure the next chars are CDATA[
                                std::istream::int_type ch = in.get();
                                if (ch != 'C')
                                    token_kind = error;
                                ch = in.get();
                                if (ch != 'D')
                                    token_kind = error;
                                ch = in.get();
                                if (ch != 'A')
                                    token_kind = error;
                                ch = in.get();
                                if (ch != 'T')
                                    token_kind = error;
                                ch = in.get();
                                if (ch != 'A')
                                    token_kind = error;
                                ch = in.get();
                                if (ch != '[')
                                    token_kind = error;
                                // if this is an error token then end
                                if (token_kind == error)
                                    break;

                                // get the rest of the chars and put them into token_text
                                int brackets_seen = 0; // this is the number of ']' chars
                                                       // we have seen in a row
                                bool seen_closing = false; // true if we have seen ]]>
                                do
                                {
                                    ch = in.get();

                                    if (ch == '\n')
                                        ++line_number;

                                    token_text += ch;

                                    // if this is the closing
                                    if (brackets_seen == 2 && ch == '>')
                                        seen_closing = true;
                                    // if we are seeing a bracket
                                    else if (ch == ']')
                                        ++brackets_seen;
                                    // if we didn't see a bracket
                                    else
                                        brackets_seen = 0;

                                } while ( (!seen_closing) && (ch != EOF) );

                                // check if this is an error token
                                if (ch == EOF)
                                {
                                    token_kind = error;
                                }
                                else
                                {
                                    token_text.erase(token_text.size()-3);
                                }

                            }
                            // this is a comment token ****************************
                            else if (in.peek() == '-')
                            {

                                token_text += ch1;
                                token_text += ch2;
                                token_text += '-';

                                token_kind = comment;

                                // throw away the '-' char
                                in.get();

                                // make sure the next char is another '-'
                                std::istream::int_type ch = in.get();
                                if (ch != '-')
                                {
                                    token_kind = error;
                                    break;
                                }

                                token_text += '-';

                                // get the rest of the chars and put them into token_text
                                int hyphens_seen = 0; // this is the number of '-' chars
                                                       // we have seen in a row
                                bool seen_closing = false; // true if we have seen ]]>
                                do
                                {
                                    ch = in.get();

                                    if (ch == '\n')
                                        ++line_number;

                                    token_text += ch;

                                    // if this should be a closing block
                                    if (hyphens_seen == 2)
                                    {
                                        if (ch == '>')
                                            seen_closing = true;
                                        else // this isn't a closing so make it signal error
                                            ch = EOF;
                                    }
                                    // if we are seeing a hyphen
                                    else if (ch == '-')
                                        ++hyphens_seen;
                                    // if we didn't see a hyphen
                                    else
                                        hyphens_seen = 0;

                                } while ( (!seen_closing) && (ch != EOF) );

                                // check if this is an error token
                                if (ch == EOF)
                                {
                                    token_kind = error;
                                }

                            }
                            else // this is a dtd token *************************
                            {

                                token_text += ch1;
                                token_text += ch2;
                                int bracket_depth = 1;  // this is the number of '<' chars seen
                                                        // minus the number of '>' chars seen

                                std::istream::int_type ch;
                                do
                                {
                                    ch = in.get();
                                    if (ch == '>')
                                        --bracket_depth;
                                    else if (ch == '<')
                                        ++bracket_depth;
                                    else if (ch == '\n')
                                        ++line_number;

                                    token_text += ch;

                                } while ( (bracket_depth > 0) && (ch != EOF) );

                                // make sure we didn't just hit EOF
                                if (bracket_depth == 0)
                                {
                                    token_kind = dtd;
                                }
                                else
                                {
                                    token_kind = error;
                                }
                            }
                        }
                        break;

                    // ---------------------------------

                        // this is a pi token
                    case '?':
                        {
                            token_text += ch1;
                            token_text += ch2;
                            std::istream::int_type ch;

                            do
                            {
                                ch = in.get();
                                token_text += ch;
                                if (ch == '\n')
                                    ++line_number;
                                // else if we hit a < then thats an error
                                else if (ch == '<')
                                    ch = EOF;
                            } while (ch != '>' && ch != EOF);
                            // if we hit the end of the pi
                            if (ch == '>')
                            {
                                // make sure there was a trailing '?'
                                if ( (token_text.size() > 3) &&
                                    (token_text[token_text.size()-2] != '?')
                                    )
                                {
                                    token_kind = error;
                                }
                                else
                                {
                                    token_kind = pi;
                                }
                            }
                            // if we hit EOF unexpectidely then error
                            else
                            {
                                token_kind = error;
                            }
                        }
                        break;

                    // ---------------------------------

                        // this is an error token
                    case EOF:
                        {
                            token_kind = error;
                        }
                        break;

                    // ---------------------------------
                        // this is an element_end token
                    case '/':
                        {
                            token_kind = element_end;
                            token_text += ch1;
                            token_text += ch2;
                            std::istream::int_type ch;
                            do
                            {
                                ch = in.get();
                                if (ch == '\n')
                                    ++line_number;
                                // else if we hit a < then thats an error
                                else if (ch == '<')
                                    ch = EOF;
                                token_text += ch;
                            } while ( (ch != '>') && (ch != EOF));

                            // check if this is an error token
                            if (ch == EOF)
                            {
                                token_kind = error;
                            }
                        }
                        break;

                    // ---------------------------------

                        // this is an element_start or empty_element token
                    default:
                        {

                            token_text += ch1;
                            token_text += ch2;
                            std::istream::int_type ch = '\0';
                            std::istream::int_type last;
                            do
                            {
                                last = ch;
                                ch = in.get();
                                if (ch == '\n')
                                    ++line_number;
                                // else if we hit a < then thats an error
                                else if (ch == '<')
                                    ch = EOF;
                                token_text += ch;
                            } while ( (ch != '>') && (ch != EOF));

                            // check if this is an error token
                            if (ch == EOF)
                            {
                                token_kind = error;
                            }
                            // if this is an empty_element
                            else if (last == '/')
                            {
                                token_kind = empty_element;
                            }
                            else
                            {
                                token_kind = element_start;
                            }

                        }
                        break;

                    // ---------------------------------

                    }

                }
                break;

            // -----------------------------------------

                // this is an eof token
            case EOF:
                {
                    token_kind = eof;
                }
                break;

            // -----------------------------------------

                // this is a chars token
            default:
                {
                    if (ch1 == '\n')
                    {
                        ++line_number;
                        token_text += ch1;
                    }
                    // if the first thing in this chars token is an entity reference
                    else if (ch1 == '&')
                    {

                        int temp = change_entity(in);
                        if (temp == -1)
                        {
                            token_kind = error;
                            break;
                        }
                        else
                        {
                            token_text += temp;
                        }
                    }
                    else
                    {
                        token_text += ch1;
                    }

                    token_kind = chars;

                    std::istream::int_type ch = 0;
                    while (in.peek() != '<' && in.peek() != EOF)
                    {
                        ch = in.get();

                        if (ch == '\n')
                            ++line_number;

                        // if this is one of the predefined entity references then change it
                        if (ch == '&')
                        {
                            int temp = change_entity(in);
                            if (temp == -1)
                            {
                                ch = EOF;
                                break;
                            }
                            else
                                token_text += temp;
                        }
                        else
                        {
                            token_text += ch;
                        }
                    }

                    // if this is an error token
                    if (ch == EOF)
                    {
                        token_kind = error;
                    }

                }
                break;

            // -----------------------------------------

            }

        }

    // ----------------------------------------------------------------------------------------

        int xml_parser::
        parse_element (
            const std::string& token,
            std::string& name,
            attrib_list& atts
        )
        {
            name.erase();
            atts.list.clear();

            // there must be at least one character between the <>
            if (token[1] == '>')
                return -1;

            std::string::size_type i;
            std::istream::int_type ch = token[1];
            i = 2;

            // fill out name.  the name can not contain any of the following characters
            while ( (ch != '>') &&
                    (ch != ' ') &&
                    (ch != '=') &&
                    (ch != '/') &&
                    (ch != '\t') &&
                    (ch != '\r') &&
                    (ch != '\n')
                )
            {
                name += ch;
                ch = token[i];
                ++i;
            }

            // skip any whitespaces
            while ( ch == ' ' || ch == '\t' || ch == '\n' || ch == '\r' )
            {
                 ch = token[i];
                 ++i;
            }

            // find any attributes
            while (ch != '>' && ch != '/')
            {
                std::string attribute_name;
                std::string attribute_value;

                // fill out attribute_name
                while ( (ch != '=') &&
                        (ch != ' ') &&
                        (ch != '\t') &&
                        (ch != '\r') &&
                        (ch != '\n') &&
                        (ch != '>')
                        )
                {
                    attribute_name += ch;
                    ch = token[i];
                    ++i;
                }

                // you can't have empty attribute names
                if (attribute_name.size() == 0)
                    return -1;

                // if we hit > too early then return error
                if (ch == '>')
                    return -1;

                // skip any whitespaces
                while (ch == ' ' || ch == '\t' || ch =='\n' || ch =='\r')
                {
                    ch = token[i];
                    ++i;
                }

                // the next char should be a '=', error if it's not
                if (ch != '=')
                    return -1;

                // get the next char
                ch = token[i];
                ++i;

                // skip any whitespaces
                while (ch == ' ' || ch == '\t' || ch =='\n' || ch =='\r')
                {
                    ch = token[i];
                    ++i;
                }

                // get the delimiter for the attribute value
                std::istream::int_type delimiter = ch; // this should be either a ' or " character
                ch = token[i];  // get the next char
                ++i;
                if (delimiter != '\'' && delimiter!='"')
                    return -1;

                // fill out attribute_value
                while ( (ch != delimiter) &&
                        (ch != '>')
                        )
                {
                    attribute_value += ch;
                    ch = token[i];
                    ++i;
                }

                // if there was no delimiter then this is an error
                if (ch == '>')
                {
                    return -1;
                }

                // go to the next char
                ch = token[i];
                ++i;

                // the next char must be either a '>' or '/' (denoting the end of the tag)
                // or a white space character
                if (ch != '>' && ch != ' ' && ch != '/' && ch != '\t' && ch !='\n' && ch !='\r')
                    return -1;

                // skip any whitespaces
                while (ch == ' ' || ch == '\t' || ch =='\n' || ch =='\r')
                {
                    ch = token[i];
                    ++i;
                }

                // add attribute_value and attribute_name to atts
                if (atts.list.is_in_domain(attribute_name))
                {
                    // attributes may not be multiply defined
                    return -1;
                }
                else
                {
                    atts.list.add(attribute_name,attribute_value);
                }

            }

            // you can't have an element with no name
            if (name.size() == 0)
                return -1;

            return 0;

        }

    // ----------------------------------------------------------------------------------------

        int xml_parser::
        parse_pi (
            const std::string& token,
            std::string& target,
            std::string& data
        )
        {
            target.erase();
            data.erase();

            std::istream::int_type ch = token[2];
            std::string::size_type i = 3;
            while (ch != ' ' && ch != '?' && ch != '\t' && ch != '\n' && ch!='\r')
            {
                target += ch;
                ch = token[i];
                ++i;
            }
            if (target.size() == 0)
                return -1;

            // if we aren't at a ? character then go to the next character
            if (ch != '?' )
            {
                ch = token[i];
                ++i;
            }

            // if we still aren't at the end of the processing instruction then
            // set this stuff in the data section
            while (ch != '?')
            {
                data += ch;
                ch = token[i];
                ++i;
            }

            return 0;
        }

    // ----------------------------------------------------------------------------------------

        int xml_parser::
        parse_element_end (
            const std::string& token,
            std::string& name
        )
        {
            name.erase();
            std::string::size_type end = token.size()-1;
            for (std::string::size_type i = 2; i < end; ++i)
            {
                if (token[i] == ' ' || token[i] == '\t' || token[i] == '\n'|| token[i] == '\r')
                    break;
                name += token[i];
            }

            if (name.size() == 0)
                return -1;

            return 0;
        }

    // ----------------------------------------------------------------------------------------

        int xml_parser::
        change_entity (
            std::istream& in
        )
        {

            std::istream::int_type buf[6];

            buf[1] = in.get();

            // if this is an undefined entity reference then return error
            if (buf[1] != 'a' &&
                buf[1] != 'l' &&
                buf[1] != 'g' &&
                buf[1] != 'q'
                )
                return -1;

            buf[2] = in.get();
            // if this is an undefined entity reference then return error
            if (buf[2] != 'm' &&
                buf[2] != 't' &&
                buf[2] != 'p' &&
                buf[2] != 'u'
                )
                return -1;

            buf[3] = in.get();
            // if this is an undefined entity reference then return error
            if (buf[3] != 'p' &&
                buf[3] != ';' &&
                buf[3] != 'o'
                )
                return -1;

            // check if this is &lt; or &gt;
            if  (buf[3] == ';')
            {
                if (buf[2] != 't')
                    return -1;

                // if this is &lt; then return '<'
                if (buf[1] == 'l')
                    return '<';
                // if this is &gt; then return '>'
                if (buf[1] == 'g')
                    return '>';

                // it is neither so it must be an undefined entity reference
                return -1;
            }

            buf[4] = in.get();
            // if this should be &amp;
            if (buf[4] == ';')
            {
                // if this is not &amp; then return error
                if (buf[1] != 'a' ||
                    buf[2] != 'm' ||
                    buf[3] != 'p'
                    )
                    return -1;

                return '&';
            }

            buf[5] = in.get();

            // if this should be &apos;
            if (buf[1] == 'a' &&
                buf[2] == 'p' &&
                buf[3] == 'o' &&
                buf[4] == 's' &&
                buf[5] == ';'
                )
                return '\'';

            // if this should be &quot;
            if (buf[1] == 'q' &&
                buf[2] == 'u' &&
                buf[3] == 'o' &&
                buf[4] == 't' &&
                buf[5] == ';'
                )
                return '"';

            // it was an undefined entity reference
            return -1;

        }

    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------

        class xml_parse_error : public error
        {
        public:
            xml_parse_error(
                const std::string& a
            ): error(a) {}
        };

        namespace impl
        {
            class default_xml_error_handler : public error_handler
            {
                std::string filename;

            public:

                default_xml_error_handler (
                ) {}

                default_xml_error_handler (
                    const std::string& filename_
                ) :filename(filename_) {}

                virtual void error (
                    const unsigned long
                )
                {
                    // just ignore non-fatal errors
                }

                virtual void fatal_error (
                    const unsigned long line_number
                )
                {
                    std::ostringstream sout;
                    if (filename.size() != 0)
                        sout << "There is a fatal error on line " << line_number << " in the XML file '"<<filename<<"'.";
                    else
                        sout << "There is a fatal error on line " << line_number << " in the XML being processed.";

                    throw xml_parse_error(sout.str());
                }
            };
        }

        inline void parse_xml (
            std::istream& in,
            document_handler& dh,
            error_handler& eh
        )
        {
            if (!in)
                throw xml_parse_error("Unexpected end of file during xml parsing.");
            xml_parser parser;
            parser.add_document_handler(dh);
            parser.add_error_handler(eh);
            parser.parse(in);
        }

        inline void parse_xml (
            std::istream& in,
            error_handler& eh,
            document_handler& dh
        )
        {
            if (!in)
                throw xml_parse_error("Unexpected end of file during xml parsing.");
            xml_parser parser;
            parser.add_document_handler(dh);
            parser.add_error_handler(eh);
            parser.parse(in);
        }

        inline void parse_xml (
            std::istream& in,
            error_handler& eh
        )
        {
            if (!in)
                throw xml_parse_error("Unexpected end of file during xml parsing.");
            xml_parser parser;
            parser.add_error_handler(eh);
            parser.parse(in);
        }

        inline void parse_xml (
            std::istream& in,
            document_handler& dh
        )
        {
            if (!in)
                throw xml_parse_error("Unexpected end of file during xml parsing.");
            xml_parser parser;
            parser.add_document_handler(dh);
            impl::default_xml_error_handler eh;
            parser.add_error_handler(eh);
            parser.parse(in);
        }

    // ----------------------------------------------------------------------------------------

        inline void parse_xml (
            const std::string& filename,
            document_handler& dh,
            error_handler& eh
        )
        {
            std::ifstream in(filename.c_str());
            if (!in)
                throw xml_parse_error("Unable to open file '" + filename + "'.");
            xml_parser parser;
            parser.add_document_handler(dh);
            parser.add_error_handler(eh);
            parser.parse(in);
        }

        inline void parse_xml (
            const std::string& filename,
            error_handler& eh,
            document_handler& dh
        )
        {
            std::ifstream in(filename.c_str());
            if (!in)
                throw xml_parse_error("Unable to open file '" + filename + "'.");
            xml_parser parser;
            parser.add_document_handler(dh);
            parser.add_error_handler(eh);
            parser.parse(in);
        }

        inline void parse_xml (
            const std::string& filename,
            error_handler& eh
        )
        {
            std::ifstream in(filename.c_str());
            if (!in)
                throw xml_parse_error("Unable to open file '" + filename + "'.");
            xml_parser parser;
            parser.add_error_handler(eh);
            parser.parse(in);
        }

        inline void parse_xml (
            const std::string& filename,
            document_handler& dh
        )
        {
            std::ifstream in(filename.c_str());
            if (!in)
                throw xml_parse_error("Unable to open file '" + filename + "'.");
            xml_parser parser;
            parser.add_document_handler(dh);
            impl::default_xml_error_handler eh(filename);
            parser.add_error_handler(eh);
            parser.parse(in);
        }

    // ----------------------------------------------------------------------------------------

    }

    #endif // DLIB_XML_PARSER_KERNEl_1_